Comprehensive study of microstructure and mechanical properties of friction stir welded 5182-O/HC260YD + Z lap joint

The welding of aluminum (Al) and steel has attracted more and more interest due to the weight reduction trend in vehicle and aerospace manufacturing industries. 5182-O/HC260YD + Z lap joint was produced by friction stir welding (FSW), and the microstructure and mechanical property of the joint were systemically characterized. The microstructure in horizontal direction of the Al and steel near interface was similar to their corresponding conventional friction stir welded joint. The joint was divided into stir zone of Al (ST-Al), stir zone of interface (ST-I), thermal-mechanically affected zone of steel (TMAZ-Fe) and base material of steel (BM-Fe) according to their distinct microstructure vertically. Three kinds of intermetallic compounds (IMCs) of FeAl₃, FeAl and Fe₃Al were formed at the interface. The horizontal micro hardness distribution exhibited a hat shape and “M” shape in Al and steel, respectively. The hardest region of the joint was located at the ST-I, with a hardness of 175 HV−210 HV. The joint was fractured along the hook structure, with an average shear strength of 73.9 MPa. Fractural morphology of Al and steel indicted a cleavage fracture mode.