Abstract:

Many aluminum alloy castings with thin section arc cast in plaster moulds. Because of the insulating nature of plaster moulds, the cooling rate of the casting is slow, which readily results in interdendritic microporosity and lower mechanical properties.By means of the apparatus that can be vacuumized before pouring molten metal and can be pressurized during crystallization, the effect of surrounding pressure, where liquid metal is freezing, on the crystal structure and mechanical properties of thin-section castings cast by plaster mould are investigated. The relations between the time of establishing the pressure and the thermal behaviors about metal and moulding material are studied theoretically. The criterion that shows whether the pressure is available for improving density and producing soundcastings with.thin section. Experimental results show that the density and the mechanical properties of thin sectional casting samples are obviously increased when using the method of crystal! i-zation under pressure.

Key words: crystallization under pressure, thin sectional castings .aluminum alloy castings, mechanical properties, plaster mould