Pre-weld friction stir processing enabling strong and ductile fusion welds on AZ91 magnesium alloy

Abstract

Liquation in the partially melted zone (PMZ) is the critical weldability issue of cast AZ91 magnesium alloy. Friction stir processing (FSP) is used as a local pre-weld treatment to create a local liquation-resistant microstructure in cast AZ91 alloy during arc welding. The effects of tool rotational speed during pre-weld FSP on the liquation-related microstructural features (i.e. grain structure, size and volume fraction of eutectic β-Mg₁₇Al₁₂) and the liquation characteristics of the fusion-welded AZ91 (i.e. PMZ size and grain boundary liquid film thickness) were investigated. The pre-weld FSP treatment of the cast AZ91 significantly improved the tensile strength and ductility of the welds mainly due to significant reduction in the thickness of the re-solidified eutectic β-Mg₁₇Al₁₂ film in the PMZ.

KEYWORDS:

• Friction stir processing
• liquation
• partially melted zone
• mechanical properties
• cast AZ91 magnesium alloy
• fusion welding

Disclosure statement

No potential conflict of interest was reported by the author(s).