Analysis of microstructure and wear resistance of friction stir welded joints of 7075-T6 aluminum alloy

The 10 mm thick 7075-T6 aluminum alloy plate is welded by friction stir welding with the inclination of the main shaft of 0.5°. There is no obvious thinning on the weld surface, and the welded joint is well formed. The microstructure of the joint as a whole is "funnel" shaped, and there are multi gradient flat "onion rings". The grains in the weld nugget zone are equiaxed and the grains are significantly refined, and the grains in the heat-mechanical affected zone appear mixed crystal phenomenon and have obvious deformation. During the welding process, the hardness of the welded joint is reduced due to high temperature annealing. When the spindle speed is 500 rpm and the welding speed is 120 mm/min, the maximum surface hardness of the welded joint is 178.77HV. Compared with the base metal after annealing, the hardness of the weld nugget area is increased by about 25% due to the grain refinement strengthening and the precipitation of the reinforcing phase. The wear resistance of welded joints is inversely proportional to the hardness. When the spindle speed is 300 rpm and the feed speed is 120 mm/min, the wear resistance is the best. The friction type is mainly adhesive wear, supplemented by particle wear and fatigue wear.