铝合金薄壁铸件压力结晶及性能的研究

 提高铝合金铸件致密性的一种有效工艺是压力下结晶,即铸件在结晶凝固期间,使之处于大于大气压力的环境中,迫使液体金属在枝晶间流动来补充显微缩孔和缩松。一般认为这项工艺只适用于较厚大的铸件,对薄壁铸件因凝固过快而无效。航天、航空工程中许多铝合金铸件的断面为薄壁或超薄铸,对铸件内部组织的致密性有一定要求。

STUDY ON THE PRESSURE CRYSTALLIZATION OF ALUMINUM ALLOY CASTING WITH THIN SECTION AND ITS MECHANICAL PROPERTIES

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.