A Study On The Preparation Methods Of CuZnAl Two-way Shape Memory Alloy

Shape memory alloy material is known as hot-driven functionality, while also have sensing function, attracted widespread attention. CuZnAl shape memory was prepared by melting in this paper. Through changing the conditions of aging process and two-way training process, the two-way CuZnAl shape memory alloy with different performance was prepared. The macrostructure of samples prepared by the aforementioned process conditions is studied by OM, SEM, DSC and XRD. Additionally, shape recovery rate and mechanical properties are also tested. Summarizations are as follows:(1) Aging has a great influence on the microstructure and properties of the alloy: Density of vacancies obtained due to the solid solution hardening was reduced during aging, thus order degree of martensitic is increased. Hence, the shape memory property of the alloy is improved. The optimal dual aging process of the experimental alloy is200℃for10min in oil bath followed by50℃for10min in water bath, lath martensite is obtained; The grain boundary of martensite is flat; the performance of memory alloy is superior:one-way recovery rate reached97.3%, two-way recovery rate of above alloy is up to40.1%after proper training of two-way.(2) There is an optimal pre-deformation strain εL(ε=2.7%) in the thermo-mechanical cycling training process, when ε<sL, the recovery rate of the shape memory alloy is increased with pre-deformation strain is increasing; when ε> εL, the recovery rate decreases rapidly with pre-deformation strain is increasing.(3) Thermo-mechanical cycling training are performed to produce dislocations which have preferred orientation in alloy, which can provide a specific preferred kinetic path for martensite transformation. Lots of martensite which has preferred orientation are obtained subsequently and the two-way memory effect is improved finally. However, dislocations and other defects will prevent the reverse martensitic transformation. Hence, the one-way shape memory alloy recovery rate decreased rapidly. Two-way memory properties of the alloy is saturated when the time of training loop is beyond12. Because during continuous thermo-mechanical cycling training process, dislocation density increase gradually and then enhance the amount of martensite variant residues while the degree of order is decreased, resulting in two-way memory alloy performance degradation, when the increased dislocation rate began to slow, making the one-way shape memory alloy performance degradation slows down, one-way memory performance is stabilized. (4) The effect of different temperatures of thermomechanical cycling training (i.e. pure martensitic zone, pure austenitic phase zone and mixed martensite and austenite phase zone) on memory performance alloy are as follows:When training in a pure martensitic state, the temperature is less than Mf, reverse martensite transformation cannot happen, thus the alloy cannot exhibit two-way memory performance; when training in pure austenitic state, the alloy with two-way shape recovery rate is increased to a maximum rapidly as training time are increased, and further training will lead to a reduced two-way memory performance; when training in mixed martensite and austenite phase, two-way shape recovery rate of the alloy are firstly increased and then decreased with the training time is increased, the exact two-way shape recovery rate is between the former two conditions.