Grain refinement of AZ91D by spinning spray of carbon dioxide gas and its effect on mechanical property

Abstract

Grain refinement of AZ91D Mg alloy by a spinning spray of Ar+CO₂ mixture gas was investigated. The results have shown that the grain size was refined significantly and effectively by this processing after 15–30 min treatment, but further extension of the treatment did not refine the grain markedly. It was shown that this processing has an ‘aging behaviour’, which means that the refining efficiency declines with the extension of holding time at melting temperature. Although the cooling rate affected the final grain size of AZ91D sample refined by the processing, it did not change the aging behaviour. The effective time is 45–60 min. It was analysed that Al₄C₃ could act as nucleation site of the primary Mg, which contributes to the grain refinement. Mechanical property testing demonstrated that refinement by the Ar+CO₂ processing significantly refined the grain size of the as cast AZ91D samples produced by sand and permanent cast and in turn enhanced the strength and improved the elongation.