Enhancing Electrical Conductivity of Commercially Pure Aluminium via Deep Cryogenic Treatment and Subsequent Annealing

Aluminium is widely used in electrical and structural applications; however, its lower electrical conductivity compared to copper limits broader adoption in high-performance systems. Deep cryogenic treatment (DCT) and DCT followed by annealing (DCT+A) have recently appeared as promising techniques to refine microstructures and enhance functional properties in metallic materials. In this study, commercially pure aluminium was subjected to DCT and DCT+A with soaking hours of 6, 12, 18, and 24 at −196 °C. The results revealed that both DCT-12 and DCT+A-12 treatments produced significant grain refinement. XRD confirmed the smallest crystallite size (32.39 nm) and maximum dislocation density (9.53 × 1014 m−2) in DCT-12, while extended soaking of 18 h facilitated recovery, yielding larger crystallite sizes (52.82 nm), reduced density, and microstrain. EBSD analysis showed texture strengthening in the (100) and (111) planes and a notable transition from HAGB to LAGB fractions. TEM and Raman analysis further confirmed defect recovery and phonon coherence at longer soaking hours. Electrical conductivity and mobility were enhanced across all treated specimens, with peak values seen for DCT-18 (4.91 × 107 S/m, 50.8 cm2/V·s) and DCT+A-18 (4.52 × 107 S/m, 46.9 cm2/V·s). These findings confirm that 18 h of soaking is optimal, particularly when combined with annealing, and yields a stable microstructure, improved electron transport, and superior conductivity.