Design of hot-tearing resistant and thermally stable aluminium alloys for advanced casting technologies

Aluminium alloys are cost-effective and lightweight materials that are widely used in the transport industry, where cost and weight are key considerations for material selection. Operating at elevated temperatures (T ≥ 0.5Tm, where Tm is the absolute melting temperature of Al) is known to be a weakness of these alloys. A new methodology is proposed to design Al alloys with improved thermal stability and reduced cracking susceptibility using both theoretical and experimental techniques. In this work, two new alloys based on the Al-Ce-Fe-Mn-Ni system were developed. To minimise hot tearing, compositions with a narrow freezing range during the final stage of solidification were selected. Thermal contraction upon solidification was then experimentally determined as a measure of hot tearing susceptibility, and compositions with low thermal strain accumulation were identified. Following exhaustive screening, the solidification behaviour was further investigated by examining the microstructural morphologies under different cooling rates, followed by mechanical testing. Results showed that a high proportion of the strength (75 to 80 %) was retained after tensile testing at 300 °C. The methodology can be applied to designing Al alloys for both casting and additive manufacturing applications.