Lightweight with excellent strength of magnesium alloys has attracted its use in transportation industries but difficulty in fusion welding of magnesium alloys restricts its application. The present research investigates solid state friction stir welding of dissimilar AZ31-AZ91 magnesium alloys with aim to achieve optimum quality welds. Surface roughness, microstructure and mechanical properties of these joints have been investigated at different tool rotational speed, welding speed and tool shoulder diameter. Maximum joint strength obtained is 89.71% (as compare to AZ31) which is more than the previously reported joint strengths of dissimilar magnesium alloys. Further, mathematical relations for responses have been developed and utilised for multi-objective optimization using teaching-learning-based optimization algorithm. Eventually, teaching-learning-based optimization algorithm results suggest that the optimum value of surface roughness (3.3925 µm), grain size (12.6869 µm), tensile strength (237.9621 MPa), microhardness (69.3652 Hv) and flexural strength (333.2285 MPa) can be achieved at 921 rpm rotational speed, 30 mm/min welding speed and 15 mm shoulder diameter with overall improvement in multiple responses.

镁合金质量轻、强度高，在交通运输行业中得到了广泛应用，但镁合金熔焊困难限制了其应用。本研究调查了异种 AZ31-AZ91 镁合金的固态搅拌摩擦焊，旨在实现最佳焊接质量。在不同的工具转速、焊接速度和工具肩部直径下研究了这些接头的表面粗糙度、微观结构和机械性能。获得的最大接头强度为 89.71%（与 AZ31 相比），这比先前报道的不同镁合金的接头强度更高。此外，已经开发出响应的数学关系并将其用于使用基于教学的优化算法的多目标优化。最终，