Microstructure and crystal growth direction of Al-Cu alloy

The microstructures and crystal growth directions of permanent mould casting (PMC) and directionally solidified (DS) Al-Cu alloys with different contents of Cu were investigated. Simultaneously, the effects of pouring temperature on the microstructure and crystal growth direction of permanent mould casting pure Al were also discussed. The results indicate that the α(Al) crystals in the pure Al do not always keep common columnar grains, but change from the columnar grains to columnar dendrites with developed arms as the pouring temperature rises. The growth direction also varies with the change of pouring temperature. Cu element has similar effects on the microstructures of the PMC and DS casting Al-Cu alloys and the α(Al) crystals gradually change from columnar crystals in turn to columnar dendrites and developed equiaxed dendrites as the Cu content increases. The crystal growth direction in the PMC alloys gradually approaches <110> orientation with increasing Cu content. But the resulting crystals with growth direction of <110> do not belong to feathery grains. There are also no feathery grains to form in all of the DS Al-Cu alloys.