【作者】 张玉明；

【导师】 刘英才；

【作者基本信息】 中国海洋大学 ， 材料物理与化学， 2009， 硕士

【摘要】 铜具有良好的导电、导热和耐腐蚀性能,在制冷行业中起着重要作用,但随着近年来铜价的攀升和铜资源的短缺,寻找铜的替代材料成为一种迫切需求。铝的密度小,具有优良的导电和导热性能,资源较丰富,可以成为铜的很好的替代材料。但铜管在一些制冷管路构件中仍是不可替代的,这就带来了铜铝管的连接问题。由于铜铝属于异种金属,焊接过程中易形成脆性相,影响接头性能。因此,焊接问题成为阻碍铜铝管应用的一个很大问题。青岛海青机械厂与中国海洋大学共同研发的插接式薄壁铜铝管电阻压焊技术,采用多种创新技术,很好的解决了薄壁铜铝管焊接问题。本文采用SEM、TEM、金相显微镜等仪器设备对此项技术焊接的铜铝连接管的界面组织及界面特征进行了研究,目的是了解铜铝焊接界面的微观结构及其产生原因,分析微观结构对性能可能存在的影响,希望找出铜铝连接管性能与焊接工艺的联系,从而优化铜铝连接管焊接的工艺,提高电阻压焊焊接接头的质量。同时对铜铝连接管进行了中性盐雾腐蚀试验,研究了铜铝连接管的腐蚀状况,从而得出铜铝连接管在海洋大气下的耐腐蚀能力。研究结果表明:1、铜铝连接管界面位于靠近外表面焊缝5mm区域范围内结合强度高,不容易撕裂;而在外表面焊缝5mm区域范围之外的一段铜铝管连接处,界面过渡层较宽,结合强度不高,容易撕裂,而且还存在气孔等缺陷。铜铝两侧发生了原子的互扩散,且铜原子向铝侧扩散的深度比铝原子向铜侧扩散的深度要大。铜铝连接管较窄界面主要由（按从铜层到铝层的顺序）铝在铜中的固溶体、CuAl薄层、CuAl₂柱状晶层和铜在铝中的固溶体构成,较宽界面主要由铝在铜中的固溶体、CuAl薄层、CuAl₂柱状晶层、α相与CuAl₂共晶组织和铜在铝中的固溶体构成。2、电阻压焊铜铝管界面形貌的形成可能与温度梯度与成分过冷两者的作用有关; CuAl₂相、CuAl相及共晶组织（α+θ）的生成与包晶反应和共晶反应有关系;分析得出柱状晶与共晶的细化可能与施加的焊接工艺有关,细化的柱状晶对接头的强度有提高作用,但厚度不可太大。共晶组织脆性大,要尽量避免其生成,所以应调整工艺参数以减少共晶组织的产生,从而优化接头质量。3、中性盐雾试验表明在海洋性大气环境下,铝管表面发生点蚀,铜管表面产生绿色和白色腐蚀产物,接头焊缝处产生白色腐蚀产物且铝腐蚀严重,甚至产生粉化现象。能谱测试结果表明腐蚀产物可能含有CuCl₂·3Cu（OH）₂,CuCl₂·3Cu（OH）₂和Al（OH）₃构成的复合膜及Al（OH）₃（三羟铝石）和Na₂O·xAl₂O₃的混合物。更多还原

【Abstract】 Copper plays important roles in refrigeration industry because of its good heat conduction, good conductivity and higher corrosion resistance. However, in recent years , it has been an urgent demand to find copper substitute material owing to the price rising of copper and lack of copper resources. Aluminum ,with low density ,high heat conductivity and good electrical conductivity, can become an ideal replacement material of copper. However, copper cannot be replaced in some pipelines and how to join Cu tubes with Al tubes is to be solved. The Cu-Al welding belongs to dissimilar metal welding and it would produce brittle compounds, which affect the performance of Cu-Al joint. Therefore, the welding problem would hinder the application of Cu/Al tubes.The electric resistance pressure welding technique developed by both Qingdao Haiqing Machinery General Factory and Ocean University of China involves many items of innovative technology and solves the welding problem of thin-wall Cu/Al Tube. In this paper, the interfacial microstructure and characteristics of Cu/Al tubes welded by the electric resistance pressure welding are studied by SEM, TEM and other instruments. The objective is to know the interfacial microstructure and its formation cause, to analyze the possible influences of microstructure on the performance and find out the relation between the performance and the welding technology, and consequently to optimize the welding process and improve the quality of Cu-Al joint. In addition, neutral salt spray test is carried on to study the corrosion resistance of Cu/Al tubes. The results show that:1、The interfacial bonding strength of Cu-Al joint in 5mm range near the welding seam of outer surface is high and the joint is hard to tear, but the interfacial bonding strength out of the range is low and the joint is easy to tear with pore and other defects. A certain interdiffusion of aluminum and copper takes place in the welding interface of the Cu/Al tubes and the diffusion from Cu side into Al side is deeper than the opposite direction. The narrow interface consists of Al solid solution in Cu, CuAl thin layer, CuAl₂ columnar crystal layer and Cu solid solution in Al （from Cu side to Al side）. The wide interface consists of Al solid solution in Cu, CuAl thin layer, CuAl₂ columnar crystal layer,α-Al/CuAl₂ eutectic layer and Cu solid solution in Al （from Cu side to Al side）.2、Formation of the interfacial morphology may be related to the influence of temperature gradient and composition undercooling and formation of CuAl₂, CuAl phase andα-Al/CuAl₂ eutectic structure may be related to peritectic reaction and eutectic reaction. The welding technology is possible relevant to the grain refinement of the columnar crystals and the eutectic and refined columnar crystals can improve the joint strength with a thinner layer. Formation of the eutectic structure should be avoided because of its great brittleness and process parameters should be improved to decrease the eutectic formation and optimize the quality of Cu-Al joint.3、The neutral salt spray test indicates that, under marine atmospheric environment, pitting occurred on the aluminum tube surface and green and white corrosion products appeared on the copper surface. White corrosion products appeared in the welding seam and the Al side of the welding seam suffered from serious corrosion and even presented powdering phenomenon. The results of EDS indicates that the corrosion products may contain CuCl₂·3Cu（OH）₂, the composite membrane with CuCl₂·3Cu（OH）₂ and Al（OH）₃ and the mixture of Al（OH）₃ and Na₂O·xAl₂O₃.更多还原