Study On Forming And Mechanical Properties Of Cu/al Friction Stir Diffusion Spot Welding Joint

In order to make rational use of the scarce metal copper resources and decrease the cost,in recent years,the copper/aluminum composite structure has developed rapidly,and the demand for its processing technology has also increased.The friction stir diffusion spot welding?FSDSW?is a kind of joining technology developed on the basis of friction stir welding.It has the advantages such as simple process and high joint quality.In this paper,the influence of the welding parameters on the joint formation and mechanical properties is analyzed.The conclusions are as following:The joint formation of the copper/aluminum FSDSW appears well,and the joining is obtained through a liquid-phase diffusion layer.Under the conventional process,when the thermal input time is too short,the uniformity of the liquid phase layer is insufficient,and the cracks and hole defects can be generated.When the thermal input time is too long,the interface intermetallic compound?IMC?layer is too thick.The cavitation effect of ultrasound in the liquid phase can effectively crush the thick IMC layer on the copper side,promoting the homogenization,and the cavitation effect becomes more fully with the time increasing.In the conventional process,the content of the copper-side IMC layer is Cu Al and Cu Al₂.The eutectic structure of Cu Al₂ and?-Al is formed in the liquid phase layer,and the columnar?-Al cell is present on the aluminum side.Under the ultrasonic process,the continuous IMC layer on the copper side is broken,and the blocky Cu Al₂,Cu Al and the flower-like eutectic structure are formed in the liquid phase layer.The results of the mechanical property are analyzed.The joint hardness distribution curve is symmetrical with respect to the center line of the joint,and the hardness value of the heat-affected zone is the lowest and the value of the interface is the highest due to IMC.The hardness of the joint under the ultrasonic-assisted process is slightly reduced.Under different parameters,the tensile shear strength of the joint decreases with the increase of the heat input.The bonding quality of the copper-side interface is the determining factor of the fracture path.Under the conventional process,all joints are fractured at the interface of the copper side and are subject to cleavage fracture.Under the ultrasonic assisted process,the joints are fractured at the interface of the copper side when the parameters are poor,and the fracture mode is subject to mixing of cleavage and plastic.When the parameter is suitable,the joint is broken at the parent material,and the fracture mode is plastic fracture.