Study On Fatigue Performance Of Mechanical Mismatched Friction Stir Welded Joint

Fatigue and fracture is the most common forms of mechanical component failure.Due to the complexity of the BT-FSW,the material at the welding joint is subjected to the mechanical stirring action of the agitating needle,the thermal cycling action and the extrusion action of the upper and lower axle shoulder,which results in the difference of the mechanical properties between the base material and the welding seam,that is,the mechanical mismatch effect is formed.The fatigue properties of friction stir welded joints with mechanical mismatch have a great influence,so it is very important to study the fatigue properties of different areas of welded joints.In this paper,BT-FSW welding test was carried out on 5083 aluminum alloy,and the microstructure observation,microhardness test and tensile test of BT-FSW joint were conducted.The results show that the NZ of 5083 aluminum alloy FSW joint is equiaxed fine grain,the TMAZ area is different size grain,and the HAZ area is larger equiaxed grain.The hardness of the base material area is greater than that of the welding,and the hardness value of the HAZ is the lowest,but the overall hardness value of the joint has a small change trend.The tensile property of the base material zone is better than that of the weld,the mismatched ratio is 0.94,and the tensile property of the HAZ is close to that of the weld core.The size of the core zone was 18mm,the size of the HAZ was 8mm,and the distance from the base material zone to the weld center was greater than 21mm.The BT-FSW joint was cut into each area by using the wire cutting technology.Fatigue test was conducted on each area of the joint,and the fracture was observed.The results show that the fatigue property of base metal is better than that of weld,and the fatigue property of heat-affected zone is the worst.The fatigue fracture of high/low fitting joints was observed,and it was found that the low fitting joints were located in the heat-affected zone,while the high fitting joints were located in the base material zone.The fatigue fracture fracture recorded the process of crack initiation,crack steady propagation and instantaneous fracture in detail.