Developing castability index for magnesium diecasting alloys

Abstract

A partial castability index has been developed for magnesium diecasting alloys based on alloy characteristics such as solid thermal conductivity, non-equilibrium freezing range and hot tear sensitivity. The partial castability index IC for thin walled castings was developed using an industrial diecasting defect index IDD of five different alloys and regression analysis to give IC −0·08(ΔF)+0·58Δκ+0·01ΔHTS+0·06ΔT′ with R2=0·9977, where ΔF=(freezing range for AZ91)−(freezing range for alloy); Δκ=(thermal conductivity of alloy)−(thermal conductivity of AZ91); ΔHTS=(hot tear sensitivity of AZ91)−(hot tear sensitivity of alloy); ΔT′=(non-equilibrium freezing range of alloy)−60°C. The hot tear test and its hot tearing susceptibility (HTS) rating determined using a constrained rod casting mould can also assess the trend in diecastabilty of magnesium alloys in thin walled castings but the prediction is not as good as the partial diecastability index IC. The HTS rating correlates with the industrial diecasting defect index IDD as IDD=0·9HTS0·5.