Size and distribution of particles and voids pre-existing in equal channel angular pressed 5083 Al alloy: their effect on cavitation during low-temperature superplastic deformation

Abstract

An ultrafine grained 5083 Al alloy was prepared by equal channel angular pressing with route Bc and an effective strain of ∼4 or ∼8. The changes of the size and distribution of second phase particles and voids pre-existing in the alloy during equal channel angular pressing (ECAP) were examined in detail. Under the present ECAP conditions, a portion of particles of 1.5–3.5 μm substantially increased. However, the further break-up of particles with these sizes became less significant and they were to be distributed more uniformly throughout the sample with increasing the ECAP pass from 4 to 8. In addition, these particles were likely to act as the preferential cavity nucleation sites during low-temperature superplastic deformation of the alloy. The population of voids with the size of 0.5–1.5 μm remarkably increased after ECAP. An analysis revealed that these voids were difficult to be sintered out at low-temperature superplastic deformation temperatures prior to deformation and might grow to larger size cavities. From the present results and analysis, it is suggested that the number of the ECAP pass less than that resulting the largest elongation may be preferable in the viewpoint of cavitation damage and commercial application of low-temperature superplasticity of ultrafine grained Al alloys, if moderate superplastic elongation is ensured.