常压铸造条件下灰铸铁表面合金化的研究

发布时间：2019-02-23 17:12

【摘要】：铸渗工艺因其成本低、生产周期短被常用于铸件表面或局部强化,以改善铸件表面耐磨、耐高温、耐腐蚀等性能。但目前用得较多的是负压铸渗工艺,该工艺由于负压的作用,其排气效果好、不易产生气孔缺陷,也可以不用粘结剂使预制合金层产生强度、不存在粘结剂分解所造成的气孔、渣孔等缺陷。但其需要专用设备且工艺过程复杂、适用的铸件有限,大部分铸件仍是采用常压铸造工艺生产出来的,因此,解决常压铸造条件下的关键技术问题意义重大。常压铸渗工艺必须使用粘结剂才能使铸渗前的预制合金层产生强度,粘结剂的加入会导致气孔、渣孔形成,因此,如何优化粘结剂,在保证强度的前提下,降低气孔、渣孔的形成,是我们首先要解决的问题。在此基础上,探索了合金粉末粒度、涂覆层厚度对铸渗效果的影响规律,在常压铸造条件下获得了质量较好的表面铸渗层,并分析铸渗层的组织结构与成分,最后测试了铸渗层的耐磨性。本文首先探讨了四种典型粘结剂(水玻璃、磷酸二氢铝、聚乙烯醇、聚乙烯醇缩丁醛)粘结强度、发气量对灰铸铁表面合金化质量的影响规律。其中水玻璃是四种粘结剂中最适合常压铸渗工艺的粘结剂,添加量为7 wt.%时,粘结强度适宜且发气量小,铸渗层质量良好,渗层厚度为5 mm且组织致密、缺陷少。研究了合金粉末粒度、涂覆层厚度对铸渗层厚度的影响,合金粉末粒度100目,涂覆层厚度4 m m为最优参数。利用金相显微镜、扫描电子显微镜、X-射线衍射分析仪、能谱仪、硬度计等分析测试方法,对铸渗层显微组织结构、成分及硬度进行分析表征,可知铸渗层存在三个明显不同的区域。不同区域的显微组织结构与成分因合金粉末与金属液之间相互的扩散作用而存在明显差异。同时,研究了厚度不同对铸渗层组织结构以及三体磨料磨损性能的影响规律。渗层厚度大,其硬度高,耐磨性好,渗层厚度为5 mm时,表面平均硬度为840 HV,耐磨性为基体的2倍。
[Abstract]:Due to its low cost and short production cycle, casting infiltration process is often used to improve the surface wear resistance, high temperature resistance and corrosion resistance of castings. However, at present, the negative die-casting infiltration process is widely used. Due to the negative pressure, the process has good exhaust effect and is not easy to produce porosity defects. It can also make the prefabricated alloy layer produce strength without binder, and there is no porosity caused by the decomposition of binder. Defects such as slag holes But the special equipment is needed and the process is complicated, the suitable casting is limited, most castings are still produced by the normal pressure casting process, therefore, it is of great significance to solve the key technical problems under the normal pressure casting condition. The bonding agent must be used to produce the strength of the prefabricated alloy layer before casting infiltration, and the addition of binder will lead to the formation of pores and slag holes. Therefore, how to optimize the binder and reduce the porosity under the premise of ensuring the strength, The formation of slag hole is the problem that we must solve first. On this basis, the influence of alloy powder granularity and coating thickness on the cast infiltration effect was explored. The surface cast infiltration layer with good quality was obtained under normal pressure casting conditions, and the microstructure and composition of the cast infiltration layer were analyzed. Finally, the wear resistance of the cast layer was tested. In this paper, the effect of four typical binders (sodium silicate, aluminum dihydrogen phosphate, polyvinyl butyral) on the surface alloying quality of gray cast iron was studied. Water glass is the most suitable binder of four binders for normal die-casting infiltration process. When the amount of binder is 7 wt.%, the bond strength is suitable and the amount of gas is small, the quality of cast infiltrating layer is good, the thickness of infiltrating layer is 5 mm, the structure is compact and the defects are less. The effect of alloy powder particle size and coating thickness on the thickness of cast coating was studied. The optimum parameters were 100 mesh of alloy powder size and 4 mm of coating thickness. By means of metallographic microscope, scanning electron microscope, X-ray diffraction analyzer, energy spectrometer and hardness meter, the microstructure, composition and hardness of the cast infiltrated layer were analyzed and characterized. It can be seen that there are three distinct areas in the cast layer. The microstructure and composition of different regions are obviously different due to the diffusion between alloy powder and liquid metal. At the same time, the influence of different thickness on the microstructure and wear properties of three-body abrasive was studied. When the thickness of the layer is 5 mm, the average surface hardness is 840 HV, and the wear resistance is twice as high as that of the matrix.
【学位授予单位】：西南科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.445

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