Effect of Welding Parameters on Microstructure and Mechanical Properties of Friction-Stir-Welded Al-Mg-Si Alloy

Friction stir welding was used to join Al-Mg-Si aluminum alloy plates, and the effect of rotational velocity to welding speed ratio (ω/ν) on joint quality was investigated. The relationships between welding peak temperature, joint formation and mechanical properties were obtained. The peak temperature was increased with the increase in ω/ν, which led to an increased width of stir zone and a larger softened region of joint. The joint hardness was decreased with the increase in ω/ν due to the increased heat input. The joint tensile strength experienced an increase and then a decrease with the increase in ω/ν, and the maximum value reached 75.43% of that of base material under the ω/ν of 4. Low ω/ν induced the formation of bending crack. Thermo-mechanically affected zone and stir zone possessed higher impact toughness compared with base material, and the impact toughness was first increased and then decreased with the increase in ω/ν. The fracture surfaces of tensile and impact specimens were covered by dimples, indicating a ductile fracture mode.