Innovate Method for Friction Stir Welding of Al-Mg-Si Alloy Thin Plate

¹ School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, 710072, China
² College of Energy Engineering, Yulin University, Yulin, 719000, China
³ State Key Laboratory of Solidification, Xi'an, 710072, China

Corresponding author: fuli@nwpu.edu.cn

Abstract

Al-Mg-Si (6061-T6) alloy with 0.8 mm thick plate was welded successfully by use of high speed friction stir welding (FSW) technology. The microstructural characteristics and mechanical property of the butt joints prepared by high speed FSW were analyzed in detail, the influence of welding parameters, fixture condition and after welding heat treatment were also explored. The results shown that sound surface topography and defect-free bonding interface were observed in the nugget zone (NZ). The microhardness of the as-welded joint was lower than that of the base metal because of the welding heat effect. Compared with the conventional speed FSW, the number of β-Mg₂Si, Al₂CuMg and Al₈Fe₂Si precipitated phases existed in the high speed FSWed NZ increased, which made the microhardness in the NZ improved significantly. The rod-shaped precipitates (Mg2Si) have the greatest influence on the microhardness distributions. The maximum tensile strength of 301.8 MPa, which was 85.8% of the base metal, was obtained at high rotation speed of 8000 rpm and fast welding speed of 1500 mm/min. The tensile strength of the ultra-high speed FSWed butt joints were improved significantly by post-weld artificial aging, with a maximum joint efficiency of 90.4%.