AZ31B镁合金与3A21铝合金的钎焊工艺及机理研究

发布时间：2018-02-01 06:06

  本文关键词： 镁合金 铝合金 Sn-Zn系钎料 异种合金钎焊 动力学　出处：《哈尔滨工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：镁合金作为最轻、最经济的金属结构材料具有比强度和比刚度高、减震吸冲性能强等优点,被誉为新世纪的绿色工程材料,尤其是与铝合金形成的复合结构,不仅能够进一步减轻构件重量,又能同时发挥各自的优点。但镁合金和铝合金在焊接过程中会不可避免地产生大量Mg-Al系金属间化合物,从而严重影响接头性能。本文采用Sn-Zn系钎料对AZ31B/3A21接头进行超声辅助低温钎焊。针对异种材料钎焊过程中出现的界面反应不对称进行分析,结合数值模拟计算和动力学数学模型的建立,指导工艺试验并得到最佳工艺参数,分析了钎料成分、工艺参数(钎焊温度、保温时间)对钎焊接头组织及性能的影响机理。Sn-Zn钎料钎焊AZ31B/3A21异种合金接头可有效阻隔Mg合金与Al合金反应生成有害金属间化合物,能够实现高质量可靠连接。采用Sn-xZn钎料钎焊AZ31B/3A21异种金属所得的接头断裂位置与钎料成分有关。Sn-3Zn、Sn-9Zn、Sn-30Zn三种钎焊接头断裂在AZ31B镁合金母材与钎料层的反应界面Mg2Sn薄层处,其中Sn-30Zn钎焊接头的平均剪切强度最高,为67.3 MPa;Sn-20Zn接头断裂在块体Mg2Sn富集区域;在Sn-40Zn接头中在镁合金母材附近大量生成的块状Mg2Sn连结成厚层,为易断裂层;Sn-50Zn接头断裂层为钎料与3A21母材反应界面,该界面生成Mg-Al系金属间化合物,平均剪切强度最低,仅20.7MPa。Sn-30Zn钎料为最适合AZ31B/3A21钎焊的最佳成分配比。分析AZ31B/Sn-30Zn/3A21钎缝接头的微观组织,在Mg合金与钎料的反应界面上存在一层Mg2Sn化合物薄层;钎缝中心区主要是块状Mg2Sn金属间化合物和固溶体Al-Sn-Zn,且其存在形式为局部弥散分布;在钎料与3A21铝合金母材侧存在一层Al-Sn-Zn固溶体过渡层。Al-Sn-Zn固溶体弥散分布于AZ31B/Sn-30Zn/3A21接头中能够有效地降低接头的脆性,钎焊接头性能显著改善。针对AZ31B/Sn-30Zn/3A21接头的Mg2Sn金属间化合物薄层,进行数值模拟计算和元素动力学扩散分析。Mg2Sn薄层厚度与接头剪切强度服从正态分布规律,并计算出Mg2Sn薄层厚度为2μm时剪切强度最大,可达69.7MPa;通过扩散分析计算出任意钎焊温度和保温时间下钎料与镁合金母材反应界面Mg2Sn薄层的理论厚度;在相同的保温时间下,钎焊温度对Sn原子在Mg中的扩散深度影响较大,在相同的钎焊温度下,保温时间对Sn原子在Mg中的扩散深度影响较小,但对不同深度处Sn原子浓度影响较大。不同的钎焊温度以及保温时间对接头的组织性能影响较大。保温时间影响焊缝宽度和Mg2Sn存在形态。钎焊温度主要决定钎缝中Al-Sn-Zn固溶体的数量及分布,以及Mg2Sn的形态和分布。当钎焊温度330℃,保温时间5s时,采用Sn-30Zn钎料,在超声辅助,大气环境下无钎剂钎焊AZ31B/3A21异种金属接头的剪切性能最佳,平均为69.2MPa。
[Abstract]:Magnesium alloy, as the lightest and most economical metal structure material, has the advantages of high specific strength and specific stiffness, strong shock absorption and impact absorption, etc. It is praised as the green engineering material in the new century, especially the composite structure formed with aluminum alloy. It can not only further reduce the weight of components, but also play their respective advantages. But magnesium alloy and aluminum alloy will inevitably produce a large number of Mg-Al intermetallics in the welding process. In this paper, ultrasonic assisted low temperature brazing of AZ31B/3A21 joint was carried out with Sn-Zn filler metal. The interface reaction asymmetry occurred in the process of dissimilar material brazing was carried out. Analysis. Combined with the numerical simulation and the establishment of the dynamic mathematical model, the process test was guided and the optimum process parameters were obtained. The composition of the solder and the process parameters (brazing temperature) were analyzed. Heat preservation time). Effect of Sn-Zn brazing filler metal on microstructure and properties of brazed joints AZ31B/3A21 dissimilar alloy joints can be effectively blocked from reaction between mg alloy and Al alloy to form harmful intermetallic compounds. The joint fracture position obtained by Sn-xZn brazing AZ31B/3A21 dissimilar metals is related to the composition of the solder Sn-3ZnN Sn-9Zn. The fracture of Sn-30Zn brazing joints is located at the reaction interface of AZ31B magnesium alloy base metal and filler metal layer, and the average shear strength of Sn-30Zn brazing joint is the highest. 67.3 MPA; The fracture of Sn-20Zn joint is in the enrichment area of block Mg2Sn. A large number of blocks of Mg2Sn formed near the base metal of magnesium alloy in the Sn-40Zn joint are joined into a thick layer, which is easy to fracture. The fracture layer of Sn-50Zn joint is the interface of brazing metal and 3A21 base metal. The intermetallic compound of Mg-Al system is formed at this interface, and the average shear strength is the lowest. Only 20.7 MPa.Sn-30Zn filler metal is the best component ratio for AZ31B/3A21 brazing. Analysis of AZ31B/Sn-30Zn/3A21 brazing joint. Weave. There is a thin layer of Mg2Sn compound on the interface between mg alloy and solder. The central region of brazing joint is mainly block Mg2Sn intermetallic compound and solid solution Al-Sn-Zn.The existence form is local dispersion distribution. A layer of Al-Sn-Zn solid solution transition layer. Al-Sn-Zn solid solution dispersed in AZ31B/Sn-30Zn/3A21 joints on the side of brazing metal and 3A21 aluminum alloy base metal. It can effectively reduce the brittleness of the joint. The properties of brazed joints were improved significantly. The Mg2Sn intermetallic compound thin layers for AZ31B/Sn-30Zn/3A21 joints were obtained. The thickness of mg _ 2SN thin layer and the shear strength of the joint are normally distributed by numerical simulation and elemental dynamic diffusion analysis. The maximum shear strength is obtained when the thickness of Mg2Sn thin layer is 2 渭 m. 69.7 MPA; The theoretical thickness of Mg2Sn thin layer at arbitrary brazing temperature and holding time was calculated by diffusion analysis. At the same holding time, the effect of brazing temperature on the diffusion depth of Sn atom in mg is greater than that on the diffusion depth of Sn atom in mg at the same brazing temperature. Different brazing temperature and holding time have great influence on the microstructure and properties of the joint. The holding time affects the width of weld and the morphology of Mg2Sn, and the main brazing temperature is the soldering temperature. The quantity and distribution of Al-Sn-Zn solid solution in brazing seam should be determined. When the brazing temperature was 330 鈩，

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