Effect of solidification rate on microstructures and orientations of Al-Cu hypereutectic alloy in thin crucible.

The microstructures and orientations of Al-40%Cu hypereutectic alloy prepared in a 0.45 mm high-purity alumina crucible at different directional solidification rates (5, 10 and 100 μm/s) were investigated. With solidification rate increasing, the primary phase Al2Cu of the alloy transits from complex dendrite morphologies to regular faceted square shapes. The surfaces of regular square morphology about Al2Cu phase are {110} facets. The orientation text results by XRD showed that at a growth rate of 5 μm/s, the phase displayed texture orientations at (310), (110), and (220). At 100 μm/s, the phase possessed a very strong preferred orientation at (310). The experimental results showed that growth in small-size samples at a higher growth rate can achieve a regular microstructure with preferred orientation. The growth morphologies are deduced from attachment energies descripted the microstructure evolution of the primary phase. [ABSTRACT FROM AUTHOR]