表面活化辅助7075铝合金钎焊工艺及机理研究

发布时间：2018-07-06 07:20

本文选题：表面活化处理 + 接触反应钎焊　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：铝合金因具有轻质、高比强度、优良的导热导电性、耐腐蚀性及良好的材料加工能力而广泛应用于航空航天领域。但铝合金表面氧化膜会对铝合金的钎焊过程产生不利的影响,导致钎焊效果较差。本论文结合离子轰击去膜及表面改性和磁控溅射镀Cu层,提出表面活化辅助铝合金钎焊连接方法并实现铝合金的钎焊连接,研究了表面活化处理对铝合金基体表面氧化膜及表面状态的影响,对比分析表面活化处理对钎焊接头界面组织及剪切强度的影响,系统研究了钎焊温度和镀层厚度对接头界面组织和力学性能的影响,综合分析接头界面组织、晶粒形貌尺寸与接头力学性能三者之间的相互关系,对钎焊接头进行固溶+T6峰时效的焊后热处理,探究焊后热处理对钎焊接头界面组织、晶粒形貌尺寸和力学性能的影响。离子轰击可有效地消除铝合金基体表面的氧化膜,并改变基体表面组织及应力分布状态,另外镀Cu层与离子轰击后的基体表面之间紧密结合,且结合界面存在着原子扩散过渡层,最终实现了铝合金的基体表面活化。通过对比试验发现,表面活化处理有效地消除了钎焊接头中残余氧化膜对原子扩散及接头组织的不利影响,促进了钎焊接头的形成和接头中的原子扩散,并改善钎焊接头界面组织,提高了钎焊接头的力学性能,最终获得了冶金结合良好且无缺陷的钎焊接头。当钎焊温度为600°C时,镀Cu层厚度分别为20μm和5μm的表面活化辅助钎焊接头均达到最大剪切强度42.2MPa和50.7MPa,但钎焊温度升高到610°C时,钎焊接头中因存在异常粗大的晶粒而导致接头剪切强度急剧下降。因此认为钎焊温度的提高一方面增大接头成分均匀化程度,有利于接头力学性能的提高;另一方面则会导致接头晶粒逐渐长大粗化,不利于接头的力学性能。在钎焊过程中,AlCu共晶液相的晶界渗透现象导致晶界的结合强度减弱,基体晶粒沿晶界剥落进入共晶液相中并逐渐溶解。焊后热处理进一步显著降低了钎缝中的金属间化合物,提高了接头成分均匀化程度,而且钎焊接头发生晶粒的再结晶现象,接头晶粒形貌尺寸发生明显变化,由原始的条形纤维态晶粒转变为块状的等轴晶粒并长大,接头晶粒相对细化,故使得钎焊接头的力学性能进一步提高,接头剪切强度的增幅最高可达47%,并且接头的断裂方式由脆性断裂转变为韧性断裂。
[Abstract]:Aluminum alloy is widely used in aerospace field because of its light weight, high specific strength, excellent thermal conductivity, corrosion resistance and good material processing ability. However, the oxide film on the surface of aluminum alloy will adversely affect the brazing process of aluminum alloy, resulting in poor brazing effect. Combined with ion bombardment, surface modification and magnetron sputtering of Cu layer, the brazing bonding method of surface activated aluminum alloy was proposed and the brazing connection of aluminum alloy was realized. The effect of surface activation treatment on oxide film and surface state of aluminum alloy substrate was studied. The effect of surface activation treatment on the interface structure and shear strength of brazed joint was compared and analyzed. The effects of brazing temperature and coating thickness on the interfacial microstructure and mechanical properties of the joints were systematically studied. The effect of post-weld heat treatment on interface microstructure, grain morphology and mechanical properties of brazed joints was investigated. Ion bombardment can effectively eliminate the oxide film on the surface of aluminum alloy, and change the structure and stress distribution of the substrate. In addition, the Cu coating is tightly bonded to the substrate surface after ion bombardment. There is an atomic diffusion transition layer at the interface, and finally the substrate surface activation of aluminum alloy is realized. It is found that the surface activation treatment can effectively eliminate the negative effects of residual oxide film on the atomic diffusion and the microstructure of brazed joints, and promote the formation of brazed joints and the diffusion of atoms in the joints. The interface structure of brazed joints was improved and the mechanical properties of brazed joints were improved. Finally, the brazed joints with good metallurgical bonding and no defects were obtained. When the brazing temperature is 600 掳C, the surface activated brazing joints with Cu coating thickness of 20 渭 m and 5 渭 m respectively reach the maximum shear strength of 42.2 MPA and 50.7 MPA, but the brazing temperature increases to 610 掳C. The shearing strength of brazed joints decreases sharply due to the existence of coarse grains. Therefore, it is considered that the increase of brazing temperature is beneficial to the improvement of the mechanical properties of the joints by increasing the homogenization degree of the joint composition, on the other hand, it will lead to the grain growth and coarsening of the joints, which is not conducive to the mechanical properties of the joints. During the brazing process, the grain boundary permeability of AlCu eutectic liquid phase decreases and the matrix grains flake along the grain boundary into eutectic liquid phase and dissolve gradually. The intermetallic compound in brazing seam was significantly reduced by post-welding heat treatment, and the homogenization degree of joint composition was increased, and the recrystallization of brazing joint occurred, and the morphology and size of joint grain changed obviously. The mechanical properties of brazed joints are further improved because of the transformation from the original stripe fibrous grains to the block equiaxed grains and the relatively fine grain size of the joints. The maximum increase of shear strength of the joint is 47 and the fracture mode of the joint is changed from brittle fracture to ductile fracture.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.14

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