EFFECTS OF AGEING CONDITIONS ON THE ELECTROCHEMICAL CORROSION AND STRESS CORROSION CHARACTERISTICS OF Al-Zn-Mg-Cu ALLOYS.

The electrochemical corrosion and stress corrosion behavior of Al-Zn-Mg-Cu alloys (AA 7075-T 6 temper) in an aqueous solution containing 5 wt. % NaCl, 3 wt. % K//2Cr//2O//7 and 3 wt. % CrO//3 were studied at a temperature of 11. 5 degree C using a potentiokinetic method and determining the failure time as a function of aging time and temperature. For underaged specimens the corrosion potential increased with aging time; however it remained nearly constant for overaged specimens. The aging temperature and a 0. 3% Cr addition increased the corrosion potential. The corrosion rate and the time to failure of Cr-free specimens increased with aging time up to the peak aging time, then decreased in the overaged stage. However, the failure time of Cr-containing alloys increased with aging time up to the peak aging time, then remained nearly constant in the overaged stage. The resistance to stress corrosion cracking (SCC) was improved by the addition of 0. 3% Cr.