Grain Refining Mechanism of Carbon Inoculation on Mg-Al Alloy

The processing parameters and refining mechanism of Mg-Al alloy treated with a newly developed carbon inoculant under different conditions were investigated experimentally in this work.Results show that the finest α-Mg grain in AZ91D alloy can be obtained after processing at about 740 ℃,and the average grain size of α-Mg grain decreases from about 180.4 to 85.6 μ m by adding mass fraction w in = 1% inoculant into melt.However,no evident refinement was achieved with excessive inoculant for Mn-free Mg-9Al alloy.Scanning electron microscope(SEM) photo,energy dispersive spectroscopy(EDS) analysis on the Mn-contained intermediate phase and differential scanning calorimetry(DSC) results indicate that Mn element plays an important role in the heterogeneous nucleation of α-Mg grain.In the early stage of solidification,Al-Mn-C compound particles formed on the surface of Al4C3 nano-particles should be the potential nuclei for primary α-Mg and probably responsible for the grain refinement achieved in the carbon inoculation process.