Effects Of Deep Cryogenic Treatment On Microstructures And Property Of Copper Alloy And Zinc Alloy

Cryogenic treatment is also known as ultra-low temperature treatment. The materials are treated under the-130℃~-190℃low temperature according to a certain process. Cryogenic treatment has been successfully used in ferrous metal materials, to improve the strength, wear resistance and dimensional stability of workpieces. However, the research in non-ferrous metals is less.Copper and brass are mainly used in the manufacture of conductive components, radiators, the heat transfer components of the heat exchanger and sets of blast furnace tuyere. But because of relatively low strength and hardness, copper and brass parts at the service conditions of high temperature and wear are bound to wear or crack. Zinc alloys can be used for sliding bearing and bushing instead of copper alloys. Deep cryogenic treatment may be a new method to improve the wear resistance of zinc alloy.In this paper, copper, brass H62 and zinc alloy ZA27 are studied, to observe hardness, tensile properties, electrical conductivity and wear resistance after deep cryogenic treatment. Combining XRD and microstructure, mechanisms of cryogenic treatment are discussed. It is found that there are certain relationships between mechanical properties and cryogenic treatment processing. The results showed that after cryogenic treatment for 24h, microhardness and tensile strength of the copper reached the peak. Compared with the non-cryogenic treatment, they were respectively increased by 15.4% and 11.9%, with a slight decrease in elongation. After cryogenic treatment for 12h, microhardness and tensile strength of the brass reached the peak. Compared with non-cryogenic treatment, they were respectively increased by 9.9% and 3.2%. After cryogenic treatment for 4h, hardness of zinc alloys reached the peak. Compared with non-cryogenic treatment, it was increased by 9.3%. Friction experiments showed that the wear resistance of zinc alloys decreased after cryogenic treatment 4h. The wears decreased by 38.3 percent under low speed (300r/min)and 13.0% under high-speed (600r/min). The electrical conductivity of the copper and brass after cryogenic treatment unchanged.Through the comparative analysis of XRD, microstructure and mechanical properties, the impact of cryogenic treatment process on the material properties was discussed.