Microstructural analysis of 7XXX semi-solid alloys series submitted to parallel plate hot compression tests

ABSTRACT

The present work aims at the microstructural analysis of 7XXX aluminum alloys series, namely: AA7004 and AA7075, in view of their application in thixoforming processes. The alloys were reheated to semi-solid temperatures, that is, the temperatures corresponding to 60% and 45% solid fractions and maintained to heat reheat treatment of 0, 30, 90 and 210 s and subsequently submitted to parallel plate hot compression tests. As a result, the 60% solid fraction condition of both alloys showed significant differences in the appearance of thixoforming samples, with to poorly filled and brittle edges, when compared to the 45% solid fraction condition, due to the microstructure bonds that were possibly still strongly bonded between themselves, requiring bigger tension to the forming; the 45% solid fraction adopted during the tests was satisfactory, since the edges of the samples did not present intense cracks and/or breaks, as well as a good surface finish. Regarding their microstructural behavior, the semisolid alloys AA7004 and AA7075 showed globular morphology in the edge region of the samples with very spheroidized grains/primary globules, due to the phenomena of ostwald ripening and coalescence and in the central region of the grain/primary globules samples fully deformed, with small liquid presence and large solid phase presence due to imposed deformation.

Keywords
Thixoforming; microstructural behavior; AA7004; AA7075