Grain refining mechanism of Al-containing Mg alloys with the addition of Mn–Al alloys

Abstract

The effect of manganese on grain refinement of Al-containing AZ31 Mg alloy has been investigated by designing a series of Mn–Al alloys composed of either pure ɛ-AlMn, γ 2-Al 8Mn 5 or both of them using optical microscopy and X-ray diffraction. It is experimentally clarified that the grain refinement of the AZ31 Mg alloy is due to the existence of the ɛ-AlMn phase in the Mn–Al alloys, not the γ 2-Al 8Mn 5 phase. The grain size of AZ31 Mg alloy is about 91 μm without any addition of Mn–Al alloys, but remarkably decreases to ∼55 μm with the addition of either Mn–34 wt% Al or Mn–28 wt% Al. With a minor addition of 0.5 wt% Mn–28Al alloy, the grain size of AZ31 alloy decreases to ∼53 μm, and the Mn–28Al alloy can be active as grain refiner for holding time up to 60 min for the melt AZ31 alloy at 750 °C.