【作者】 赵铁钧；

【导师】 涂赣峰；

【作者基本信息】 东北大学 ， 有色金属冶金， 2009， 博士

【摘要】 强流脉冲电子束处理是近十几年来发展起来的一门新兴材料表面改性技术。大量研究工作表明,强流脉冲电子束表面处理能显著提高铝和钢表面的抗腐蚀及耐摩擦磨损性能,因此为进一步扩大镁合金及铝硅合金的服役范围,本论文采用强流脉冲电子束对ZK60镁合金和过共晶铝硅合金进行表面改性,改善其抗腐蚀和耐摩擦磨损性能,研究改性层组织结构特征变化以及不同参数对合金耐腐蚀性能和摩擦磨损性能的影响；同时本论文首次尝试将微弧氧化和强流脉冲电子束复合改性应用于ZK60镁合金的表面改性中,初步探索此两种表面改性技术复合处理的可行性。研究主要结果如下：(1)经强流脉冲电子束处理后ZK60镁合金表面生成了一层厚度约为5-11μm的重熔层。重熔层最表层有少量裂纹和熔坑；同时由于镁的蒸发,表面沉积有细小的纯镁颗粒；重熔层组织晶粒细小,合金元素偏析程度显著降低、固溶度增加；3.5%NaCl溶液中动电位极化曲线测试结果表明ZK60镁合金强流脉冲电子束改性后耐腐蚀性得到显著提高,其中23KV加速电压下电子束轰击15次的ZK60镁合金腐蚀电流密度从311μA/cm2下降至42.2μA/cm2,下降了86%,腐蚀电位从-1312mV上升至-1220mV,升高了92mV；另一方面,摩擦磨损实验结果证明改性后的合金摩擦系数降低,磨损体积减少,耐磨擦性能得到提高,加速电压为27KV,轰击15次的样品摩擦系数和磨损量均优于其它样品,其磨损量下降了80%；(2)ZK60镁合金经微弧氧化处理后表面生成了一层厚度约为18μm的陶瓷层,陶瓷层由疏松层和致密层组成,疏松层分布有孔洞,约占整个膜层厚度的90%；经微弧氧化再经强流脉冲电子束处理的ZK60镁合金改性层厚度约为3～4μm,陶瓷层变的致密；经强流脉冲电子束再经微弧氧化处理的ZK60镁合金表面同样生成了一层厚度不均匀的陶瓷改性层；建立了强流脉冲电子束再微弧氧化处理表面改性层的简单生长模型。3.5%NaCl溶液中动电位极化曲线测试及摩擦磨损实验结果表明：经过复合表面改性处理的试样耐腐蚀性、耐摩擦性能均得到了提高,其中经强流脉冲电子束处理再经微弧氧化处理试样的耐腐蚀性能得到显著提高,腐蚀电流密度从311μA/cm2下降至0.2μA/cm2,降低了3个数量级；经微弧氧化再经强流脉冲电子束处理的试样磨损量降低了80%。复合表面处理实验同时验证了强流脉冲电子束的快速熔凝作用对微弧氧化形成的疏孔具有封孔作用,其具体实验参数的优化设置还有待进一步探索改进。(3)强流脉冲电子束轰击实现铝硅合金表面快速熔凝,显著细化改性层内晶粒尺寸,提高合金元素Si的固溶度,Si相在合金中分布弥散,合金成分均匀化。强流脉冲电子束轰击处理使合金表面局部出现熔坑和微裂纹的特征形貌。熔坑形成过程可达到净化表层的效果,而微裂纹通过截面形貌观察只在最表层,对基体性能影响不大。性能测试结果表明强流脉冲电子束处理后三种过共晶铝硅合金摩擦系数降低,磨损量减小,耐磨性能提高。强流脉冲电子束处理后合金在3.5%NaCl溶液中的腐蚀电流降低,24小时盐浸实验表明改性合金平均腐蚀速率均降低。处理合金耐蚀性能提高。更多还原

【Abstract】 High current pulsed electron beam (HCPEB) has been developed intensively as a new high-power energetic beam used for surface modification of materials in the last few decades. It has been confirmed that the properties of modified surface layers of pure Al and mold steels treated by HCPEB such as wear and corrosion resistance could be improved significantly in the previous works. As a consequent, HCPEB treatment was selected to improve the surface properties of ZK60 Mg alloy because of the inferior corrosion and wear resistance with an aim of expanding its scope of application in this paper. While the characteristics of the modified surface and optimum parameters for the treatment operation were studied. Then HCPEB technology was compounded with another surface modification technology micro-arc oxidation (MAO) as a new technology for the Mg alloy surface modification treatment basing on the available study with the purpose of developing a new surface treatment technology of Mg alloy.The microstructure characteristic of modified surface of Mg alloy ZK60 after HCPEB and/or MAO complex treatment were analysis by XRD and SEM, and corrosion and wear resistance were tested. The results were as following:(1) There was a remelted layer with the thickness of 4-8μm on the top surface of the alloy irradiated by HCPEB characterized with a few of cracks and craters. As the temperature of the melting layer was much higher than that of evaporation of Mg, particles of pure Mg were found on the surface of the treated sample. The grain of alloy surface was refined, and the degree of segregation phenomenon of alloying agents was reduced significantly. Solid solubility of alloying element in Mg base was increased as the result of the rapid solidification process. Effects of HCPEB surface treatment on the corrosion resistance of Mg alloy ZK60 was investigated by means of potentiodynamic polarization curves in 3.5% NaCl solution. It can be concluded that the treated samples exhibited an improved corrosion resistance as the result of the refined grain and homogeneous distribution of alloying agents. The sample treated with 10 pulses at the accelerating voltage of 23KV performed better than any other treated samples as the corrosion current decreased 86%, from 311μA/cm2 to 42.2μA/cm2, and corrosion potential increased from-1312mV to-1220mV. The friction and wear test results showed that the friction coefficients of treated alloys surfaces were decreased, of which was treated with 15 pulses at the accelerating voltage of 27KV represented lower wear rate as it was just 80%.(2) ZK60 Mg alloy treated by MAO showed that a ceramic coating formed on the sample surface. The average thickness of this layer was about 18μm. The ceramic layer comprised two layers, an outer looser layer and inner denser layer, the thickness of the former was 90% compared with that of the whole coating. The pores and cracks were observed on the outer layer. After MAO then HCPEB treatments, the sample surface became rougher with a melted layer of 3-4μm. While with the converse process, the sample surface was formed a similar ceramic coating as the sample after MAO treatment. The model for the modified layer with HCPEB then MAO treatments was established. The potentiodynamic polarization curves in 3.5% NaCl solution indicated that the corrosion resistance of alloys treated with MAO and/or HCPEB treatment were improved significantly. Especially that, the sample modified by HCPEB then MAO exhibited better corrosion resistance than any other samples and the corrosion current density decreased 3 orders, from 311μA/cm2 to 0.2μA/cm2. The frictional wear test was showed that the friction coefficients and wear rates of all treated samples were decreased. The wear rate of alloy treated by MAO then HCPEB decreased 80% compared with that of initial sample. The result of the complex treatment with MAO then HCPEB illustrated that the superfast fused process decreased the porosity of ceramic layer similar as a plugging agent.(3) HCBEB bombardment induces hypereutectic Al-Si alloys surface rapid melting and solidification. As a result, grains of remelted layer have been significantly refined, content of Si in a(Al) solid solutions was improved and Si element distribution in the alloys intended to be homogenous.The typical surface morphology-crater and a few crack are observed on the surface layer after the bombardment of HCPEB. It is confirmed that temperature rises faster at a sublayer instead of on the top surface. Such a special sub-layer heating and melting mode causes eruptions of the sub-layer liquid through the outer surface and produces the typical surface crater morphology and this process can purify the matrix. The micro-cracks are only on the top surface by cross-section SEM analysis and the mechanical performances of alloys have been little influenced.The friction coefficient decreases and wear resistance was improved of the alloys after HCPEB treatment. According to potential-dynamic polarization curves measurement, the treated samples exhibit an improved corrosion resistance in 3.5%NaCl solution compared with the initial samples. In the weight-loss experiment, the corrosion rate of the treated alloys significantly decreased Corrosion resistance in 3.5%NaCl solution of all the modified alloys was improved.更多还原