Mechanical Performance of Friction Stir Linear Welds of Al to Mg Alloys

Lightweight metals such as Al and Mg alloys have been increasingly used for reducing mass in both structural and non-structural applications in transportation industries. Joining these lightweight materials using traditional fusion welding techniques is a critical challenge for achieving optimum mechanical performance, due to degradation of the constituent materials properties during the process. Friction stir welding (FSW), a solid-state joining technique, has emerged as a promising method for joining these lightweight materials. In particular, high joining efficiency has been achieved for FSW of various Al alloys and Mg alloys separately. Recent work on FSW of dissimilar lightweight materials also show encouraging results based on quasi-static shear performance. However, coach-peel performance of such joints has not been sufficiently examined. In this study, a rolled Al alloy AA6022 and a high pressure die cast Mg alloy AM60 were friction stir linear welded (FSLW) in a lap configuration under various welding speeds. Both lap-shear and coach-peel performances of the dissimilar welds under quasi-static conditions were evaluated, indicating high lap-shear strength, but much lower coach-peel strength. The ratio of coach-peel to lap-shear failure load is between 0.19 and 0.34. The dramatic differences in weld performance under different loading configurations are explored through metallurgical and fractography analysis. Moreover, the lap-shear performance of weld-bonded FSLW joints is explored, displaying a noteworthy increase in the load-bearing capacity upon addition of structural adhesives.