Role of manganese on the grain refining efficiency of AZ91D magnesium alloy refined by Al4C3

A novel Mg–50% Al4C3 (hereafter in wt.%) master alloy has been developed by powder in situ synthesis process, the role of manganese on the grain refining efficiency of AZ91D magnesium alloy refined by this master alloy has been investigated. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) results show the existence of Al4C3 particles in this master alloy. After addition of 0.6% Al4C3 or combined addition of 0.6% Al4C3 and 0.27% Mn, the average grain size of AZ91D decreased dramatically from 360 μm to 210 μm, and from 360 μm to130 μm, respectively. However, no further refinement of grain size was achieved with additional amount of Mn exceeding 0.27% for AZ91D alloy refined by 0.6% Al4C3 in the present investigation. Al–C–O–Mn–Fe-rich intermetallic particles with an Al–C–O-rich coating film, often observed in the central region of magnesium grains of the AZ91D alloy treated by the combination of Al4C3 and Mn, are proposed to be the potent nucleating substrates for primary α-Mg.