Castable Al-Ce Alloys For High Temperature Applications

The advancement of aluminum alloys for high-temperature applications has become essential to meet the engineering demands of aerospace, automotive, and energy sectors. Current aluminum-cerium (Al-Ce) alloys demonstrate thermal stability, yet the formation of complex ternary and quaternary phases limits effective strengthening mechanisms. This dissertation introduces a novel alloy design methodology based on Hume-Rothery principles and the formation of isotropic Laves phases. The research culminates in the discovery of a high-symmetry, isotropic rhombicuboctahedron (RCO) phase (Al_25.3Ce₃Cu_3.6Ni_3.1Mn), which increases the elastic modulus of the cast aluminum alloy, achieving a specific modulus that exceeds those of conventional aluminum, magnesium, steel, and titanium alloys. Further investigated are the high-temperature mechanical performance of the Al-RCO alloy through Hot Shear Punch Testing (HSPT), providing insights into the alloy’s resistance to deformation across varying cooling rates. This process-property relationship analysis highlights the superior compressive and shear strength retention of the RCO-containing alloy at elevated temperatures, supporting its viability in thermally demanding environments. Flux Growth Casting (FGC) is demonstrated as a method that can control the nucleation and growth of the RCO phase, making its formation cooling rate independent wherein the RCO forms uniform, low-aspect-ratio particles. Further work examines the effects of addition of alloying elements (such as Ni, Cu, and Zn) on the nucleation and growth of the RCO phase. These modifications were found to influence intermetallic phase stability and refine the RCO particle morphology, yielding further gains in tensile strength while maintaining the phase’s isotropic properties.

The RCO phase's unique isotropic structure offers a significant advancement in high-temperature aluminum alloys by enhancing modulus without resorting to more complex casting methods for Metal Matrix Composites (MMC). This work contributes to the field by establishing a foundation for developing high-performance, castable Al-Ce alloys suitable for applications where both strength and thermal stability are critical. This work uses a combination of advanced characterization techniques to explore and validate the thermomechanical stability of the RCO phase. The results underscore the potential for broader adoption of Al-RCO alloys in high-temperature structural applications, promising significant improvements in component longevity and energy efficiency across multiple industries.