LAUSR

Abstract High efficiency, increasing power densities, lower weight and pollution reduction require new materials for combustion engine components in order to withstand the higher thermo-mechanical loads. Cast Al-Si alloys are used for cylinder heads where they combine light weight, good castability and suitable mechanical properties. Despite casting difficulties and their vulnerability to hot tearing these Al-Cu alloys can be used as candidates to achieve even better mechanical properties at elevated temperatures. These alloys are formed by a ductile precipitation hardening α-Al matrix and brittle intermetallics, mostly Al2Cu. Tensile deformation of AlCu4 as cast and AlCu7 solutionized and aged conditions is investigated by combined application of non-destructive testing and imaging methods (using electron, neutron and synchrotron radiation) to study the stress distribution between the Al2Cu structures and the surrounding Al matrix. The external loads are transferred into the microstructure by strain control due to percolating eutectic structures in AlCu4 and AlCu7 as cast. Homogenization by solution treatment and age hardening significantly increases the strength, although stress controlled behavior becomes dominant. (Some damage tolerance is observed in the as cast as well as in the heat treated condition, as load is transferred from particles which were broken first to the remaining ones maintaining some deformation strengthening.) The stress-strain behavior of the samples is compared, conclusions on deformation mechanisms and internal architectures are drawn.