Carbon footprint reduction by using secondary aluminum alloys in conventional and innovative processes: microstructural and mechanical characterization

The global demand for lightweight materials in automotive, aerospace, and advanced manufacturing sectors is driving the growth of the aluminum market. In this context, secondary aluminum alloys (SAAs) offer a strategic opportunity to reduce CO₂ emissions while promoting a circular economy. The production of aluminum from recycled scrap requires only a fraction of the energy needed for primary aluminum, resulting in substantial reductions in carbon footprint. However, the presence of impurities, particularly iron, limits the use of SAAs in high-performance structural components. Excessive iron promotes the formation of brittle intermetallic compounds that impair castability, increase porosity, and reduce tensile and fatigue properties. The addition of neutralizing elements, such as manganese, can modify Fe-based intermetallics into more compact morphologies, partially mitigating their detrimental effects. Innovative casting technologies, including semisolid processes such as thixocasting and rheocasting, offer further opportunities to enhance the mechanical performance of recycled alloys by improving feedability, refining microstructure, and reducing defects, while also decreasing energy consumption compared with conventional high-pressure die casting (HPDC). The present PhD dissertation investigates the use of recycled aluminum alloys in both conventional and innovative casting processes, focusing on Al-Si-Mg alloys, specifically AlSi10MnMg and AlSi7Mg. The research aims: to assess the influence of Fe-based intermetallics on microstructure, mechanical performance, and physical properties, to identify mitigation strategies through alloying and heat treatment, and to evaluate the potential of semisolid processing as a sustainable route for high-recycled-content alloys. Experimental activities were conducted not only at laboratory scale but also on real automotive components, ensuring industrial relevance and applicability.