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(PDF) Aluminium alloys welding processes: Challenges, joint types and process selection

(PDF) Aluminium alloys welding processes: Challenges, joint types and process selection welding process selection

Aluminium and its alloys have gained increasing importance in structural engineering due to advantageous properties such as light weight, ease of machining and corrosion resistance. This article presents surface-related challenges facing aluminium welding, specifically weld process limitations and joint limitations. The methodological approach is a critical review of published literature and results based on eight industrial welding processes for aluminium and six joint types. It is shown that challenges such as heat input control, hot cracking, porosity and weldable thickness vary with the process used and that there is no optimal general weld process for all aluminium alloys and thicknesses. A selection table is presented to assist in selection of the optimal process for specific applications. This study illustrates that knowledge of weld limitations is valuable in selection of appropriate weld processes.

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(PDF) Aluminium alloys welding processes: Challenges, joint types and process selection welding process selection

Manufacture

Engineers, Part B: Journal of Engineering

Proceedings of the Institution of Mechanical

(PDF) Aluminium alloys welding processes: Challenges, joint types and process selection welding process selection

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The online version of this article can be found at:

DOI: 10.1177/0954405413484015

(PDF) Aluminium alloys welding processes: Challenges, joint types and process selection welding process selection

originally published online 23 May 2013 2013 227: 1129Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture

Muyiwa Olabode, Paul Kah and Jukka Martikainen

Aluminium alloys welding processes: Challenges, joint types and process selection

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Review Article

Proc IMechE Part B:

J Engineering Manufacture

227(8) 1129–1137

ÓIMechE 2013

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DOI: 10.1177/0954405413484015

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Aluminium alloys welding processes:

Challenges, joint types and process

selection

Muyiwa Olabode, Paul Kah and Jukka Martikainen

Abstract

Aluminium and its alloys have gained increasing importance in structural engineering due to advantageous properties

such as light weight, ease of machining and corrosion resistance. This article presents surface-related challenges facing

aluminium welding, specifically weld process limitations and joint limitations. The methodological approach is a critical

review of published literature and results based on eight industrial welding processes for aluminium and six joint types. It

is shown that challenges such as heat input control, hot cracking, porosity and weldable thickness vary with the process

used and that there is no optimal general weld process for all aluminium alloys and thicknesses. A selection table is pre-

sented to assist in selection of the optimal process for specific applications. This study illustrates that knowledge of weld

limitations is valuable in selection of appropriate weld processes.

Keywords

Aluminium alloys, aluminium oxide, shielding gases, anodising, aluminium welding process selection

Date received: 17 September 2012; accepted: 4 March 2013

Introduction

Aluminium and its alloys are widely used in welding

industries due to economic advantages such as light

weight, good corrosion resistance, high toughness,

extreme temperature capabilities and easy recyclabil-

ity.

1

Aluminium alloys are used for construction of air-

planes, cars, rail coaches and marine transports.

Aluminium alloys are used in manufacture of tanks

and pressure vessels because of their high specific

strength, good heat conductivity and beneficial proper-

ties at low temperatures.

2

Aluminium is the second

most used metal after iron and steel in the industry; for

example, aluminium is the second most used material

taking about 15% of total body weight of average cars

and about 34% in Audi A2.

3

There are comprehensive

reviews on the uses and applications of aluminium and

its alloys.

4,5

Welding is a means of joining metals by

creating coalescence due to heat. The work piece is

melted at the joint point (weld pool) that solidifies on

cooling. Welding of aluminium alloys is important for

fabricating structural constructions and mechanical

fabrications like aircrafts. However, welding has prob-

lems and can be challenging. Welding defects common

to aluminium include porosity, hot cracking, incom-

plete fusion and so on.

2,6

Researches

7,8

have shown that welding aluminium

demands greater caution compared with steel, particu-

larly as regards the amount of heat input and pre-weld

cleaning, and that acceptable weld processes for alumi-

nium joints are limited because the weldable thickness

varies considerably with the different welding processes.

It is therefore of interest to study the limitations facing

aluminium welding, particularly joint- and process-

specific limitations.

The aim of this article is to present a comprehensive

guide to understanding aluminium-welding challenges.

In the field of aluminium welding, there are eight

industrially common welding processes and six basic

joint types that have been analysed. For comparison

purposes, a table is designed that shows the influence of

joint and process limitations on optimum welding pro-

cess selection. The remainder of this article is divided

into two main parts, which are surface-related welding

challenges and joint types and process limitations.

Lappeenranta University of Technology, Lappeenranta, Finland

Corresponding author:

Muyiwa Olabode, Lappeenranta University of Technology, Skinnarilankatu

34, 53850 Lappeenranta, Finland.

Email: muyiwa.olabode@lut.fi

at Lappeenrannan Teknillinen on September 3, 2013pib.sagepub.comDownloaded from

Evaluation of the findings shows that there is no sin-

gular optimum process for welding aluminium.

However, understanding of the limitations of individ-

ual welding processes helps in selection of the optimal

process for specific aluminium weld applications.

Surface-related welding considerations

A clean, smooth and protected surface is important in

pre-weld aluminium structures to ensure good alumi-

nium weldments except in high energy density welding

processes like hybrid laser beam welding (LBW) (using

pulsed metal inert gas (MIG)).

9

It is therefore impor-

tant to understand different surface-related phenomena

and their effect on the weldability of the work piece. In

addition, knowledge of preventative measures ensuring

the attainment of acceptable welds, despite any adverse

surface effects, is also important.

Presence of aluminium oxide surface

Oxide formation in aluminium occurs due to the strong

chemical affinity of aluminium for oxygen on exposure

to air. The aluminium oxide thickness increases as a

result of thermal treatment, moist storage conditions

and electrochemical treatment (anodising).

10–14

It is

also important to note that Al

2

O

3

melts at about

2050 °C, while aluminium alloys melts at about 660 °C

9

(as illustrated in Figure 1). Therefore, the layer is

removed by pickling or dry machining just before weld.

However, the difference in melting point is not a prob-

lem during the processing by means of high energy den-

sity welding processes; it can also be an advantage, for

example, the presence of oxide layer during laser weld-

ing increases the absorptivity of aluminium and its

alloys to laser radiation.

15,16

It should be noted, that a

main challenge in applying most joining technologies to

aluminium is its tendency to form a thick, coherent

oxide layer. This oxide layer has a melting temperature

much higher than that of aluminium itself; moreover, it

has a significant mechanical strength. Therefore, this

oxide layer can remain as a solid film (or fractured in

small particles) due to the flow of the molten material,

16

even when the surrounding metal is molten. This can

result in severe incomplete fusion defects. Therefore,

the removal of the oxide layer just before welding is

important.

The aluminium oxide layer is, furthermore, an elec-

trical insulator, and the layer may sometimes be thick

enough to prevent arc initiation. In MIG processes, a

thick oxide layer can produce erratic electrical com-

mutation in the gun’s contact tube, resulting in poor

welds.

It is thus evident that aluminium oxide has to be

removed before welding because it compromises the

quality of the weld. Generally, the oxide removal can

be done by mechanical processes like brushing with a

stainless steel brush, cutting with a saw or grinding with

semi-flexible aluminium oxide grinding discs.

9

Some

welding processes enhance additional oxide removal

processes, for example, in ultrasound metal welding

processes (UW), oxides and contaminates are removed

by high-frequency motion, thus providing metal–metal

contact and allowing for the work pieces to bond prop-

erly.

17

In hybrid laser MIG-welding of aluminium

alloys, the MIG-welding process has a cleaning effect

that removes the aluminium oxide layer. However, it is

recommended that pre-weld cleaning of the weld sur-

face should be carried out preferably by pickling or dry

machining.

18

In gas-shielded arc welding, aluminium

oxide removal from the weld pool can be done by cath-

ode etching (which is controlled chemical surface corro-

sion done to reveal the details of the microstructure).

19

A direct current passes through the electrode connected

to the positive pole of the power source. There is thus a

flow of electrons from the work piece to the electrode

and the ions flow in the opposite direction, bombarding

the work piece surface. The aluminium oxide film is

broken and dispersed by the ion bombardment, thereby

allowing the flowing weld metal to fuse with the parent

metal. It is advantageous to remove the aluminium

oxide layer before welding because

2,9

1. It significantly reduces the amount of hydrogen

porosity in the weld.

2. It helps to improve the stability of the weld process

especially in tungsten inert gas welding (TIG).

3. It allows for complete fusion of the weld. Cathode

cleaning is important in TIG process as the oxide

starts to form immediately after wire brushing.

Figure 1. Schematic of aluminium showing its oxide layer and the anodised surface.

1130 Proc IMechE Part B: J Engineering Manufacture 227(8)

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Aluminium oxide can also be removed by chemical

etching or pickling. Table 1 presents chemical treat-

ments for oxide layer removal.

9

One of the causes of the oxide layer is from anodisa-

tion, which is an electrochemical process by which a

metal surface is converted into a decorative, durable,

corrosion resistant anodic oxide finish.

20,21

Anodisation

utilises the unique ability of amorphous alumina to build

up an even porous morphology

22

formed in alkaline and

acidic electrolytes. During anodising, aluminium oxide is

not applied like paint or plating. Rather, it is integrated

fully with the underlying aluminium substrate.

Therefore, it cannot peel or chip off. The anodic oxide

structure is highly ordered and porous, thereby allowing

for further processing like sealing and colouring.

20

The reasons for the utilisation of anodisation are to

increase corrosion resistance and ensure the metal sur-

face is fade proof for up to 50 years,

23

to improve dec-

orative appearance, to increase abrasion resistance and

paint adhesion, to improve adhesive bonding and lubri-

city, to provide unique decorative colours or electrical

insulation, to permit subsequent plating, to detect sur-

face flaws, to increase emissivity and to permit applica-

tion of photographic and lithographic emulsions.

14,20,24

Anodising of aluminium alloys is generally advanta-

geous. However, it poses challenges for aluminium

welding because the arc cleaning effect of the AC cur-

rent cannot remove the double layer (the anodised layer

and oxide layer as in Figure 1). Before welding, the

anodised surface needs to be removed.

20

Shielding gas selection

Shielding gas protects the molten weld pool from the

atmosphere, which is important because aluminium has

a tendency to react with atmospheric air to form oxide

and nitrides. The shielding gases commonly used in

welding aluminium and its alloys are inert gases such

as argon and helium.

Argon is used as a shielding gas for manual and

automatic welding. Argon is cheaper than helium, and

the use of argon produces a more stable arc and

smoother welds. However, argon gives lower heat input

and lower attainable welding speed, and therefore there

is the possibility of a lack of fusion and porosity in

thick sections. In addition, use of argon can result in a

black sooty deposit on weld surfaces, although this can

be wire brushed away. It has been observed that with

helium shielding gas, the arc voltage is increased by

20%, resulting in a higher, hotter arc, deeper penetra-

tion and wider weld beads. This implies that the criti-

cality of arc positioning (aids avoidance of missed edge

and insufficient penetration defects) is lower with

helium. There is a reduction in the level of porosity

when helium shielding gas is used because the weld

pool is hotter and there is slower cooling, which allows

hydrogen to diffuse from the weld pool. Due to the

higher heat produced, the use of helium allows that

welding speeds up to three times higher than with

argon. The high cost of helium and the inherent arc

instability mean, however, that helium is used mainly

in mechanised and automatic welding processes.

9

It is common practice to use a mixture of helium and

argon as it provides a compromise on the advantages of

each gas. Common combinations are 50% or 75% of

helium in argon, which allow for better productivity by

increasing the welding speed and provide a wider toler-

ance for acceptable welds. The purity of the shielding

gas is of importance. At the torch, not at the cylinder

regulator, a minimum purity requirement of 99.998%

and low moisture levels of less than 250 °C (less than

39 parts per million (ppm) H

2

O) are expected.

9

Generally, the shielding gas should be selected with the

following considerations.

2,9,25,26

Table 1. Chemical treatments for cleaning and oxide removal.

9

Solution Concentration Temp (°C) Procedure Container material Purpose

Nitric acid 50% water

50% HNO

3

(technical

grade)

18–24 Immerse 15 min

Rinse in cold water

Rinse in hot water

Dry

Stainless steel Removal of thin oxide

film for fusion welding

Sodium hydroxide

followed

by nitric acid

5% NaOH in

water

Concentrated

HNO

3

70

18–24

Immerse for 10–60 s

Rinse in cold water

Immerse 30 s

Rinse in cold water

Rinse in hot water

Dry

Mild steel

Stainless steel

Removal of thick oxide

film for all welding and

brazing operations

Sulphuric chromic

acid

5LH

2

SO

4

1.4 kg CrO

3

40 L water

70–80 Dip for 2–3 min

Rinse in cold water

Rinse in hot water

Dry

Antimonial

lead lined steel

tank

Removal of films and

stains from heat treating

and oxide coatings

Phosphoric chromic

acid

1.98 L of 75%

H

3

PO

3

0.65 kg of CrO

3

45 L of water

95 Dip for 5–10 min

Rinse in cold water

Rinse in hot water

Dry

Stainless steel Removal of anodic

coatings

Olabode et al. 1131

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1. The gas must be able to generate plasma and a sta-

ble arc mechanism and characteristics.

2. It should provide smooth detachment of molten

metal from the wire and fulfil the desired mode of

metal transfer.

3. It should protect the welding head (in the arc’s

immediate vicinity), molten pool and wire tip from

oxidation.

4. It should help to attain good penetration and good

weld bead profile.

5. It should not affect the welding speed of the

process.

6. It should prevent undercutting tendencies.

7. It should limit the need for post-weld cleaning.

8. It should not be detrimental to the weld metal

mechanical properties.

The recommended shielding gas for welding alumi-

nium using pulsed MIG is argon (99.998%)

25,27

at a

flow rate of about 20 L/min.

27

A mixture of argon and

helium can also be used and even helium alone. Helium

increases the weld penetration and offers higher arc

energy and thus increased deposition rate,

27,28

and it

should be used when the section is greater than 50 mm.

9

More details can be seen in Table 2, which presents

MIG shielding gases for aluminium, and Table 3 pre-

sents the effects of shielding gases on aluminium weld-

ing. Studies have shown that welding of aluminium can

be improved (arc stability) by oxygen doping of inert

shielding gas.

29

In addition, the alternating shielding

gases reduces weld porosity.

30–32

Joint types and process limitations

This article considers eight industrially accepted welding

processes and six joint types. Joint design is important

because it costs money to buy weld metal. The fillet throat,

weld accessibility and the functionality of the welded work

piece are taken into consideration in this design. The six

joints considered are butt, T-joint, corner, cruciform, edge

and lap joint (see Table 4), which are derived from the

three basic welding joints (fillet, lap and butt joints). Joint

designs are based on the strength requirements, the alloys

to be joined, the thickness of the material, the joint type

and location, weld accessibility and the welding process.

Before choosing the joint design, it is important to note

that welding in the flat or downward position is preferable

in all arc-welding processes, as there is the easier possibility

of depositing high-quality weld metal at a high deposition

rate in a flat position. Additionally, the weld pool is larger,

allowing for a slower cooling and solidification rate, which

enhances the escape of trapped gases in the weld pool. The

flat position reduces weld porosity, reduces weld cost, and

gives the best weld metal quality compared with other

positions. The static tensile strength of the weld is deter-

mined by the throat thickness, which must be designed to

ensure that it can carry the workload for which the weld is

designed. Conventional TIG and MIG processes produce

Table 3. Effect of shielding gas on aluminium welding.

9,29–34

Shielding gas Relative effect (100% argon as the reference)

100% Ar Ar + He 100% He

Gas flow Nominal Higher Highest

Arc voltage (MIG) Nominal Higher Highest

Arc (MIG) Nominal stability More unstable Most unstable

Weld seam width and depth Nominal width and depth Higher width

Shorter depth

Highest width

Shortest depth

Weld seam appearance Nominal smoothness Smoother Smoothest

Penetration Nominal depth and roundness Deeper and more round Deepest and most round

Welding speed Nominal welding speed Higher attainability Highest attainability

Lack of fusion Nominal Lower Lowest

Porosity Nominal Lower Lowest

Pre-heating Nominal Less needed Least needed

Heat production Nominal warmth Warmer work piece Warmest work piece

Cost of shielding gas Nominal price More expensive Most expensive

MIG: metal inert gas welding.

Table 2. MIG shielding gases for aluminium.

26

Metal transfer mode Shielding gas Characteristics

Spray transfer 100% Argon Best metal transfer and arc stability, least spatter, and good cleaning action.

35% Argon–65% Helium Higher heat input than 100% argon; improved fusion characteristics on thicker

material; minimises porosity.

25% Argon–75% Helium Highest heat input; minimises porosity; least cleaning action

Short circuiting Argon or Argon + Helium Argon satisfactory on sheet metal; argon–helium preferred for thicker base

material.

1132 Proc IMechE Part B: J Engineering Manufacture 227(8)

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Table 4. Joint types and process limitations of aluminium alloys.

2,8,9,17,18,35–52

Processes

Joints

MIG TIG PAW FSW LBW RW EBW UW

Butt joint (a) 

Lap joint (b) 

T-joint (c) 

Edge joint (d) 

Corner joint (e) 

Cruciform (f)  

Limitation Limitation Limitation Limitation Limitation Limitation Limitation Limitation

(a)

(b)

(c)

(d)

(e)

(f)

With argon, weldable

thickness is limited to

25 mm, and with helium,

it is limited to 75 mm.

Limited torch distance of

10–19 mm to ensure

properly shielded weld

metal limits flexibility.

Limited outdoor

application because air

drafts can disperse the

shielding gas.

Limited operator

acceptability of the

process because of the

relatively high levels of

radiated heat and arc

intensity.

Limited to thin gauges of

up to 6 mm thickness.

Limited (shallower)

penetration into parent

metal compared to MIG.

With argon shielding gas,

the economical weld

thickness limit is 10–

18 mm with helium

(DCEN).

Difficult to penetrate

into corners and into the

roots of fillet welds.

Limited by the lower

deposition rate, low

tolerance on filler and

base metal, and cost for

thick sections compared

to MIG.

Plasma MIG weld

thicknesses limited to 6–

60 mm range.

Plasma TIG weld

thicknesses range can be

less than 2.5–16 mm in a

single pass.

Limited by the high

capital equipment and

material cost compared

to TIG.

Limited tolerance of the

process to joint gaps and

misalignment.

Limited operator

acceptability of the

process due to the

complex torch

architecture that

requires more

maintenance and

accurate set-back of the

electrode tip with

respect to the nozzle

orifice, which is

challenging.

Weldable thickness

ranges from 1–50 mm

(single pass).

Tool design, process

parameters, and

mechanical properties

database is limited and

only available for limited

alloys and thicknesses

(up to 70 mm).

Limited to lower

productivity cases

compared to LBW.

Insufficient design

guidelines and limited

education for

implementation.

Exit hole left when tool

is withdrawn.

Large down forces

required with heavy duty

clamping necessary to

hold the plates together

during welding.

Environmentally friendly

welding process because

fumes and spatters are

not generated.

Limited conversion

efficiency of electrical

power to focused

infrared laser beam also

called wall plug efficiency

(about 10%–30% and up

to 40% in fibre lasers).

Limited fit up tolerance.

Precise fit up (15% of

material thickness)

needed for butt and lap

joints.

Limited operator

acceptability of the

process due to the large

capital investment

needed, therefore

requiring high volume

production or critical

applications to justify the

expenditure.

Limited weld thickness

range (0.9–3.2 mm)

Lower tensile and fatigue

strength compared to

other fusion welding

processes.

Limited joint designs or

configuration. Seam

welds can generate

unzipping effect.

Limited operator

acceptability of the

process because, in

thick-sectioned upset

welds; there is lack of

good non-destructive

weld quality testing high

electrode wear rate and

deterioration.

In addition, it requires

access to both sides of

the joint.

High cost of

equipment.

Work chamber size

constraints.

Time delay when

welding in a vacuum.

High weld preparation

costs.

X-rays produced

during welding can be a

health risk.

Rapid solidification

rates can cause

cracking in some

materials.

Can weld up to

450 mm thick plates.

Expensive high

powered transducers

are needed to enable

welding of thick gauges,

castings, extrusions,

and hydro-formed

components.

Alternative welding

configurations are

needed to weld a wide

variety of component

geometries and joint

configurations.

Vibration control

strategies are needed

to ensure weld quality

across a wide range of

component geometries

and the thickness of

the weld piece is

limited.

DCEN: direct current electrode negative; EBW: electron beam welding; FSW: friction stir welding; LBW: laser beam welding; MIG: metal inert gas welding; PAW: plasma arc welding; RW: resistance welding; TIG, tungsten inert

gas welding; UW: ultrasonic welding.

Olabode et al. 1133

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weld metal on the surface of a plate during bead-on-plate

weldstoadepthof3mmforTIGand6mmforMIG.

Therefore, to attain complete penetration for welds over

3 mm (MIG) and 6 mm (TIG), there is the need for bevel-

ling on butt joints, for example. The bevel can be single or

double sided.

9

As presented in Table 4, eight considered welding

processes are correlated with their applicability on six

different welding joints. Butt and lap joints are applica-

ble to all the selected weld processes. Cruciform joints

have the least applicability across the processes, which

is due to limited fixturing possibility during welding.

Table 4 provides additional information on the viabi-

lity of six joint types on the eighth selected welding pro-

cesses by presenting the process-specific limitations.

An application of this review article is to use the pre-

stated information to influence the selection case-

specific optimum welding process. It can be challenging

to determine an appropriate welding process to be used

for aluminium. However, the challenge can be simpli-

fied by considering various comparison selection factors

as presented in Table 5. The solution to the challenge is

case specific. An understanding of the selection factors

considered provides better process selection and thus a

better evaluation.

It is important to point out that the scaling is subject

to the designer’s discretion and not completely objective.

The welding designer determines the importance level of

the selected aluminium-welding project by answering a

question like ‘how important is’ strength, elongation,

chemical stability, etc., to the finished product. The

designer defines the importance level on a scale of 1–3

(1= least, 2 = moderate and 3 = high). In a similar

fashion, the advantageous level is determined by answer-

ing a question like ‘how advantageous is’ the selected

welding process to the selected consideration. The

importance level is multiplied by the advantage level

and the result is called an impact factor. The impact fac-

tor is summed up for each selected welding process, and

the welding process with the highest impact factor sum-

mation is selected as the optimal welding process.

Case study

Awelding process for high-strength aluminium for aero-

space is to be selected. The available welding processes

Table 5. Weld process selection (the highest factor summation is the best of the processes considered).

Selection factors Process A (TIG) Process B (FSW) Process C (PAW) Process D (MIG)

Quality of the welded joint Imp. Ad. I. Fac. Imp. Ad. I. Fac. Imp. Ad. I. Fac. Imp. Ad. I. Fac.

Strength 3 2 6 3 2 6 – – 3 2 6

Elongation 2 2 4 2 3 6 2 2 4 2 3 6

Chemical stability 2 2 4 2 3 6 2 3 6 2 3 6

Weld defects 2 3 6 2 1 2 2 1 2 2 1 2

Penetration 1 3 3 1 3 3 1 3 3 1 3 3

Distortion 1 1 1 1 2 2 1 2 2 1 2 2

Suitability for use

Welding thin sheet (\1mm)224 236 236 224

Sheet welding (.3mm) 111 122 122 133

Welding Al-Mg alloys 1 2 2 1 2 2 1 2 2 1 2 2

Overhead welding 1 1 1 1 3 3 – – – –

Variable material thickness 2 1 2 2 1 2 2 2 4 2 2 4

Variable welding speed 1 1 1 1 2 2 1 3 3 1 2 2

Welding of castings 2 2 4 2 3 6 2 2 4 2 2 4

Joining cast to wrought alloys 1 3 3 1 3 3 1 1 1 1 2 2

Repair welds on castings 2 3 6 2 3 6 2 1 2 2 2 4

Suitability for automation

With filler 1 1 1 1 3 3 1 2 2 1 3 3

Without filler 2 3 6 2 1 2 2 1 2 2 1 2

Butt welding \3mm 2 12 2 24 2 24 2 24

.3mm 1 22 1 11 1 33 1 11

Suitability for joint type

Butt joint 1 2 2 1 1 1 1 1 1 – –

Lap joint 1 3 3 1 3 3 1 1 1 1 1 1

Economic aspects

Equipment costs 3 2 6 3 3 9 3 2 6 3 1 3

Maintenance costs 3 2 6 3 2 6 3 3 9 3 2 6

Labour costs 1 3 3 1 2 2 1 3 3 1 3 3

Welder’s training time 1 1 1 1 1 1 1 1 1 1 3 3

Process rating (P) 80897376

Imp.: importance level; Ad.: advantage level; I. Fac.: impact factor; EBW: electron beam welding; FSW: friction stir welding; LBW: laser beam welding;

MIG: metal inert gas welding; PAW: plasma arc welding; RW: resistance welding; TIG, tungsten inert gas welding; UW: ultrasonic welding.

1134 Proc IMechE Part B: J Engineering Manufacture 227(8)

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are as presented in Table 5. A blank table is constructed

and the considered welding processes are selected and

filled into the table.

The selection factors under consideration are as pre-

sented in Table 5, which are categorised under quality

of the weld joint, suitability for use, suitability of fillers,

joint suitability and economics. Therefore, at this stage

in the design, the processes row and the selection factor

column are filled in the table.

As the designer, the importance level is determined

and designed on a scale of 1–3, and using a scale of five

is also applicable, but the calculation becomes more

complex. Choosing a scale of 1–3 (1 = low, 2 = moder-

ate and 3 = high), a number is assigned to the consid-

ered selection factor. Therefore, at this stage, the

importance level of the selection factor under consider-

ation is filled into the ‘Imp.’ column (Table 5). It is

important to note that the number is the same across

row (all processes) because the importance of a selec-

tion factor is independent of the process.

The advantage level is determined and designed by

the designer on the same scaling used for importance

level. If the scaling used in importance level is five, the

scaling of five should be used. In this case, a scaling of

1–3 is used where 1 = low, 2 = moderate and 3 = high.

At this stage, the entire advantageous level column on

Table 5 is filled for all the considered selection factors

into the ‘Ad.’ column.

The calculation for the impact factor and the process

rating is carried out. The impact factor for each consid-

ered selection factor is derived by multiplying the

importance level column of each process by advanta-

geous level column of each process. The derived value

is filled into the ‘I. Fac.’ (impact factor) column of

Table 5. The process rating (welding process) is derived

by the summation of all the impact values column of

each process. Therefore, the process rating row is filled

in Table 5.

The optimum weld process is the process with the

highest process rating, which in this case study is pro-

cess C friction stir welding (FSW).

Conclusion

This article examined the surface-related challenges,

joint types and limitations of aluminium alloys with the

focus on providing a guide on how to select an optimal

welding process. Aluminium and its alloys have welding

challenges, which include the presence of aluminium

oxide on surfaces, welding of anodised aluminium and

limited shielding gas options. The aluminium oxide sur-

face is formed when aluminium is exposed to an atmo-

sphere containing oxygen, and the aluminium oxide has

to be cleaned away from the surface before welding

because its causes weld defects like porosity.

The chemical affinity of aluminium for oxygen is uti-

lised for anodising aluminium alloys and then painting

to improve corrosion resistance. However, it can be

detrimental when welding anodised aluminium as the

anodised layer has to be cleaned before welding. The

melting point of aluminium alloys is generally around

660 °C and the melting point of aluminium oxide is

2050 °C. It is therefore recommended that the aluminium

oxide layer or the anodised layer be removed, mechani-

cally or chemically, just before welding.

Aluminium alloys have high chemical affinity; there-

fore only inert gases can be used as shielding gases dur-

ing welding. Argon and helium gases are used in

aluminium welding to protect the weld pool. The pres-

ence of helium increases the arc heat input and there-

fore allows for deeper penetration compared with

argon gas, but on the other hand, helium is more

expensive than argon. A mixture of helium and argon

is sometimes used to improve weldability of some alu-

minium alloys. A wider range of shielding gases would

increase the manipulation possibility for aluminium

alloy welding, but currently argon and helium are the

only gases used.

The industrial welding processes considered in this

work include MIG, TIG, plasma arc welding (PAW),

FSW, LBW, resistance welding (RW), electron beam

welding (EBW) and UW. The weldable thickness is a

limitation in all the processes; the highest weldable

thickness of up to 70 mm is achieved with EBW. FSW

produces the best weld because the mechanical property

deterioration is minimal, and the process is friendly as

no fumes or spatters are produced during welding.

The joint configurations considered include the butt

joint, lap joint, T-joint, edge joint, corner joints and

cruciform joint. The butt joint and lap joint are appli-

cable to all the considered welding processes. The pos-

sibility of using different joint orientations with the

considered welding processes depends on the manipula-

tion of the work piece (fixturing).

Although FSW produces the best weld for alumi-

nium alloys, the optimal welding process is case spe-

cific. The designed table for weld process selection

provides information on how to select the optimal

process based on case-specific considerations for alu-

minium alloys.

Declaration of conflicting interests

The authors declare that there are no conflicts of

interest.

Funding

This research received no specific grant from any fund-

ing agency in the public, commercial or not-for-profit

sectors.

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Appendix 1

Notation

EBW electron beam welding

FSW friction stir welding

LBW laser beam welding

MIG metal inert gas welding

PAW plasma arc welding

ppm parts per million

RW resistance welding

TIG tungsten inert gas welding

UW ultrasonic welding

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... FSW has been invented for aluminum (Al) and this pairing is found to perform optimally: Joining sheets with FSW generally avoids hot cracking, porosity, distortion and other problems which typically pertain to fusion welding and especially Al is said to be troublesome to weld by fusion. If welded by friction, however, its low melting point is makes it easy to plasticize [1]. The versatility of this process also allows for joining dissimilar metals [2][3][4]. ...

... Stop time of the simulation is dependent on the deformation speed ε ˙and the number of turns N and can be evaluated using =⁄ (1) Calculations are known to be a time-consuming process. In order to avoid error by configuration they were initially executed on a simpler model with fewer steps and nodes or made to break specifically early in the process to compare the calculated values with the expected one. ...

... The curves given in Fig. 4, which depict the relevant part of the recorded temperature and torque time series for experiments at a deformation speed of 700 rpm with one full twist, may thus be understood as representative for each material's response behavior. The end of twisting operation for the given parameters according to (1) is at about 900 ms. Further space on the time axis is to provide context. ...

To physically simulate Friction Stir Welding (FSW) the hot high strain rate torsion tests were realized on Gleeble-3800 System for different Al-based materials: technically pure A5 (ISO equivalent 1050), AMg5 (5056) and D16 (2024). A finite element model was built and validated using temperature and torque data obtained after physical simulation. Experimental data was compared with a numerical simulation of the process. The possibility to use physical simulation for description of the processes during FSW is discussed.

... The GTAW is an easy and inexpensive welding technique that can produce sound and high quality weldements, however, it is slower than most of other welding techniques. The weld quality in GTAW is primarily controlled by many factors such as workpiece characteristics, electrode quality, filler material, power source type, and welder procedure [2,3]. ...

... Aluminum alloys have been widely used in manufacturing aeronautical and aerospace structures thanks to their high specific strengths and moderate cost. Gas tungsten arc welding (GTAW) is one of the main welding processes employed in welding such structures of aluminum alloys, within which complex three-dimensional (3D) weld paths may exist [1,2]. In GTAW of such 3D welds, it is often impractical to realize and maintain the conventional flat welding position by manipulating the structures for fixed arc because of their large dimensions and/or weights. ...

This study aims to reveal the cause of different weld formation quality for varying welding position in the GTAW (Gas Tungsten Arc Welding) of a thick-sheet aluminum alloy structure. The fluid flow characteristics of weld pools are investigated by CFD (Computational Fluid Dynamic) modeling and high-speed imaging for the climbing and flat welding positions, which correspond to the start and finish ends of the welds of the structure, respectively. Results show that the directions of gravity relative to weld pools may notably affect the fluid flows in weld pools for different welding positions. For flat welding, gravity will accelerate the fluid flow in the direction of sheet thickness only and in turn result in a high velocity downwards, which implies a good penetrating capability. Welds of good formation with smooth surface and consistent width can be produced under flat welding position. In contrast, for climbing welding, gravity will act on the molten metal in both the direction of sheet thickness and the lateral direction of the weld pool. As a result, the velocity in sheet-thickness direction is decreased, which implies a decreased penetrating capability. Meanwhile, the velocity backwards is increased in the top portion of the weld pool, which makes the molten metal apt to flow out of the weld pool. Both the decreased penetrating capability and the accelerated molten metal outflow would render the climbing welding process unstable, and result in welds of poor formation with uneven weld surface and inconsistent weld width. Based on the study, possible methods are proposed that could be used to improve the weld formation quality when welding thick-sheet aluminum alloys structures using various welding positions.

... Currently, there are various ways of connecting dis- similar metals, such as tungsten inert gas (TIG) weld- ing, 1 laser welding 2 and friction stir welding. 3 However, TIG welding is relatively traditional and technologically mature. ...

Auto-body lightweight is becoming an important trend of energy saving and emission reduction. Various materials assembled together would be used to fabricate the auto-body to satisfy this demand. However, the assembly dimensional quality is difficult to be controlled in the real processing due to the huge differences in material properties. Therefore, it is necessary to control and analyze the welding deformation of aluminum alloy and steel. In this work, the orthogonal design experiment has been adopted to analyze the welding deformation of steel–aluminum sheet parts. Subsequently, the response surface model is proposed to establish the relationship between welding deformation and welding parameters by finite element analysis, which is verified by physical experiments again. Meanwhile, the anti-deformation method is also used to decrease the assembly deformation successfully. And the case of Z-shaped planes is applied to further illustrate the proposed method of this work. Finally, the results show that both the methods have a good simulation effect and a high prediction accuracy for the assembly dimensional quality.

... Shaping (LENS) [7][8][9] 、Laser Metal Forming (LMF) [10][11][12][13] 、Direct Metal Deposition (DMD) [14,15] 、Directed Light Fabrication (DLF) [16] 、Laser Additive Manufacturing (LAM) [17][18][19] 、Selective Laser Melting (SLM) [20][21][22][23] [25,26] 、气孔/夹 杂 [27][28][29] 、裂纹 [30][31][32][33][34] )和组织成分控制(枝晶粗化 [35][36][37][38] 、凝固取向 [39,40] 、宏观/微 观偏析 [41,42] 、金属间化合物 [43,44] ...

... Furthermore, to implement the welding of a compact oxide film on the surface of aluminum alloys, the cathode atomization effect resulting from an intense heat source is required. Therefore, the heat input into the base metal must be strictly controlled [12]. The welding power supply should not only ensure welding stability and form aesthetic welding seam, but it should also reduce the heat input and decrease deformation during the welding process [13,14]. ...

In this investigation, a sinusoid modulated pulse gas metal arc welding (SP-GMAW) method based on a current waveform control method and on the welding mechanism of pulsed gas metal arc welding (P-GMAW) was proposed. This method achieved smooth control over the welding current. The process formulas were simplified. Then, the control parameters were discussed and optimized. Finally, three comparison experiments were conducted. The results indicated that the SP-GMAW method, as an improved double-pulsed gas metal arc welding (DP-GMAW) method, had the following features: The SP-GMAW minimized porosity rate and generated palpable weld ripples in contrast with the P-GMAW. The SP-GMAW produced the finest fusion zone grain, highest fusion zone microhardness, and highest tensile strength among three welding methods. The feasibility and superiority of the method for welding aluminum sheet were verified.

The concept of “sustainability” has recently risen to take the old concept of going “green” further. This article presents general methodologies for sustainability assessments. These were then adapted to measure and assess the sustainability of welding processes through building a complete framework, to determine the best welding process for a particular application. To apply this methodology, data about the welding processes would be collected and segregated into four categories: environmental impact, economic impact, social impact, and physical performance. The performance of each category would then be aggregated into a single sustainability score. To demonstrate the capability of this methodology, case studies of three different welding processes were performed. Friction stir welding obtained the highest overall sustainability score compared to gas tungsten arc welding and gas metal arc welding.

The suspension system of a vehicle is responsible for absorbing the vibrations during vehicle movement, thereby providing reliability and stability to the vehicle. The components of the suspension system enable damping the vibrations and avoid transmitting them to the frame. The major components of the suspension system along with their loading conditions are discussed in this paper. An attempt is made to analyze the structural behavior of the trailing arm of the suspension using FEM simulation by meshing and strength analysis using ANSYS analysis software. ANSYS static structural analysis module is used to verify the stress developed in the automobile suspension system. The distribution of the load on the trailing arm and the critical section are presented in this paper.

Dual laser-beam bilateral synchronous welding technique is considered to replace riveting in terms of skin–stringer joints. The 2.0-mm thick Al-Li alloy T-joint, which is welded by dual laser-beam bilateral synchronous welding between 2099-T83 stringer and 2060-T8 skin, is investigated in the current study. Under the tailored process conditions, the examinations and analyses of microstructures, microhardness distribution, hoop tensile mechanical properties, and fractographies of the T-joint are conducted. Experimental results show that the maximum tensile strength of the weld seam is up to 85% of the tensile strength of the skin material. In order to explore the special fracture characteristics of dual laser-beam bilateral synchronous welding joints after tensile test, a three-dimensional finite element model is established and the residual stress of the weldment is analyzed. Considering the scanning electron microscopy results and simulation results comprehensively, stress concentration is the main reason for the weldment failure in tensile test.

Metal inert gas arc welding process was implemented to join 6063T6 wrought alloy and ADC12 die-casting alloy using ER4047 filler metal. The microstructure of the weld seam and weld interface was investigated. The bonding strength of the butt joints was tested by Charpy U-notch impact test and tensile test. The results showed that a sound welding butt joint with finely silicon particles and excellent mechanical properties was formed, and the size of the silicon particles was nearly 2 μm. Compared with 6063T6 wrought alloy, the impact absorbing energies and the tensile strengths of the butt joint were higher and reached 1.173 kJ/cm² and 205 MPa, respectively, and the fractures of all tensile specimens occur at the 6063T6 aluminum.

Hybrid laser-arc welding (HLAW) is a combination of laser welding with arc welding that overcomes many of the shortfalls of both processes. This important book gives a comprehensive account of hybrid laser-arc welding technology and applications. The first part of the book reviews the characteristics of the process, including the properties of joints produced by hybrid laser-arc welding and ways of assessing weld quality. Part two discusses applications of the process to such metals as magnesium alloys, aluminium and steel as well as the use of hybrid laser-arc welding in such sectors as ship building and the automotive industry. With its distinguished editor and international team of contributors, Hybrid laser-arc welding is a valuable source of reference for all those using this important welding technology. Reviews arc and laser welding including both advantages and disadvantages of the hybrid laser-arc approach. Explores the characteristics of the process including the properties of joints produced by hybrid laser-arc welding and ways of assessing weld quality. Examines applications of the process including magnesium alloys, aluminium and steel with specific focus on applications in the shipbuilding and automotive industries.

Ultrasonic metal welding has many advantages including speed, weld quality consistency, and efficiency compared to other joining methods. In order to further improve the process, this work focused on enhancing process consistency. A comparison between three control modes: energy, height (post height), and time was conducted and the results were analyzed. Thus, the main objective of this study was to characterize and compare the weld consistencies of the various control modes. In this study, 60 welds made with optimum welding parameters with each mode were made, and the average weld strength and variance of the population were statistically compared. It was determined by analyzing the data with an F-test with a probability a = 0.05 that there was a slight improvement in weld strength consistency for the time mode compared to the other two modes (energy and post height). No significant difference in the average weld strength was seen for the three modes, only in the consistency of the welds. It is believed that in the energy and post height modes, while the average weld strengths were similar to the time mode, these modes were affected by sample fixture loading and sample variations.

Aluminium alloys are well established as engineering materials for a wide range of applications because they offer a combination of low weight, high strength, good corrosion resistance, formability and weldability. This article identifies the common weldable aluminium alloys and processes used. It also highlights the growth of aluminium as a structural material, giving applications and references to the current British and European standards relating to welding aluminium.

This paper reviews the function of shielding gases in GTAW and GMAW processes and discusses the mixtures currently available and their applications. In addition, an attempt is made to enable the user to critically assess the shielding gas requirements for given applications.

Double-pulse MIG welding of aluminum alloy can improve the efficiency of welding and meanwhile get beautiful weld surface with scaly figures. Based on single-pulse welding, the experiments of double-pulse MIG welding of aluminum alloy were carried out by changing the current, high-frequency, low-frequency and welding velocity of the power which is the self-developed double-pulse MIG welding inverter power. Tests shows that strong/weak pulse peak current and high-frequency have great influence on die stability of welding process and spatters. When the difference between strong and weak pulse peak current is 40 A and high-frequency is 250 Hz, the weld forming is good. To a certain extent, the width of the scaly figure on the weld surface is directly related to low-frequency and welding velocity: the width of the scaly figure will decrease with the improvement of low-frequency and widen with acceleration of welding velocity. An empirical formula reflecting the relationship between low-frequency, welding velocity and the width of the scaly figure through statistical methods is obtained, and the results show that when the ratio of welding velocity to low-frequency is from 0.19 to 0.30, the width of the scaly figure is from 2 to 3 mm, which means good welding performance.

Some of the many applications of aluminum within the welding fabrication industry and its use which has aroused in these industries are discussed. Aluminum became an economically viable competitor to steel within the engineering environment as recently as the end of the 19th century. Aluminum-intensive vehicles provide better handling and braking capability, improving their ability to avoid crashes. Fast ferry projects have advanced the use of aluminum in shipbuilding through development of a new concept in marine transportation. Defense and aerospace industries use high-strength 5xxx series (Al-Mg) non heat-treatable base alloys for some applications, but also make use of some of the more specialized heat- treatable aluminum alloys with superior mechanical properties. The use of aluminum continues to grow within the welding fabrication industry in both size and complexity, and with it the need for aluminum filler metals that will meet these needs, the advancement.

Ultrasonic metal welding is a promising joining method for aluminum automotive body construction applications. In order to achieve technology implementation readiness, process robustness to weld orientation, aluminum sheet rolling direction, residual stamping lubricant level, and material age must be assessed. Experiments were conducted to characterize variations in weld failure loads and microstructural features resulting from the directional nature of the energy input during ultrasonic welding to ensure that the angle at which components are ultrasonically welded together does not affect weld performance. These experiments were also designed to ascertain whether the orientation of a welding machine with respect to the rolling lines on an AA6111 sheet component or the relative orientation of the rolling directions of two components being joined is critical. A second set of experiments was conducted to determine the effects of surface lubricant level on tensile-shear and T-peel failure loads and fatigue performance for AA6111 and AA5754 sheet. Robustness to surface lubricant level is important because often in North American automotive production facilities, components are not cleaned prior to welding; rather, they are welded with residual stamping lubricant on the surfaces. Finally, because AA6111 naturally ages at room temperature for an extended period of time in the T4 temper, experiments were performed to ascertain the impact of AA6111 material age on ultrasonic weld tensile-shear and T-peel failure loads. For all factors considered in this study, ultrasonic metal welding process robustness was demonstrated.

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