Mechanical behavior associated with metallurgical aspects of friction stir welded Al-Li alloy exposed to exfoliation corrosion test

This research aims to investigate the effect of the exfoliation corrosion exposure time on the mechanical properties, the strength and elongation, of friction stir welded Al-Li alloy type 2195-T8. The exfoliation corrosion test was performed using the exfoliation corrosion (EXCO) solution, based on ASTM G34. The samples were exposed to different exposure times 24, 48, 96, 192 and 384 h. The results showed that both the strength and elongation of the welded specimens-exposed to the exfoliation corrosion tests-were reduced. For example, the samples that were exposed to 384 h, their initial tensile strength and elongation were reduced by 13% and 17% respectively. The degradation process due to the exfoliation corrosion on the tensile strength was divided into three stages: fast (0-96 h: 443.7 MPa-416.3 MPa, the degraded rate was 0.29 MPa/h), steady (96-192 h: 416.3 MPa-413.4 MPa, the degraded rate was 0.03 MPa h−1) and medium rate (192-384 h: 413.4 MPa-386.7 MPa, the degraded rate was 0.14 MPa h−1). For the elongation, in general, the reduction was similar to the style of strength, but with different rates. The TEM images showed that this degradation was due to the dissolution of T1 (Al2CuLi) and S′ (Al2CuMg) phase. Also, the corrosion products and their role of adherence on the surface of the tested specimens were investigated. An empirical equation p-t (mechanical properties-exposure time) was established to calculate the effect of exposure corrosion time on the performance of welded specimens.