Microstructural characterisation of several magnesium alloys in AM series

The as cast microstructures of several magnesium alloys in the AM series have been characterised, including the dendritic structure, Al segregation and the Mn containing phases. Two types of Mn containing particles were found and studied in the alloys mainly by using TEM. Type I is of equiaxed morphologies and a higher Mn/ Al ratio in the composition. The flower shaped and dendritic type II phase has a lower Mn/Al ratio. The equiaxed type I could originate in the particle residues in the melts retained in the as cast alloy and the type II might form around a small type I particle. Electron diffraction has determined that both type I and type II have bcc crystal structure with lattice parameter a=0 center dot 91 nm. The higher Mn content in an alloy may lead to a higher amount of Mn containing particles.