INFLUENCE OF GROWTH-RATE ON MECHANICAL-PR OPERTIES OF MODIFIED AL-SI EUTECTICS

The effect of growth rate on mechanical properties of Al-12.87Si-0.04S r (wt.%) alloy was studied. This material was directionally solidified by Bridgman method at growth rate in the range from 3 to 1250 mu m/s. It was revealed, that the growth rate has a strong effect on the inte rparticle spacing of silicon particles and hence on mechanical propert ies, as well. The higher growth rate, the smaller interparticle spacin g and the higher values of ultimate tensile strength, yield strength, elongation to fracture, reductions of area, and hardness. The validity of modified Hall-Fetch equation was confirmed for relations UTS, Y.S. and hardness versus growth rate and interparticle spacing for growth rate in the range from 3 to 100 mu m/s. The strong dependence of yield strength on hardness in the range of the studied growth rate provides a possibility to predict the mechanical properties on the basis of th e hardness results. The increase of elongation to fracture with increa sing growth rate was proved by the fracture observation.