Influences of Welding Process Parameters on Friction Stir Welded Joints of 5052 Aluminium Alloy Plate with 6 mm Thickness

The friction stir welding process for 5052 aluminium alloy plate with 6 mm thickness was carried out, and the effects of rotation rate of spindle and welding rate on the macrograph, tensile properties and hardness of the joint were studied, and the tensile fracture morphology was observed. The results show that the joint without defect and with excellent mechanical properties was obtained when the spindle rate was 800-1 600 r·min-1 and welding rate was 80-560 mm·min-1, respectively. But a tunnel type defect emerged acrossing the joint at low spindle rate. With the spindle rate increasing or welding rate decreasing, the area of weld nugget decreased and the distance between rings increased gradually. The weld nugget area was composed of fine equiaxed grains with average grain size of 5 μm, which was 1/10 of that for the base material. Futhermore, the process parameters had no significant influence on mechanical properties of the joint, and the tensile strength and microhardness of the joint were more than 90 % and 88% of those for the base material, respectively. The fracture was initiated from the back side and fractured along the original interface of the joint, and ended in the return side lastly, exhibited typical cut-off fracture morphology.