Experimental investigation of compressive failure behaviour and image-based micromechanical analysis of hypereutectic Al–Mg2Si composites

Abstract

This study combines detailed experimental characterization with image-based finite element modelling to investigate the compressive micromechanical response of hypereutectic Al–Mg2Si composites containing 15–30 wt.% Mg2Si . Optical microscopy and SEM–EDS observations reveal a three-phase microstructure consisting of an α-Al matrix, eutectic (Al + Mg2Si ), and primary faceted Mg2Si particles. The size, morphology, and distribution of these phases strongly influence the mechanical response and damage evolution. Hardness, compressive yield strength, and ultimate compressive strength increase with increasing Mg2Si content owing to enhanced load transfer, increased matrix constraint, and the higher volume fraction of hard Mg2Si reinforcement. However, increasing Mg2Si content also promotes the formation of coarse, dendritic, clustered, and hollow primary Mg2Si particles, resulting in increased stress concentration and reduced deformation capability. Fractographic analysis indicates that particle fragmentation and interface-related damage are associated with sharp particle corners, internal hollows, eutectic bridges, and particle–matrix interfaces, where deformation incompatibility is most pronounced. Image-based representative volume element models employing a Ramberg–Osgood constitutive formulation reproduce the experimental compressive stress–strain response and compressive yield strength with good agreement. The simulations reveal progressively increasing stress concentration, equivalent plastic strain localization, stress-triaxiality gradients, and localized plastic-dissipation zones with increasing Mg2Si content, providing a micromechanical interpretation of the experimentally observed deformation behaviour. The numerical model identifies regions susceptible to damage initiation but does not explicitly simulate particle fracture, interfacial debonding, or crack propagation. Localized plastic dissipation is interpreted as an indicator of intense irreversible deformation and damage susceptibility rather than the driving mechanism for fracture. Overall, increasing Mg2Si content enhances the load-bearing capability and compressive strength of the composites while promoting deformation localization that reduces strain-to-failure. The combined experimental and numerical approach provides a robust framework for correlating microstructural morphology with localized micromechanical response in hypereutectic Al– Mg2Si composites.