利用熔体余热在镁合金铸件表面原位生成陶瓷基复合涂层的研究

Due to limited fossil fuel stores and environmental problems associated with fuel emission products, there is a push in the industry to decrease fuel consumption, especially in the automotive and aircraft industries. Under this background, magnesium and magnesium alloy have got more and more attention. Indeed, magnesium alloys exhibit an attractive combination of low density and high strength/weight ratio, high thermal conductivity, good electromagnetic features and be easily recycled. These properties make it an excellent candidates for lightweight engineering applications. However, the poor corrosion resistance of magnesium and its alloys has limited their widespread use in many applications. .Most of current anti-corrosion measures on magnsium have been used as post-processing for shaped magnsium alloy, which makes the processing more complex and more expensive. This proposal will give an idea to develop an ceramic-based composite coating in situ on magnesium casting during the processing. It makes the fused magnsium alloy as the resource of heat for pyrolysis of polymeric pre-coating. The microstructure transformation of ceramic-based composite coating before and after pyrolysis will be analyzed by FTIR、SEM、TEM and X-ray diffraction. In this proposal, we will study the pyrolysis mechanism of the polymeric pre-coating under complex and intractable condition, analyze the interaction and variation of the interfacial microstructure among ingredients, build an effective connection among ingredients, casting processing and property of the coating. Results of this study will give an possibility and theoretical basis for the development of a new surface modification method on magnium alloy to improve its corrosion resistance.

镁合金耐蚀性差的缺点已成为制约其进一步广泛应用的瓶颈问题，现有的防护手段多是对已成型产品进行后期处理，增加了镁合金的生产处理步骤及成本。本项目拟以先驱体转化法结合消失模铸造技术，利用镁合金熔体余热对消失模泡沫模样上的预陶瓷涂层进行热裂解，在镁合金铸件表面原位生成陶瓷基复合涂层。本项目拟通过数值模拟和浇铸实验，综合利用FTIR、SEM、TEM、X射线衍射等技术对先驱体涂层在热裂解前后的组织结构变化进行分析，系统研究先驱体涂层在与热源直接接触，并且多个影响因素难控的复杂条件下的热裂解机理。深入探讨复合涂层中各组成部分的相互影响和界面结构在热裂解过程中的演变规律，再结合最终所得涂层性能的分析测试，建立涂层成分、浇铸工艺和涂层性能之间的有效联系，为研制出适合镁合金表面改性新技术提供材料和工艺的可能性及理论依据。

硅基陶瓷类涂层是提高金属耐蚀性的很有效手段之一。目前，制备该类涂层主要集中在物理（化学）气相沉积或者溶胶-凝胶方法上，而这些方法在涂层质量控制或者制备条件上均难以应用在镁合金上，而先驱体转化法近年来呈现的一种低成本且简单的制备硅基类陶瓷涂层的方法，本项目的目就是采用先驱体转化法在镁合金上面制备耐蚀性SiOx涂层。. 本项目对两种先驱体DVB(二乙烯基苯)/PSO(聚硅氧烷)及PHPS(全氢硅氮烷)在不同的温度及气氛下的热裂解行为进行了系统研究，采用FTIR、SEM及XRD等多种表征手段研究涂层的微观结构，并对涂层的耐蚀性进行了评估。. 本项目的主要研究结果如下：. (1). 真空并不有利于镀层保持其完整性，真空条件下，先驱体的支链小分子更易于分解、挥发，降低了其陶瓷化率；. (2). 基体的抗氧化性能严重影响镀层的结构及其与基体的结合力。在空气气氛中，镁元素会参与到涂层的氧化过程中，并致使镀层与基体的化学键结合遭到破坏；而增加加温速度则可以抑制镁基体的氧化过程，从而获得致密完整的涂层。. (3). DVB/PSO在添加催化剂的情况下能在较低温度交联成透明坚硬的固体薄膜，但如果热裂解程度不够（温度不够高），涂层未能完全转变为氧化硅，则在严苛的腐蚀条件下，涂层会逐步失效，难以得到长期有效的防护，因此，该体系的使用至少需要在700°C以上的温度进行热裂解处理。