| Cu-Cr-Zr alloy is a kind of aging strengthening copper alloys with high strength andhigh conductivity, it has the characters of high strength and hardness, good wear resistanceand excellent electrical conductivity. The physical and mechanical properties of copper,especially the softening temperature and hardness, has been dramatically improved byadding a small amount of precipitation strengthening effect strong Cr and Zr alloyingelements. Therefore, Cu-Cr-Zr alloy is often used in the automotive industry as resistancewelding electrode, which is mainly used for spot welding low carbon steel and coated steel.However, Cu-Cr-Zr alloy electrode head is easy to failure under high temperature and highpressure environment. The failure electrode was connected by fusion welding, and thewelding heat quickly went out of the heating surface because of the larger thermalconductivity, which made the base material and the filler metal difficult to fusion. Greaterliquidity also made the filler metal loss easily, which made the weldability become verypoor. Continuous drive friction welding, as a kind of solid-state welding methods, has thecharacters of high efficiency and high quality. Without melting during welding process, thewelding joint is forging organization and the strength of welding joint is better than fusionwelding and brazing. So it has the important value of engineering application to connectCu-Cr-Zr alloy by continuous drive friction welding.In this paper, the spot welding electrode materials Cu-Cr-Zr alloy is chosen as theresearch object. The Cu-Cr-Zr alloy rods were prepared by adding alloy element such as Cr、Zr, vacuum induction melting furnace, hot forging, solid solution, cold drawing and agingtreatment. The Cu-Cr-Zr alloy was connected by different welding process parameters andthe welding joints were studied by different heat treatment process. The micro-hardness,electrical conductivity and room-temperature tensile properties of welding joints was tested.The microstructure and fracture morphology of welding joints was analyzed by opticalmicroscope and scanning electron microscope. The phase composition and the changes ofthe main crystal plane diffraction peak characteristics value before and after cryogenictreatment was studied by X-ray diffraction.The results showed that: the primary friction time is the biggest factor influence on thejoint quality, followed by the upsetting pressure and the last is secondary pressure. Theoptimal welding process paraments are as follows: rotating speed1470r/min, primaryfriction time8s, primary friction pressure1MPa, secondary displacement2mm, secondaryfriction pressure2Mpa, upsetting time5s and upsetting pressure5.2MPa. The joints properties of Cu-Cr-Zr alloy were reduced relative to the base metal after continuous drivefriction welding under the optimum technological parameters. The tensile strength ofCu-Cr-Zr alloy welding joint decreased from410MPa to280MPa and the hardness of weldzone reduced from163HV to93.27HV. The main reasons of welding joint softened includedtwo aspects, on the one hand, the changes of joint organization morphology made itsdislocation density decrease, on the other hand, the strengthening phase particles dissolvedduring the welding process. The conductivity of welding joint decreased from79.31%IACSto58.61%IACS, and the main reason of conductivity decrease was the dissolution ofstrengthening phase particles.The heat treatment test at different aging temperatures and times were carried out onthe Cu-Cr-Zr alloy welding joints. The results indicated that the best post weld heattreatment of welding joints was aging at460℃for3h, air-cooled, and the properties ofwelding joints overall increased. The hardness increased to153.01HV, electricalconductivity increased to77.41%IACS and the tensile strength reached to373MPa. Thecryogenic treatment for4h was carried out on the welding joints after aging at460℃for3h,and the half high width of the X-ray diffraction peak of welding joints became wider withthe increasing of cryogenic treatment time, which made the properties of welding jointsincrease significantly. The hardness increased to160.38HV, electrical conduction reached to78.55%IACS and the tensile strength was407.08MPa, which closed to the base materiallevel. |
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