差压铸造薄壁铝硅合金铸件的位置效应

采用差压铸造工艺,研究垂直缝隙式浇注系统浇注的铝合金硅铸件不同位置的组织和力学性能变化.采用石英砂型、SiC砂型和冷铁,浇口处铸件的晶粒最细小,致密度高、力学性能最好;铸件冷端的组织和性能次之;位于两者之间的铸件的组织和性能最差.分析表明对于具有垂直缝隙式浇注系统,差压铸造凝固压力对金属的凝固作用具有位置效应,浇口处液态金属温度高,凝固时间长,凝固压力对浇口处金属的凝固作用显著;铸件冷端金属凝固时间短,凝固压力对该处金属的凝固作用不显著,铸型的冷却速度对铸件组织和性能的影响起显著作用.浇口处与冷端之间的金属液体的凝固受压力和冷却速度的影响小,铸件的晶粒尺寸最大、密度最小、性能最低.冷却速度提高,铸件的任意位置的组织和性能都相应得到提高.

Site Effectiveness of Thin-wall Aluminum-silicon Alloy Castings in Differential Pressure Casting Process

Different site microstructure and mechanical properties of aluminum-silicon alloy in differential pressure casting process were investigated. The gate system was adopted vertical slitting gate system. In the investigation at the inner-gate site of the castings the grain is finer, the density is higher and the mechanical properties is best than that of at the cooling site of castings no matter with SiO_(2) sand mould, SiC sand mould or chill. However, the grain size, density and mechanical properties of castings between inner-gate site and cooling site are minimum. The analysis results reveal that solidification pressure has site effectiveness during producing aluminum alloy castings by using vertical slitting gate system with a differential pressure casting process. At the inner-gate site the molten metal has higher temperature and longer solidification time that make solidification pressure has longer performance time during molten metal solidification process. Thus solidification pressure has prominent effect on solidification of molten metal at inner-gate site. At the cooling site of the casting the molten metal has the lowest temperature and the shortest solidification time. The solidification pressure has little effect on the solidification of the molten metal at this site. By contraries, the cooling rate has prominent effect on grain size, density and mechanical properties. The solidification of molten metal between the inner-gate site and the cooling site of casting receives little effect from solidification pressure and cooling rate and give rise to biggest grain size, minimal density and lowest mechanical properties. With the increase of cooling rate, the microstructure and properties of castings at every site are improved.