Development of ultrafine grained high strength age hardenable Al 7075 alloy by cryorolling

High strength age hardenable Al 7XXX series alloys are difficult to process by many of the severe plastic deformation processes at room temperature. The Al 7075 alloy has been processed at cryogenic temperature and room temperature up to different rolling strains, in the present work, with the objective of developing a processing strategy to obtain ultrafine grained microstructure with enhanced mechanical properties in the alloy. It has been identified that the Al 7075 alloy samples can be successfully cryorolled to higher strains (up to 3.4) if the reduction per pass is less than 0.3 mm, however it was found to be difficult to deform the samples at room temperature. A cryorolling strain of 3.4 has been found to be desirable for producing the ultrafine grained Al 7075 alloys with the high angle grain boundaries. However, the subgrains are not recrystallized up to this strain in the case of room temperature rolled Al alloys. The strength and hardness of the cryorolled Al 7075 alloy samples are higher than that of the room temperature rolled samples as observed in the present work. The improved strength and hardness of cryorolled samples are due to the grain size effect and higher dislocation density. The reduction in dimple size of cryorolled Al 7075 alloy upon failure confirms the grain refinement and strain hardening mechanism operating in the heavily deformed samples.