CuCr合金为原材料制备的电触头作为电接触元件是真空灭弧室的核心部件，广泛应用于高压电网输变电等电力行业。目前，真空灭弧室正面向高电压、大容量、小型化的目标发展，迫切需要提升触头材料的力学性能及包括电学性能在内的物理性能。研究表明，触头表面燃弧层（~100μm）的失稳是引起灭弧室关断失效的最主要原因，且晶粒细化和弥散化能有效提高合金的使用寿命。在高密度激光作用下，CuCr合金工件表面经快速熔化和快速凝固后形成的Cr相晶粒细化和弥散化效果显著，但是由于表面熔凝的熔池动力学机理研究尚不完善，阻碍了激光表面熔凝应用于工程实际。本文主要开展高密度激光表面熔凝实验，研究了单道熔凝的特征状态、单一变量及复杂参数下的工艺研究及其对性能的影响，探讨了高密度激光熔凝CuCr合金工艺、组织和性能三者之间的关联，并结合数值模拟对CuCr合金熔凝机理进行了深入的研究，为激光表面熔凝CuCr合金用于工程实际提供了有力的理论与实验支撑。本文的主要研究内容及结论如下：

        1. 针对CuCr合金高热导率、高反射率、易氧化、难混溶等材料特性，搭建、调试并优化了高密度激光表面快速熔凝实验装备，实现了激光功率0~2kW、扫描速度0~20000mm/min等实验条件，优化后激光功率密度可达10⁷W/cm²，单个光斑与材料的接触作用时间低于1ms，工艺参数的调节范围相比优化前的实验系统提升1倍以上。

        2. 以单道的熔凝道作为研究对象，研究不同的工艺参数组合下，CuCr合金单道熔凝的表面形貌和横截面熔池形貌。实验使用的激光功率范围600~900W，扫描速度范围为1000~10000mm/min，建立起熔凝深度H、熔凝宽度W、熔凝深宽比H/W和熔凝面积A等特征参量与工艺参数组合之间的关系，结合实验结果将表面熔凝状态定义为“尖”状深熔模式、“指”状深熔模式和热传导熔凝模式这三种模式。从微观组织和熔池内部流动及传热特性出发，利用数值模拟推断了三种熔凝状态的形成机理，即“尖”和“指”状深熔模式主要是由于在高能量输入下，熔池最高温度达到沸点，考虑金属蒸汽形成的反冲压力作用在熔池上形成的匙孔效应，从而影响熔池传热及流动；热传导熔凝模式则主要由于在低能量输入下，熔池主要由热传导形式主导，显示出传导不充分的熔凝状态。

        3. 开展CuCr合金激光表面熔凝的工艺实验研究，以表面粗糙度和熔凝深度作为主要的评价指标研究控制单一工艺变量的一次加工和复杂工艺参数组合的二次加工。结果表明，一次加工时，激光功率越大、扫描速度越低，即单位时间单位面积内的能量输入越高时，表面的粗糙程度越高，熔凝深度越大，且统计发现熔凝深度与能量输入/耗散比R_E呈现出很强的线性相关关系；二次加工情况下，建立起不同工艺参数与CuCr合金表面粗糙度和熔凝深度之间的量化联系，结果表明，重复加工可以增加表面熔凝深度，且激光功率越高效果越明显；相同工艺参数组合下加工次序的不同对熔凝深度影响不大，但是在二次加工的功率比一次加工低的次序下进行熔凝处理的CuCr合金表面平整度更好，这为今后工艺优化和复杂工艺的探索提供参考借鉴。

        4. 通过显微硬度测试和电导率测试研究激光表面熔凝处理对CuCr合金力学和电学性能的影响。结果表明，不同工艺参数下CuCr合金熔凝处理后的熔凝层显微硬度较基体均有大幅提升，随扫描速度从2000mm/min增加到10000mm/min，熔凝层的平均硬度值由203HV提升至250HV，熔凝层硬度是基体硬度（85HV）的2.4~2.9倍。由此得到结论：细晶强化、弥散强化和固溶强化作用共同引起显微硬度的提升。熔凝处理后CuCr合金的导电率为20.18 MS/m，与熔凝前性能一致，可正常地投入到实际生产和应用中。

    The electric contact made of CuCr alloy is the core component of vacuum interrupter, which is widely used in high voltage grid transmission industry. At present, the vacuum interrupter turns in the direction of high voltage, large capacity and miniaturization. It is urgent to improve the mechanical properties and physical properties including electrical properties of contact materials. The failure of the arcing layer (~100μm) on the contact surface is the main reason for the failure of the interrupter and grain refinement and dispersion can effectively improve the service life of the alloy. Under the high power density laser, the Cr phase grains formed on the surface of CuCr alloy after rapid remelting and solidification are significantly refined and dispersed. However, the research on the dynamic mechanism of molten pool during surface remelting is still unclear, which hinders the application of laser surface remelting in engineering. In this paper, laser surface remelting experiments under high power density are carried out, including the characteristic states of single track remelting, the processing research under single and complex parameters and their effects on properties. The relationship among processing, microstructure and properties of CuCr alloy by high power density laser remelting was discussed, and the remelting mechanism of CuCr alloy was studied by numerical simulation, which provides a strong theoretical and experimental support for the application of laser surface remelting CuCr alloy in engineering. The main research contents and conclusions are as follows:

    1. According to the characteristics of CuCr alloy, such as high thermal conductivity, high reflectivity, easy oxidation and immiscibility, an experimental system of laser surface rapid remelting by a high power density laser was built, debugged and optimized, which achieve the experimental conditions of laser power of 0~2kW, scanning speed of 0~20000mm/min and so on. After optimization, the laser power density can reach 10⁷W/cm², the contact time between single laser spot and material is less than 1ms, and the adjustment range of processing parameters is more than one time higher than before.

    2. Take single track remelting as the research object, the surface morphology and cross-section molten pool morphology of CuCr alloy were studied under different processing parameters. The relationship between the characteristic parameters and the combination of processing parameters is established, such as remelting depth H, remelting width W, remelting depth to width ratio H/W and remelting area A in the range of 600~900W laser power and 1000~10000mm/min scanning speed. Combined with the experimental results, the surface remelting states are defined as "sharp" deep remelting mode, "finger" deep remelting mode and heat conduction remelting mode, respectively. Based on the microstructure, flow and heat transfer characteristics in the molten pool, the formation mechanism of three kinds of remelting states were deduced by experimental phenomena and numerical simulation. The "sharp" and "finger" deep remelting modes are mainly due to the fact that the maximum temperature of the molten pool reaches the boiling point under high energy input, and the keyhole effect formed on the molten pool by the recoil pressure of metal vapor formation is considered, which affects the heat transfer and flow of the molten pool; the heat conduction remelting mode is mainly due to the low energy input and the molten pool is dominated by the heat conduction mode, which shows that the conduction is insufficient.

    3. The experimental study on laser surface remelting of CuCr alloy was carried out, which the surface roughness and remelting depth were used as the main evaluation indexes to study the primary processing of controlling single processing variable and the secondary processing of complex processing parameters combination. The results show that the surface roughness is higher and the remelting depth is deeper due to the energy input per unit area per unit time is higher with higher laser power and lower the scanning speed and it is found that there is a strong linear correlation between remelting depth and energy input to dissipation ratio R_E. In the case of secondary processing, the quantitative relationship between different processing parameters and surface roughness and remelting depth of CuCr alloy is established. The results show that repeated processing can increase the surface remelting depth, and the higher the laser power is, the more obvious the effect is. Under the same process parameters combination, the different processing sequence has little effect on the remelting depth, but the surface flatness of CuCr alloy is better when the power of secondary processing is lower than that of primary processing, which provides a reference for processing optimization and complex processing exploration in the future.

    4. The effect of laser surface remelting treatment on mechanical and electrical properties of CuCr alloy was studied by microhardness and conductivity test. The results show that the microhardness of the remelting layer of CuCr alloy is significantly higher than that of the substrate under different process parameters. With the increase of scanning speed from 2000mm/min to 10000mm/min, the average microhardness increases from 203HV to 250HV, which is about 2.4~2.9 times of the substrate microhardness(85HV). It can be concluded that the fine grain strengthening, dispersion strengthening and solid solution strengthening together give rise to the increase of microhardness. The conductivity of CuCr alloy after remelting treatment is 20.18MS/m and it can be put into practical production and application normally, which is the same as that before remelting treatment.