Study of AC-44300 aluminium-silicon alloy processed through semisolid rheocasting

Semisolid rheocasting of aluminium alloys offers a cost-effective and energy-efficient route to produce components with fair mechanical properties and reduced porosity. This process is increasingly relevant in the automobile and electric industries, where lightweight, thermally conductive, and structurally reliable parts are essential for improved performance and sustainability. This study presents the metallographic and mechanical characterisation of a heat dissipator manufactured using semisolid rheocasting with AC-44300 aluminium-silicon alloy. Metallographic analysis was performed through macrographic and micrographic observations of both the base and the fins, while mechanical tests included Vickers hardness measurements and uniaxial tensile strength evaluations. Non-destructive testing, including dye-penetrant inspection and radiographic inspection, was also performed to assess the distribution of surface and internal defects. The results revealed a heterogeneous distribution of porosity within the base, with pore size increasing with distance from the material feeding entry. Cavities generally remained below 100 μm close to the feeding entry but frequently exceeded 300 μm in the most remote region. Microstructural analysis confirmed significant variations across the component, with a progressive change from a globular α-Al structure surrounded by a fine eutectic constituent to a coarser, more heterogeneous eutectic microstructure in the component base. In contrast, the fins retained the characteristic globular microstructure associated with semisolid processing and exhibited comparatively low porosity. Hardness varied moderately across the component, from 99 to 109 HV, whereas ultimate tensile strength ranged from 189 to 259 MPa, with an average elongation of 4.9%. These findings highlight the strong dependence of mechanical properties and defect formation on the interaction between local geometry, solidification conditions and feeding efficiency, rather than on distance from the feeding entry alone.