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

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References

Pouranvari

Critical review on fusion welding of magnesium alloys: metallurgical challenges and opportunities. Sci Technol Weld Join. 2021;26:559–580.

Liu

, Kou

Susceptibility of magnesium alloys to solidification cracking. Sci Technol Weld Join. 2020;25:251–257.

Chai

, Yuan

, Kou

Liquation and liquation cracking in partially melted zones of magnesium welds. Weld J. 2016;95:57–67.

Pouranvari

, Sharahi

, Movahedi

Effect of liquation on the tensile properties of cast Mg–9Al–1Zn alloy fusion welds. Sci Technol Weld Join. 2020;25:698–705.

Kou

Welding metallurgy. 3rd ed. Hoboken, NJ: John Wiley; 2020.

Yuan

, Chai

, Luo

, . Predicting susceptibility of magnesium alloys to weld-edge cracking. Acta Mater. 2015;90:242–251.

Yuan

, Yu

, Wang

, . Effect of intermetallics on susceptibility of Mg alloy welds to liquation cracking. Sci Technol Weld Join. 2020;25:496–502.

Radhakrishnan

, Thompson

RG.

A model for the formation and solidification of grain boundary liquid in the heat-affected zone (HAZ) of welds. Metall Trans A. 1992;23:1783–1799.

Mousavizade

, Ghaini

, Torkamany

, . Effect of severe plastic deformation on grain boundary liquation of a nickel-base superalloy. Scr Mater. 2009;60:244–247.

10.

Rule JR , Rodelas

, Lippold

JC.

Application of friction stir processing as a pretreatment to fusion welding. Weld J. 2013;92:283–290.

11.

Malekshahi Beiranvand

, Malek Ghaini

, Sheikhi

, . Effect of severe plastic deformation on hot cracking of wrought aluminium alloy in pulsed laser welding. Sci Technol Weld Join. 2013;18:473–477.

12.

Karthik

, Janaki Ram

, Kottada

RS.

Use of friction stir processing for improving heat-affected zone liquation cracking resistance of a cast magnesium alloy AZ91D. Metall Mater Trans B Process Metall Mater Process Sci. 2017;48:3270–3280.

13.

Sharahi

, Pouranvari

, Movahedi

Enhanced resistance to liquation cracking during fusion welding of cast magnesium alloys: microstructure tailoring via friction stir processing pre-weld treatment. Mater Sci Eng A. 2020;798:140142.

14.

Mishra

, Ma

ZY.

Friction stir welding and processing. Mater Sci Eng R. 2005;50:1–78.

15.

Sharahi

, Pouranvari

, Movahedi

Strengthening and ductilization mechanisms of friction stir processed cast Mg–Al–Zn alloy. Mater Sci Eng A. 2020;781:139249.

16.

ASTM E112-10. Standard test methods for determining average grain size.

17.

Dahle

, Lee

, Nave

, . Development of the as-cast microstructure in magnesium-aluminium alloys. J Light Met. 2001;1:61–72.

18.

Zhu

, Chen

, Gao

Dissolution of eutectic β-Mg₁₇Al₁₂ phase in magnesium AZ91 cast alloy at temperatures close to eutectic temperature. J Mater Eng Perform. 2010;19:860–867.