Dendrite Morphology Evolution of Al(6)Mn Phase in Suction Casting Al–Mn Alloys

The effects of solute element content and cooling rate on the morphology of Al(6)Mn phase in suction casting Al–Mn alloys were investigated by transmission electron microscope, scanning electron microscope, and X-ray diffractometer. Results show that Al(6)Mn dendrite morphology with different degrees of development can occur in the microstructure of as-cast Al–Mn alloys. For the Al–4 wt.% Mn alloy, there are small amounts of block Al(6)Mn crystals at the center of sample, while we see a block Al(6)Mn phase and a feathery Al(6)Mn phase in the sample of Al–6 wt.% Mn alloy. Moreover, the block Al(6)Mn phases in the Al–8 wt.% Mn alloy disappear, and only snowflake-like Al(6)Mn phases play a dominant role in the microstructure. However, with an increase in Mn content to 10 wt.%, more dendritic trunks are formed, and secondary dendrite arms are degraded more seriously due to the formation of an icosahedral quasicrystal in suction casting. In addition to the effect of Mn content on Al(6)Mn morphology, with the increase in cooling rate from the center to the edge of samples, the outline diameter of equiaxed dendrite decreases. The evolution of Al(6)Mn dendrite morphology and the formation of quasicrystal are further discussed.