Amin Shakoori - MSc student, Sahand University of Technology, Iran
Tohid Saeid - Professor, Sahand University of Technology, Iran

Dissimilar joining of AZ۳۱ magnesium alloy and St۳۷ low carbon steel was performed through friction stir butt welding (FSW) at constant tool rotation rate of ۷۱۰ rpm and travel speed of ۴۰ mm/min. The effect of welding parameters on joining mechanism, interface microstructure and mechanical properties was investigated. The experimental results revealed that sound defect-free joint could be obtained when the harder St۳۷ plate was fixed at the advancing side. A steel-strip was formed at the bottom of the Mg side weld nugget. Steel fragments were dispatched from the interface into the Mg alloy matrix, which formed a composite structure during the welding process. Fine and equiaxed grains were formed in the SZ and TMAZ at the Mg alloy side. On the otherhand, St۳۷ experienced a low amount of deformation, and therefore, TMAZ zone with elongated grains was only formed near the interface at the steel side. Tensile strength of the sound joint was about ۱۶۶ MPa, which is ۶۲% of magnesium base alloy. The relatively high hardness value in the Mg SZ was attributed not only to the grain refinement strengthening, but also to the composite structure consisting of steel fragments.

Dissimilar joining; Friction stir welding;Mechanical properties; Composite structure.