Friction stir welding process of dissimilar metals of 6061-T6 aluminum alloy to AZ31B magnesium alloy

•Effect of welding conditions during Al–Mg FSW was investigated.•Heat input in Al–Mg FSW was calculated from torque.•Effect factors of welding conditions were revealed.•Sound joints were obtained with 73% tensile strength of Mg BM. Sound friction stir welded joints of 6061-T6 aluminum alloy to AZ31B magnesium alloy are obtained with the combination of intermediate rotation rate of tool (600–800rpm) and low traverse speed (30–60mm/min) when Mg was on advancing side, tool offset to Mg 0.3mm, and the tensile strength of the joints could reach up to 70% of that of Mg base metal. Intermetallics consisted of Al12Mg17 and Al3Mg2 formed and the eutectic structure existed in the nugget zone. Heat input in Al–Mg dissimilar metal FSW could be calculated accurately based on measuring x-axis torque and spindle torque. Because of the differences in friction coefficient, liquation tendency and deformability between Al alloy and Mg alloy, as well as the extent of mixing, the heat input increased by placing Al on advancing side and tool offsetting to Al, the increased rotation rate and traverse speed could decrease heat input. The effect of welding conditions was explained based on the extent of material intermixing and heat input. Welding conditions which resulted in sufficient intermixing between dissimilar materials and the intermediate heat input were helpful to obtain high weld properties.