Study On The Grain Refining And Shape Memory Effect Of Cu-Zn-Al Alloy

Shape memory effect is formed through phase transformation induced by temperature or stress. Cu-based shape memory alloy has received considerable research for its wide range of transformation temperature, broad source of raw materials, good electric conduction, simple preparation technology, low cost and so on.The alloy with the composition of 70.1Cu-26.4Zn-3.5Al (wt%) was prepared and fine grains were obtain in the alloy by adding elements of Ti and B. The relationship between the shape memory effect and the heat treatment of Cu-based shape memory alloy was studied. The influence of number of the training cycles and heating temperature on the two-way shape memory effect has also been investigated. The microstructure and phase composition were studied by means of optical microscope, XRD, TEM and so on. Some experimental results were analyzed by using of some applied software such as Photoshop, Origin and AUTOCAD. The size of grains has been calculated approximately by using the software of Photoshop.Results show that martensite is formed when quenched at higher temperature and the microstructure of plate-like martensite consists of stacking faults. The hardness of the alloys increases with the quenching temperature, and then decreases when temperature is above 850℃. It is important that alloy should be at the state of 6 phase at high temperature for good shape memory effect. Even little of a phase remnant would reduce the recovery of the alloy. The alloy should be quenched completely so that thermal elastic martensite can be obtained as much as possible. The appropriate ageing temperature and ageing time are necessary to make the vacancy full diffusion and the equilibrium phase not precipitation. Better shape memory effect of the alloy can be obtained by 850℃ quenching and proper ageing.Results also show that the addition of Ti and B can make the size of grains smaller and the mechanical properties are improved obviously in the alloy of 70.1Cu-26.4Zn-3.5Al(wt %). The average size of grains is as smaller as one third as 0.17%Ti and 0.034% B are added to the alloy.The thermo-mechanical cycling has very important influence on the two-way shape memory effect of the alloy. Stable two-way shape memory effect can be gained by thermo-mechanical cycling. When the constrained temperature is 160℃-220℃ and cycling number is 10-12 times, the two-way shape memory effect is better.