Microstructures and mechanical properties of vacuum counter-pressure casting A357 alloys solidified under grade-pressurising: effects of melt temperature.

The effects of the melt temperature on the relative densities, microstructures and mechanical properties of vacuum counter-pressure casting A357 alloys solidified under grade-pressurising (200kPa) were investigated. The results indicated that the relative densities and mechanical properties of samples solidified under grade-pressurising were affected by the melt temperature (580-610°C). The optimal relative density and mechanical properties were achieved at a melt temperature of 590°C. The microstructures varied with the melt temperature as a result of the differences in the strengths of the feeding flow and dendrites. The powerful feeding flow caused by grade-pressurising solidification can induce stress on the dendrites, resulting in the collapse of the primary dendrite network to form equiaxed dendrites. Decreasing the feeding pressure proportionally to the solid volume fraction was proposed to obtain a suitable melt temperature for improving the density and refining the microstructure. [ABSTRACT FROM AUTHOR]