Study on porosity of al alloy in LFC process

摘要

It is a difficult task to decrease the porosity and improve the tightness for aluminum castings in lost foam casting (LFC) process. In this paper, the effects of modification, grain refinement, polystyrene pattern, pouring temperature and reduced pressure degree on aluminum alloy pinhole in LFC process have been studied. The results show that the solidification rate in LFC process is slower than that in resin sand process or clay sand process. So, the castings in LFC are more prone to porosity. The effects of modification and refinement on the aluminum alloy casting density in LFC are greater than that in resin sand process. The unique grain refinement with an Al-Ti-B masteralloy for LFC aluminum melt would greatly weaken the subversive effect of lower solidification rate on the casting pinhole. The experimental results show that the refined casting densities with 0.2% Ti are nearly equal in both LFC and resin sand processes. Polystyrene will enhance the casting porosity. Lower reduced pressure is helpful to decrease porosity during mold filling. But higher reduced pressure will induce turbulence in aluminum melt and increase the casting pinholes and decrease its density. Besides, high reduced pressure would decrease the solubility of hydrogen and enhance the precipitation of hydrogen in the aluminum melt to form porosity. The results show that, to decrease the pinholes for aluminum castings in LFC process, lower density of polystyrene pattern, higher pouring temperature (760-780℃ or 1400-1436F) and lower reduced pressure degree (≤0.02MPa) should be applied.