Mechanical properties as a function of microstructure and solidification thermal variables of Al–Si castings

Abstract

The aim of the present study was to investigate the influence of solidification thermal variables on the as-cast microstructure of hypoeutectic Al–Si alloys and to establish correlations with the casting mechanical properties. Experimental results include transient metal/mold heat transfer coefficients, tip growth rate, local solidification time, secondary dendrite arm spacing, ultimate tensile strength and yield strength as a function of solidification conditions imposed by the metal/mold system. It was found that the ultimate tensile strength increases with increasing alloy solute content and with decreasing secondary dendrite arm spacing. Yield strength seems to be independent of both alloy composition and dendritic arrangement. Such results have permitted general expressions correlating dendrite spacing with transient solidification processing variables to be established. The correlation of such expressions with experimental equations relating the ultimate tensile strength and dendrite spacing provides an insight in the preprogramming of solidification in terms of mechanical strength of Al–Si castings. Predictive theoretical and experimental approaches for dendritic growth have been compared with the present experimental observations.