Study And Preparation Of High Strength And High Conductivity Copper For Electric Train

Electric train pantograph copper need keep stable current under harsh conditions, such as: arcerosion, high temperature, high speed, extreme weather, This kind of working conditions putforward a very high request about hardness, conductivity and current carrying friction ofpropertiespantograph copper. How to greatly improve hardness under condition of sacrificing lessconductivity, and how to simplify the process in order to make the technology suitable for theproduction are the main target of the study at home and abroad. The research and development ofnew high strength and high conductivity copper material has significance academic value andimportant engineering value. In this research, the alloying method and composite materials methodwere used to prepared high strength and high conductivity copper. The former makes heterogeneousatoms Cr and Zr precipitation become strengthened particles by hot stretching process of CuCrZralloy; the latter added WC particles artificially as reinforcing particles by hot pressing sintering toprepared WC/Cu composites materials.CuCrZr alloys which possess high electrical conductivity and moderately high toughness is usedfor manufacturing contact line. Aging treatment usually applied to this kind of alloy as reinforcingmethod to obtain dispersed hard phase. The preparation process, optimization technique andstrengthening mechanism have been deeply studied by researchers around the world. Too muchsteps and too much factors difficult to grasp made the volume production of this kind of alloys hardto realized. The CuCrZr alloys were thermo-mechanically treated by heating up to varioustemperatures from100℃to300℃for aging treatments. Different tensile elongations were exertedon the materials to accelerate the introduction of high density dislocations during the agingtreatments. The effects of thermo-mechanical treatment on microstructure and properties of CuCrZrhigh strength and high conductivity alloys were discussed.Adding hard particles to the copper matrix artificial could enhance the copper based compositematerials and avoid the influence of residual impurity atoms in Cu matrix on the conductivity.CoMPAred to other copper based reinforcement particle WC, who usually used as the main rawmaterials for the production of cemented carbide, has the advantages of good wettability with copperand electric conductivity. In this research, WC was appended to Cu matix by hot pressed sintering. Influence of different content, different sintering temperature and different particle size of WC oncopper based composite materials have been discussed.Finally, for evaluating the current carrying wear performance of those two different typescopper based materials, a pin on disc friction wear testing machine has been used to simulate highspeed train operating environment. The main findings are: with thermal tensile rate increased, theconductivity of CuCrZr alloy decreases slightly when the micro-hardness is greatly improved. Themicrohardness of the samples exerted with22%tensile elongations under300℃increased35.5%and the conductivity decreased by only12.7%. TEM results show that precipitated phase particleshave already exist on the microstructure after300℃hot stretching. The number and size ofprecipitates all grew up with the tensile rate. Combined with precipitate observation, the variation ofgrain size, non complete linear change of conductivity, hardness and other properties, the highstrength and high conductivity properties is the synthetic action of solid solution precipitation ofimpurity atoms, dislocations, grain refinement, precipitate strengthening effect and diffusion effect.The relative density of WC/Cu composite continuous increased along with the increase of sinteringtemperature. However, when the temperature exceeds900℃, the too fast growth of copper grainlead to crystal obturator foramen which result in declining quality of sintering. In the process of hotpressing sintering, WC hinder the movement of the deformation of copper powder, grain boundariesand pores. When the WC content reaches a certain value, agglomeration phenomenon would causedhardness declining trend. The larger specific surface area of nanoscale WC particles than micronWC make them reunite more easily. The dispersion strengthening effect reduced as soon as theparticle agglomeration occure.