Environment-induced cracking of Al–Cu alloy (AA2017P-T3) under constant load in distilled water and sodium chloride solutions

The environment-induced cracking (EIC) of a commercial Al–Cu alloy has been investigated as functions of applied stress, chloride ion concentration and test temperature in distilled water and sodium chloride solutions by using a constant load method. The effect of chloride ion on EIC is complex. The EIC susceptibility increased, unchanged and then decreased with increasing the chloride ion concentration. However, whenever EIC takes place with and without chloride ion, the fracture appearance and the value of tss (transition time to deviation from linear elongation)/tf (time to failure) are the same, and further the relationship between log tf and log lss (steady state elongation rate) becomes the identical straight line irrespective of applied stress, chloride ion concentration and test temperature. The latter means that lss becomes a relevant parameter for predicting tf. It has been concluded that EIC of Al–Cu alloy takes place by hydrogen embrittlement (HE) associated with the fracture of hydride, and a HE mechanism is qualitatively proposed to explain the results obtained.

Research highlights
► The stress dependence of tf, lss and tss was divided into three regions.
► The tss/tf held constant independent of stress, temperature and Cl concentration.
► The relationship between the logarithms of tf and lss became a straight line.
► The HE mechanism was proposed in terms of the cyclic hydride formation-rupture.