Mechanical and microstructural behaviour of AA7075 aluminium alloy for sub-zero temperature sheet stamping process

Age-hardenable aluminium 7XXX alloy sheets represents a very attractive material for the aerospace field; however, their limited formability at room temperature restricts their adoption in the industrial context. In the present study, deformation of AA7075 sheets at temperatures lower than the room one is presented as a possible strategy to overcome this limitation. To this aim, a comprehensive experimental campaign was carried out on AA7075 sheets in peak aged condition at varying temperature and triaxiality states. Specifically, the temperature was changed from -100 degrees C to 300 degrees C whereas different stress triaxialities states were achieved by adopting different specimen configurations, namely smooth, notched and shear. A necking locus curve was presented and modelled. Results show that, regardless of the stress state, the uniform elongation monotonically increased as the testing temperature was reduced, favouring material formability. Microstructural and mechanical investigations carried out on the deformed samples revealed that deforming at temperatures higher than the room one drastically increased the number of coarse intermetallic particles. On the contrary, sub-zero deforming temperatures favoured the intermetallic particle fragmentation and the formation of high density of precipitates and dislocations.