Heat Treatment Induced Precipitation and Residual Stress Effects on Tensile Plasticity of Cold-Sprayed Scalmalloy Deposits

Abstract

Cold spray has emerged as an effective technique for fabricating high-strength aluminum alloys, leveraging its solid-state nature to prevent melting and oxidation. Despite these advantages, challenges like porosity and residual stresses introduced during deposition necessitate post-deposition treatments to enhance mechanical properties. This study explores the evolution of microstructure and residual stress and their influence on hardness and tensile properties in cold-sprayed Scalmalloy deposits produced using helium (He) and nitrogen (N₂) as carrier gases, followed by direct aging and solution treatment with aging. He-sprayed deposits exhibited lower initial porosity (0.12 ± 0.03%) than N₂-deposits (1.20 ± 0.51%). Solution treatment increased porosity to 6.9% (He) and 2.5% (N₂) due to gas expansion within defects, while porosity remained unchanged after direct aging. Direct aging significantly reduced residual stresses, with a 69% reduction in He-deposit and a 55% reduction in N₂-deposit. The formation of Al₃(Sc_x, Zr_1−x) precipitates during aging led to precipitation strengthening, increasing hardness by 20% (He) and 25% (N₂) relative to the as-deposited condition. Hardness increase contributed to a 23% rise in tensile strength in He-deposits (575 ± 9 MPa) and 58% in N₂-deposits (542 ± 23 MPa). Additionally, profilometry-based indentation plastometry revealed anisotropy in pileup distribution, which was more pronounced in the as-deposited state but significantly reduced after aging, indicating improved structural uniformity. These findings emphasize the importance of residual stress relaxation, defect reduction, and precipitation in achieving superior mechanical properties in cold-sprayed Scalmalloy deposits for structural applications.