铝合金表面激光熔覆稀土镍基合金强化层基础研究

Combing the laser cladding technology with the rare earth modification technology, laser cladding of rare earth doped nickel based alloy on the surface of aluminum alloy will be investigated to obtain comprehensive strengthening coatings with high wear resistance and high corrosion resistant, enhancing the comprehensive practical properties and expanding its scope of application. The following five parts of experiments will be carried out:.(1)Investigate the effects of species of the rare earth (lanthanum, cerium, dysprosium, erbium, yttrium) and nickel based alloy powders, the powder ratio, the process parameters of the laser cladding (the power of the laser, the diameter of the light spot, the scanning speed) on the properties of the laser cladding layers on the surface of the sixth series aluminum based alloys (such as 6061, 6063, etc.)..(2) Investigate the effects of species of the rare earth and nickel based alloy powders, the powder ratio, the process parameters of the laser cladding on the microstructure, composition, phase structures, the appearance of the laser cladding layers, the density, hardness, combining strength, wear resistance, high temperature oxidation resistance and corrosion resistance of the laser cladding layers, and analyze the impact mechanism deeply..(3) Investigate the variation of the microstructure and composition of the cladding layers, the distribution of the rare earth elements in the metal cladding layers and their impact mechanism..(4) Investigate the surface hardness, red hardness, density, combining strength, wear resistance, corrosion resistance and high temperature performance of the comprehensive strengthened surface..(5) The basic theoretical studies of the aluminum alloy laser cladding.

为提高铝合金的综合使用性能，扩大其应用范围，本研究拟在六系列铝合金基体表面，将激光熔覆技术和稀土改性技术结合，激光熔覆添加有稀土元素的镍基合金粉末，获得冶金结合的高耐磨高耐腐蚀复合强化涂层。本课题拟进行：①在六系列铝合金基体（如6061、6063等）表面，研究稀土粉末（镧、铈、镝、铒、钇等）和镍基合金粉末的种类、配比及激光工艺参数（激光功率、光斑直径、扫描速度等）对熔覆层性能的影响，获得最佳工艺；②研究稀土和镍基合金粉末的种类、配比及激光工艺参数的变化对激光熔覆层显微组织、成分、相结构等微观结构及激光熔覆层外观、致密度、硬度、结合强度、耐磨性、抗高温氧化性、耐蚀性等性能的影响，并深入分析其影响机理；③熔覆层组织成分的变化规律，稀土元素在熔覆层金属中的分布情况和作用机理；④复合强化处理后表面硬度、红硬性、致密度、结合强度、耐磨性、耐蚀性及耐高温性能研究；⑤铝合金激光熔覆的基础理论研究。

利用激光熔覆和稀土改性技术，结合温度场模拟，进行了铝合金激光溶覆工艺研究，找到了最佳工艺参数。采用最佳工艺参数，在6063表面制备了添加不同含量三种稀土的Ni60熔覆层。探讨稀土作用效果和机制，研究不同稀土对6063表面激光熔覆Ni基熔覆涂层的宏观、形貌、硬度、相结构、元素分布、微观组织、摩擦磨损、耐腐蚀影响，获得较佳稀土配比。主要结论如下：①最佳工艺参数：功率4kW，光斑直径6mm，扫描速率600mm/min，步距6mm；②未加稀土熔覆层出现大量的“团状”或“根瘤状”的熔凝组织和气体溅射孔洞，添加三种稀土的熔覆层表面形貌均有改善；加入稀土含量低于3%~4%时，熔覆层仍然具有气孔、组织脱落和表面不平整等缺陷，加入4%~10%稀土时，熔覆层表面平整，无脱落层，表面形貌良好；③熔覆层厚度约800 μm～1 000 μm，三种稀土添加量低于4%时，随稀土含量增加，气孔、裂纹等缺陷得到改善；④未加稀土熔覆层硬度值1020HV0.1，高于6063硬度值147.2HV0.1，加入5%~10% 的三种稀土可提高熔覆层表层硬度，最高可达1300HV0.1～1400HV0.1；在熔覆层底层，未加稀土熔覆层硬度值200HV0.1～400HV0.1，比加稀土熔覆层低100HV0.1～400HV0.1；⑤添加La2O3熔覆层相结构为β-NiAl(Cr)和少量Al3Ni、AlNi3、Al等，添加稀土La2O3以后，XRD图中出现了微量稀土化合物La2O3、Al4La；⑥添加Y2O3熔覆层相结构为β-NiAl(Cr)、Al3Ni、AlNi3、Al等，同时有Y2O3、YAl3、AlNiY、Ni17Y2等多种稀土化合物的衍射峰；⑦加入CeO2熔覆层相结构为β-NiAl(Cr)、Al3Ni、AlNi3等，熔覆层中有CeNi5、Ce3Ni6Si2；⑧相比未加稀土熔覆层，添加三种稀土熔覆层中Ni、Al、Cr等成分随深度过渡明显，无Cr元素偏聚，表层Ni含量由未添加稀土前的34.62 %提高到60 %以上，熔覆层稀释率低，稀土含量从表层大于1.0%到底部逐渐降低；⑨添加三种稀土可改善微观结构，促进熔覆层晶粒细化，减少气孔，熔覆层主要成分为NiAl-Cr共晶组织，稀土偏聚在晶界位置并形成了稳定Al4La等稀土化合物；⑩加入稀土熔覆层耐磨性和耐腐蚀性比未加稀土熔覆层有所提高。