Stress corrosion cracking susceptibility of Al-Mg alloy sheet with high Mg content

Abstract

Slow strain rate testing (SSRT) was used to study the effect of the microstructure on the stress corrosion cracking (SCC) susceptibility of Al-Mg alloy sheet containing 6.8 wt.% Mg. In the cold-rolled and fully annealed conditions, high SCC susceptibility was experienced. In those cases the ductility was strongly affected by the presence of corrosive environment (for hard temper: El(air) = 13.6%, El(SCC) = 0.6%; for annealed condition: El(air), = 24.1-25.3%, El(SCC) = 3.2-4.2%) and the elongation loss was great, E-loss = 81.7-95.6%. It is supposed that the high SCC susceptibility results from a continuous network of the P-phase (Mg5Al8) precipitate at grain boundaries for the annealed temper, and heavy precipitation of P-phase along the planes of localized deformation for the hard temper. High SCC resistance attained after thermal exposure at the temperature range 225-285 degreesC (stabilized condition). The ductility was almost unaffected by the presence of corrosive environment (El(air), = 12.8-23.2%, El(SCC) = 12.8-22%) and the elongation loss was small, E-loss lt 7%. High SCC resistance was related to the stabilized structure, which causes discontinuous P-phase (Mg5Al8) precipitation in a globular form, uniformly distributed throughout the structure.