# The Effect of Process Parameters on the Performance of the RFSSW of ZK61M-T5 Magnesium Alloy

## TL;DR

This study examines how different welding parameters affect the quality and strength of magnesium alloy joints using a specific welding technique.

## Contribution

The study identifies optimal rotational and welding speeds for minimizing defects and improving the mechanical performance of RFSSW joints in ZK61M-T5 magnesium alloy.

## Key findings

- Sound joints were achieved at 1000 rpm and 1500 rpm with welding speeds of 30–50 mm/min.
- Higher rotational speeds reduced pores but decreased ultimate lap shear force due to increased annealing and Zr segregation.
- Grain refinement occurred in thermomechanically and sleeve-affected zones, while coarsening occurred in the pin-affected zone.

## Abstract

This study investigates refill friction stir spot welding (RFSSW) of 2 mm thick ZK61M-T5 magnesium alloy. Sound joints were obtained at rotational speeds of 1000 rpm and 1500 rpm with welding speeds of 30–50 mm/min. At 1000 rpm, micro-pores appeared at the sleeve-affected zone bottom, exhibiting a full-fillet fracture and a maximum ultimate lap shear force (ULSF) of 8.3 kN. Increasing the speed to 1500 rpm eliminated the pores and changed the fracture mode to partial fillet, but reduced the ULSF to 7.7 kN. Higher welding speeds caused the Hook feature to shift from upward to downward. Compared with the base material, grains in the thermomechanically and sleeve-affected zones were refined, while those in the pin-affected zone coarsened with increasing rotational speed. Overall, higher rotational speed increased heat input and mitigated internal defects, but enhanced annealing and Zr segregation, leading to reduced mechanical performance.