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

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: Elair=13.6%, ElSCC=0.6%; for annealed condition: Elair=24.1–25.3%, ElSCC=3.2–4.2%) and the elongation loss was great, Elloss=81.7–95.6%. It is supposed that the high SCC susceptibility results from a continuous network of the β-phase (Mg5Al8) precipitate at grain boundaries for the annealed temper, and heavy precipitation of β-phase along the planes of localized deformation for the hard temper. High SCC resistance attained after thermal exposure at the temperature range 225–285 °C (stabilized condition). The ductility was almost unaffected by the presence of corrosive environment (Elair=12.8–23.2%, ElSCC=12.8–22%) and the elongation loss was small, Elloss<7%. High SCC resistance was related to the stabilized structure, which causes discontinuous β-phase (Mg5Al8) precipitation in a globular form, uniformly distributed throughout the structure.