Transgranular environment-induced cracking of 7050 aluminium alloy under cyclic loading conditions at low frequencies

The environment sensitive cracking behaviour of alloy 7050 plate in different tempers was studied under cyclic loading conditions using short transverse oriented notched tension specimens immersed in substitute ocean water. The cyclic loading tests were carried out at displacement rates in the range from 2 × 10−6 to 2 × 10−4 mm s−1 applying a sawtooth wave form. The maximum load corresponded to an initial stress of 600 MPa, except for alloy 7050-T7651 being loaded up to 500 MPa. Number of cycles to failure decreased with decreasing displacement rate. A linear relationship was found between log values of the number of cycles to failure and the loading frequency. Fractographic examinations of failed specimens revealed brittle transgranular fracture with crack arrest markings on flat facets. The sensitivity to transgranular environment-induced cracking proposed to be associated with hydrogen embrittlement did not depend on heat treatment conditions.