黄河科技学院材料成型毕业论文 - 图文(2)

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2.3.3 扩渗过程 ·································································································· 13 2.4 组织分析和性能测试 ·························································································· 14

2.4.1 组织分析 ·································································································· 14 2.4.2 显微硬度测试 ·························································································· 15 2.4.3 失重腐蚀速率测定 ·················································································· 15 2.4.4 电化学腐蚀性能测试 ·············································································· 16

3 结果与讨论 ····················································································································· 17

3.1 AZ91D镁合金渗层的表面形貌 ········································································· 17

3.1.1 原AZ91镁合金试样表面形貌 ······························································· 17 3.1.2 渗铝后的AZ91D镁合金表面形貌 ························································ 18 3.1.3 AZ91D镁合金渗A1-Zn层的表面形貌 ················································· 19 3.2 镁合金表面热扩散机理的研究 ········································································· 21

3.2.1 扩渗层形成与扩渗机制 ·········································································· 21 3.2.2 渗层形成的主要影响因素 ······································································ 24 3.3 试样硬度测试分析 ······························································································ 26 3.4 腐蚀性能测试 ····································································································· 28

3.4.1 浸液腐蚀 ·································································································· 28 3.4.2 电极腐蚀 ·································································································· 29 3.5 热扩渗层提高镁合金耐蚀性能的分析 ····························································· 32 4 结论 ······························································································································· 34 致谢 ····································································································································· 35 参考文献 ····························································································································· 36

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1 绪 论

1.1 镁及镁合金的历史

早在1808年，英国化学家Sir Humphrey.Davy就制备出少量含有杂质的镁[1]，从此，历史掀起新的一页。世界各国的科学家们都在努力寻找提炼镁的方法以及解决镁应用的问题。然而由于技术水平以及其它方面的影响，镁的应用一直受到限制。当今的世界面临着能源的危机，环境的严重污染，降低能源消耗、提高能源利用率、减少环境污染以及节约地球有限资源是当今人们所面临的一个十分重要而紧迫的问题。例如，汽车生产厂家都在以减轻汽车的自重，从而降低能耗、减少污染、提高效率这一重要措施来提高自身的竞争力。有关资料显示：汽车自重每减轻100kg，油耗可减少0.7L/km[2]；汽车自重每减轻10%，燃油的效率可提高5.5%[3]。由此，镁合金的研究与应用又被提上日程，世界各大汽车公司已经将镁合金制造汽车的零部件作为重要的发展方向[4-8]。

镁是金属结构材料中最轻的元素，它的密度为 14 g/cm-3，为铝的2/3，钢的1/4[9]，甚至低于某些 工程塑料的，具有高的比强度、比刚度、减振性、导热性、可切削加工性和可回收性，因而被称为21世纪的“绿色”工程材料。镁合金的比强度不仅高于某些高强度钢的，甚至还高于一些铝合金的；它还有良好的导电、导热和电磁屏蔽性能。所以在汽车、航空和电子工业等方面正得到日益广泛的应用 [10-13] 。镁合金具有比强度高、切削加工性优良、导热性和减振性好以及易于回收利用等特点，被誉为21世纪的绿色金属材料。

镁在地球上储藏量丰富(约占地壳质量的 2.7 …… 此处隐藏：2304字，全部文档内容请下载后查看。喜欢就下载吧 ……