Effetto della velocità di deformazione sulla corrosione sotto sforzo di leghe di alluminio saldate tramite friction stir welding

The work is devoted to the study of the stress corrosion cracking behavior of AA 2024-T3 and AA 7075-T6 joints welded by friction stir welding technology. Stress corrosion cracking tests under controlled temperature and humidity were performed after exposure in 0.6 M NaCl solution. The FSW process modifies the microstructure of the alloys due to the occurrence of severe plastic strain at the welding and the heat generated by the friction. The hardness values measured at the bare material, the nugget and the thermo-mechanically affected zones are very different, thus confirming significant differences in terms of intrinsic tensile properties. During the tensile test, the distribution of the plastic deformation as well as the strain rate at these zones is strictly dependent upon the local tensile behavior of the material. Digital image correlation techniques were then applied during the tensile tests to quantify the local material behavior during the loading. For both the alloys, a significant increase in the local plastic deformation was noticed at the thermo-mechanically affected zones. Therefore, the susceptibility to stress corrosion cracking (SCC) evaluated by means of slow strain rate (SSR) tests showed a marked dependency upon the local material behavior after the FSW process.