INVESTIGATION ON THE STEEL PREHEATING …umpir.ump.edu.my/8595/1/CD8067_@_55.pdf · Aluminium alloy AA 6061 was welded with stainless steel ... dengan sama atau berbeza bahan ...

INVESTIGATION ON THE STEEL PREHEATING EFFECTS ON THE

ALUMINIUM-STEEL WELDING

MUHAMMAD NABIL BIN ABDUL RAZAK

Report submitted in partial fulfillment of the requirements for the award of the degree of

Bachelor of Mechanical Engineering

Faculty of Mechanical Engineering

UNIVERSITI MALAYSIA PAHANG

June 2013

v

ABSTRACT

Dissimilar welding or Tailor Welded Blanks (TWBs) joint is defined as two or

more sheets with equal or different materials, thickness, strength, or surface coatings are

welded together. The objective of this project is to investigate the effect of heat

treatment on the weld joints quality and determine the mechanical properties of the

steel-aluminium weld joint. Aluminium alloy AA 6061 was welded with stainless steel

SUS 304 in the thickness range of 2mm in lap joint configuration. Among the process

parameters varied were filler metal and preheating temperature. By metallurgy cross

sections, hardness test and tensile test, the effect of those process parameters on joint

properties such as welding joint hardness, macrostructure defect and tensile strength

could be elucidated. Based on the results, the penetration of stainless steel with

aluminium alloy occurs when the preheating process is applied. Sample C yield the best

result in hardness with value at 830HV and 19.91 Mpa in tensile test. The optimum

temperature for preheating is 85ºC and by using ER 4043 filler metal.

vi

ABSTRAK

Kimpalan berbeza atau Tailor Welded Blanks (TWBs) sambungan didefinisikan

sebagai dua atau lebih kepingan dengan sama atau berbeza bahan, ketebalan, kekuatan,

atau lapisan permukaan yang dikimpalkan bersama. Objektif projek ini adalah untuk

menyiasat kualiti kesan dari pemanasan dan sifat-sifat mekanikal sambungan aluminium

keluli. Aloi aluminium AA 6061telah di kimpal dengan keluli tahan karat SUS 304

dalam julat ketebalan 2mm dengan tata rajah sambungan tindih. Antara parameter yang

dipelbagaikan merupakan logam pengisi dan suhu pemanasan awal. Dengan keratan

rentas metalurgi, ujian ketahanan, kesan dari parameter yang pelbagai, kecacatan

makrostruktur dapat dilihat dan dijelaskan. Berdasarkan keputusan kajian, penembusan

keluli tahan karat terhadap aloi aluminium terjadi semasa proses pemanasan awal di

aplikasikan. Sampel C menunjukkan keputusan terbaik melalui ujian kekerasan dengan

nilai 850HV dan nilai ujian ketahanan iaitu 19.91 Mpa. Suhu pemanasan awal yang

optimum adalah 85ºC dan dengan menggunakan logam pengisi ER 4043.

vii

TABLE OF CONTENTS

Page

SUPERVISOR’S DECLARATION ii

STUDENT’S DECLARATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xiv

LIST OF ABBREVIATIONS xvi

CHAPTER 1 INTRODUCTION

1.1 Introduction 1

1.2 Problem Statement 2

1.3 Objectives of the Research 3

1.4 Scopes of the Research 3

viii

CHAPTER 2 LITERATURE REVIEW

2.1 Automotive Industry 4

2.2 Welded Part 5

2.3 Welding Types 6

2.4 Gas Tungsten Arc Welding 7

2.5 Heat Treatment (Preheating) 9

2.6 Aluminium 6061 10

2.7 Stainless Steel 12

CHAPTER 3 METHODOLOGY

3.1 Introduction 13

3.2 Material Selection 13

3.2.1 Aluminium 13

3.2.2 Stainless Steel 15

3.2.3 Filler Metals 16

3.3 Dimensions and Position of Specimens 17

3.4 Fabrication Process 18

3.4.1 Process Involve 18

3.4.1.1 Measuring and Cutting 18

3.4.1.2 Joining Process 19

3.5 Specimen’s Mechanical Properties 21

ix

3.5.1 Tensile test 21

3.5.1.1 The Tensile Test Specimen 23

3.5.2 Hardness Test 23

3.6 Microstructure and Phase Composition Analysis 25

3.6.1 Cold Mounting 25

3.6.2 Grinding 25

3.6.3 Polishing 26

3.6.4 Etching 27

3.6.5 Analysis of Microstructure 28

3.7 Flow Chart 29

CHAPTER 4 RESULTS AND DISCUSSION

4.1 Introduction 30

4.2 Appearance and macrostructure 30

4.2.1 Group 1: With ER 4043 filler metal 30

4.2.2 Group 2: With ER 4047 filler metal 32

4.3 Microstructure of the welding joints 36

4.3.1 Group 1: Without preheating process 36

4.3.2 Group 2: 85ºC preheating process 37


4.4 Hardness distribution test 42

4.4.1 Group 1: Without preheating process 42



x

4.5 Mechanical properties 46

CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Introduction 48

5.2 Conclusion 48

5.3 Recommendation 49

5.3.1 Cracks 49

5.3.2 Cold cracking 49

5.3.3 Pre-heating 50

5.3.4 Post Weld Heat Treatment (PWHT) 50

REFERENCES 51

APPENDICES 54

A Without preheat properties table 54

B 85ºC preheat properties table 54

C 150ºC preheat properties table 55

xi

LIST OF TABLES

Table No. Title Page

3.1 Nominal chemical composition of aluminum wrought alloys 14

3.2 Mechanical properties of Aluminum 14

3.3 Physical properties of aluminum alloy 14

3.4 Mechanical properties of stainless steel 15

3.5 Physical properties of stainless steel 15

3.6 Nominal chemical composition of ER 4043 16

3.7 Nominal chemical composition of ER 4047 16

3.8 Welding parameters without preheating temperature 20

3.9 Welding parameters with preheating temperature (85 ºC) 21

3.10 Welding parameters with preheating temperature (150 ºC) 21

xii

LIST OF FIGURES

Figure No. Title Page

2.1 Exploded view of current or potential tailor welded blanks body 5

2.2 Parts of a fillet weld 6

2.3 AWS master chart of welding and joining process 7

2.4 Tungsten Inert Gas (TIG) Welding 8

2.5 Sheet of aluminium 6061 11

2.6 Stainless steel sheet 12

3.7 Dimension for aluminium 6061 and stainless steel 17

3.8 The butt joint position of stainless steel and also aluminium 17

6061 during the welding process

3.9 Shearing machine 19

3.10 TIG welding machine and process 20

3.11 Tensile test machine 22

3.12 Geometry of tensile test specimens (ASTM D1002) 23

3.13 Vickers hardness test machine 24

3.14 Cold mounting machine 25

3.15 Buehler grinding machine 26

3.16 Polishing machine 26

3.17 (a) Solution for etching (b) fume hood 27

3.18 Optical microscope 28

3.19 Flowchart of overall methodology 29

4.20 Cross section of welding for Group 1 using filler metal ER 4043 31

4.21 Cross section of welding for Group 2 using filler metal ER 4047 32

4.22 The microstructure image of the cross section on the weldment area 36

xiii


(85 ºC)


(150 ºC)

4.25 Hardness distribution for group 1 42



4.28 Bar chart represents the tensile and hardness test for specimens 46

welded at 45A with filler metal ER 4043 and ER 4047

xiv

LIST OF SYMBOLS

Strain

Stress

A Area

A Ampere

F Force

Kg Kilogram

mm Millimeter

Mpa Mega pascal (10x6)

N Newton

Lo Initial length

L Final length

HV Hardness value

°C Degree celcius

T Temperature

To Initial temperature

V Welding speed

Π Pi (3.142)

K Thermal conductivity

Q Heat density

U Voltage

xv

I Current

s Seconds

% Percentage

xvi

LIST OF ABBREVIATIONS

TIG Tungsten Inert Gas

AC Alternating current

DC Direct current

TWBs Tailor Welded Blanks

GTAW Gas Tungsten Arc Welding

HAZ Heat Affected Zone

UMP Universiti Malaysia Pahang

IMC Intermetallic compound

PPE Personal protective equipment

ASTM American Standard Test Method

CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

Welding is the most common method of joining two or more pieces of metal to

make them act as a single piece. It allows us to produce a monolithic structure (formed a

single structure) that is strong in all directions (Helzer, 2005). Welding is used to join

all the commercial metals, alloys and to join metals of different types and strength.

Welding and joining process can be divided into 7 main types. There are arc welding

(AW), resistance welding (RW), soldering (S), solid state-welding (SSW), oxyfuel gas

welding (OFW), brazing (B), other type of welding and joining process (adhesive

bonding, flow brazing, flow welding). Nowadays, we are trying to produce an

improvement in welding process known as Tailor Welded Blanks (TWBs).

TWBs is the process where two or more materials with similar or different

strengths or thicknesses joined together to form a single part before the forming

operation. TWBs can be performed in any type of welding process. The common

method used to perform this dissimilar welding is arc welding (AW). Gas tungsten arc

welding (GTAW) is one type of arc welding that can be use in order to perform this

task. GTAW uses a non consumable electrode that does not melt in the arc, and filler

metal is added separately to the welding.

2

1.2 PROBLEM STATEMENT

There are so many advantages of TWBs. Automakers are using tailor-welded

blanks to make cars safer, lighter, and more environmentally efficient and tailored

blanks have become the future of automaking. Vehicle weight savings, part-count

reduction, an improved stiffness/weight ratio, enhanced crash energy management, and

an overall reduction in manufacturing costs are the results of TWBs (Sierra, 2008).

Even so, the dissimilar welding still has the drawbacks. The main problem that most of

the welder faces in order to performed TWBs is that the joints obtained between the

stainless steel-aluminium alloys are not strong enough. This problem happened due to

the different mechanical properties that is melting point of each material and most of all

because the near zero solubility of iron in aluminium (Sierra, 2008). This two major

problem has lead to the formation of brittle intermetallic compound (IMC) inside the

transition zone which increased the weakness of the joint. In order to overcome these

problems and produce a sound joint between these materials, a method of preheating the

material and different type of filler metal is proposed.

Preheating involves raising the temperature of the parent material (stainless

steel) on the joint side to a value above ambient temperature (Croft, 2003). Based on

previous research formed by Aida Syamsiah bt Mohd Yusof (ME 08061), this

preheating method had showed us a promising results to achieve a sound joint between

stainless steel-aluminium alloys dissimilar welding joint (Aida, 2011). This research had

been continued to improve the results obtained by Aida by making some modification

regarding on the temperature of the preheating involved. This research looks into the

effect of preheating of the stainless steel and its effect on the joints quality. This

research also will investigate the relationship between different type of filler metal used

and the mechanical properties gained. All specimens will be investigating regarding on

the mechanical properties of the weld joint.

3

1.3 OBJECTIVES

The main objectives of this study are as follows:

i. Fabrication of welded stainless steel to aluminium alloys sheets using

different fillers and with the help of steel preheating.

ii. To investigate the mechanical properties of dissimilar stainless steel to

aluminium alloys lap joint welding with the preheating of steel.

iii. To investigate the microstructure of the welded part formed between stainless

steel-aluminium alloys weld.

1.4 PROJECT SCOPE

The main scopes of this study are as follows:

i. Fabrication of welded stainless steel to aluminium alloys sheets using different

fillers and with the help of steel preheating.

ii. Investigate the heat treatment (preheat) and type of filler metal used on the

strength of the welded part joints by using Vickers hardness test and also tensile

test.

iii. Investigate the microstructure of the welded part by using optical microscope

and to compare the mechanical properties of the welded part relation with the

type of filler metal used.

CHAPTER 2

LITERATURE REVIEW

2.1 AUTOMOTIVE INDUSTRY

Nowadays, the automotive are trying to produces cars that has a very low fuel

consumption in order to follow the anti pollution standard and also to attract the buyers.

This goal can mostly be achieved by producing lightweight vehicles. But, the car needs

to maintain their body strength and must be high in endurance. No wonder that

automotive industries nowadays are using several methods for example like high

strength steel and light metal such as aluminium to make car are being investigated.

Automakers are using tailor-welded blanks to make cars safer, lighter, and more

environmentally efficient and tailored blanks have become the future of automaking

TWBs is the process where two or more materials with similar or different strengths or

thicknesses joined together to form a single part before the forming operation. Figure 1

shows the usage of TWB in automotive industry.

5

Figure 1: Exploded view of current or potential tailor welded blanks body

Source: (Kinsey, Viswanathan, Cao, 2001)

This implies the joining of dissimilar metal such as steel and also aluminium.

The steel to aluminium welding is not an easy way to achieve due to their great

difference in both of their properties especially melting temperature and near zero

solubility of iron in aluminium which lead to the creation of brittle intermetallic

compound (IMC) (Sierra, 2008).

2.2 WELDED PART

Welded joints normally consist of several parts. Normally, a part that had been

welded contains weld leg, weld face, weld toe, actual throat, theoretical throat, effective

throat, weld root and also joint root (Miller, 2010). Each of these parts plays an

important role in making the joint to be strong. Weld leg is actually the distance from

the joint root to the toe of a fillet weld. Weld toe is the junction of the weld metal and

the weld face. Weld face is the exposed surface of the weld, bounded by the weld toes

on the side which the welding was done. Weld root is the area where the filler metals

intersect the base metal and extends the furthest into the weld joint. The actual throat is

the shortest distance from the face of a fillet weld to the weld root after welding. The

theoretical throat is the distance from the joint root, perpendicular to the hypotenuse of

6

the largest right-angle triangle that can be inscribed within the cross section of a fillet

weld. The effective throat on the other hand is the minimum distance, minus the

convexity between the weld face and the weld root. Lastly, joint root is the portion of a

weld joint where joint members are the closest to each other. Figure 2 shows the parts of

a fillet weld.

Figure 2: Parts of a fillet weld

Source: (http://www.weldguru.com/SMAWNomenclatureandJoints)

2.3 WELDING TYPES

Till nowadays, both of this steel and aluminium were only be joined by using

mechanical means such as screwing or riveting and also using solid state welding

process like explosion welding (Andrews, 1962) or friction stir welding (Bel'chuk,

1961). Welding is the most common method of joining two or more pieces of metal to

make them act as a single piece. It allows us to produce monolithic structure that is

strong in all direction. Welding and joining process can be divided into 7 main types.

Figure 3 below shows AWS master chart of welding and joining process.

http://www.weldguru.com/SMAWNomenclatureandJoints

7

Figure 3: AWS master chart of welding and joining process.

Source: (http://www.lbl.gov/ehs/pub3000/CH33)

2.4 GAS TUNGSTEN ARC WELDING (GTAW)

The method that will be used to perform this task is by using the gas tungsten arc

welding (GTAW) process. GTAW uses a non consumable electrode that does not melt

in the arc and filler metal is added separately to the welding. GTAW process will supply

the inert gasses (usually argon gas) in order to protect contaminants and oxidation

process from happen which will cause defect to the joints area. GTAW welding uses

torch as the main heat source in order to fuse the filler with the material. GTAW torches

are available water cooled or air cooled. The heat transfer efficiency for GTAW welding

may be as low as 20%. This means that 80% of the heat generated does not enter the

http://www.lbl.gov/ehs/pub3000/CH33

8

weld but stay in the torch. To avoid damage to the torch, the heat must be removing.

(Jeffus, 2010)

a) Following are some of the advantages of air cooled GTAW torch:

Lighter weight for the same amperage range

More portable

Easier to maintain

No water supply required

No water leakage danger

b) But there are also disadvantages of air cooled GTAW torch:

Cannot continuous operation without over heating

High torch temperature means more tungsten erosion

More torch handle temperature in the welder’s hands

Figure 4 shows the Tungsten Inert Gas (TIG) welding machine

Figure 4: Tungsten Inert Gas (TIG) Welding

Source: (Jeffus, 2010)

9

2.5 HEAT TREATMENT (PREHEATING)

Although that TIG welding process have a lot of advantages, a sound dissimilar

welding between aluminium alloys to stainless steel are still hard to be obtained. This is

due to high differences of the melting points between these materials. Heat treatment

(preheat) is one of the methods that can be done in order to solve this major problem.

Preheating involves raising the temperature of the parent material (stainless steel) on

side of the joint to a value above ambient temperature. Normally, there are 4 main

functions of preheat (Funderburk, 1997). Firstly, preheating is applied because it can

slow down the cooling rate in the weld metal and base metal, producing a more ductile

metallurgical structure with greater resistance to cracking. Secondly, the slower cooling

rate that had been obtained can provide an opportunity for hydrogen that may present to

diffuse out harmlessly, reducing the potential for cracking to happen. Thirdly, preheat

can helps to reduce shrinkage stresses in the weld and adjacent base metal. Lastly, it can

raise some steels above the temperature at which brittle fracture would occur in

fabrication.

This research was designed to investigate so that the function of preheating can

be added with another one more unique purpose. This research will investigate the

effect of preheating in order to raise the initial temperature of the stainless steel so that

the melting temperature of the steel can be obtained at the time the aluminium alloys

melt. When this happen, a sound joint between these two materials since both of the

metal had exist in molten state and fusion can be performed during this liquid state. As

we know, the melting point of aluminium is between 550°c - 660°c while the melting

temperature of stainless steel is between 1300°c - 1400°c. When the welding process

starts, the temperature of both materials will increase. At 550°c - 660°c, the aluminium

starts to melt and perform the bonding. Unfortunately, the steel still did not achieve the

melting temperature and exist in solid state. So, the bonds that form between these two

materials are still not strong enough. By using preheat; we want to increase the initial

temperature of the stainless steel so that when the aluminium reaches its melting

temperature, the steel reach a near melting point.

10

Besides that, aluminium to steel welding will produce the brittle IMC at the

welded area due to near zero solubility and extreme different in melting point. This

compound can cause the bonding between the aluminium alloys and stainless steel to be

weak due to its brittle behavior. This research will investigate two type of different filler

metal that is Al-5%Si (ER 4043) and Al-12%Si (ER 4047) on the strength of the weld

area and also the formation of the IMC. Each filler metal can affect the thickness

formation of the IMC. Normally, the formation of the IMC layer is due to the reaction

between the Fe (Ferum) and the Al (Aluminium) atom inside the welding area. The

formation of the IMC need to be avoided since this compound can weaken the joint

between those steel and aluminium due to its brittle behavior. So, because of this

problem, this research will investigate the most suitable filler metal in order to decrease

the thickness of the IMC formation on the weld area (Sierra, 2008).

H. Dong (Dong, 2011) had obtained a result of TIG dissimilar welding between

galvanized steel and aluminium alloys until 136Mpa of tensile strength at the joint area

by using ER 4047 filler metal. The research said that the addition of Si (Silicon) into the

weld could suppress the diffusion of Fe from the steel base metal into the weld, reduce

the thickness of IMC and improve the tensile strength of the joint. Based on that

research, the thickness of the IMC layer could be controlled with using of ER 4047 filler

metal. For the ER 4043 filler wire has a result of 134Mpa of tensile strength at the joint

area. In this research, we will investigate the effect of these filler metal on the joint

formation and compare the results between these two experiments.

2.6 ALUMINIUM 6061

In this experiment, aluminium 6061 and galvanized steel will be used. The

unique combination of light weight relatively high strength makes aluminum the second

most popular metal that is welded. Aluminum is not difficult to joint, but aluminum

welding is different from welding steels. A system of four digit numbers has been

developed by Aluminum Association, Inc., and adopted by the American Society for

Testing Materials (ASTM) designate the wrought aluminum alloy types. The series that

11

used for this project is 6XXX series which designates magnesium and silicon as the

major alloys (The Virtual Machine Shop website, 2006).

Aluminum possesses a number of properties that make welding different than

welding steel, these are:

Aluminum oxide surface coating

High thermal conductivity

High thermal expansion coefficient

Low melting temperature

The absence of color change as temperature approaches the melting point

(dull red)

Figure 5 shows the sheet of aluminium 6061 that will be used in the experiment.

Figure 5: Sheet of aluminium 6061

Source: http://image.made-in-china.com/2f0j00bCLEReWsZBzS/Sheet-of-Aluminium-

6061

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