Microstructure and mechanical properties of friction stir welding of large-thickness 2219 aluminum alloy and analysis of engineering factors

For 2219 aluminum alloy with 22 mm thickness, a special stirring tool for FSW of 2219 aluminum alloy was firstly designed, and FSW experiments of 2219 aluminum alloy were carried out, welded joints with good shape and excellent performance were obtained. Effects of different assembly clearance and misalignment on mechanical properties of 2219 aluminum alloy FSWed joints were studied. The results showed that when rotating speed was 300~450 r/min and welding speed was 100~150 mm/min, FSWed joints were divided into welding nugget zone (WNZ), thermal-mechanical affected zone (TMAZ), heat-affected zone (HAZ) and base metal (BM). Among them, WNZ was composed of all fine equiaxed grains. Microhardness distribution of FSWed joints was U-shaped, the lowest microhardness was located in HAZ and the highest microhardness was located in BM. The average tensile strength of FSWed joints was 341 MPa, which was 74% of BM, and elongation of FSWed joints was 6.1%. FSWed joints all fractured in TMAZ and exhibited characteristics of ductile fracture. In addition, tensile strength of FSWed joints gradually decreased with the increase of assembly clearance. On the contrary, with the increase of misalignment, tensile strength of FSWed joints increased first and then decreased. When assembly clearance was 1 mm and misalignment was 1.5 mm, FSWed joints had no defects and had the optimal mechanical properties.