Degassing of magnesium alloy by rotating impeller degasser Part 2 – effect on microstructure and mechanical properties

Abstract

Magnesium alloy shows great potential application in automatic industry. In production practice, recycled magnesium alloys are normally used in order to reduce the production costs. In this work, a rotary impeller was used to degas AZ91 magnesium alloy with 10 wt-% recycled alloy in order to investigate the effect of degassing on mechanical properties. Microstructure and fracture surface of AZ91 samples with and without degassing were observed by SEM to reveal the control mechanism. Mechanical properties measurements have shown that degassing significantly increased the tensile strength and especially the elongation of the as cast magnesium alloy. Microstructure and fracture surface observation indicated that high hydrogen content resulted in an increase in shrinkage in magnesium casting, which contributes to low mechanical properties. Casting condition also affected the influence of hydrogen content on the mechanical properties. High increase in strength and elongation was observed in the permanent and the low pressure sand magnesium castings by reducing hydrogen content. It has been shown that rotary degassing as a degassing technology exhibits high degassing efficiency to magnesium melt.