Abstract:The effects of grain refining parameters on microstructure of AM60B magnesium alloy with MgCO₃ were investigated and then a refining technique was developed. Simultaneously, the corresponding mechanisms were discussed. The results indicate that increasing addition temperature of MgCO₃ or pouring temperature is beneficial for obtaining fine grains. There is an optimal addition amount of 1.2% at the addition temperature of 790 °C. Prolonging holding time at 790 °C will increase grain size. The grain refining technique that 1.2% MgCO₃ is added at 790 °C followed by holding for 10 min and pouring can decrease the grain size from 348 µm of the un-refined alloy to 69 µm. The nucleation substrates are actually the Al₄C₃ particles formed from reactions between the MgCO₃ and alloying elements in the melt. Besides the heterogeneous nucleation regime, growth restriction of the Al₄C₃ particles agglomerated at growing front is the other mechanism.

Key words: AM60B magnesium alloy; grain refinement; MgCO₃