Hot plastic deformation of aluminium alloy 2009 - 15%SiC w composite

Abstract

The hot deformation behaviour of the discontinuously reinforced metal matrix composite aluminium alloy 2009(Al-3.8 wt-%Cu-1.3 wt-%Mg) - 15 vol.-%SiC_w, produced via powder metallurgy, was studied by compression testing in the strain rate range 10^-4 - 10¹ s^-1 at temperatures ranging from 450 to 525 ^°C. It was shown that the composite exhibits superplasticlike behaviour, which can be explained in terms of a threshold stress. This approach allowed calculation of the true activation energy and true values of the stress exponent. A strong temperature dependence of the threshold stresses was determined. Optical metallographic studies and TEM investigations were carried out to examine microstructural evolution. It was shown that superplastic deformation does not lead to the formation of a new macrostructure. Under superplastic conditions the SiC whiskers retain their orientation, while at both lower and higher strain rates the reinforcements rotate during deformation. As a result, superplastic deformation yields increased service properties. The origin of this phenomenon is discussed. MST/4998