Transient micromechanical deformation and thermomechanical fatigue damage in AlSi based piston alloys under superimposed high cycle mechanical and low cycle thermal loading

Presently, AlSi based alloys, consisting up to 12 element systems, are used in the manufacture of automotive pistons for diesel engines. The pistons combustion wall is subject to complex superimposed transient mechanical and thermal loading with peak operating temperature representing a homologous temperature range Thom of 0.8 to 0.9. Using a special superimposed thermomechanical bench test apparatus, engine-like TMF loading has been reproduced and a number of semi in-situ experiments have been carried out to evaluate key microstructure damage mechanisms. The evolution of microstructural damage at the interface between hard Si inclusions and the softer Al matrix has been documented using scanning electron microscopy. The deformation characteristics at the Si/Al interface have been recreated using FEA techniques incorporating non-linear elasto-viscoplastic properties for the matrix material. Comparisons of bench test fatigue lives for transient superimposed high frequency and microstructural TMF loading for two different thermal cycles are then compared to isothermal mechanical load histories.