【作者】 张晓丽；

【导师】 贺定勇； 蒋建敏；

【作者基本信息】 北京工业大学 ， 材料加工工程， 2010， 硕士

【摘要】 LY12铝合金具有高的比强度,将其应用于飞机、汽车、船舶等结构中,可以减轻这些结构的重量,提高它们的综合性能,因而具有广阔的应用前景。但由于加工成形困难和自身熔点低等问题,硬铝合金的连接受到限制。如采用合理的焊接工艺,可以加工结构更复杂、尺寸更大的硬铝合金部件,进一步扩大LY12铝合金的应用范围。本文设计了用于钎焊硬铝合金LY12的低熔点钎料,为实现铝合金在更低的温度下连接提供基础。本文研制了一系列Al-Si-Cu-Ge系钎料,并通过坩埚熔炼和熔剂覆盖保护的熔炼工艺制备钎料合金,利用差热分析、光学金相显微分析、扫描电子显微镜及能谱分析、X射线衍射分析及荧光分析等手段,通过铺展和润湿试验、钎焊接头剪切强度试验等方法,分别对所研制钎料的熔化特征、微观组织、铺展和润湿性能、钎焊接头剪切性能进行了测定和分析。本文研究成果如下:1.与Al-9.6Si-20Cu钎料相比,添加Ge后钎料熔化温度大幅降低,熔化温度区间处在408~486℃之间,钎焊温度为510℃。钎焊温度较低,有利于高强度低熔点铝合金的钎焊。利用感应钎焊的方法,在氩气保护下实现LY12铝合金的钎焊具有良好的效果。2.对铸态钎料组织进行分析发现:随着wt.(Ge)%的增加,钎料熔化温度下降明显,主要是出现Al-Si-Cu-Ge、Al-Si-Ge等低熔点共晶相。并且随着Ge元素的加入,钎料对母材的润湿性和铺展性能提高,润湿角最小为4.5°。但是钎料中存在大量Al2Cu(θ)金属间化合物和Si-Ge先析出相,Ge的加入使钎料中脆性相聚集,导致钎料脆性增加。3.钎料焊接性能良好,焊缝无明显缺陷。焊缝组织形貌与铸态钎料组织差别较小,主要由α-Al,Si-Ge先析出相以及Al2Cu(θ)组成。产生的脆性相对接头性能有不利的影响。所研制钎料中3#钎料钎焊所得搭接接头的剪切强度最高为93.7MPa,约为母材的40%。钎料钎焊接头的断裂位置在钎缝处,为明显的脆性断裂。4.对3#钎料进一步研究,调整其预留间隙为0.2mm,搭接面积为60mm2,焊后接头抗剪强度最高可达到99.7MPa。在3#钎料的基础上,又探索了添加Er后,钎料熔化温度、铺展性能、微观组织的变化,结果表明:钎料熔化温度变化不大;相对于3#钎料,7#钎料铺展性能有所提高,焊后接头强度也有所提高,主要是钎料中Si-Ge相减少,晶粒细化。更多还原

【Abstract】 The high strength aluminum alloy LY12 applicant in the structure of airplane、automobile and watercraft will reduce weight and synthetic properties. These advantages causes wide application. However, the current development and application of aluminum and aluminum alloys are restricted by its processing and low melting point. Applying proper welding technology, components with more complicated structure and larger size can be produced, thus expanding the application of high strength aluminum alloy. In this paper, low-melting filler metals for LY12 aluminum alloy were developed, which can be the foundation of aluminum alloy joining at a lower temperature.In this paper, Al-Si-Cu-Ge filler metals were prepared through crucible melting and flux protecting. Their melting characteristics, metallographic structure, spread abilities, wetting abilities, shear strength of the lap joints of the butt joints were measured through spreading and wetting capacity test, shear test as well as differential thermal analysis, optical microscopic structure inspection, SEM and energy spectrum analysis, X-ray diffraction analysis. The research results are as follows:1. Compared with Al-9.6Si-20Cu filler metal, the solidus and liquids temperatures of the filler metals added with the element Ge reduced a lot. The melting temperatures of the filler metals ranged from 407℃to 486℃, and the brazing temperatures were comparatively low, the highest of which was 510℃. The low temperature was conducive to the brazing with the lower melting point. The high frequency induction brazing equipment with self-designed argon protection device had received good effects, when being used brazing LY12 aluminum alloy.2. A large number of oversize primary precipitated phases of Si-Ge and Al2Cu(θ)in as-cast filler metals were found through the analysis of the metallographic structure of the filler metals. Thus generate several kinds of intermetallic compounds that cause the fragility of the metals increased largely. As the increase of wt.(Ge)%, the melting temperature decreases because of the increase of low melt point eutectic phase. Adding the element Ge, the wet abilities and spread abilities of the filler metals were comparatively good, with the minimum wetting angle of 4.5°.3. The brazing filler metals show good performance and no deficiency, which can be found in brazing seam. There was no difference between the metallographic structure of the joints and the as-cast filler metals. The bases were allα-Al, around which were Si-Ge phase and Al2Cu(θ)brittle phase. These brittle structures showed unfavorable impact on properties of the joints. The lap joint of the 3# filler metal had the highest shear strength, which was 93MPa, up to 40% of the base metal. The fractures of the joints were all brittle fractures which extended along the brittle phase in the joints.4. The brazing joint of filler 3# obtained the maximum strength 99MPa under its optimal process parameters which were 0.2mm width of clearance and 60mm2 of overlap area. On the other hand, the influence of melting temperatures, wetting ability, microstructures, and the fragility is explored when adding Er on the base of 3# filler metal. It is found that the melting temperatures changed not so much; but the wetting ability increased while the shear strength of joint; and the microstructures changed a lot, for example, precipitation Si-Ge phase reduced and the other grain size refined.更多还原