Research of Hydrogen Induced Cracking and Stress Corrosion Cracking in an Aluminum Alloy

For a high strength aluminum alloy, the dynamic processes of nucleation and propagation of hydrogen induced delayed cracking of a charged and modified WOL specimen were followed metallographically. The results showed that the size of the plastic zone in front of the crack enlarged continuously with time, i.e., a hydrogen induced delayed plasticity was observed. Hydrogen induced delayed cracking then nucleated in the grain boundary or at inclusions when hydrogen induced delayed plasticity developed to a certain extent. Under the conditions of stress corrosion in high purity water and a 3.5% NaCl aqueous solution, stress corrosion cracking nucleated and propogated after the delayed plastic deformation had developed to a critical condition. The effects of the test temperature, polarization voltage, and chloride ion on KISCC and da/dt in high purity water were investigated. The results were identical with the effects of the aforesaid factors on the amount of hydrogen evolution of the specimens immersed in HCl solution with pH = 3.5 or 1.0. These results suggest that the mechanism of stress corrosion cracking of high strength aluminum alloys in aqueous solution is one of hydrogen induced delayed cracking.