Microstructure Distribution and Tensile Anisotropy of Dissimilar Friction Stir Welded AM60 and AZ31 Magnesium Alloys

Abstract

The microstructure distribution, tensile anisotropy and fracture behaviors in the dissimilar friction stir welded joint of AM60/AZ31 alloys were investigated. Experimental results showed that a significant grain refinement and an orientation fluctuation occurred in the weld. The grain size of AZ31 side in joint was obviously smaller than that of AM60 side. There was a higher percentage of low angle grain boundaries (LAGBs) and a lower degree of recrystallization in AZ31 side compared with those in AM60 side, especially for the thermo-mechanically affected zone in AZ31 side. The discrepancies of grain size distribution, recrystallization behavior and LAGBs in joint depended on the different initial state of two metals and the inhomogeneous temperature distribution in joint. In addition, the (0001) basal plane in weld was roughly parallel to the surface of the pin, showing the symmetrically distributed texture characteristics. The joint showed an obvious tensile anisotropy due to the special texture distribution. The comprehensive tensile properties of joint along the three directions decreased in the order: welding direction, 45° direction and transverse direction. The maximum ultimate tensile strength, yield strength and elongation of the joint were 242 MPa, 116 MPa and 21.2%, respectively. The fluctuations of grain size and texture in joint affected the fracture behavior of samples in the three directions.