Microstructure, thermo-physical and mechanical properties of heterogeneous Al/Al–70Si composites

To address the brittleness of Al–50Si alloys caused by coarse and angular silicon (Si) phases, three Al/Al–70Si composites with distinct heterogeneous structures were fabricated and analyzed. Three composites, designated SAl–50Si, FAl–50Si, and MAl-50Si, were produced by hot-pressing mixtures of Al–70Si alloy powder with spherical, flaky, and ball-milled aluminum (Al) powders, respectively. All three composites exhibited a heterogeneous microstructure comprising two distinct regions: pure Al and Al–70Si alloy. However, the size and distribution of these regions, along with the grain characteristics (e.g., size and boundary misorientation) of the Al and Si phases, differed significantly depending on the morphology of the initial Al powder. The thermal conductivity and coefficient of thermal expansion of the three composites followed a descending order of SAl–50Si, MAl-50Si, and FAl–50Si. Compared to the Al–50Si alloy, the SAl–50Si composite exhibits a 72.1 % increase in fracture strain while maintaining a comparable bending strength. The FAl–50Si composite exhibited an 11.43 % increase in bending strength and a 19.6 % enhancement in fracture strain. Room-temperature fracture toughness measurements using the single edge notch bending (SENB) method confirmed the significantly enhanced toughness of the SAl–50Si and FAl–50Si composites. Spherical and flaky Al powders improve toughness while maintaining strength, offering a feasible, scalable strategy for high-performance high-silicon Al alloys and providing reference for their practical use in fields requiring good thermal management and structural reliability.