Nd-YAG laser surface melting of aluminum alloy 6013 for improving stress corrosion cracking resistance

Laser surface melting (LSM) of aluminum alloy 6013 was conducted using a high power Nd-YAG laser under nitrogen gas with the aim of improving the stress corrosion cracking (SCC) resistance of the alloy. The SCC behavior was studied in a 3.5% NaCl solution using a slow strain rate test (SSRT). A laser-melted layer in the order of 500 [in] thick was produced, which consists of fine dendritic and cellular structures with some Al-Si-Cu-Fe-Mn phase particles formed at interdentritic boundaries. The results of the SSRT test showed that the susceptibility of the alloy to SCC, in terms of total elongation to failure, was decreased after the laser surface modification. This was considered to be attributed to the presence of the laser-formed AlN film, which acted as a barrier to the ingress of the corrosive Cl-into the material and enhanced the pitting resistance of the material. An examination of the fractured surface indicated that the crack propagation path, in the early stage of SCC, was along the tortuous dendrite and cell boundaries. This caused the crack path deviated from the growing direction and resulted in a longer crack length covered before failure thus increasing the overall crack propagation resistance.