Comprehending Precipitation Process and Strengthening in Stressaging of Magnesium Alloys

Magnesium alloys exhibit substantial promise as lightweight structural materials, poised to replace their aluminum and steel counterparts in various applications, including vehicles, electronics, and aerospace technologies. A significant impediment to the widespread adoption of magnesium lies in its low absolute strength, resulting in inadequate load-bearing capabilities in structural applications. Stress-aging is a promising strategy to leverage the potential of precipitation strengthening to overcome this obstacle. Nonetheless, the fundamental understanding of stress-aging process in magnesium alloys is still far from adequate for applications. This proposed research project seeks to address this gap by comprehending the thermodynamic and kinetic characteristics for stress-aging process and resulting strengthening in magnesium alloys through hypothesis-driven experiment and dedicated analyses. To resolve the underlying reason for the faster formation of denser, more equiaxed precipitate particles in stress aging of magnesium alloys, we will select representative binary magnesium alloys, conduct comparative investigation into stressand stress-free precipitation processes, and compare their strengthening efficacy. Furthermore, we will evaluate vacancy concentration and migration barrier in magnesium alloy under applied stress to identify their role in precipitation kinetics. We will also assess how applied stress influences the anisotropic diffusion kinetics and anisotropic matrix/precipitate interface energy in magnesium crystal. When translating the precipitate characteristics to strengthening efficacy, we will carefully examine how stress-aged precipitates with different types (prismatic rod, basal lath, and prismatic plate) affect plastic carriers (dislocation and twinning) in deformation. The experimental observations of precipitation evolution during stress-aging are expected to serve as a benchmark for future computational modeling endeavours in the field of phase transformation under external fields. Ultimately, this project aims to provide valuable insights into the mechanistic understanding of stress-aging phenomenon in magnesium anchored to thermodynamic and kinetics perspectives. The scientific knowledge generated by this research will directly inform the advancement of developing high-strength magnesium alloys via precipitation strengthening.