The effect of manganese on the grain size of commercial AZ31 alloy

The effect of manganese on gain refinement of a commercial AZ31 alloy has been investigated using an Al-60%Mn master alloy splatter as an alloying additive at 730 degrees C in aluminium titanite crucibles. It is shown that grain refinement by manganese is readily achievable in AZ31. Electron microprobe analyses reveal that prior to the addition of extra manganese the majority of the intermetallic particles found in AZ31 are of the AL(8)Mn(5) type. However, after the addition of extra manganese in the range from 0.1% to 0.8%, the predominant group of intermetallic particles changes to the metastable AlMn type. This leads to a hypothesis that the metastable AlMn intermetallic particles are more effective than Al8Mn5 as nucleation sites for magnesium grains. The hypothesis is supported by the observation that a long period of holding at 730 degrees C leads to an increase in grain size, due probably to the transformation of the metastable AlMn to the stable Al8Mn5. The hypothesis has also been used to understand the mechanism of grain refinement by superheating.

Effect of manganese on grain refinement of Mg-Al based alloys

Manganese is a grain refiner for high purity Mg-3%Al, Mg-6%Al, Mg-9%Al, and commercial AZ31 (Mg-3%Al-1%Zn) alloys when introduced in the form of an Al-60%Mn master alloy splatter but the use of pure Mn flakes and ALTAB (TM) Mn75 tablets shows no grain refinement. Long time holding of the melt at 730 degrees C leads to an increase in grain size. The mechanism is attributed to the presence of all epsilon-AlMn phase (hexagonal close-packed) in the master alloy splatter. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.