Investigation on the Effects of Welding Speed on Bobbin Tool Friction Stir Welding of 2219 Aluminum Alloy
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Investigation on the Effects of Welding Speed on Bobbin Tool Friction Stir Welding of 2219 Aluminum Alloy Quan Wen1 · Wenya Li1 · Vivek Patel1,2 · Yanjun Gao3 · Achilles Vairis4 Received: 10 July 2019 / Accepted: 2 September 2019 © The Korean Institute of Metals and Materials 2019
Abstract The microstructure and mechanical properties of bobbin tool friction stir welded joints for 2219-T87 aluminum alloy using different welding speeds were investigated based on the experimental results together with a thermo-mechanical model developed. The stir zone created in the joint shows a dumbbell shape. As welding speed increases, both the width and grain size of stir zone decrease. The symmetrical hardness distribution forms across the joint thickness, while the asymmetric hardness is measured along the width of the stir zone. The hardness of the stir zone on the retreating side is lower than that on the advancing side. The hardness profile presents a W-shape, with the minimum values measured increasing with welding speed. The tensile residual stresses increase gradually towards the center of the joint from the outer surface, presenting a symmetrical feature as well. As welding speed increases, both the tensile strength and elongation show a maximum value 70% of joint efficiency. Tensile fracture occurs in the stir zone and shows a symmetrical surface with three different layer fracture modes identified. In layers I and III, the fracture surface presents 45° direction, while fracture propagates along the S-line in layer II. Keywords Bobbin tool friction stir welding · Microstructure · Tensile strength · Symmetry characteristics
1 Introduction The 2219 aluminum alloy has a high strength-to-weight ratio, sound fracture toughness and resistance to stress corrosion cracking, and has been widely applied in the rocket fuel tanks [1, 2]. It is a precipitation strengthened alloy in which the θ precipitate is mainly responsible for its strength. Various conventional fusion welding processes such as gas
* Wenya Li [email protected] 1
State Key Laboratory of Solidification Processing, Shaanxi Key Laboratory of Friction Welding Technologies, Northwestern Polytechnical University, Xi’an 710072, Shaanxi, People’s Republic of China
2
Mechanical Engineering Department, School of Technology, Pandit Deendayal Petroleum University, Gandhinagar, Gujarat 382007, India
3
Manufacturing Engineering Department, Capital Aerospace Machinery Company, Beijing 100076, People’s Republic of China
4
Mechanical Engineering Department, TEI of Crete, 71004 Heraklion, Crete, Greece
metal arc welding [3] and plasma arc welding [4] have been successfully performed to joint it, and the joint efficiency of 51.4% was obtained in case of gas metal arc welding. Friction stir welding (FSW) has been used to join light alloys such as magnesium and aluminum alloys due to solid-state nature, avoiding the defects associated with conventional fusion methods [5]. Considerable effort has been devoted to study the microstructure evolution [6, 7] and mecha
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