MECHANICAL BEHAVIOR OF ULTRAFINE/NANOGRAINED AEROSPACE AI-ALLOYS

Abstract

The mechanical behavior and microstructure of the cryorolled aerospace 6061 Al alloy and the cryorolled alloy subjected to ageing treatments are reported in the present investigation. The results were compared with properties of the starting material i.e. solution treated water quenched and the samples subjected to peak aged conditions. The precipitation hardenable 6061 Al alloy (Al-Mg-Si) plates were solutionised and rolled up to 90% reductions at liquid nitrogen temperatures to produce ultra fine . grain microstructure. The specimens were then artificially aged at different temperatures to optimize the peak ageing' condition. The effect of cryorolling on mechanical properties, microstructures and fracture morphologies of these samples were investigated by using macro vicker's hardness measurements, tensile tests, and FE-SEM/EBSD. XRD was used to analyse the formation of different phases during cryorolling of the Al alloys and the phases present in the bulk alloys. The severe strain induced during plastic deformation ofAl 6061 alloy produces ultrafine microstructures with improved mechanical properties. such as strength and hardness which are due to grain size effect and higher dislocation density. The cryorolled specimens after peak ageing treatment show marked improvement in strength and ductility due to the combined effect of grain refinement, precipitation hardening and substructure coarsening.