Study On Process And Properties Of Dual Change Channel Angle Extrusion —— Cold Rolling Formed AZ31 Magnesium Alloy

In this paper, for improving on Equal Channel Angular Extrusion (ECAE), a new extrusion technology was devised which called Change Channel Angle Extrusion (CCAE). This experimentation introduced two deformation processes to improve magnesium alloy's mechanical properties. The first process was CCAE, the second process was cold rolling.AZ31 magnesium alloy was studied in this paper. With the methods of optical microscopy (OM), mechanical properties test, hardness test, the changing of samples microstructure and mechanical properties was detected and analyzed. Concretely, the experimentation involved: the effect of CCAE temperature to samples'molding zone, the sample microstructure changing at CCAE deformation, CCAE samples'room temperature mechanical properties; the effect of middle annealing temperature to CCAE samples'microstructure and mechanical properties; the effect of cold rolling deformation to samples'microstructure and mechanical properties after CCAE deformation and annealing treatment; the effect of final annealing temperature and time to samples'microstructure and mechanical properties. In addition, this paper discussed the main factors of CCAE deformation, analyzed samples'three direction changing during cold rolling. With the scan electron microscopy (SEM), the CCAE and final annealing samples'fracture mechanism were analyzed. The kinetics analysis of static recrystallization during annealing process of cold-rolled AZ31 magnesium alloy sheet was investigated by the JMAK equation.The results showed that CCAE deformation process effectively refined the AZ31 magnesium alloy grains, the operation of CCAE was simple and the efficiency of it was high. While the microstructure of AZ31 magnesium alloy after CCAE still had long grains, the distribution of the grains was asymmetry. The tensile strength was 265MPa, the yield stress was 167MPa, the elongation was 14.2%. CCAE samples need more process to improve their properties.The middle annealing treatment eliminated the long grains caused by CCAE. For the samples of cold rolling deformation 15%, final annealing treatment was taken. After this treatment the samples'mechanical properties got 286MPa tensile strength, 185MPa yield stress, 19.8% elongation. For the samples of cold rolling deformation 15%, the preferable deformation process was: 250℃CCAE sample annealed at 300℃, 2h, then cold rolled for 15%, finally the cold rolled sample annealed at 250℃, 2h. The recrystallization kinetics curve of AZ31B magnesium alloy was worked out.Compared with single CCAE deformation process, the CCAE——Cold Rolling deformation process advanced the AZ31 magnesium alloy's mechanical properties. The fracture way of CCAE samples were toughness with brittleness. After the second deformation process, the fracture way of final annealing samples were toughness.