5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

Al-Mn-Fe intermetallics are important for the corrosion resistance of cast Mg alloys but there have been few studies on their solidification mechanisms or microstructure development. Here EBSD, deep etching and FIB-tomography are combined to study the nucleation and equaixed growth crystallography of B2-Al(Mn,Fe), Al8Mn5, and Al11Mn4 in Mg-Al-Mn-based alloys. It is shown that twinning readily occurs during the solidification of all three compounds. In the case of rhombohedral Al8Mn5, the twinned particles consist of four orientations related by ~90° rotations around three common 〈1-102〉, which is discussed in terms of the pseudo-cubic <100> axes of the Al8Mn5 rhombohedral gamma brass. Under a wide range of solidification conditions, Al8Mn5 grew as equiaxed polyhedra that are explained by polyhedron models based on different combinations of {100}, {110} and {112} facets using a pseudo-cubic Al8Mn5 cell. It is shown that twinning also plays a role in the preferred orientation relationships that develop between the different Al-Mn-Fe compounds. Reproducible orientation relationships (ORs) and the lattice match between the phases are discussed in terms of the group-subgroup relationship between these phases. The role of solute rejection on the continuous nucleation of Al-Mn-Fe particles during cooling in a near-uniform thermal field and on the final number density of Al-Mn-Fe intermetallics is then discussed based on analysis of synchrotron radiogaraphy image sequences.