Effect of change in Si and Cu contents on Primary silicon size and distribution in hypereutectic Al-Si alloys in lost foam casting process

摘要

Hypereutectic Al-Si alloys are known for their high wear resistance due to formation of primary silicon crystals (psc) during solidification. Previous study suggested that density, distribution and size of psc play a dominant role in controlling the properties and behaviour of Al-Si alloys. Experiments in Lost Foam Casting (LFC) were conducted to relate the size of psc to fluidity for these Al-Si alloys. Si content was varied from 12 percent to 25 percent in order to vary the size of psc. Also, an attempt was made to discuss the possible reasons for any change in the fluidity due to variation in psc size. Cu content was also varied from 0 percent to 2.5 percent to understand the effect of Cu on fluidity. Use of LFC process has a particular significance in this research. Because of it's unique mold filling mechanism, uniform distribution of psc was expected. Four different section thicknesses were used for a better understanding of distribution of psc with change in local solidification time. Typical behaviour of curves for cooling rate and velocity were explained and related to the microstructure.