Transient microstructural thermomechanical fatigue and deformation characteristics under superimposed mechanical and thermal loading, in AlSi based automotive diesel pistons

Abstract

Presently AISi based alloys, consisting up to 12 element systems, are used in the manufacture of automotive pistons for light vehicle (LVD) and heavy (HD) duty 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 of 0.8–0.9 Thom. Using specialist 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 micro structure damage mechanisms. The evolution of micro structural 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 α-Al/ Si 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 micro structural TMF loading, with fatigue lives from isothermal mechanical loading are also made.