Strengthening mechanisms and work hardening in a heterostructured cast aluminum alloy under compressive loading: Correlation with nanomechanical properties

Abstract

The compressive deformation behavior of a high-pressure die-cast Silafont®-36 aluminum alloy was evaluated in relation to the microstructural changes during deformation. No strain rate sensitivity was observed for the alloy compressed at room temperature. The as-cast microstructure consisted of softer primary α-Al dendrites and harder Al-Si eutectic structure, which was well depicted by the difference in the nanohardness values using high-speed nanoindentation mapping. The load-bearing capacity of eutectic Si particles and thermal mismatch enhanced dislocation density strengthening were identified to be the predominant strengthening mechanisms in the alloy, plus a certain degree of Orowan strengthening mechanism. The work hardening capacity of the cast alloy was mainly attributed to the increase in the dislocation density in the softer α-Al matrix, which was further assisted by the presence of eutectic Si particles. The relative increase in the flow stresses also corresponded well to that in the nanohardness values of the α-Al grains with increasing strain levels.