Grain refinement of Mg–Al based alloys by a new Al–C master alloy

A new Al–C master alloy for grain refinement on Mg–Al based alloys has been fabricated by powder metallurgy. Al4C3 is formed by reaction between part of f.c.c Al(C) solid solution and aluminum during fabrication, and the net-like mixture of Al4C3 and Al(C) solid solution is located at the boundaries of aluminum particles. Milling and pressing of graphite and aluminum powders change the nature of graphite and ensure the kinetics conditions of the reaction between the two phases. Grain refinement experiment shows Al–1C master alloy can efficiently refine AZ31 (Mg–3%Al–1%Zn). At 760 °C, when adding 2 wt.% Al–1C master alloy, the grain size is reduced sharply from 400 μm to 140 μm comparing to the sample added 2 wt.% commercial pure aluminum, and the grain morphology of α-Mg transits from a characteristic sixfold symmetrical shape to a petal-like shape.