【作者】 吕维玲；

【导师】 郝远；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2010， 博士

【摘要】 通过恒定小电流密度工艺和快速成膜工艺研究了微弧氧化工艺参数对膜层特征参量和性能的影响:膜层的厚度随着氧化时间和加压时间间隔的延长及电流密度的增大而增长,随加压幅度的增大先增大后减小,平均成膜速率反映的是微弧氧化的效率;粗糙度呈增大趋势;表面孔隙率先增大后减小;表面形貌定性的反映了膜层表面的孔隙和熔融物颗粒的尺寸及数目;膜层的主要组成相为Mg₂SiO₄和MgO。膜层的结合力随着氧化时间、电流密度和加压幅度的增大先增大后减小,随加压时间间隔的延长而增大;与基体相比,膜层的耐磨性和耐蚀性均明显增强。通过分析微弧氧化工艺参数、膜层特征参量和膜层性能之间的关系得出AZ91D镁合金微弧氧化膜层制备的调控原则如下:调整电流密度和时间控制膜层厚度;调整工艺参数使得微弧氧化反应尽量减缓来减小粗糙度;调整工艺参数均使其适中或采用较大的电参数或较长的氧化时间可制备表面孔隙率较大的膜层;调整工艺参数使得电参数较小的同时氧化时间较长可制备结合力较高的膜层;调整工艺参数均使其适中或采用较大的电参数或较长的氧化时间制备耐蚀性和耐磨性较佳的膜层。通过恒定电压工艺验证微弧氧化膜层制备调控原则,结果表明:膜层的特征参量和性能均与微弧氧化膜层制备的调控原则相吻合。这充分说明了微弧氧化膜层的调控原则准确,且符合微弧氧化的机理,具有普适性。膜层厚度用涡流测厚法表征快速,截面法表征精确;粗糙度用表面轮廓仪表征快速,要求试样平行度好;表面形貌在SEM上获得;用通用图像分析软件在清晰的截面和表面照片上可表征厚度、表面孔隙率及孔径;用分段制样法在假设孔隙为圆柱形通孔和半球体孔的情况下可估算体积孔隙率。划痕法表征结合力的条件:加载速度50N/m,终止载荷为20N,采用摩擦力和声信号双重加载模式,并与划痕形貌相结合进行判断,测试时如果终止载荷20N,没有测出其结合力,将终止载荷调整为30N;热震法表征结合强度时,根据具体的使用环境确定保温温度和保温时间。硬度表征采用在膜层表面涂覆颜色后测量显微维氏硬度,测试条件:保压时间5 s,膜层表面载荷至少为1000 g,而膜层致密层载荷至少为25 g,中间层和疏松层载荷为不大于10 g。更多还原

【Abstract】 The effects of MAO technical parameters on characteristic parameters and properties of MAO coatings were researched by invariable small current density process and rapid forming MAO coatings process: thickness increased with the increase of oxidation time, current density and interval time of enhancive voltage, but it first increased and then decreased with the increase of increase extent of voltage, average growth rate was the efficiency of MAO; roughness had a increased trend; surface porosity first increasedand then decreased; surface morphology reflected qualitatively the size and quantity of surface pores and granules of coating;MAO coating was mainly composed of Mg₂SiO₄ and MgO. Adhesion stress first increased and then decreased with the increase of oxidation time, current density and increase extent of voltage, but it increased with the increase of interval time of enhancive voltage; compared with the matrix, corrosion resistance and wear resistance were obviously increased.Control principles of AZ91D magnesium alloys prepared by MAO were gained by analyzed the relationship between technical parameters of MAO, characteristic parameters and properties of MAO coatings: adjusting the current density and time to control the thickness; adjusting the technical parameters of the reaction as mitigation to reduce the roughness; surface porosity can be controlled in a larger extent by adjusted the technical parameters wer moderate or the greater electrical parameters or the longer oxidation time; adjustting the smaller electrical parameters or the longer oxidation time to increase the adhesion stress; adjusting the technical parameters wer moderate or the greater electrical parameters or the longer oxidation time to enhance the corrosion resistance and improve the wear resistance.Control principles of AZ91D magnesium alloys prepared by MAO were verified by invariable voltage process: Characteristic parameters and properties of MAO coatings under the invariable voltage craftwork agrees well with control principles prepared by MAO,indicating that control principles is accurate, consistent with the mechanism of MAO and has universality.Thickness of MAO coating was characterized rapidly by eddy current thickness measurement, and accurate characterization by cross-section method; roughness was characterized rapidly by surface profiling instrument, but it demanded sample had a good parallel; surface morphology gained by SEM; the thickness, surface porosity and pore size were characterized with general image analysis software on the clear surface and section morphologies photos; the volumetric porosities were estimation calculated by Sub-sampling methods with the assumption that pores were cylindrical and hemisphere. The test conditions of adhesion stress characterized by scratch test: Loading speed was 50 N/m, End loading was 20 N, with a double loading mode, to judge adhesion stress combined with the sscratch morphology, the end loading adjusted to 30N if did not detect the adhesion stress when the end loading was 20 N in the test; to determine the holding temperature and holding time according to the concretely environment as the adhesion stress characterized by thermal shock method. The test conditions of hardness characterized by micro Vickers hardness after the suface of coating painted: holding time was 5 s, the surface coating applied load at least 1000 g, while the density layer applied load was at least 25 g, the middle layer and porous layer applied load not more than 10 g.更多还原