Dissimilar Friction Stir Welding between Magnesium and Aluminum Alloys

Abstract

Joining two dissimilar metals, specifically Mg and Al alloys, using conventional welding techniques is extraordinarily challenging. Even when these alloys can be joined, the weld is littered with defects such as cracks, cavities, and wormholes. The focus of this study was to use friction stir welding to create a defect-free joint between Al 2139 and Mg WE43. The design included an 11 mm scrolled and concave shoulder in addition to a 6 mm length pin comprised of two tapering, threaded re-entrant flutes that promoted and amplified material flow. Upon completion of this project, an improved experimental setup process was created as well as successful welds between the two alloys. These successful joints, albeit containing defects, lead to the conclusion that the tool used in the project was ill-fit to join the Al and Mg alloy plates. As a result of this aggressive pin design, there was a lack of heat generation towards the bottom of the pin even at higher (800-1000 rpm) rotation speeds. This lack of heat generation prohibited the material from reaching plastic deformation thus preventing the needed material flow to form the defect-free joint.