Improved mechanical properties of cast Mg alloy welds via texture weakening by differential rotation refill friction stir spot welding

Banglong Fu,Junjun Shen,Uceu F.H.R Suhuddin,Ting Chen,Jorge F Dos Santos,Benjamin Klusemann,Michael Rethmeier

doi:10.1016/j.scriptamat.2021.114113

Abstract

Cast magnesium alloys welds produced by refill friction stir spot welding (refill FSSW) show low lap shear strength (LSS) and constantly fail in stirred zone (SZ) shear mode. The cause is most probably related to the heavily textured microstructure. Here, to re-engineer the resulting microstructure, we propose a novel process variant, the differential rotation refill FSSW (DR-refill FSSW). DR-refill FSSW stimulates discontinuous dynamic recrystallization and produces a bimodal microstructure with weakened texture. Therefore, the deformation incompatibility between SZ and thermal-mechanically affected zone is avoided. The welds have 50% higher LSS than that of standard refill FSSW welds, and fail in a different failure mode, i.e., SZ pull-out mode. DR-refill FSSW provides a new and effective strategy for improving the performance of spot welds based on microstructural engineering.

Highlights

Cast magnesium alloys welds produced by refill friction stir spot welding show low lap shear strength (LSS) and constantly fail in stirred zone (SZ) shear mode
The present study aims at introducing a novel refill FSSW
When the rotation directions of shoulder and probe are opposite, i.e. variant II as ωP−robe, the LSS increases significantly, and most produced welds fulfill the strength requirement of referred standard [29]. For these welds, when ωP−robe is higher than ω+ 1800 Shoulder ω− 2400 Probe and ωP−ro3b0e00, during LSS test, the circular cracks mainly grow along the SZ edge and close on the upper sheet surface, the SZ remains entirely on the lower sheet, resulting in a different failure mode: SZ

Summary

Introduction

Cast magnesium alloys welds produced by refill friction stir spot welding (refill FSSW) show low lap shear strength (LSS) and constantly fail in stirred zone (SZ) shear mode. To achieve a sound refill FSSW Mg alloys weld with superior mechanical properties, the texture intensity needs to be reduced. LSS compared to conventional refill FSSW, through texture weakening.

Results

Conclusion