导　　师： 马颖;陈体军

学科专业： 080503

授予学位： 硕士

作　　者： ;

机构地区： 兰州理工大学

摘　　要： 镁合金因其低密度、高比强度和好的机加工性能，是目前在航空和汽车工业领域具有巨大的潜在应用的结构材料。AZ91D镁合金作为一种商用镁合金，在强度、延展性、抗疲劳、抗蠕变、耐蚀耐磨性方面正面临着巨大的挑战。 本文首先研究了触变成形/(thixoforming/(TF/)/)过程中模具温度、坯料加热温度和加热时间对触变成形AZ91D镁合金滑动摩擦磨损性能的影响。结果表明，随着模具温度的升高，合金的磨损率逐渐升高；随着坯料加热温度的升高，合金的磨损率先降低后升高；随着坯料加热时间的增加，合金的磨损率逐渐升高。不同的触变成形工艺参数对AZ91D镁合金的摩擦系数影响不大。 其次，在往复式滑动干摩擦条件下研究触变成形/(thixoforming/(TF/)/)和金属型铸造/(permanent mould casting/(PMC/)/)的AZ91D镁合金的摩擦磨损性能。与PMC相比，TF工艺可以提高AZ91D镁合金的耐磨性。随着滑动频率和载荷的增加，TF和PMC拥有类似的磨损机制的变化，从轻微磨损/(氧化磨损和微切屑磨损/)向严重磨损/(塑性变形磨损和伴有粘着的塑性变形磨损/)转变。磨损机制对摩擦系数的影响比对磨损率的影响大。 第三，采用以Na/_2SiO/_3为主体电解液，对TF镁合金进行微弧氧化处理，研究了电流密度和反应时间对微弧氧化膜生长的影响，对不同反应时间下微弧氧化膜的形貌和硬度进行了讨论，对微弧氧化前后的TF镁合金进行了力学性能的比较。结果表明，随着电流密度的增大，微弧氧化膜生长速率加快，但是电流密度达到一定数值/(5.0A／dm~2/)后，氧化膜生长速度减缓。随着反应时间的延长，微弧氧化膜厚度和硬度增加明显，但是达到一定反应时间/(10min/)后，氧化膜厚度增加缓慢，显微硬度开始下降。微弧氧化处理后，TF镁合金的抗拉强度和抗弯� Magnesium alloys present a great potential as structural materials in the aerospace and automobile industries because of several advantages, such as low densities, high specific strength and good machinability. However, AZ91D alloy, as one of the most common commercial magnesium alloys, is suffering the challenge for meeting the requirements of strength, ductility, fatigue, creep and wear resistance. Firstly, the effects of mould temperature, reheating temperature and reheating duration on sliding wear and friction properties of thixoformed AZ91D alloy were investigated. The results indicated that the wear rate increased gradually with the increasing of the mould temperature and the heating time of the feedstock. The wear rate firstly decreased and then increased with the increasing temperature of the feedstock. The thixoforming parameters had no obvious influence on the friction coefficient. Secondly, the friction and wear properties of thixoformed /(TF/) and permanent mould cast /(PMC/) AZ91D magnesium alloys were investigated under dry reciprocating sliding conditions. The results showed that the wear resistance of the TF alloy was significantly superior to that of the PMC alloy. The wear mechanism of both alloys presented similar tendency to change from mild wear regime /(oxidation wear and//or micro-machine wear/) to severe wear regime /(plastic deformation induced wear or//and severe plastic deformation accompanied by severe adhesive wear/) with reciprocating frequency or load increased. The effect of wear mechanism on the friction coefficient was larger than that of the wear rate. Thirdly, the effects of current density and treatment time on the growth of the micro-arc oxidation /(MAO/) coating on the thixoformed AZ91D magnesium alloy by adopting a electrolytic solution maining including Na/_2SO/_3 were investigated. Surface morphology and hardness of MAO coatings were discussed under different treatment time, and mechanical properties of TF magnesium alloy with or without

关 键 词： 镁合金 触变成形 磨损率 摩擦系数 磨损机制 微弧氧化膜 电流密度 力学性能

领　　域： [金属学及工艺] [一般工业技术] [金属学及工艺] [金属学及工艺] [金属学及工艺] [金属学及工艺] [金属学及工艺]