In-situ determination of the influence of composition on the damage accumulation of Al-Si piston alloys

Cast near eutectic Al-Si alloys are used in automotive pistons due to their high strength-to-weight ratio as well as excellent castability and heat conductivity. Particularly, the piston bowl rim in modern diesel engines must be able to withstand compressive and tensile stresses at temperatures up to 400°C. The microstructure of cast near eutectic Al-Si piston alloys consists of interconnected 3D hybrid networks formed by Si (primary and eutectic) and intermetallic phases embedded in a comparatively soft α-Al matrix. The load carrying capability of these networks is affected by topological and morphological changes that they can undergo during thermal heat treatments and due to the thermo-mechanical conditions during service. The damage formation and evolution of different cast, near eutectic Al-Si piston alloys during tensile deformation was investigated as a function of chemical composition and test-temperature by means of in-situ synchrotron microtomography. A clear influence of the test-temperature on damage mechanisms und tensile behaviour was determined. Furthermore, a correlation between load carrying capability and local connectedness of the rigid phase network owing to variations in chemical composition was established.