稀土镁合金微弧氧化工艺及陶瓷层性能研究

【作者】 郭雪锋；

【导师】 张小联；

【作者基本信息】 赣南师范学院 ， 应用化学， 2010， 硕士

【摘要】 微弧氧化是在Al、Mg、Ti等金属或其合金表面原位生长一层陶瓷膜的技术,该膜与基体结合力强,耐磨损和耐腐蚀性能高,是一种极有发展前景的镁合金表面处理技术。本文采用微弧氧化法在Mg-4Gd-3Ymm-0.5Zr镁合金上制得一层均匀的浅灰色微弧氧化陶瓷层。膜层表面有类似“火山堆”的形貌放电微孔,且经微弧氧化处理过的镁合金耐蚀性能均显著提高。借助SEM观察了膜层表面和截面的形貌,采用能谱仪和XRD分析了膜层的成分和结构。结果表明:镁合金表面形成的较致密氧化膜层可分为三层,靠近基体致密层、多孔的疏松层和中间的过渡层,致密层与基体结合紧密。膜层主要由MgO组成。采用覆层测厚仪、SEM、XRD和电化学工作站等研究了不同工艺参数对Mg-4Gd-3Ymm-0.5Zr镁合金双脉冲微弧氧化处理膜的组织微观结构及耐腐蚀性能的影响。在硅酸盐电解液体系中采用单因素试验,分别研究了Na₂SiO₃、KOH、NaF和甘油在不同浓度下所制备的陶瓷膜的厚度和性能。结果表明:随着Na₂SiO₃、KOH、NaF和甘油浓度的变化,氧化膜的厚度、硬度及耐蚀性都表现出一定程度的变化规律,当Na₂SiO₃、KOH、NaF和甘油的浓度分别为6g/L,2g/L,2g/L和10ml/L时,氧化膜质量最佳。在此溶液体系的基础上,研究了正负向电压、频率、占空比和处理时间对膜层厚度、形貌和性能的影响,试验结果表明:随氧化处理时间的延长,膜层不断增厚,表面微孔数量减小,孔径增大,30min后膜层增长缓慢,粗糙度增大。硬度和耐蚀性先增后减。镁合金微弧氧化成膜效果中,正负电压对氧化膜微观结构及性能影响明显,随着正电压升高,膜层厚度增加,膜层表面微孔数量减少、孔径增大,烧结强度增加,裂纹增大,耐蚀性能先增强后降低,最佳正脉冲电压为450V。随负脉冲电压由0V增加到100V,膜层厚度先增加后小幅减小,再明显增加;膜层表面微孔由小变大再变小,数量变化则相反,负脉冲电压为40V时耐蚀性能最佳。脉冲频率和占空比对微弧氧化膜层厚度影响较小。随着频率的增加,膜层表面微孔数量增加,孔径减小;占空比增加,变化趋势则相反。随频率和占空比的增大,膜层耐蚀性总体趋势均为先增强后降低,最佳频率和占空比分别为600Hz,10%。综合以上各因素,最终确定了一套有关Mg-4Gd-3Ymm-0.5Zr镁合金微弧氧化最佳工艺参数,Na₂SiO₃ 6g/L,KOH 2g/L,NaF 2g/L,甘油10ml/L,正脉冲电压450V,负脉冲电压40V,频率和占空比分别为600Hz,10%,氧化时间30min。更多还原

【Abstract】 Micro-arc oxidation（MAO） is new type of surface treating technology that occurs at Al, Mg, Ti and their alloys, grows oxidation coating on original position of metal surface which can improve wear resistant, corrosion resistant and bonging strength.Therefore, MAO is one of the most prospective method of surface treatment for magnesium alloys. A gray oxidation ceramic film was prepaped by micro-arc oxidation on Mg-4Gd-3Ymm-0.5Zr magnesium alloy in the paper.The coating surface has many pores in the center of volcano-like heap, the microarc oxidation treatment obviously improved the corrosive resistance of Mg alloy. The coating surfaces and cross-sections morphology were characterized by scanning electron microscopy, phase composition and microstructure are studied by XRD and EDS analysis. The results show that there are three layers in oxidation coating, of which inner layer is dense, outer layer is loose and porous, transition layer between compact layer and porous layer in structure. The coating is mainly composed of MgO.The effect of different technical parameters on the microstructure and corrosion resistance of microarc oxidation film of Mg-4Gd-3Ymm-0.5Zr alloy treated by micro-arc technique was investigated by SEM, XRD, coating thickness gauge and electrochemical workstation etc. By one factor experiment in silicate system, thickness and properties of prepared coating of different electrolyte （include Na₂SiO₃, KOH, NaF and glycerol）content were studied.The results indicated coating thickness,hardness and corrosion resistance show certain orderwith electrolyte content. When Na₂SiO₃ 6g/L, KOH 2g/L, NaF2g/L, glycerol 10ml/L, coating quality was optimize.Then on the foundation of silicate system, the effect of positive&negative pulse voltage, pulse frequency, duty cycle, treatment time on oxidation film thickness, morpholog and properties were studied.The experiment results show the coating thickness increased, fewer pores with larger diameters with the prolonging of MAO process, film thickness growth slowly and rougher. Hard- ness and corrosion resistance of the film increases first and thereafter decreases as oxidation time prolonging.The positive&negative pulse voltage greatly influences the microstructure and properties of micro-arc oxidation film in micro-arc oxidation for magnesium alloy. With the increasing of pulse positive, the film thickness increased, fewer pores with larger diameters, more strength sintering and larger crack were found on the film. corrosion resistance of the film increases first and thereafter decreases as positive pulse raise, The optimal positive pulse voltage was 450 V.The film thickness firstly increases and then decreases a little followed by a vital increasing when the negative pulse voltage varies from zero to 100V. The pores diameter of microarc oxidation film surface change from small to large and then small again, whereas the pore amount goes in the opposite way, and the best corrosion resistance of the film was achieved when negative pulse voltage was 40V.The duty cycle and frequency have little effect on growth thickness. More pores with smaller diameters and rougher surface were found on the film when the frequency increased while opposite changes occurred with the increase of duty cycle. Corrosion resistance of the film increases first and thereafter decreases as frequency and duty cycle raise gradually and the optimal conditions were 600Hz and 10%.In this paper through a lot of tests, studies about composition ,positive&negative pulse voltage,frequency, duty cycle and oxidation time on the Mg-4Gd-3Ymm-0.5Zr Mg alloy ceramic coating. The result of experiment shows , best technical parameters is : 6g/L Na₂SiO₃, 2g/L KOH, 2g/L NaF, 10ml/L glycerol, positive&negative pulse voltage 450&40V, frequency 600 Hz, duty cycle 10 %, oxidation time 30min.更多还原