镁合金低熔点钎剂的研制

发布时间：2018-06-23 04:29

本文选题：镁合金 + Sn-9Zn钎料　；参考：《山东大学》2015年硕士论文

【摘要】：镁合金具有高的比强度、比刚度和优良的减震性、导热性、电磁屏蔽性及可回收性等优点,在汽车交通、航空航天等领域日益展现其优越的使用价值和广阔的应用前景。在镁合金日益增加的应用中,无论是镁合金结构件之间,还是镁合金结构件与其他材料构件之间都离不开连接。钎焊具有加热温度低、对母材组织和性能的影响小、焊后应力和变形小、工艺过程简单等特点。镁合金钎焊可以避免熔化焊中常出现的镁的氧化以及气孔、裂纹等缺陷,逐渐成为镁合金材料连接方法的首选之一。去除氧化膜作为钎焊过程中关键步骤,主要方法有钎剂去膜、气体介质去膜、机械及物理去膜。钎剂去膜作为目前应用最广泛有效的去膜方法,在液态钎料和母材润湿的过程中起主要作用。然而镁合金钎剂的研究,特别是软钎剂的研究、钎剂去除镁合金氧化膜机理的研究等均刚刚开始,这些都制约了钎焊技术在镁合金连接中的推广和应用。本课题从低熔点镁合金钎剂入手,通过对镁合金表面氧化膜成分分析、软钎剂组元的选定、软钎剂配方的设计和优化、钎焊接头组织和性能的研究、钎剂性能评价等一系列问题的研究,试图找到一种适合镁合金软钎焊的钎剂配方。论文首先分析了AZ31B镁合金表面氧化膜的组成。XRD和XPS数据表明,AZ31B镁合金表面氧化膜中含有A1203以及MgO。对Sn-9Zn钎料进行铺展试验的结果表明,当有机酸A+(5～10wt.%) NH4CI或者(1～10wt%) ZnCl2时,钎料铺展面积较大；钎剂可以以有机酸A为基体组元,ZnCl2和NH4Cl作为活性剂或者去膜剂少量加入。通过有限制的均匀设计试验方法对钎剂配方进行优化设计,得到x1(NH4Cl)、x2 (ZnCl2)与铺展面积S之间的显著可信的回归方程表达式为S=84.643-734.588x1+819.382x2-1408.509X1X2+3092.476x12-5144.404x22。经过对方程求最优解知,当ZnC12与有机酸A质量比为8：92时为最佳钎剂配方,此时钎料的铺展面积最大达到117.52mm2。对钎焊接头组织的微观形态、组织结构和性能研究表明,在靠近钎缝侧会有一层亮白的界面层,该处可能为Mg2Sn金属间化合物相与固溶了少量铝、锌的β-Sn固溶体相。钎缝中心区域主要是富锌相和β-Sn相组成,其中有一部分细长的针状富锌相由于耐腐蚀性差,发生选择性腐蚀后脱落而显示黑色的沟槽。对钎焊接头内各部分的显微硬度测试发现,由于亮白色的界面区含金属间化合物硬质相,硬度较钎缝有所提高,平均为130HV左右。分别对钎剂进行分类和性能评价。结果表明,所研制的钎剂编号为FS222B,不挥发物含量高达86.4%,腐蚀率平均值为0.0133g/cm2,说明该钎剂腐蚀性很强,焊后需要进行彻底的清洗。
[Abstract]:Magnesium alloys have the advantages of high specific strength, specific stiffness, excellent shock absorption, thermal conductivity, electromagnetic shielding and recoverability, etc., which are increasingly showing their superior use value and broad application prospects in automotive traffic, aerospace and other fields. In the increasing application of magnesium alloy, no matter between magnesium alloy structure or magnesium alloy structure and other material components can not be separated from the connection. Brazing is characterized by low heating temperature, little influence on microstructure and properties of base metal, small stress and deformation after welding, and simple process. Magnesium alloy brazing can avoid the defects such as oxidation of magnesium, porosity, crack and so on, which becomes one of the preferred bonding methods for magnesium alloys. The removal of oxide film is a key step in brazing process. The main methods are flux defilm, gas medium film removal, mechanical and physical film removal. As the most widely used and effective method of film removal, flux film removal plays an important role in the wetting process of liquid solder and base metal. However, the research of magnesium alloy flux, especially the study of soft flux, and the mechanism of flux removing magnesium alloy oxide film are just beginning, which restrict the application of brazing technology in magnesium alloy connection. Starting with the flux of low melting point magnesium alloy, the composition of oxide film on magnesium alloy surface, the selection of soft flux component, the design and optimization of soft flux formula, the microstructure and properties of brazing joint are studied. A series of problems such as flux performance evaluation are studied to find a flux formula suitable for soft brazing of magnesium alloy. The composition of oxidation film on AZ31B magnesium alloy was analyzed. XRD and XPS data showed that A1203 and MgO were found in the oxide film of AZ31B magnesium alloy. The results of spreading test on Sn-9Zn solder show that when organic acid A (5 ~ 10wt.%) NH _ 4CI or (1 ~ 10 wt ~%) ZnCl _ 2 is used, the spreading area of the filler metal is larger, and the flux can be added with organic acid A as the base components, ZnCl _ 2 and NH _ 4Cl as active agents or defilm remover in a small amount. The formula of flux was optimized by a limited uniform design test method, and the significant and credible regression equation between x 1 (NH 4Cl) x 2 (ZnCl 2) and spreading area S was obtained as follows: s 84.643-734.588x 1 819.382x 2-1408.509x 2 3092.476x 12-5144.404x22. By finding the best solution to the equation, when the mass ratio of ZnC12 to organic acid A is 8:92, the best flux formulation is obtained, and the maximum spreading area of the solder is 117.52 mm ~ 2 mm ~ (2). The microstructure, microstructure and properties of brazed joints show that there will be a bright white interfacial layer near the brazing seam side, where there may be Mg2Sn intermetallic compound phase and 尾 -Sn solid solution phase with a small amount of aluminum and zinc solution. Zinc rich phase and 尾 -Sn phase are the main components in the center of brazing seam. Some of the thin needle-rich zinc-rich phases show black grooves due to their poor corrosion resistance and selective corrosion. The microhardness test of each part of brazed joint shows that the hardness is higher than that of brazing joint due to the intermetallic hard phase in the bright white interfacial area, and the average hardness is about 130 HV. The fluxes were classified and evaluated. The results show that the flux number is FS222B, the content of non-volatile matter is up to 86.4 and the average corrosion rate is 0.0133g / cm ~ 2, which indicates that the flux is very corrosive and needs to be cleaned thoroughly after welding.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG425.1

【参考文献】