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

Abstract

The main limitation of cast Al-Si-Mg alloys is
the considerable influence of the solidification
and heat treatment conditions on the final
microstructure and consequently on the
mechanical properties, that can thus widely
vary in the same cast component. In this work
we perform a deep microstructural and
mechanical characterisation on specimens
extracted from some A356 T6 gravity die cast
cylinder heads. The aim of the work is to
develop empirical models to successfully
predict the local tensile properties of the
casting from the main microstructural
parameters and alloy hardness. As the former
we considered and measured secondary
dendrite arm spacing, shape and size of the
eutectic silicon, grain size and percentage
area of defects. The latter instead primarily
depends on the heat treatment conditions. On
the base of these data we propose a set of
simple equations to predict the ultimate tensile
strength and the proof strength with a mean
error of 2% and the elongation to failure with
a mean error of 20%. The equations allow the
designer to know the local tensile behaviour
without any tensile tests. Moreover, in a coengineered
design approach, the equations
can link the post-processing results of the
casting simulation software to the preprocessing
phase of the structural software.
This leads to less bench tests and to a great
reduction of validation time of a new product.