In this paper the microstructure evolution of AZ91HP magnesium alloy casts produced
under different disturbing treatment conditions such as non-disturbing, argon blowing and
mechanical stirring in semi-solid state after holding a short time was studied. The results show that
the grains of AZ91HP alloy casts refined, the secondary dendritic arms grown and the dendrites tend
to rosette shape with the decrease of holding temperature. External disturbance can accelerate the
evolution process, and the spherical primary α phase formed easily under mechanical stirring
treatment condition. The formation of non-dendritic structure is owing to ripening of the dendritic
arms, refinement of the grains and movement of the primary formed solid phases. Disturbing
treatments in semi-solid state induce more equilibrium solidification and decrease the amount of
brittle β-Mg17Al12 phase. Blowing argon into the refined and modified magnesium alloy in semi-solid
state can obtain homogeneous non-dendritic structure and the net shaped β phase distributed on α-Mg
phase boundaries become fine and thin, this may be have a good effect on the mechanical properties
of the magnesium alloy casts. Due to the low disturbing strength, argon blowing can maintain the
metallurgy quality of the semi-solid slurry well, and also have high efficiency to make it. This
technology need not new complex equipments and can be practiced in conventional casting
conditions, so it may be used in industrialize manufacture.
Fluidity of AZ91D magnesium alloy chips stirred at semi-solid state and mechanical properties after press-forming.
