Abstract
Commonly used commercial cast aluminum alloys for the automotive industry are viable for temperatures only up to 250鈥癈, despite decades of study and development. Affordable cast aluminum alloys with improved high-temperature mechanical properties are needed to enable the next generation of higher efficiency passenger car engines. Metastable 胃鈥� (Al2Cu) precipitates contribute to strengthening in Al鈥揅u alloys, but above 250鈥癈 coarsen and transform, leading to poor mechanical properties. A major challenge has been to inhibit coarsening and transformation by stabilizing the metastable precipitates to higher temperatures. Here, we report compositions and associated counter-intuitive microstructures that allow cast Al鈥揅u alloys to retain their strength after lengthy exposures up to 350鈥癈, 鈭�70% of their absolute melting point. Atomic-scale characterization along with first-principles calculations demonstrate that microalloying with Mn and Zr (while simultaneously limiting Si to鈥�<鈥�0.1鈥痺t %) is key to stabilization of high-energy interfaces. It is suggested that segregation of Mn and Zr to the 胃鈥� precipitate-matrix interfaces provides the mechanism by which the precipitates are stabilized to a higher homologous temperature.
