Effect of processing variables on structure and tensile properties of investment cast Al-Si-Mg casting alloy

A research programme was conducted to study the effects of grain refinement , eutectic silicon modification, filtering, pouring and shell preheat tempe ratures, and heat treatment on the structure and tensile properties of an i nvestment cast Al-Si-Mg alloy, LM25 (BS 1490 : 1988). The principal finding s of the research were that: an increase in shell preheat temperature adver sely affects the structure and, hence, the tensile properties, grain refine ment was enhanced as the titanium content was increased to about 0.8% but t he tensile properties were not affected. a modified eutectic silicon struct ure was achieved with strontium additions in the range 0.01-0.02%, with the optimum addition, based on tensile properties, being 0.01%; and, as would be expected, heat treatment improved the tensile properties. On the basis o f the interrelationships between process variables, structural changes, and tensile properties observed an optimum professing route was identified. Th e optimum tensile properties were obtained in fully heat treated specimens that had been both grain refined and modified and produced in moulds poured at ambient temperature.