Analysis on Stress Corrosion Fracture of Cu-Mg Alloy Lift Sub

Cu-Mg alloy lift sub fractured frequently in the tunnel of southwestern area. To find the cause, macro and micro analysis, energy spectrum analysis, metallographic examination, and micro-hardness testing were carried out. It was found that the fracture initiated from the outside. The fracture surface presented intergranular brittle morphology and corrosion characteristic, covered by an amount of chloride. Several intergranular cracks perpendicular to the propagation direction were found. Metallographic examination shows that longitudinal structure was fibrous, and the amount of mechining deformation was large. Hardness testing shows work-hardening was obvious. Environmental monitoring shows that damp air included an amount of Cl^-. Based on the failure mechanism, reducing residual stress and spraying paint can effectively prevent such failures.