Development of sustainable aluminum alloys from mixed automotive scrap

This thesis thoroughly examines the challenges associated with recycling aluminum scraps from end-of-life vehicles and the role of the automotive industry in promoting the sustainability of aluminum alloys. An average car built in the European Union in 2019 contained 26 different aluminum alloys from nearly all wrought alloy groups, in addition to significant amounts of secondary cast alloys. The melting of these alloys together results in compositions that exceed the standards' composition limits. Consequently, the predominant recycling route involves shredding the car, diluting the melt with primary aluminum, or downcycling to secondary aluminum cast-alloys. The demand for such alloys persists in the context of internal-combustion engine technology; however, the transition to battery-electric vehicle transmission will curtail this market, resulting in a substantial accumulation of scrap materials lacking adequate recyclability. This study addresses theoretical propositions for sustainable aluminum alloy development from a metallurgical perspective. The investigation encompasses three theoretical compositions that extend beyond conventional standards, derived from the recycling of diverse vehicle types (an average EU vehicle, a US pickup truck, and an electric vehicle). The study explores the impact of high concentrations of alloying elements on mechanical and microstructural properties. Experimental methodologies encompass casting with three distinct cooling rates (laboratory 60 K/s and industrial 1 and 3 K/s), heat treatment procedures, and tensile and bending tests. The alloy derived from the pickup exhibited the optimal combination of strength and ductility, with tensile strength reaching 400 MPa and elongation at break measuring 13 % after undergoing pre-straining treatment. This outcome is consistent for both laboratory and industrial 3 K/s cooling rates. However, with the exception of the electric-vehicle-derived alloy, the bending performance is less favorable and requires further work. The investigation of the aforementioned alloys has revealed a paradigm shift towards sustainable secondary aluminum alloys, thereby eliminating the reliance on downcycling processes towards secondary cast alloys and effectively postponing the issue to a future date. These alloys exhibit a combination of strength and ductility that can surpass those of conventional wrought aluminum alloys. Consequently, they emerge as promising candidates for utilization in various components of vehicles, contingent upon successful industrial evaluation. It is anticipated that the compositional scenarios are the maximum concentrations, as the increase in aluminum usage in passenger vehicles is predominantly driven by wrought alloys, which exhibit lower overall concentrations of alloying elements.