Effect Of Heat Treatments On Microstructure & Shape Memory Capability Of Cu-Zn-Al Shape Memory Alloys

As a functional material of heat-driven, the shape memory alloy which sensor function has been attached, received its extensive recognition. In this paper, morphology and structure of martensite are studied by means of optical microscope, XRD and so on, and the influence of different heat treatment on microstructure and shape memory effect has also been studied. The result is as follows:The quenching temperature has a notable influence on shape memory of alloy. The alloy grain growth increases and Ms is also continually increasing as well when the quenching temperature is higher and higher. This kind of alloy has a lot ofαphase in its microstructure when it be quenched at 600℃～750℃, while the shape memory effects reaches the peak value at 800℃.The martensite produced by quenching has a clear interface and there is no precipitation on the grain boundary. The Shape memory effect of alloy has not clear weakening when it is soaked at 800℃～900℃.Shape memory effect is very sensitive to quenching soaking time. Different soaking time has been continued at 800℃, the shape memory effect increases rapidly and then it has a mini-devaluation. The shape memory effect will decline if the soaking time is too long or too short. In order to obtain an excellent shape memory effect, the quenching soaking time should be appropriate. The alloy obtains the satisfied shape memory effect when it was soaked for 15 minutes at 800℃.The prestrain of alloy with same heat treatment technology has a notable influence on shape memory effect. Experimental alloy have a critical prestrain(ε=3.3%),the shape memory effect increases with the increase of prestrain whenε<ε_L, however, it would be weaken with the increase of prestrain whenε<ε_L.Shape memory effect is not same when quenching medium is different. A big phasetransformation driving force can gain coarse martensite and the shape memory effect has improved significantly.The shape memory effect shows a little downtrend when aging at room-temperature lasts for a long time. One-way recovery ratio of alloy shows an increase within 100℃～150℃in a short aging time. Bainite phase transformation will happen when the aging temperature(200～300℃) is high and then the alloy will lost the shape memory effect. The two-way shape memory recovery ratio of alloy shows a downtrend at 100℃～150℃. Bainite phase transformation will happen when the aging temperature(200～300℃) raises, thus the shape memory effect lost.This kind of alloy can obtain preferred orientation martensite by SEM so a stable two-way can be obtained, while one-way shape memory effect decline little by little. As the thermal cycling goes on, both one-way shape memory effects and two-way memory effects substantively show a downward trend.