Effect of welding parameters on the microstructures and mechanical properties of double-pass aluminum/magnesium dissimilar metal friction stir lap welding joint

Abstract

Different welding parameters (rotation speed, traverse speed, and overlap ratio) were used to perform friction stir lap welding (FSLW) on 1060 aluminum/AZ31B magnesium dissimilar metals. A response surface model was established in order to optimize the welding parameters. Compared with results at other traverse speeds, the joint exhibited a high welding efficiency and a tensile shear force at a welding speed of ν = 70 mm/min. When the same length is welded, the time required for welding speed 70 mm/min is 43 % of welding speed 30 mm/min and 71 % of welding speed 50 mm/min, respectively. Subsequently, through optical microscopy (OM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), the effect of the overlap ratio (OR) on the macro and microstructure, mechanical properties of the joint were examined. A good metallurgical bond and mechanical interlocking combination were formed at the interface. As the OR was increased, the fluidity of the material was further improved, and the content of intermetallic compounds (IMCs) also increased sharply. The micro-hardness test results showed that the weld-nugget area exhibited a higher hardness due to the formation of IMCs. When ν = 70 mm/min and ω = 1500 rpm, an increase in the OR from 50 % to 75 % caused the maximum tensile shear force of the joint to decrease sharply, and three fracture modes of the joint fractures were identified.