Research On Microstructure And Properties Of The Aluminum Alloy Sheets By Friction Stir Spot Welding

The 6005A-T6 aluminum alloy with the thickness of 1.0+1.2mm and 1.0+1.5mm were welded by friction stir spot welding in this paper, in order to solve the conventional shortcomings of resistance spot welding and riveting on aluminum alloy. Analysis the microstructure, influence of process parameters on the mechanical properties, corrosion resistance and other issues of the friction stir spot welding joints by the two welding ways of refill friction stir spot welding(RFSSW) and pinless friction stir spot welding(FSSW).The research results show that RFSSW joint has a good forming surface and internal microstructure defect-free on the junction of the pin and sleeve, the cross-section of the joint can be divided into the stir zone, thermal mechanical affected zone, heat affected zone and base metal, the stir zone presents the most slight crystalline grain compared with others, and the heat affected zone presents coarse grain with second-phase particles precipitated. The microhardness of the joint presents centrosymmetric distribution, the microhardness curve of upper sheet was “W” shape distributed, and the lower sheet was“U” shape distributed. The RFSSW joint can be obtained higher tensile shear properties when the stir tool press into the aluminum sheets 1.7mm depth and 2000 rpm filling rotational rate. The rotational speed of stir tool has little effect on the mechanical properties of the joint when the stir tool press down, the joint has better peeling properties when the filling rotational speed achieve 2000 rpm. The thickness of 1.0+1.2mm can be obtained tensile shear properties of RFSSW joint better than the 1.0+1.5mm when the same process parameters, but the relationship of peeling properties are opposite. The thickness of the sheet has a little influence on the corrosion resistance of the joint surface, and they are not as good as the base material.The joint will be forming smooth surface and left a keyhole after pinless FSSW, the stir zone presents the most slight crystalline grain compared with others of the cross-section of the joint, the area of thermal mechanical affected zone is small and there are more black second-phase particles in heat affected zone. The microhardness of the joint presents centrosymmetric distribution, the microhardness curve of upper sheet was double“V” shape distributed, and the lower sheet was “W” shape distributed. Welding time has less impact on the tensile shear properties of pinless FSSW joint, but a great impact on the peeling properties, it can obtain a large peeling load when the welding time is 10 s.The tensile properties of the thinkness of 1.0+1.2mm are better than 1.0+1.5mm in pinless FSSW joint, but both of them have little difference on corrosion resistance and lower than the base material.