Effects of ultrasonic assisted friction stir welding on flow behavior,microstructure and mechanical properties of 7N01-T4 aluminum alloy joints  

作　　者：Zhiqiang Zhang Changshu He Ying Li Lei Yu Su Zhaoc Xiang Zhao 

机构地区：[1]School of Materials Science&Engineering,Northeastern University,Shenyang 110819,China [2]Key Laboratory for Anisotropy and Texture of Materials,Northeastern University,Shenyang 110819,China [3]Ningbo Institute of Industrial Technology Chinese Academy of Sciences,Ningbo 315201,China

出　　处：《Journal of Materials Science & Technology》2020年第8期1-13,共13页材料科学技术（英文版）

基　　金：funded by the National Key Research and Development Program of China(No.2016YFB1200506–12);Project of Promoting Talents in Liaoning Province(No.XLYC1808038)。

摘　　要：Conventional friction stir welding(FSW)and ultrasonic assisted friction stir welding(UAFSW)were employed to weld 6-mm thick 7 N01-T4 aluminum alloy plates.Weld forming characteristics and material flow behavior in these two different welding processes were studied and compared.Ultrasonic vibration was applied directly on the weld in axial direction through the welding tool.Metal flow behavior,microstructure characteristics in the nugget zone(NZ)and evolution of the mechanical properties of naturally aged joints were studied.Results show that the ultrasonic vibration can significantly increase the welding speed of defect-free welded joint.At the rotation speed of 1200 rpm,the UAFSW can produce defect-free welded joints at a welding speed that is 50%higher than that of the conventional FSW.Ultrasonic vibrations can also improve surface quality of the joints and reduce axial force by 9%.Moreover,ultrasonic vibrations significantly increase the volume of the pin-driven zone(PDZ)and decrease the thickness of the transition zone(TZ).The number of subgrains and deformed grains resulting from the UAFSW is higher than that from the FSW.By increase the strain level and strain gradient in the NZ,the ultrasonic vibrations can refine the grains.Ultrasonic energy is the most at the top of the NZ,and gradually reduces along the thickness of the plate.The difference in strengths between the FSW and the UAFSW joints after post-weld natural aging(PWNA)is small.However,the elongation of the UAFSW is8.8%higher than that of the FSW(PWNA for 4320 h).Fracture surface observation demonstrates that all the specimens fail by ductile fracture,and the fracture position of the UAFSW joint changes from HAZ(PWNA for 120 h)to NZ(PWNA for 720 and 4320 h).

关 键 词：Ultrasonic-assisted friction stir welding Aluminum alloy Material flow behavior Microstructure Mechanical property Natural aging 

分 类 号：TG453.9[金属学及工艺—焊接] TG146.21[一般工业技术—材料科学与工程]