Investigation of the Effect of Process Parameters on the Mechanical Properties (Tensile) of Al-7%Si Alloy Castings Produced by Evaporative Pattern Casting Process

摘要

Evaporative pattern casting (EPC) process, a sand moulding process, utilises physical bonding only in dry and free flowing sand without any conventional binder. In this process, all the limitations imposed by the binders and additives are absent as it is a binderless process. The process claims many advantages over conventional sand moulding processes. This paper investigates the effect of the EPC process parameters on the mechanical properties (tensile strength and per cent elongation) properties of Al -7% Si alloy castings. The response surface methodology was used for this investigation. A second order response surface was found correct to correlate the independent factors with the quality characteristic. Central composite second order experimental design is adopted to plan the experiments. The tensile strength decreases with the increase in the sand grain fineness number. However, the effect of sand grain fineness number on per cent elongation is not significant. The tensile strength increases with the increase in degree of vacuum imposed, However, the effect of vibration frequency and vibration time on tensile strength is insignificant. Per cent elongation increases with the increase in vibration frequency, vibration time, and degree of vacuum imposed. The higher temperature of liquid metal provides a better feeding of liquid metal at the inter-dendrite cavities. But solubility of hydrogen gas with the liquid metal increases at higher pouring temperature of the liquid metal. The dissolved hydrogen gas in the liquid metal has lower solubility at lower temperature during solidification; thereby hydrogen gas comes out of the molten metal. Some of it is entrapped, which increases the extent of porosity in the castings. Hence tensile strength and per cent elongation are reduced with the increase in -pouring temperature.