Research On Microstructure And Stress Of 5A01aluminium Alloy Joint By Friction Stir Welding

5A01 aluminum alloy is high-strength and antirust alloy for marine, which has excellent corrosion resistance and high specific strength, so it has a broad application prospects in the ship manufacturing engineering. Friction stir welding is a method of connecting metals in solid phase. The joints welded by it have high quality. However, the residual stress also generates, affecting fatigue strength and fracture resistance capability of the structure and welded joints. Thus the study of welding process on the microstructure and performance and residual stress distribution of 5A01 aluminum alloy welded by friction stir welding is very important, applying theoretical basis for its application.In this paper, 5mm thick 5A01 aluminum alloy is selected as the experiment object. By changing the welding parameters, welding passes and directions to study the influence of the welding process on welding morphology, microstructure and mechanical properties of the joint. Under reasonable welding parameters, the tensile strength of the joint welded by double passes in different directions can reach 92% of that of base metal, meanwhile the tensile strength of joint welded by double passes in the same direction decreased obviously.The hardness of cross-section of joint welded by FSW is in "W" type. The hardness of nugget zone is slightly higher than that of heat-affected zone and thermal-mechanical affected zone.Secondly, residual stresses are measured by hole-drilling for each test plate. The results show that longitudinal stress distribution curves of the joints welded by single pass and double passes in different directions have the similarity that peak value appears in the weld center. The curve of longitudinal residual stress of the joint welded by double passes in the same direction has two peaks in the stirring area, on both sides of the shoulders. After the second pass, the weld heat input increases and the distribution area of the residual stress is wider. Longitudinal residual stress is asymmetry, which is higher of retreating side than that of the advancing side. Different welding passes and directions will influence the residual stress distribution differently.At the same time, a three-dimensional finite element model is established to analyze the temperature field and residual stress distribution. It is found that the temperature of testing points experiencing two passes is slightly higher than that of testing points undergoing only one pass. Peak temperature appears in the center of the weld. In both kinds of welds, longitudinal stress curves appear two peaks in metal mixing region, but the highstress area is relatively wider after the second pass, and it is lower in the center of weld. The residual stress gradient of the initial stage is large, and in the end stage of the welding stress gradient is small. Simulation and experimental results are in agreement basically.