【作者】 张靓颖；

【导师】 刘胜新； 龙伟民；

【作者基本信息】 郑州大学 ， 材料加工工程， 2012， 硕士

【摘要】 在铜铝的连接方法上,应用最为广泛的是钎焊。钎焊铜铝时,最常用的钎料是锌铝钎料。锌铝钎料在放置的过程中会随时间的延长而发生“脆断”现象,此现象给实际生产和应用带来了极大的不便和经济损失。本文的目的是找出造成锌铝钎料发生“脆断”的原因,从而避免此现象的发生。本文采用金相观察、扫描电子显微镜、能谱分析、硬度测定以及韧度测定等分析手段,研究了ZnAl2和ZnAl15两种钎料在118℃水蒸气环境下、118℃干燥环境下、低温湿润环境下和盐雾环境下的组织演变规律及力学性能变化。研究表明,在118℃水蒸气环境下放置10h, ZnAl2和ZnAl15钎料外围出现了大量的周向及径向裂纹,且ZnAl15钎料裂纹比ZnAl2钎料多。两种钎料均发生晶间腐蚀,氧含量明显高于腐蚀之前,晶界有腐蚀产物堆积。钎料硬度变大,ZnAl2为92.5HV10, ZnAl15为98.6HV10；韧性变差,ZnAl2弯折3次即发生断裂,ZnAl15弯折2次即发生断裂。两种钎料均出现“脆断”现象。118℃干燥环境下放置10h后,ZnAl2和ZnAl15钎料组织变得均匀,晶粒长大。ZnAl15钎料中富锌的α相脱溶分解,生成层片状的组织。力学性能未发生太大变化,硬度上升,ZnAl2由55.6HV10增大到65.7HV10;ZnAl15由64.9HV10增大到77HV10。韧性下降,但未出现“脆断”现象。在低温潮湿环境下放置,时间为4个月时,5℃和—18℃下同一种钎料的组织及力学性能变化不大。随着放置时间的延长,放置时间为12个月时,5℃环境下放置的ZnAl2钎料与—18℃环境下放置的ZnAl2钎料相比,晶间腐蚀更严重,β相的脱溶分解非常明显；硬度增大,韧性降低,力学性能下降。ZnAl15钎料的情况与ZnAl2钎料类似。在中性盐雾环境中放置64h, ZnAl2钎料出现晶间腐蚀,树枝状α相变得粗大,晶界上有腐蚀产物的堆积；硬度值由53.5HV10增大到62.3HV10,韧性变差。综上所述：锌铝钎料发生“脆断”是由晶间腐蚀及相变共同引起的,而水汽是引起晶间腐蚀的主要因素,温度越高,相变越大,盐雾会加速晶间腐蚀及相变的进行。更多还原

【Abstract】 Braze welding is widely applied in the connection of Cu-Al. The Zn-Al solder is the most commonly used to weld Cu-Al. The Zn-Al solder is going to be brittle in the environment with time passing, which makes a lot of economic loss and brings inconvenience in use. The object of this essay is to find out why the Zn-Al solder becomes brittle and avoid it.The microstructure and mechanical properties of Zn-Al solder in 118℃water vapour,118℃dry condition, humid and cool condition and saline-fog environment are investigated through metallographic observation, SEM, EDAX, hardness measurement and toughness test.Many circumferential cracks and radial cracks appear on the periphery of ZnAl2 and ZnAl15 solder when treated by high temperature steam for 10 hours. The crack number of ZnAl15 is much more than that of ZnAl2. Intergranular corrosion was found in ZnAl2 and ZnAl15, the oxygen content of which is increased. The solder became harder. The micro-hardness of ZnA12 is 92.5HV10, which of ZnAl15 is 98.6HV10. The toughness turns bad. Flex the ZnAl2 solder thrice, it broke up. ZnAl15 was worse than ZnAl2. Both ZnAl2 and ZnAl15 became brittle.The microstructure became more homogeneous and the grain size became larger at 118℃dry condition for 10 hours. The aluminium-rich a phase of ZnAl15 solder was decomposed and a lamellar microstructure was found. The mechanical properties did not change much. The hardness of ZnAl2 increased from 55.6HV10 to 65.7HV and from 64.9HV to 77HV, respectively. Both of them were not brittle.The microstructure and mechanical properties of the same Zn-Al solder didn’t change much in 5℃癈and -18℃environment after 4 months. Intergranular corrosion of ZnAl2 at 5℃environment was more serious than that at -18℃environment, when the time was 12 months.Moreover,βphase decomposition was obvious. The mechanical properties of ZnAl2 decreased. It became harder and it’s toughness decreased. The situation of ZnAl15 was similar to ZnAl2.In neutral salt spray, standing time-64 hours, intergranular corrosion was found in ZnAl2. The dendritic a phase became thick and big. There were corrosion products at the grain boundaries. The hardness of ZnAl2 increased from 53.5HV10 to 62.3HV10. The toughness turned bad. Comparing with ZnAl2 which is already brittle, the mechanical properties of ZnAl2 in neutral salt spray was a little better. It did not btittle.The conclusions are as follows:Intergranular corrosion and phase transition cause the solder become brittle. Water vapor is the main cause of intergranular corrosion. Besides, the higher the temperature is, the greater the phase transition. Salt spray accelerates intergranular corrosion and phase transition.更多还原