Friction Stir Weldability of High Tensile Strength Mg Alloy to Al Alloy

Friction stir weldability of a fine-grained high tensile strength AZ31 magnesium alloy to an Al-Mg alloy A5083 was evaluated by changing joining parameters, such as tool rotating speed, welding speed and insertion position of probe. A square butt dissimilar joint without any defect was obtained at the condition of welding speed 100 mm/min, tool rotating speed 500 rpm and offset 0 mm, by using a tool with shoulder diameter of 15 mm, pin diameter of 5 mm and pin length of 3.9 mm. Higher or lower welding speeds or rotating speeds led to the lack of bonding in the joint. Defects also occurred in the case that the offset was not 0 mm, i.e. the insertion position of the probe was shifted to either Mg side or Al side, even though the tool rotating speed was about 500 rpm and welding speed 100 mm/min. The maximum tensile strength of the dissimilar joints was about 115 MPa, lower than that of Al alloy base metal (about 308 MPa). Based on transmission electron microscopy, it can be suggested that the tensile strength of the dissimilar joint is mainly controlled by the thickness of IMC layer, which consists of Al12Mg17 and Al3Mg2, and mechanical interlock between magnesium and aluminum alloys. Bond strength decreases remarkably when the mechanical interlock becomes weak due to the increase of the thickness of IMC layer.