Heat Treatment Impact On The Mechancial Behavior Of Ultr-Fine Commercial Pure Aluminum

Ultra-fine grain (UFG) material exhibits much higher flow strength than its coarse-grain (CG) counterpart. Because of the huge difference in microscopic structure with coarse grain material, ultra-fine grain metals present unique mechanical behaviors like hardening by annealing, etc. In this dissertation, the mechanical behavior of UFG commercial pure aluminum with/without annealing treatment is studied, from which the material's micro-mechanism could be deduced and some propositions are prompted to further improve the theory of mechanical properties of ultra-fine materials.Equal channel angular pressing (ECAP), known as a super plastic deformation (SPD) method, is among the most effective approaches to prepare ultra-fine or even nano-crystalline materials. Commercial pure aluminums, pressed through a die with a 90°channel angle, prepared by room temperature rolling and heat treatment, are studied by means of tension tests and repeated relaxation tests.This dissertation covers two parts: relationship between mechanical behavior of UFG aluminum and the heat treatment in tension test, and the variation of activation volumes in repeated relaxation test:In tension tests, it is apparent that UFG aluminum mechanical behavior differs from CG aluminum, such as strengthening by grain refining, the loss of ductility, hardening by annealing and the rapid raise in strain-rate sensitivity, etc. The fundamental reason behind these phenomenon is the variation of the microscopic deformation mechanism between two types of material.Activation volumes can be estimated from repeated relaxation tests, including apparent activation volumes and physical activation volumes. Through the study of activation volumes, it is possible to comprehend the microscopic structure of ultra-fine materials in an indirect way. From the very experiments, it is confirmed that the activation volume in UFG is of over an order of magnitude smaller than in CG aluminum, and the heat treatment and the processing have impact on activation volumes, which implies the alteration of a microstructure in UFG commercial aluminum.