Study On Friction Stir Lap Welding Of Aluminum Alloy And Thermoplastic Polymer Dissimilar Materials Under Auxiliary Heating

Due to the great difference of physical and chemical properties between the welding materials,there are holes caused by incongruous shrinkage deformation and material separation defects caused by excessive interface stress in the friction stir lap welding(FSLW)joint between aluminum alloy and thermoplastic polymer.These defects seriously affect the mechanical properties of the joint.In order to solve these problems,the idea of "reducing the rotational speed under isothermal peak conditions" and "preventing separation by reducing stress" was put forward.In this paper,the influence of auxiliary heating process on FSLW joint of 7075 aluminum alloy and PEEK polymer was studied by surface forming,microstructure,mechanical properties and fracture behavior of joint under different welding parameters.The simulation and experiment results showed that the "reducing the rotational speed under isothermal peak conditions" was effectively achieved by the auxiliary heating process,which enhanced the sealing effect of the upper aluminum alloy on the overflow behavior of the polymer material,thereby improved the surface formation of the joint.Meanwhile,the auxiliary heating on both sides of the weld reduced the peak residual tensile stress at the joint interface by 15.8% through providing hot stretching during the welding process,eliminating the material separation defect of the conventional FSLW joint,which confirmed the effectiveness of "preventing separation by reducing stress".In the process of FSLW,the auxiliary heating broadened the high-temperature bonding area of the interface and alleviated the temperature rising and cooling trend.Besides,it also increased the material fluidity of the stirring zone.Based on the mentioned above,non-defect FSLW joint with the macro-mechanical interlock of the "aluminum anchor" was obtained with the welding parameter of 500 rpm-40 mm/min under auxiliary heating,and the maximum tensile-shear strength of the joint reached 22.21 MPa,which was 52.64% higher than that of the joint under conventional FSLW.Due to the change of the weak position,the joint fracture modes were changed from the tensile fracture of I,II types and the shear fracture of type III under the conventional FSLW to the III and IV fracture types under the auxiliary heating FSLW.