Possibility of Al–Sc alloys as shape memory alloys

Aluminum (Al) is the most abundant and lightweight structural metal, yet no Al-based shape memory alloys (SMAs) have been established, unlike those based on titanium (Ti) and magnesium (Mg). Developing Al-based SMAs, potentially lighter than Ti-based and more thermally stable than Mg-based systems, would represent a major advance for both scientific understanding and lightweight engineering applications in the automotive and aerospace fields. Previous experimental and computational studies on Al–Sc alloys have suggested the possibility of a shape memory effect, yet their phase stability and mechanical behavior remain insufficiently understood. Previous literature has shown that Al–Sc alloys exhibit a martensitic-like microstructure, suggesting their potential as shape memory alloys. In this study, we investigated the phase stability and mechanical response with possible shape memory behavior of Al-Sc alloys. The Al-Sc alloy with near equiatomic composition exhibited an orthorhombic Au₂CuZn-type structure, while the slight increase of Sc stabilized the B2-type ordered phase. Compression tests revealed two-stage work hardening with a distinct stress plateau, and some specimens achieved specific strengths exceeding that of Ti–6Al–4V. SEM-EBSD analyses of the B2 specimens before and after deformation indicated a stress-induced transformation to the orthorhombic phase, and transmission electron microscopy (TEM) observations confirmed orientation relationships between the two structures. These findings imply that the Al–Sc system can undergo shape memory characteristics, and we also confirmed that Al-Sc alloys show superelastic-like stress-strain response in compression test. This discovery opens a new avenue for designing lightweight, high-performance SMAs with superior thermal stability.