Study On Damping Capacity Of CuZnAl Alloys

The vibration and noise pollition have already touched the daily life of people badly, which arouses the overseas experts and the scholars in our country to attach importance to the study on the damping alloys. At present, the sthdy on the danping capacity of CuZnAl alloys is not thorough and mature in comparition with the investigation on the shape memory effect. The crucial parameters for engineering application of copper-based shape memory alloys are their shape memory effect, mechanical properties and damping capacity. The microelement of CuZnAl alloys as well as the effects of predeformation, heat treatment and the condition on the damping capacity, shape memory effect and mechanical properties of CuZnAl alloys have been investigated systematically by means of scanning electron microscopy (SEM) and the inverted torsion pendulum technique (JN-1 vacuum internal friction technique).The micro-mechanism for high damping properties of martensite in CuZnAl alloys has been discussed.In addition, the inherent relation between shape memory effect and damping capacity is discussed.The experiment results show that the damping capacity of CuZnAl alloys increases sharply with the increase of strain amplitude at low strain amplitude(0.5×10^-4＜γ_max＜1.5×10^-4) and the fiction- strain is not liner; when the strain amplitude is up to a certain value(about 3.5×10^-4), the damping capacity increases slowly with increase of strain amplitude at high strain amplitude and the damping capacity tend to become stable.The movements of twin interfaces under outside force action are responsible for the high damping properties of CuZnAl alloys. Heat-treating temperature affects obviously the damping capacity of these alloys. As the heat-treating temperature rises,αphase will betatizeβgradually, which increasesβ′martensite due to queching, thus the damping capacity of CuZnAl increases obviously. It has the best damping capacity at 800～900℃for fifteen minutes followed by water cooling. With further increasing of heat-treating temperature,βgrain grows up rapidly andβ′martensite due to queching crassitudes, which leads to the twin-interfaces ofβ′and the interfaces betweenβ′andβ′reduce, thus the damping capacity of the alloys decreases.The damping capacity of CuZnAl alloys first increases and then decreases with the increase of predeformation. On the one hand, it is associated to stess-induced martensite transformation and it increases martensite quantities when being deformed; on the other hand it brings residual stress and high density crystal lattice defects which nail the interfaces of the damping fountain due to ductile deformation. The damping capacity comes to maximum at 1～2％predeformation, then it presents downtrend with the increase ofpredeformation.By studying the shape recovery ratio of CuZnAl alloys, the result shows thatαphase will be betatizedβgradually as the heat-treating temperature rises, the shape recovery ratio of CuZnAl increases gradually, it comes to maxium at 750～800℃for fifteen minutes followed by water cooling. With further increasing of heat-treating temperature, martensite plates are not uniformly oriented, the crystal boundaries appear the landscape oriention martensites and minute martensites, then the secondly phase particles begin to separate on the crystal boundaries and in the grains inner, thus the shape recovery ratio of the alloys decreases gradually. As far as the alloys with not Zr are concerned, after betatizing treatment, martensite plates are rather ordered and uniformly oriented, in addition, no Zr grain nails the interfaces, so the alloys with not Zr have the better shape recovery ratio compared to the alloys with Zr.The tensile properties are investigated. The results indicate CuZnAl alloys posses the better tensile strength and subdued strength and the worse ductility under cold rolling state. After being betatizing at 650℃for 15 minutes and up-quenched, the ductility of the alloy reaches the maxium due toαphase. With the highering of betatizing temperature,the tensile srength and ductility of the alloy both decreased as a result of the reduction ofαphase and the growth of grain size.In the same heat treament condition ,the alloy with not Zr has the best shape recovery ratio and danping property. It can be shown that the SME and the camping property are inherent. The SMA posses the shape memory effect thanks to thermoelastical martensite transformation or martensite variants reorientation. In addition, the SMA is provided with the better damping capacity in virtue of the harmony of martensite transformation and the anelasticity movement of varient intefaces(twin intefaces, phase intefaces, varient intefaces) formed in martensite. It can be concluded that it is thermoelastical martensite phase transformation that contacts the SMA and the damping capacity closely.