太原理工大学 硕士学位论文 AZ31B镁合金激光表面熔覆复合涂层的研究 姓名：吴宏亮 申请学位级别：硕士 专业：材料加工工程 指导教师：王文先 20100501 太原理工大学硕士研究生学位论文 I AZ31B 镁合金激光表面熔覆复合涂层的研究 摘 要 “节能、绿色、环保”是当今工业的发展趋势，镁合金作为“21 世纪的绿 色工程材料”以其轻质高强的优异性能备受各行业的青睐，但由于镁合金材料 耐腐蚀性、硬度、耐磨损性差，在某种程度上制约了它的应用为了拓展和开 发镁合金的潜力，针对镁合金耐蚀性、耐磨性差的问题，提出适当的表面改性 方法，对镁合金现实应用有重要的意义 本文采用 5kW 横流 CO2气体激光器在 AZ31B 镁合金表面进行了激光熔覆 Al-Si 合金涂层和 Al-Si+Al2O3/TiO2复合涂层的试验，以期提高镁合金表面的耐 磨性能和耐腐蚀性能采用光学显微镜、扫描电镜、能谱仪、显微硬度仪、摩 擦磨损试验机以及电化学测量系统，深入分析和研究了两种熔覆层的显微组 织、界面结合、成分分布、显微硬度、磨损性能以及抗腐蚀性能等 AZ31B 镁合金表面激光熔覆低熔点 Al-Si 共晶合金粉的试验结果表明，涂 层与基体结合界面清晰，形成了良好的冶金结合。
与原始镁合金相比，涂层的 晶粒明显得到细化XRD 分析结果表明涂层主要由 Mg、Mg17Al12、Mg3Al2、 Mg2Si、Al2Mg 等物相组成Al-Si 涂层的显微硬度由基体 50HV0.05提高到 150HV0.05，是基体的 3 倍从磨痕宽度、摩擦系数、磨损量三方面分析了涂层 的耐磨性，磨痕宽度大约为 780μm，比基材降低了 35.0%；摩擦系数波动不 大，平均摩擦系数是 0.26 左右，比基材降低 0.34；磨损量大约为 2.0×10-3g，比 原始镁合金 3.5×10-3g 减少 42.8%；电化学腐蚀试验分析表明 Al-Si 涂层的腐蚀 电位为-1.14V，比基材-1.51V 提高 0.37V，腐蚀电流密度为 0.0358A/cm2，比基 材 （ 0.1185A/cm2） 降 低 了 0.0827A/cm2； 腐 蚀 质 量 0.0216g ， 比 基 材 （0.0410g）减少 47.0% 为了获得更良好的性能，把 Al-Si 粉末和 Al2O3/TiO2陶瓷粉末以 4:1、 6:1、10:1 的质量比混合，采用激光熔覆技术，分别获得良好的多道搭接冶金涂 层熔覆层组织均由灰色基体和树枝晶及弥散分布的白色颗粒状物质组成。
物 相分析表明，三种比例涂层均是由 Mg17Al12、Al3Mg2、Mg2Si、Al2O3、TiO2五 种化合物组成，比例 6:1 时，Al2O3、TiO2峰值较高，熔覆层中的陶瓷相最多 太原理工大学硕士研究生学位论文 II 硬度检测表明，三种比例涂层硬度都有所提高，其最高硬度基本都在 225HV0.05左右，比 AZ31B 镁合金基体 50HV0.05提高 3.5 倍，且比单一 Al-Si 涂 层的硬度 150HV0.05还要提高 50.0%；三种比例下涂层的磨痕宽度分别为 430μm、400μm、450μm，远远小于原始镁合金；摩擦系数分别是 0.25、0.25、 0.27 左右，比基体减少 0.35、0.35、0.33；磨损量分别是 0.8×10-3g、0.6×10- 3g、1.0×10-3g，比原始镁合金减少 77.1%、82.8%、71.4%；三种比例的涂层的 腐蚀电位分别是-1.19V、-1.16V、-1.06V，均比基材（-1.51V）提高 0.32V、 0.35V、0.45V，而腐蚀电流均降低了一个数量级；腐蚀质量分别是 0.0190g、 0.0178g、0.0256g，比基材 0.0410g 减少 53.6%、56.5%、37.5%。
关键词：AZ31B 镁合金，激光熔覆，Al-Si 涂层，Al-Si/Al2O3+TiO2复合涂 层，耐蚀性，耐磨性 太原理工大学硕士研究生学位论文 III STUDY ON THE LASER SURFACE COMPOSITE COATING OF AZ31B MAGNESIUM ALLOY ABSTRACT “Energy saving, green, environment protecting” is the developing trend in nowdays. As “Green Engineering Materials in 21st Century“, magnesium alloy is the favor of industry for its unique excellent properties (low density, specific strength and stiffness, etc.). But the poor performance in corrosion resistance, hardness, wear resistance，magnesium alloy is limited to applied to industry widely to some extent. In order to expend and explore the magnesium alloy's potential, we have to adopt some technology to improve its corrosion resistance and wear resistance, which is important to the application of magnesium alloy. In this paper, in order to improve the property of anticorrosion and wear resistance, AZ31B magnesium alloy is treated with laser cladding technology by 5kW transverse flow CO2 gas laser. The Al-Si coating and Al-Si+Al2O3/TiO2 composite coating is studied by OM、SEM、EDS、microhardness tesster、friction and wear tester、electromical tester from the following aspects: microstructure, phase, micro hardness, wear properties and electrochemical corrosion resistance. Obtained well metallurgical bonding and interface is clear after laser cladding treatment with low melting point Al-Si powder on AZ31B magnesium alloy. Compared with the original magnesium alloy, grains becomed much more refined. Coating mainly consists of Mg、Mg17Al12、Mg3Al2、Mg2Si、Al2Mg composition. The value of hardness lifted from 50HV0.05 to 150HV0.05, 3 times than substrate. Wear resistance is studied from morphology, friction coefficient and wear loss. Wear scar width is 780μm, 35.0% lower than the substrate; the friction coefficient tends to invariant, average value of friction coefficient is 0.26, 0.34 lower than that of matrix; The wear loss is about 2.0×10-3g, lower 42.8% than that of original magnesium alloy; The result of electrochemical corrsion show that the corrosion potential of AZ31B 太原理工大学硕士研究生学位论文 IV magnesium alloy is -1.14V, 0.37V higher than that of matrix, and the corrosion current is 0.0358A/cm2, 0.0827A/cm2 lower than that of matrix, corrosion mass is 0.0216g, 47.0% higher than that of matrix. In order to obtain better performance, the Al-Si powder and Al2O3/TiO2 ceramic powder were mixtured with different mass ration, which were 4:1、6:1、 10:1 respectively. The cladding is composed of gray matrix、black dendrite、white particle. Phase analysis showed that three types of coating were composed of Mg17Al12、Al3Mg2、Mg2Si、Al2O3、TiO2 five compounds. The peak of Al2O3、 TiO2 were high when the propotion is 6:1, which indicated that there were much ceramic phase in the cladding. Hardness testing showed that three rations have improved. The maximum hardness is about 225 HV0.05, icreased 3.5 times than the substrate, and raised 50.0% than Al-Si coating. Wear track width of three ratios coatings were 430μm、400μm、 450μm，much smaller than the original magnesium alloy. Friction coefficient is 0.25、0.25、0.27 respectively, 0.35、0.35、0.33 less than that of matrix. The wear loss is 0.8×10-3g、0.6×10-3g、1.0×10-3g, which decreased 77.1%、82.8%、71.4% than the original magnesium alloy. Corrosion potential of three ration coatings were - 1.19V、-1.16V、-1.06V, improved 0.32V、0.35V、0.45V than base metal, while the corros。