Effect of post-weld heat treatment on 6156 aluminum alloy joint formed by electron beam welding

The 6156 aluminum alloy is welded by electron beam welding, and different post-weld heat treatments (PWHTs) are carried out on the joints. The microstructure, mechanical property, and corrosion behavior of the welded joint before and after PWHT are investigated, respectively. Results show that the fusion zone is composed of columnar crystal and equiaxed grain in as-welded (AW) condition. There are mainly alpha-Al matrix phase, and some strengthening phases beta '' (Mg2Si) and Q(Al4CuMg5Si4) in weld metal. After PWHT, the quantity of strengthening phases in weldment is greatly increased, and their distribution is also improved. The tensile strength of welded joint is 65.8% of that of the base metal (BM) in AW condition. After the heat treatment of HT2, the strength coefficient of joint reaches 85.1%. There are many dimples on the tensile fracture surface, and the joint obviously presents the characteristic of ductile fracture. The electrochemical corrosion performance and resistance to intergranular corrosion of weldment in AW condition are higher than that of the BM. However, they are decreased to a certain extent after PWHT. Compared with that of the AW joint, the resistance to intergranular corrosion is slightly decreased after PWHT, and that of the HT2 joint is the best among them.