Study On Microstructures And Mechanical Properties Of 5052-h112 Aluminum Alloy Joints Welded By Stationary Shoulder Friction Stir Welding Technology

6mm thick 5052-H112 aluminum alloy butt joints were successfully obtained by stationary shoulder friction stir welding process with the use of self-developed tool.Based on experimental research,influences of the change of the welding process parameters on welding surfaces,microstructures,hardness profiles and tensile properties of the obtained joints were studied in detail.The results provided an important basis for further study of the subsequent SSFSW technology.The 5052-H112 aluminum alloy joints by SSFSW process have smooth surfaces and beautiful appearances.Compared with conventional FSW,SSFSW joints have few flash and thickness reduction.The SSFSW nugget zone has bowl-like shapes,which is quite different from that of conventional FSW joint.5052-H112 aluminum alloy SSFSW joint consists of four parts,that is welding nugget zone(NZ),thermal mechanically affected zone(TMAZ),heat affected zone(HAZ)and base metaI(BM).SSFSW joint has fairly narrow thermal mechanically affected zone(TMAZ)and heat affected zone(HAZ),which is different from conventional FSW joint.The grains near AS in welding nugget zone have obviously elongated shape,but the size and shape of grains in the central part and near RS are similar,which are equiaxed and have no obvious deformation.The hardness distribution of 5052-H112 aluminum alloy SSFSW joints is "W"shape.Hardness of welding nugget zone is close to the base metal.The hardness is minimum in the heat affected zone(HAZ).The welding speed shows an evident effect on the tensile strength of 5052-H112 aluminum alloy butt joints under various rotation speed.But rotation speed makes little effect on the tensile strength of 5052-H112 aluminum alloy butt joints.The elongation of the joint is not regular with the change of the welding speed and the rotation speed,showing a trend of fluctuation.When the rotation speed is 1000 rpm and the welding speed is 300mm/min,the tensile strength reaches the maximum 221.7MPa,which is up to 98.5%of the base metal.All the tensile test sample were fractured at the advancing side interface,and the AS interface was the weakest area where the fracture occurred.The fractograph exhibited typical ductile fracture with dimples.