The Effect of Fatigue Damage on the Corrosion Fatigue Crack Growth Mechanism in A7N01P-T4 Aluminum Alloy

A7N01P-T4 aluminum alloy plates for high-speed trains will experience a certain amount of fatigue damage under alternating loads. Three groups of samples, P-0 (no fatigue damage), P-1 (loading stress 30 MPa), and P-2 (loading stress 70 MPa), were created, and corrosion fatigue crack growth (CFCG) tests were conducted in 3.5 wt.% NaC1 solution. The crack growth rate was found to increase after fatigue damage as the damage degree increased. In addition, the A7N01P-T4 aluminum alloy base metal exhibited obvious secondary cracks and crack bifurcations after fatigue damage. It is believed that fatigue damage causes stress concentration in the material, while a certain degree of stress corrosion cracking occurs during the CFCG growth process. This is because hydrogen (H) easily accumulates and diffuses along the grain boundary, which reduces the strength of the grain boundary, thereby becoming the preferred orientation for crack growth. This explains why the CFCG rate of the material is accelerated following fatigue damage to a certain extent.