Research on Microstructure and Properties of Friction Stir Welding Joint of 2A16 and 7075 Aluminum Alloy

Abstract

The joint of 2A16-7075,7075-7075 and 2A16-2A16 aluminum alloy were obtained by friction stir welding under the condition of the stir head rotating speed of 1000rpm and welding speed of 100mm/min. The morphology of nugget area in different joints by metallographic microscope and tensile test, impact test and hardness test of joints were done. The results show that the microstructure in weld nugget is equiaxed grain，fine isometric crystal structure，which has been dynamic recrystallized. Grain of TMAZ changed greatly, which has elongated microstructure, the microstructure in HAZ was coarsened compared with base material. The tensile strength of 2A16-2A16 friction stir welding joint is 188Mpa and that of the 7075-7075 joint is 172Mpa, but that of the 2A16-7075 joints is only 93Mpa. Impact test showed that impact energy of the same material of friction stir welding joint is higher than that of the dissimilar joint, the impact energy of 2A16-2A16 joint is the highest, which is 22.81J, Impact absorbing energy of base material is less than that of the weld nugget zone at room temperature. The hardness distribution of three friction stir welding joint show W type roughly. The hardness on both sides of the base material is the maximum, the hardness in the HAZ and TMAZ decline. The hardness values of NZ is higher than that of the HAZ, hardness at the junction of different regions has abrupt change.