Duplex nucleation in Mg–Al–Zn–Mn alloys with carbon inoculation

Duplex nucleation in Mg–Al–Zn–Mn alloys with carbon inoculation was investigated in this study. Carbon addition brought remarkable grain refinement to both AZ31 (Mg–3Al–1Zn–0.45Mn) and AZ63 (Mg–6Al–3Zn–0.35Mn). Al4C3-coated Al0.89Mn1.11 and Al4C3-coated Al8Mn5 act as the duplex nucleation sites in carbon-treated AZ31 and AZ63, respectively. The morphologies and sizes of dominant Al–Mn phases in both alloys (Al0.89Mn1.11 in AZ31 and Al8Mn5 in AZ63) did not change significantly after grain refinement of the alloys, and these Al–Mn particles are believed to have low nucleating efficiency for primary α-Mg. In contrast, Al4C3, the interfacial phase between primary α-Mg and duplex nucleating particles, is the direct potent nucleating substrate for primary α-Mg.