Improving creep age formability of an Al-Cu-Li alloy by electropulsing

Electrically assisted creep age (ECA) forming of an Al-Cu-Li alloy, when applied electropulsing during the different stages, has been experimentally investigated under the applied stress of 160 MPa at 160 degrees C for 20 h. Creep strain of the sample assisted by electropulsing when introduced during the initial creep stage in-creased by similar to 27.2% comparing with that of conventional creep ageing test (CCA) at the end of 20 h. However, there is almost no effect on creep strain when applied electropulsing at the beginning of 4, 8 and 19 h. Tensile tests indicate that strength of the aged specimens assisted by electropulsing when applied during the different creep stages is almost the same, but a slight reduction in elongation for the ECA specimen when introduced electropulsing during the initial stage and an increase by similar to 27.4% in elongation of the ECA specimen when introduced electropulsing during the last stage, compared to that of the CCA specimen. The fractograph of aged samples assisted by electropulsing when applied during the various creep stages, was observed to an obvious difference. Transmission electron microscopy (TEM) observations show that applying electropulsing during the early creep stage can accelerate dislocation motion, which for the first time proven by the observed larger dislocation structure, and promote Li solutes diffusion to grain-boundary, which is responsible for an increased creep strain and a decreased elongation, respectively. And dissolution of the Cu-rich at grain-boundary and GPI zone/.' precipitates within the grain, induced by electropulsing when applied during the last creep stage, is considered as the cause of an increased elongation. Thus, applying electropulsing during both the initial and last creep age forming stages is a promising method to control the microstructure to attain a sound sheet metal forming/property synergy. (c) 2021 Published by Elsevier B.V.