Microstresses and crack formation in AlSi7MgCu and AlSi17Cu4 alloys for engine components

The increasing demand on light weight and efficiency of modern combustion engines requires sophisticated light alloys with improved high temperature strength and creep resistance. Thus, new cast AlSi alloys are developed for structural parts to increase their wear resistance and long term stability under operation conditions. The heterogeneous micro structure of AlSi combines the thermal properties of stiff Si particles with a ductile α-Al to a composite with improved thermo-mechanical strength. However, different Young’s moduli and coefficients of thermal expansion are responsible for large micro stress gradients and unpredictable micro crack formation under operation. The micro-mechanical deformation mechanisms in AlSi systems, responsible for crack initiation and growth, are unknown so far. The current work describes an experimental approach of combining non-destructive diffraction and imaging techniques to investigate the elasto-plastic deformation behavior of two engineering alloys, e.g. the hypoeutectic AlSi7MgCu standard alloy for castings and the hypereutectic AlSi17Cu4 piston alloy for improved surface wear resistance. Neutron diffraction was applied for micro stress measurements under external load and during thermal cycling. Complementary synchrotron tomography was performed for imaging of micro crack formation and damage within the micro structure. Stress induced micro-mechanic deformation mechanisms could be revealed and correlated to damage mechanisms critical for engine components under operation conditions.     «

The increasing demand on light weight and efficiency of modern combustion engines requires sophisticated light alloys with improved high temperature strength and creep resistance. Thus, new cast AlSi alloys are developed for structural parts to increase their wear resistance and long term stability under operation conditions. The heterogeneous micro structure of AlSi combines the thermal properties of stiff Si particles with a ductile α-Al to a composite with improved thermo-mechanical strength....     »