EFFECT OF HEAT TREATMENT ON CORROSION BEHAVIOR OF ALUMINUM-LITHIUM ALLOY 8090

摘要

Al-Li 8090 alloy was subjected to different retrogression and reaging (RRA) treatments to investigate their effects on the mechanical and corrosion properties in comparison to peak aged (PA) condition. Optical microscopy, scanning electron microscopy, X-ray diffraction, hardness and tensile measurements were used. Stress corrosion cracking and salt spray tests were carried out and results were compared with microstructure and mechanical properties. The RRA 170 and 190 treatments' corrosion resistance have deteriorated in both tests compared to the PA, while the RRA 210 treatment showed the same atmospheric corrosion resistance as PA. However, RRA 210 showed a much lower SCC resistance, even lower than the RRA 170 and 190 treatments. The results have been explained by the anodic dissolution of uneven distributed phases on the grain boundaries. These precipitations created micro-galvanic cells and thus accelerating localized anodic dissolution mechanism. Pitting and intergranular stress corrosion cracking were found to be the corrosion mechanisms.