Stress corrosion cracking susceptibility of ultrafine grained Al-Mg-Sc alloy

General corrosion and stress corrosion cracking (SCC) behavior of coarse grained, fine grained and ultrafine grained (UFG) AA5083 and Al-Mg-Sc-Zr alloy in different thermomechanical conditions were studied in the present work. Friction stir processing (FSP) was carried out to refine the grain size. The average grain size achieved after FSP for AA5083 was 7±3 μm, whereas that for Al-4Mg-0.8Sc-0.08Zr was 0.39±0.16 μm with 100% UFG microstructure. Linear polarization resistance and cyclic polarization techniques were used to study general corrosion behavior of these alloys in 3.5 wt% NaCl solution. The UFG microstructure showed the highest polarization resistance (Rp) of ∼93 kΩ which increased to ∼160 kΩ after 24 h of exposure in chloride solution. The peak aged Al-Mg-0.8Sc-0.08Zr showed the most positive breakdown potential with passivity in the range of −800 to −600 mV vs SCE. A power law type relationship was observed between grain size and Rp for Al-Mg alloys. SCC susceptibility was estimated in 3.5 wt% NaCl solution using slow strain rate testing (SSRT) at initial strain rate of 10−6 s−1.The parent AA5083 alloy showed moderate susceptibility while the FSP AA5083 microstructure showed no susceptibility. The UFG Al-Mg-0.8Sc-0.08Zr condition showed >55% loss in ductility when tested in chloride solution.