This paper deals with the mechanical, microstructural and fatigue analysis of welded joints.
In the study, 6061-T6 aluminium alloy plates in 4mm thickness, that are particularly used for aerospace and in automotive industries, were welded using Tungsten Inert Gas (TIG) welding and Friction Stir Welding (FSW) methods as similar joints with one side pass and parameters of varying tool rotation, weld speed and 2.3 degree tool tilt angle. The weld zones cross sections were analysed with light optical microscopy (LOM).
During recent years several investigations have been made of fatigue properties of friction stir welded joints. The great majority of available data from the fatigue analysis of friction stir welded joints are concerned with uniaxial loading conditions for a simple geometry. In uniaxial loading nominal stress is normally used as reference stress and it is easy to determine. However, fatigue failure is a highly localized phenomenon in engineering components and determining the nominal stress is not always possible due to the complexity of structures and presence of stress concentrators such as notches and cracks in which many approaches based on local parameters.
Table of Contents
1. Introduction
2. Materials and experimental procedure
3. Results and discussions
3.1 Microstructural behaviour
3.2 Micro hardness Test
3.3 Tensile Test
3.4 Fatigue behavior
4. Conclusions
Research Objectives and Themes
This study aims to conduct a comparative analysis of mechanical, microstructural, and fatigue properties of AA6061-T6 aluminium alloy plates joined via Friction Stir Welding (FSW) and Tungsten Inert Gas (TIG) welding to determine performance efficiency for aerospace and automotive applications.
- Comparative analysis of FSW and TIG welding processes.
- Evaluation of microstructural characteristics using light optical microscopy.
- Assessment of mechanical performance via Micro Vickers hardness and tensile testing.
- Investigation of fatigue life and crack behavior under cyclic loading.
Excerpt from the Book
3.1 Microstructural behaviour
By using LOM, the microstructural behaviour of FSW and TIG welded joints of aluminium alloy were studied. Images of different types of Friction Stir weld zones evaluated are shown in Fig. 3.
Basically, there are four types of zones observed in FSW joints: Thermo-mechanical Heat Affected Zone(TMAZ), Heat Affected Zone(HAZ), Nugget Zone(NZ), Base Metal Zone. From the obtained microstructure it is obseved that NZ has equi-axed grains. This zone is also called Stir Zone. A unique feature of the stir zone is the common occurrence of several concentric rings which has been referred to as an "onion-ring" structure. It is obseved that the size of grains in NZ is smaller than in the other zones. While in TMAZ, unlike the stir zone the microstructure is recognizably that of the parent material. Also the strain and temperature are lower and the effect of welding on the microstructure is correspondingly smaller. In HAZ, the temperatures are lower than those in the TMAZ but may still have a significant effect if the microstructure is thermally unstable. In fact, in age-hardened aluminium alloys this region commonly exhibits the poorest mechanical properties. Now coming to the obsevred microstructure of TIG welded joints, its shown in the Fig. 4.
Chapter Summary
1. Introduction: Outlines the scope of the study, focusing on the mechanical and fatigue properties of AA6061-T6 alloy joints fabricated by FSW and TIG welding processes.
2. Materials and experimental procedure: Details the chemical composition of the welding tools, the parameters used for joining the alloy plates, and the methods employed for microstructural and fatigue testing.
3. Results and discussions: Analyzes the gathered data on grain structure, microhardness profiles, tensile strength, and fatigue behavior observed in the welded joints.
4. Conclusions: Summarizes the key findings, highlighting the superior performance of FSW joints regarding tensile strength and fatigue life compared to TIG welded specimens.
Keywords
Weld Zones, Friction stir welding, Metallurgical Test, Mechanical Test, AA6061-T6, Aluminium Alloy, Fatigue Analysis, Microstructural Analysis, Vickers Hardness, Tensile Strength, TIG Welding, Strain Hardening, Recrystallization, Aero-space Materials, Joint Integrity.
Frequently Asked Questions
What is the primary focus of this research?
The research focuses on a comparative analysis of the mechanical, microstructural, and fatigue properties of AA6061-T6 aluminium alloy plates joined by FSW and TIG welding.
Which materials were tested in this study?
The study specifically utilized 4mm thick AA6061-T6 aluminium alloy plates, a material commonly found in aerospace and automotive industries.
What is the main objective of the paper?
The objective is to evaluate which welding method, FSW or TIG, provides better mechanical strength and fatigue resistance for these specific alloy plates.
Which scientific methods were employed?
The authors utilized light optical microscopy (LOM) for microstructural evaluation, Micro Vickers hardness testing, tensile strength testing, and low-cycle fatigue testing.
What key findings are discussed in the main body?
The main body evaluates how different weld zones, such as the Nugget Zone and Heat Affected Zone, influence the overall hardness and structural integrity of the joints.
Which keywords best describe this study?
Key terms include Friction Stir Welding, TIG Welding, AA6061-T6, Fatigue Analysis, and Metallurgical Test.
Why is the "onion-ring" structure significant in the nugget zone?
The "onion-ring" structure is a characteristic feature of the Stir Zone in FSW, indicating the specific grain flow and recrystallization processes during the joining of the aluminium plates.
Does the hardness graph show symmetry across the weld?
No, the hardness graph is not symmetrical; the authors attribute this variation to improper material flow during the FSW process.
How does the fatigue life of FSW joints compare to TIG joints?
The results indicate that the FSW method generally provides greater fatigue life and higher yield stress compared to the TIG welding method for this alloy.
Where does failure typically occur in the welded joints?
Failure was generally observed in the zone characterized by lower hardness, specifically within the weld zone, due to strength loss during the recrystallization process.
- Arbeit zitieren
- Akshansh Mishra (Autor:in), Dr. A Razal Rose (Autor:in), Saravanan .M (Autor:in), Anand Singh (Autor:in), 2017, Mechanical, Metallurgical and Fatigue Properties of Friction Stir Welded and Tungsten Inert Gas Welded AA6061-T6 Aluminium Alloys, München, GRIN Verlag, https://www.grin.com/document/373965
