Grain refining technique of AM60B magnesium alloy by MgCO3

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 degrees C. Prolonging holding time at 790 degrees C will increase grain size. The grain refining technique that 1.2% MgCO3 is added at 790 degrees C followed by holding for 10 min and pouring can decrease the grain size from 348 mu m of the un-refined alloy to 69 mu m. 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.