Empirical models of mechanical behaviour of Al-Si-Mg cast alloys for high performance engine applications

The main limitation of cast Al-Si-Mg alloys isthe considerable influence of the solidificationand heat treatment conditions on the finalmicrostructure and consequently on themechanical properties, that can thus widelyvary in the same cast component. In this workwe perform a deep microstructural andmechanical characterisation on specimensextracted from some A356 T6 gravity die castcylinder heads. The aim of the work is todevelop empirical models to successfullypredict the local tensile properties of thecasting from the main microstructuralparameters and alloy hardness. As the formerwe considered and measured secondarydendrite arm spacing, shape and size of theeutectic silicon, grain size and percentagearea of defects. The latter instead primarilydepends on the heat treatment conditions. Onthe base of these data we propose a set ofsimple equations to predict the ultimate tensilestrength and the proof strength with a meanerror of 2% and the elongation to failure witha mean error of 20%. The equations allow thedesigner to know the local tensile behaviourwithout any tensile tests. Moreover, in a coengineereddesign approach, the equationscan link the post-processing results of thecasting simulation software to the preprocessingphase of the structural software.This leads to less bench tests and to a greatreduction of validation time of a new product