High temperature compressive behaviour of as-cast Al-Cu alloys of varying composition

Abstract

Al-Cu alloys with different copper contents ranging from 10 to 45 wt% were deformed in compression in the as-cast condition. Measurements of the strain-rate sensitivity parameterm using the crosshead speed jump technique show that alloys of composition close to the eutectic become superplastic after about 25% strain, withm increasing from about 0.2 at the beginning of deformation to about 0.5 or more, depending on composition. This transition to the superplastic state is accompanied by an important decrease of the flow stress during compression and it is associated by the breakdown of the initially lamellar structure of the eutectic phase in the highly deformed regions of the specimen. Moreover for the alloy with 37 wt% copper, the transition corresponds also to the degeneration of the dendritic primary phase and this alloy shows a particularly high value ofm and a low steady state flow stress in spite of the large volume fraction of the hard CuAl2 compound. Alloys of composition far away from the eutectic do not exhibit superplastic behaviour during compression, at least in the range of strain rate investigated and this is due to the large grain size and the important grain growth that occurs during deformation.