Friction Stir Welding Techonlogy And Joint Microstructure And Properties Of Aluminum Alloy Thick Plate Additive

In this paper,5083-H111 aluminum alloy was taken as the research object,and the metal flow behavior and defect formation law at the weld of special-shaped welding tool were explored through the optimization design of welding tool.The friction stir welding of aluminum alloy thick plate was realized by the optimization of welding parameters and the feasibility analysis of thick plate additive test.The microstructure and mechanical properties of the joint were evaluated.Optimum design of welding tool showed that Under the condition of ensuring the strength of the welding tool,the larger the ratio of the surface area of the shaft shoulder to the volume of the welding tool,the more favorable it was for molding.The nugget size obtained by using special-shaped welding tool was much larger than that obtained by ordinary welding tool.The non-smooth surface of the special-shaped welding tool was beneficial to the metal flow in the welding process,and the plasticized metal was driven by the shaft shoulder and the screw thread of the non-smooth surface of the welding tool to produce metal flow in two directions.It was found that the height of the interface migration increased with the increased of welding angle,decreased with the increased of the traveling speed,and decreased with the increased of the rotation speed.The nugget size and effective nugget size increased with the increased of welding angle and decrease with the increased of traveling speed.The results showed that the width of the upper and middle HAZ increased with the increased of welding angle and rotation speed,and decreased with the increased of travel speed.There was no obvious effect on the hardness near the interface.Optimization results of friction stir welding process with additive in stepped groove showed that a defect free weld line could be obtained by unidirectional addition from right to left.The change of axial force in the welding process could be divided into three stages:holding down,smooth welding and pulling out.Among them,the pressure reached the maximum in the holding down stage,gradually decreased in the process of smooth welding,and gradually decreased until it disappeared in the process of pull-out.The hardness distribution of the cross section of the additive weld was higher at the bottom of the nugget than that of the base metal.The test results of delamination tensile properties showed that The tensile strength,yield strength and fracture elongation of upper,middle and lower layers were decreasing,and the tensile strength of the upper layer weld is improved compared with the base metal.The tensile strength,yield strength and elongation at break of the upper weld were101.8 %,94.2 % and 80 % of that of the base metal respectively.The tensile strength,yield strength and elongation at break of the middle weld were 83.8 %,75.8 % and 60 %of that of the base metal respectively.The tensile strength,yield strength and elongation at break of the lower weld were 63.8 %,75.3 % and 20 % of that of the base metal respectively.