On the 18th of SMM9, today, at SMM's 2020 (2nd) China Industry Expo New Materials Forum-China Automotive New Materials Application Summit, and China (8th) Aluminum processing Industry chain supply and demand Trading Summit, and China (second) Copper processing Industry chain supply and demand Trading Summit, Peng Lijun, a senior engineer from the Institute of Advanced Copper Alloy preparation and processing Technology of Youyan Engineering and Technology Research Institute Co., Ltd. (Beijing General Research Institute of Nonferrous Metals), gave a speech on the theme of "Research and application of copper alloy materials for high current connectors of charging piles". It is mainly carried out from three aspects: the demand for copper alloy materials of charging piles, the research of high-performance copper alloy materials and the research and application of industrialization.
Demand of copper alloy material for charging pile
According to the National Strategic emerging Industry Development Plan of the 13th five-year Plan issued by the State Council, the application proportion of new energy vehicles will be greatly increased. In the major strategy of "made in China 2025", "energy-saving and new energy vehicles" are listed as the top ten key research and development areas.
In 2015, the National Development and Reform Commission issued the "Electric vehicle charging Infrastructure Development Guide (2015-2020)" (hereinafter referred to as the guide), which defined the market target for the production and sales of 5 million new energy vehicles.
According to the guidelines for the Development of Electric vehicle charging Infrastructure issued by the National Development and Reform Commission and other four ministries (2015-2020), about 12000 new charging stations and 4.8 million charging piles will be built in 2020 to meet the charging needs of 5 million new energy vehicles. The main power equipment of the charging station is power cable and transformer, in addition, it also includes circuit breakers, fuses, various switches, connectors, etc.; the main copper components of the charging pile include charging cables, charger modules, connectors and various switches, etc. It is estimated that the charging infrastructure of new energy vehicles will bring about 100,000 tons of copper demand.
Cu-Cr alloys are ideal materials for components such as high-power connectors, connectors and power converters, and have become the focus of high-performance copper alloy research.
Research and Application of High performance Copper Alloy Materials
Existing problems:
Lack of independently developed alloy brands and products
The key technology of production has not been completely broken through, and the stability of product performance is poor.
Study on the effect of Alloy elements on Microstructure and Properties of Cu-Cr Alloy
The influence degree of four alloy elements on the hardness of Cu-Cr alloy is Zr > Sn ≈ Ag ≈ Mg.
The effects of four alloy elements on the electrical conductivity of Cu-Cr alloys are in the following order: Sn > Zr > Mg > Ag.
Effect of alloying elements on softening properties of Cu-Cr alloys
The softening temperature is Cu-Cr-Zr > Cu-Cr-Sn ≈ Cu-Cr-Ag ≈ Cu-Cr-Mg > Cu-Cr.
The softening temperatures of Cu-Cr-Zr alloy and Cu-Cr-Mg/Sn/Ag alloy are 600C ~ 650C and 550C ~ 600C, respectively.
The alloy element Mg can improve the heat resistance of the alloy, but it is slightly inferior to the Zr element.
Cu-Cr alloy and Cu-Cr-Mg alloy
Under the peak aging condition, dislocation cells are formed in the matrix of the two alloys.
After annealing at 550C, recrystallization occurs in Cu-Cr alloy, accompanied by the formation of annealing twins, while only subgrains are formed in Cu-Cr-Mg alloy.
After annealing at 700C, the grain size of Cu-Cr alloy grows again, and the grain size of Cu-Cr-Mg alloy is smaller than that of its Cu-Cr alloy.
After annealing at 550 ℃, the precipitates in the two alloys are still Monel stripe and bean petal, and the bean petal precipitates are distributed along the < 100 > Cu direction of the matrix, and the Monel stripe precipitates are distributed along the < 110 > Cu direction.
When annealed at 700 ℃, the precipitated phase grows up and is nearly spherical, and the density decreases. The precipitated phase pins the dislocation to form a dislocation ring.
When annealed at 700 ℃, the size of precipitated phase in Cu-Cr-Mg alloy is smaller because Mg element hinders the growth of precipitated phase.
During the softening process of the alloy (the atomic percentage content of the), Cu element in the precipitated phase decreased from 71.63% of the peak aging state to 0.08% (); Mg element from 1.03% to 0.08%), while the Cr content increased from 27.34% to 99.84% during the alloy softening process, indicating that the Cu element and the Mg element diffused from the precipitated phase to the matrix during the softening process.
Mg element neither dissolves in Cr, nor reacts with it to form new precipitates, and the diffusion coefficient of Mg in Cu is lower than that in Cr, so it can not be diffused into Cu matrix in a short time, resulting in the enrichment of Mg atoms at the precipitate-matrix interface.
Study on stress relaxation behavior of Cu-Cr alloy
It can be seen that the stress variation trend of the two alloys is similar. From the beginning of stress relaxation to 10 hours, the stress decreases rapidly with time, and the decreasing trend slows down and tends to stabilize gradually after 10 hours.
It can be seen that the stress relaxation rate of Cu-Cr-Mg alloy is lower than that of Cu-Cr alloy, indicating that Mg element can significantly improve the stress relaxation resistance of Cu-Cr alloy.
The stress relaxation behavior is very sensitive to temperature, and the increase of temperature can accelerate the stress relaxation rate.
Industrialization research and application
The effects of alloying elements such as Zr, Ag, Mg and Sn on the properties of Cu-Cr alloy were studied systematically, and the mechanism of high temperature resistance and stress relaxation resistance of Cu-Cr-Zr alloy was clarified.
Based on the function fitting of the properties of Cu-Cr-Zr alloys with different Cr and Zr contents, the empirical formulas of ultimate strength and maximum electrical conductivity under specific conditions are obtained, which have been used to guide practical production.
Ag, Mg and other alloy elements are added to Cu-Cr-Zr ternary alloy to further improve the high temperature stability of alloy materials. The composition design criteria of high strength, high conductivity and high temperature resistant copper alloy strip materials are established, and a series of copper alloy materials are developed to meet the needs of different application fields.
Cu-Cr-Zr series alloys with independent intellectual property rights have been obtained.
Key production technology 1: high quality and large size ingot forming control technology in atmospheric environment
Based on thermodynamic calculation, Cr and Zr elements are easy to react with oxygen and furnace body materials, suitable furnace lining materials are selected, a sealed atmosphere protection system is constructed to prevent Zr element burnout, and the effects of melting and casting process and optimization of gating pipe and flow trough structure on melt quality and composition uniformity stability are studied to guide the industrial production of high quality ingots.
Key production technology 2: high precision strip surface quality and high efficiency integrated control technology
Solution treatment is an important heat treatment to improve the comprehensive properties of copper-chromium alloys. Make full use of the waste heat of the strip after high temperature on-line solution treatment, and use the mixture to brighten the surface of the strip, which can effectively solve the bottleneck of high temperature solution treatment and subsequent surface brightening technology.
Key production technology 3: control technology of strength and bending forming properties of copper-chromium-zirconium alloy
Carry out the research on the precise control of the amount of deformation in the alloy forming process and the heat treatment temperature process on the types of alloy texture, so that the material has high strength and excellent bending forming properties at the same time.
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