Effects of Postweld Heat Treatment on Microstructure and Mechanical Properties of 6063-T6 Aluminum Alloy Friction Stir Welding Joints

Author of the article:PU Jianxin 1,2 , SUN Wei 2,3 ， ZHANG Hui 1,2

Author's Workplace：1. College of Materials Science and Engineering, Northeastern University, Shenyang 110819, China; 2. Key Laboratory of Material Electromagnetic Process Research, Ministry of Education, Northeastern University, Shenyang 110819, China; 3. Research Institute of Liaoning Zhongwang Group Co., Ltd., Liaoyang 111003, China

Key Words： friction stir welding; 6063-T6 aluminum alloy; solution aging; abnormal grain growth

Abstract：The effects of solution treatment (540 ℃×1 h), aging treatment (175 ℃×8 h) and solution+aging treatment (540 ℃×
1 h+175 ℃×8 h) on the microstructure and mechanical properties of friction stir welded 6063-T6 aluminum alloy sheet
with 3 mm thickness were investigated. The results show that the average grain size of the welded joint is only 3.2 μm.
After solution treatment, due to the weak pinning effect of the second phase particles on grain boundaries, some grain
boundaries migrate in the joint structure, and abnormal grain growth occurs in different degrees, with some large grains
exceeding 500 μm. After aging treatment, the microstructure of the joint does not change significantly, and the average
grains size of the welded core zone is 4.5 μm. The microstructure of the joint after solution+aging treatment is similar to
that after solution. After solution, the tensile strength and hardness of the joint decrease, but the elongation increases. Due
to precipitation strengthening, the strength and hardness of the joint are increased after aging and solution+aging, but the
elongation is decreased. The tensile strength of joints after aging is 212.6 MPa, which is the highest. After solution, the
tensile strength is the lowest, 138.8 MPa.