Failure Analysis On TIG Weldment.

FAILURE ANALYSIS ON TIG WELDMENT

AHMAD MUSLIM BIN OTHMAN

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

FAILURE ANALYSIS ON TIG WELDMENT

Report submitted in accordance with the partial requirements of the Universiti Teknikal Malaysia Melaka for the

Bachelor of Manufacturing Engineering (Manufacturing Process) with Honours

By

AHMAD MUSLIM BIN OTHMAN

Faculty of Manufacturing Engineering March 2008

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APPROVAL

This report submitted to the senate of UTeM and has been accepted as partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Manufacturing Process). The members of the supervisory committee are as follow:

………. Main Supervisor

(Official Stamp & Date)

……… Co-Supervisor

DECLARATION

I hereby, declare this thesis entitled “Failure Analysis on TIG Weldment” is the result of my own research except as cited in the reference.

Signature : ……….

Author Name : ………

Date : ………

AHMAD MUSLIM BIN OTHMAN 25TH March 2008

ABSTRAK

Projek sarjana muda ini mendedahkan dan membincangkan kajian tentang analisa kegagalan dalam kimpalan arca gas tungsten (TIG Welding). Objektif projek kajian menganalisa kegagalan dalam TIG welding ini adalah untuk mengenalpasti jenis kegagalan atau kecacatan yang berlaku dalam proses lekatan atau pengabungan produk. Parameter atau keadaan yang menyebabkan kegagalan atau kecacatan ini akan dikaji dan dianalisa. Projek ini akan dijalankan di makmal mesin syop, di Universiti Teknikal Malaysia, Melaka dan mesin yang akan digunakan ialah kimpalan arca gas tungsten (TIG welding). Bahan yang sama seperti mild steel akan digunakan untuk tujuan proses kimpalan, dan proses ini akan diulangi. Kegagalan atau kecacatan yang berlaku pada proses kimpalan tersebut akan direkodkan. Kegagalan atau kecacatan yang dijangka akan berlaku pada proses kimpalan tersebut adalah seperti “root crack”, “porosity”, “slag inclusion” dan “lack of root fusion”. Method yang digunakan dalam mengkaji dan menganalisa kecacatan yang berlaku ialah “Fault Tree Analysis” (FTA) dan gambarajah tulang ikan atau gambarajah Ishikawa. Method ini digunakan untuk mencari sebab dan penyebab yang menyumbang berlakunya kegagalan atau kecacatan dalam proses kimpalan dan penyelesaian akan diberi untuk teknik penggunaan kimpalan dengan betul dan mesin “setting” dengan betul.

ABSTRACT

This project is discussed about failure analysis on Tungsten Inert Gas (TIG) weldment. The objective of this failure analysis project is to determine and identify the type of failure that most occur in TIG welding. The parameter that contribute to this failure occur also will be study and identify. This failure analysis project will be held in machine syop laboratory at Universiti Teknikal Malaysia, Melaka and the machine that will be used is Tungstent Inert Gas welding. The same material such as mild steel will be used to do the joining process, and this action will be repeated and all the failure or defects that occur during this process will be recorded. The failure that expected to be occurring during this joining process is root crack, porosity, slag inclusion, and lack of root fusion. These all defects or failures will be analyzed using Fault Tree Analysis (FTA) and fishbone or cause and effect diagram. This method is used to determine the causes for this failure occur and recommendation for proper welding technique and proper parameter setting for this machine can be suggested after that.

DEDICATION

ACKNOWLEDGEMENTS

This Final Year Project Report (Projek Sarjana Muda) is realized by the courtesy of Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka (UTeM) in partial fulfillment for Bachelor of Engineering.

I would like to take this opportunity to express my sincere and gratitude to my Final Year Project Supervisor, Mr. Khairul Anuar A. Rahman for his guidance, contribution and opinion during this PSM report completion. He also gave me a lot of advice, encouragement and support to ensure I can get what I need during this project research and he always had a meeting with me to discuss about this project.

My greatest thanks to Manufacturing Faculty (FKP) especially to Professor Dr. Mohd Razali b. Muhamad, Dean of Faculty of Manufacturing Engineering, UTeM, Mr Mohd Hadzley b. Abu Bakar and all the lectures in the faculty because their commitment to support and encourage the final year student.

I also would like to acknowledge to all FKP technicians for supporting and gave me a lot of information about this project (PSM) and with this information, I can complete and finished this PSM project as schedule.

Last but not list, to my entire friend and everyone who had gave me a lot of support and valuable information during this project report completion.

TABLE OF CONTENTS

Abstrak………...i

Abstract……….ii

Dedication………iii

Acknowledgement………...iv

Table of Contents………...v

List of Figures………..ix

List of Tables………...xi

Sign and Symbols………...…xii

List of Appendices……….viii

CHAPTER 1 INTRODUCTION………...1

1.1 Background introduction………1

1.1.1 TIG Welding………2

1.1.2 Failure Analysis………...3

1.2 Problem Statements………4

1.3 Objectives………...4

1.4 Scope of Research………...4

CHAPTER 2 LITERATURE REVIEW………..5

2.1 Introduction……….5

2.2 Tungsten Inert Gas (TIG) Welding………...11

2.2.1 TIG Welding Aluminum………12

2.2.2 Aluminum Characteristic for TIG Welding………...13

2.2.3 Filling the Gap………...14

2.2.4 Recommendation Filler Metal for Various Aluminum Alloys ……….15

2.2.5 Cleanliness of the Welding Surface………...16

2.3 The TIG Welding System……….18

2.3.1 Power Source……….18

2.3.2 TIG Torch………..20

2.3.4 TIG Luxuries………..21

2.3.5 TIG Electrodes………...22

2.3.6 TIG Filler Metal……….23

2.4 Type of Material Compatible with TIG………23

2.4.1 Aluminum and Magnesium………24

2.4.2 Steel………25

2.4.3 Copper Alloys………25

2.4.4 Dissimilar Metals………...25

2.5 Process Variations………26

2.6 Safe Working Procedures for Welding Workshop………...27

2.6.1 Personal Protective Equipment………..29

2.6.2 Other Safety Precaution……….29

2.6.3 Manufacturing Consideration………30

2.6.4 Finish Consideration………..31

2.7 Type of Weld Joints in TIG………..31

2.8 TIG Welding Defects/Failure………...32

2.9 Failure Analysis Method………...36

2.9.1 Fishbone Diagram………..36

2.9.2 Fault Tree Analysis (FTA)……….39

CHAPTER 3 METHODOLOGY………...43

3.1 Introduction………...43

3.1.1 Discussion and Confirmation on Project Title………...45

3.1.2 Literature Review about Project Title………45

3.1.3 Welding Equipment………...45

3.2 Identify the Failure Occur……….46

3.3 Analyze Using Fishbone Diagram………47

3.4 Apply the Method of Fault Tree Analysis………49

3.5 Failure Analysis Methodology………..51

CHAPTER 4 RESULT……….53

4.1 Introduction………...53

4.2 Type of defects and discontinuities found………....53

4.2.1 Result for 60A current consumption………..54

4.2.2 Result for 80A current consumption………..55

4.2.3 Result for 100A current consumption………....56

4.2.4 Result for 120A current consumption………58

4.3 Misalignment discontinuities………60

4.4 Failure analysis using FTA method………..61

4.4.1 Porosity………..61

4.4.2 Overlap………...62

4.4.3 Incomplete fusion and penetration……….…63

4.4.4 Underfill……….64

4.4.5 Misalignment……….65

CHAPTER 5 DISCUSSION………67

5.1 Discussion……….67

5.2 Accepted joint………...………67

5.3 Further analysis for porosity……….68

5.4 Unrecognized Joint Defect……….………..69

5.5 TIG polarity………..70

5.6 Different between discontinuities and welding defect………..…71

5.7 Causes for rejection and how to avoid welding defect……….71

5.8 Welding inspection………...72

CHAPTER 6 CONCLUSION……….73

6.1 Conclusion………73

6.2 Recommendation for further research………..74

APPENDICES

A List of Recommended Tungsten Electrodes B Fault Tree Analysis Example

C Suggested Setting for TIG Welding Aluminum D Suggested Setting for TIG Welding Stainless Steel E Suggested Setting for TIG Welding Plain Steel F Gantt chart for PSM 1

LIST OF FIGURES

Figure 2.1 TIG Welding 11

Figure 2.2 Automotive Application 13

Figure 2.3 Power Source 18

Figure 2.4 TIG Torch Disassembled 20

Figure 2.5 Foot Pedal Controller 22

Figure 2.6 TIG Electrodes 22

Figure 2.7 TIG Filler Metal 23

Figure 2.8 Type of Welds Joints 31

Figure 2.9 Type of Welds 32

Figure 2.9.1 Example of Fishbone Diagram 38

Figure 2.9.2 Example of FTA Diagram 40

Figure 3.1 Process Planning of the Project 44

Figure 3.2.1 Failure Occur during TIG Welding (bar graph) 46 Figure 3.2.2 Failure Occur During TIG Welding (Pareto Diagram) 47

Figure 3.3 Fishbone Diagram 48

Figure 3.5 Flow Chart of Failure Analysis Using TIG Welding 51 Figure 4.2 Type of defects and discontinuities found 54

Figure 4.2.1a Incomplete fusion occur 54

Figure 4.2.1b Incomplete fusion occur 55

Figure 4.2.1c Incomplete penetration occur 55

Figure 4.2.2a Underfill occur 55

Figure 4.2.2b Underfill occur 56

Figure 4.2.3a Incomplete fusion occur 56

Figure 4.2.3b Incomplete fusion occur 56

Figure 4.2.3c Porosity occur 57

Figure 4.2.3d Porosity occur 57

Figure 4.2.3e Porosity occur 57

Figure 4.2.4a Porosity and incomplete fusion occurs 58 Figure 4.2.4b Porosity and incomplete fusion occurs 58

Figure 4.2.4c Porosity occur 58

Figure 4.2.4d Overlap occur 59

Figure 4.2.4e Overlap occur 59

Figure 4.2.4f Overlap occur 59

Figure 4.3a Misalignment defect 60

Figure 4.3b Misalignment defect 60

Figure 4.3c Misalignment plate 60

Figure 4.4.1 FTA diagram of porosity 61

Figure 4.4.2 FTA diagram of overlap 62

Figure 4.4.3 FTA diagram of incomplete fusion and penetration 63

Figure 4.4.4 FTA diagram of underfill 64

Figure 4.4.5 FTA diagram of misalignment 65

Figure 5.2 Acceptance joint 67

Figure 5.3a Pore 68

Figure 5.3b Double pores 68

Figure 5.3c Entrapped bubble 68

Figure 5.4.1 Inclusion 69

LIST OF TABLES

Table 2.1 Recommendation for Filler Metal 15

Table 2.2 General Cleaning Procedures for Aluminum 17

LIST OF ABBREVIATIONS, SYMBOLS, SPECIALIZED

NOMENCLATURE

TIG - Tungsten Inert Gas Welding GTAW - Gas Tungsten Arc Welding SMAW - Shielded Metal Arc Welding FTA - Fault Tree Analysis

FMEA - Failure Mode and Effect Analysis AC - Alternating current

DC - Direct Current

AMC - Aluminum matrix composite

DCEP - Direct current with positive charge electrode DCEN - Direct current with negative charge electrode

CHAPTER 1

INTRODUCTION

1.1 Background Introduction

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld puddle) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the workpieces.

There are about 100 different types of welding. Arc welding is the most common type. It uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, or an evaporating filler material. The process of arc welding is widely used because of its low capital and running costs.

Welders use many types of welding equipment set up in a variety of positions, such as flat, vertical, horizontal, and overhead. They may perform manual welding, in which the work is entirely controlled by the welder, or semiautomatic welding, in which the welder uses machinery, such as a wire feeder, to perform welding tasks.

1.1.1 Tungsten Inert Gas welding (TIG)

Tungsten Inert Gas (TIG) Welding is another name for Gas Tungsten Arc Welding. In arc-welding, developed in the mid – 1800s, the heat required is obtained from electrical energy. The process involves is either a consumable or a nonconsumable electrode. An arc is produced between the tip of the electrode and the workpiece to be welded, by using an AC or a DC power supply. The arc temperature is about 30,000 degree Celsius that had much higher temperature than those developed in oxyfuel-gas welding.

Tungsten Inert Gas (TIG) Welding uses a nonconsumable tungsten electrode that creates an arc between the electrode and the weld pool. An inert shielding gas is used in the process at no applied pressure. Argon is most commonly used as the shielding gas, and the process may be employed with or without the addition of filler metal.

The TIG welding process is used for a wide variety of metals and applications, particularly aluminum, magnesium, titanium, and the refractory metals. TIG welding also suitable especially for thin metals. The cost of the inert gas makes this process more expensive than shielded metal arc welding (SMAW) but provides a high quality welds and surface finish. It is used in a variety of critical applications with a wide range of work piece thicknesses and shape and the equipment is portable.

Typical applications for TIG welding include pipes, pressure vessels and heat exchangers. Since TIG welding can be used to weld thin metals and small objects, the method is also used in the electronics industry.

1.1.2 Failure Analysis

Failure analysis can be defined as a method or a series of actions undertaken to find the reasons a particular failure exists and correcting the causes. It is also the process of collecting and analyzing data to determine the cause of a failure and how to prevent it from recurring. It is an important discipline in many branches of manufacturing industry, where it is a vital tool used in the development of new products and for the improvement of existing products. It is vitally important to understand that these two distinct elements are both essential if one is to embark on a study of failure analysis.

There is no particular relevance to knowing the cause or causes of a certain failure are if the problem cannot be resolved. In this definition, failure analysis can obviously apply to numerous fields of study. In this project, I was studying failure analysis as it applies to the TIG welding techniques.

The purpose of this project is to analyze, collecting and determine the cause of a failure in Tungsten Inert Gas Welding (TIG) and how to prevent it from occurring. The various technique of TIG welding also will be discuss to ensure the best technique will be apply in various condition of welding. The welding technique will be analyzed with the result that it produces.

In this failure analysis of TIG weldment, The Fault Tree Analysis (FTA), and Fish bone method will be use to analyze the failure that occur in various condition of TIG welding techniques.

1.2 Problem Statements

The failure analysis will be carried on at welding laboratory in Universiti Teknikal Malaysia, Melaka (UTEM) at Ayer Keroh, Malacca. Before that, this failure analysis on TIG welding were be study and the method to be used was recognize to ensure all the probably or actual failure on TIG welding were identified. The TIG welding was very hard to handle and because of that, it may produce a various type of failure in product or component to be joint. The main problem of this welding is it needs a proper technique that must be used according to the situation such as a DC power and current setting must be matching and the use of filler metal in welding.

1.3 Objective

1) To identify the type of failure that occurs in TIG welding. 2) To analyze the failures occur in TIG welding using FTA.

3) To identify parameter that contribute to failure occur in TIG welding.

1.4 Scopes of the Research

This project focuses on failures that occur during Tungsten Inert Gas (TIG) welding. The failures than will be analyze using Failure Tree analysis (FTA) and before that, a statistic such as histogram must be created to identify the type of failure that occur. A proper welding technique must be applied to decrease the probability of failure in TIG welding. In this project, the TIG welding instruments will be used at Manufacturing Laboratory in UTem to complete the analysis of failure that will be produced.

CHAPTER 2

LITERATURE REVIEW

2.1 IINTRODUCTION (JURNAL)

Pantazopoulos, G. and Sampani, A. (2006) doing a case study on weld failure of a rolled Zn- alloy strip that mainly used in construction industry. They found that significant welding defects, such as linear discontinuities, edge micro cracks and fusion zone gas porosity are detected during the investigation procedure. The size and distribution of pores in the fusion zone affect directly the mechanical behaviors and the workability of the welded tube. They also found that Welding defects due to the application of improper welding procedure is a significant contributor of limited weld workability and premature failure. [1]

Jha, A. K. et al. (2003) doing a Metallurgical analysis of cracking in weldment of propellant tank for satellite launch vehicles that use a Medium strength Al–Zn–Mg aluminum alloy. They found that various type of crack occur in TIG welding area at propellant tank and cracking initiated from the root of pit, followed the path of solute enriched dendrite caused intergranular mode of fracture. This confirmed the cracking was due to stress corrosion. The stress introduced during welding as contractional strain in accommodating the nozzle facilitated the cracking phenomena. [2]

Meola, C. et al. (2004) have conduct a testing and analysis of stainless steel welded joints between destructive and non-destructive techniques. They have found three techniques for weld joints analysis that use micrographs, Vickers micro-hardness measurements, and Lockin thermography. These three techniques are synergic and helpful for a complete characterization welded joints and for improvement of the welding method. [3]

Tarng, Y. S., Tsai, H.L. and Yeh, S.S. (1999) have done an experiment in Modeling, optimization and classification of weld quality in tungsten inert gas welding. In the project, they describe an intelligent modeling, optimization and classification of weld quality in TIG welding process. A back-propagation network is used to construct the relationships between the process parameters and the features on the weld pool geometry. A gobal optimization algorithm called simulated annealing is then applied to the network for solving the process parameters with optimal weld pool geometry based on an objective function. Furthermore, the fuzzy c-means algorithm is adopted here to classify and verify the weld quality using the features on the weld pool geometry. Through this study, highly non-linear, strongly coupled, multivariable TIG welding processes can be further understood, analyzed and controlled. [4]

Liming, L. and Shengxi, W. (2006) have doing a study on the dissimilar magnesium alloy and copper lap joint by TIG welding. During his study, they have found that in the TIG welding of dissimilar magnesium alloy and copper, intermetallic compounds were produced in the interfacial region. Intermetallic compounds were the main cause of embrittleness of the joints.By using iron plate as interlayer between magnesium alloy and copper, the embrittleness of joint was obviously decreased and the tensile strength of the joint is higher compared with that, without iron plate. They also noticed that Metallic oxides in the interfacial region between iron plate and magnesium alloy were the main reasons influenced the strength. [5]

UrenÄ, A. et al. (2000) has describes about the influence of interface reactions on fracture mechanisms in TIG arc-welded aluminum matrix composites. They conclude that: [6]

• TIG arc welding of aluminum matrix composites (AMC) reinforced with SiC particles produced severe degradation of the materials because of the formation of Al4C3 in the matrix/reinforcement interface.

• The failure mechanisms in the studied AMCs were mainly: particle fracture for particles larger than 10 mm; and ductile matrix failure in the proximity of the SiC/Al interface for particles smaller than 10 mm.

• Fracture of the welded composites was mainly controlled by interface debonding through the continuous interface reaction layer, although the formation of discontinuous tabular Al4C3 aggregates with preferential dissolution of some SiC planes also favoured damage to particles smaller then 10 mm.

• Interfacial reactions between SiC particles and molten aluminium during welding also produced degradation of fracture behavior of the aluminum matrix which was associated with the Si enrichment.

• Arc welding of the studied composites presented an additional problem of porosity in the weld, which was enhanced by the increase of the reinforcement grade and welding power. It has been mainly characterised as interdendritic porosity associated to the low wettability of the SiC particles by molten aluminum.

1.1.1 Tungsten Inert Gas welding (TIG)

Tungsten Inert Gas (TIG) Welding is another name for Gas Tungsten Arc Welding. In arc-welding, developed in the mid – 1800s, the heat required is obtained from electrical energy. The process involves is either a consumable or a nonconsumable electrode. An arc is produced between the tip of the electrode and the workpiece to be welded, by using an AC or a DC power supply. The arc temperature is about 30,000 degree Celsius that had much higher temperature than those developed in oxyfuel-gas welding.

Tungsten Inert Gas (TIG) Welding uses a nonconsumable tungsten electrode that creates an arc between the electrode and the weld pool. An inert shielding gas is used in the process at no applied pressure. Argon is most commonly used as the shielding gas, and the process may be employed with or without the addition of filler metal.

The TIG welding process is used for a wide variety of metals and applications, particularly aluminum, magnesium, titanium, and the refractory metals. TIG welding also suitable especially for thin metals. The cost of the inert gas makes this process more expensive than shielded metal arc welding (SMAW) but provides a high quality welds and surface finish. It is used in a variety of critical applications with a wide range of work piece thicknesses and shape and the equipment is portable.

Typical applications for TIG welding include pipes, pressure vessels and heat exchangers. Since TIG welding can be used to weld thin metals and small objects, the method is also used in the electronics industry.

1.1.2 Failure Analysis

Failure analysis can be defined as a method or a series of actions undertaken to find the reasons a particular failure exists and correcting the causes. It is also the process of collecting and analyzing data to determine the cause of a failure and how to prevent it from recurring. It is an important discipline in many branches of manufacturing industry, where it is a vital tool used in the development of new products and for the improvement of existing products. It is vitally important to understand that these two distinct elements are both essential if one is to embark on a study of failure analysis.

There is no particular relevance to knowing the cause or causes of a certain failure are if the problem cannot be resolved. In this definition, failure analysis can obviously apply to numerous fields of study. In this project, I was studying failure analysis as it applies to the TIG welding techniques.

The purpose of this project is to analyze, collecting and determine the cause of a failure in Tungsten Inert Gas Welding (TIG) and how to prevent it from occurring. The various technique of TIG welding also will be discuss to ensure the best technique will be apply in various condition of welding. The welding technique will be analyzed with the result that it produces.

In this failure analysis of TIG weldment, The Fault Tree Analysis (FTA), and Fish bone method will be use to analyze the failure that occur in various condition of TIG welding techniques.

1.2 Problem Statements

The failure analysis will be carried on at welding laboratory in Universiti Teknikal Malaysia, Melaka (UTEM) at Ayer Keroh, Malacca. Before that, this failure analysis on TIG welding were be study and the method to be used was recognize to ensure all the probably or actual failure on TIG welding were identified. The TIG welding was very hard to handle and because of that, it may produce a various type of failure in product or component to be joint. The main problem of this welding is it needs a proper technique that must be used according to the situation such as a DC power and current setting must be matching and the use of filler metal in welding.

1.3 Objective

1) To identify the type of failure that occurs in TIG welding. 2) To analyze the failures occur in TIG welding using FTA.

3) To identify parameter that contribute to failure occur in TIG welding.

1.4 Scopes of the Research

This project focuses on failures that occur during Tungsten Inert Gas (TIG) welding. The failures than will be analyze using Failure Tree analysis (FTA) and before that, a statistic such as histogram must be created to identify the type of failure that occur. A proper welding technique must be applied to decrease the probability of failure in TIG welding. In this project, the TIG welding instruments will be used at Manufacturing Laboratory in UTem to complete the analysis of failure that will be produced.

CHAPTER 2

LITERATURE REVIEW

2.1 IINTRODUCTION (JURNAL)

Pantazopoulos, G. and Sampani, A. (2006) doing a case study on weld failure of a rolled Zn- alloy strip that mainly used in construction industry. They found that significant welding defects, such as linear discontinuities, edge micro cracks and fusion zone gas porosity are detected during the investigation procedure. The size and distribution of pores in the fusion zone affect directly the mechanical behaviors and the workability of the welded tube. They also found that Welding defects due to the application of improper welding procedure is a significant contributor of limited weld workability and premature failure. [1]

Jha, A. K. et al. (2003) doing a Metallurgical analysis of cracking in weldment of propellant tank for satellite launch vehicles that use a Medium strength Al–Zn–Mg aluminum alloy. They found that various type of crack occur in TIG welding area at propellant tank and cracking initiated from the root of pit, followed the path of solute enriched dendrite caused intergranular mode of fracture. This confirmed the cracking was due to stress corrosion. The stress introduced during welding as contractional strain in accommodating the nozzle facilitated the cracking phenomena. [2]

Meola, C. et al. (2004) have conduct a testing and analysis of stainless steel welded joints between destructive and non-destructive techniques. They have found three techniques for weld joints analysis that use micrographs, Vickers micro-hardness measurements, and Lockin thermography. These three techniques are synergic and helpful for a complete characterization welded joints and for improvement of the welding method. [3]

Tarng, Y. S., Tsai, H.L. and Yeh, S.S. (1999) have done an experiment in Modeling, optimization and classification of weld quality in tungsten inert gas welding. In the project, they describe an intelligent modeling, optimization and classification of weld quality in TIG welding process. A back-propagation network is used to construct the relationships between the process parameters and the features on the weld pool geometry. A gobal optimization algorithm called simulated annealing is then applied to the network for solving the process parameters with optimal weld pool geometry based on an objective function. Furthermore, the fuzzy c-means algorithm is adopted here to classify and verify the weld quality using the features on the weld pool geometry. Through this study, highly non-linear, strongly coupled, multivariable TIG welding processes can be further understood, analyzed and controlled. [4]

Liming, L. and Shengxi, W. (2006) have doing a study on the dissimilar magnesium alloy and copper lap joint by TIG welding. During his study, they have found that in the TIG welding of dissimilar magnesium alloy and copper, intermetallic compounds were produced in the interfacial region. Intermetallic compounds were the main cause of embrittleness of the joints.By using iron plate as interlayer between magnesium alloy and copper, the embrittleness of joint was obviously decreased and the tensile strength of the joint is higher compared with that, without iron plate. They also noticed that Metallic oxides in the interfacial region between iron plate and magnesium alloy were the main reasons influenced the strength. [5]

UrenÄ, A. et al. (2000) has describes about the influence of interface reactions on fracture mechanisms in TIG arc-welded aluminum matrix composites. They conclude that: [6]

• TIG arc welding of aluminum matrix composites (AMC) reinforced with SiC particles produced severe degradation of the materials because of the formation of Al4C3 in the matrix/reinforcement interface.

• The failure mechanisms in the studied AMCs were mainly: particle fracture for particles larger than 10 mm; and ductile matrix failure in the proximity of the SiC/Al interface for particles smaller than 10 mm.

• Fracture of the welded composites was mainly controlled by interface debonding through the continuous interface reaction layer, although the formation of discontinuous tabular Al4C3 aggregates with preferential dissolution of some SiC planes also favoured damage to particles smaller then 10 mm.

• Interfacial reactions between SiC particles and molten aluminium during welding also produced degradation of fracture behavior of the aluminum matrix which was associated with the Si enrichment.

• Arc welding of the studied composites presented an additional problem of porosity in the weld, which was enhanced by the increase of the reinforcement grade and welding power. It has been mainly characterised as interdendritic porosity associated to the low wettability of the SiC particles by molten aluminum.