Stress corrosion cracking of cabinet of 7003 aluminum alloy

Cracks, discovered on the edge of 7003 Al-alloy cabinet of the high speed train was analyzed by means of optical microscope, scanning electric microscope (SEM) and electronic differential system (EDS). It is found that cracks with many branches propagated along the grain boundaries, the fracture is sugar candy pattern, and capillary and chicken claw cracks are on the grain plane. The crack is stress corrosion crack (SCC) induced by the hydrogen embrittlement. The SCC sensitivity of 7003 Al-alloy was evaluated by slow strain rate test (SSRT) and constant displacement test. The result of SSRT shows that the sensitivity index of 7003 Al-alloy is 0.2. Its fracture is mixture fracture of transgranular and intergranular in 3.5% NaCl solution. There are many second cracks, cleavage steps and river patterns on the transgranular fracture. The result of constant displacement test indicates that the cracks propagate to 700 μm after corrosion for 28 days, and tongue protrusions and grooves occur in the stress corrosion zone. The 7003 Al-alloy is obviously sensitive to the SCC. ©, 2015, Beijing Institute of Aeronautical Materials (BIAM). All right reserved.