【作者】 赖忠民；

【导师】 薛松柏；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2011， 博士

【摘要】 含镉银钎料的熔点适中,工艺性好,并具有良好的强度、韧性、导电性、导热性和抗腐蚀性而广泛应用于航空航天、家电、电子电器、五金等领域。但镉是有毒元素,世界各国纷纷出台相关法规禁止含镉银钎料的应用。基于材料成本的考虑,环保型无镉、低银钎料的研发成为国内外诸多科研院所和诸多研究者的重要研究课题。本文研究发现,适量地添加Ga/In元素,银钎料的固、液相线温度能显著降低。添加3.0wt.%Ga可使Ag30CuZnSn银钎料的固相线降低约52℃,液相线降低约68℃;添加约2.0wt.%In可使Ag30CuZnSn银钎料的固相线降低约23℃,液相线则可降低约54℃。单独添加合金元素Ga时,Ag30CuZnSn银钎料的润湿铺展面积随着Ga含量的增加而增加,Ga的添加量超过3.0wt.%后,钎料的润湿铺展性能变化较为平缓。而单独添加In时,Ag30CuZnSn银钎料的铺展面积也随着In添加量的增加而显著改善。添加In为1.5 wt.%~2.0wt.%时,Ag30CuZnSn银钎料的润湿铺展性能已经和传统Ag40CuZnCd含镉银钎料相当。添加少量的Ga、In元素,能使Ag30CuZnSn银钎料在紫铜板、黄铜板上的铺展面积分别提高70%、108%、71%、146%。研究发现,Ag30CuZnSn银钎料中单独添加Ga元素时,钎焊接头的抗拉强度随着银钎料中Ga含量的增加逐渐提高,添加Ga为3.0wt.%时,钎焊接头抗拉强度达到最大值;当Ga添加量进一步增加,钎焊接头抗拉强度趋于稳定。含3.0wt.%Ga的Ag30CuZnSn银钎料的抗拉强度(325MPa)比不含Ga的银钎料提高75MPa,实验结果表明,在银钎料中添加Ga能显著改善钎焊接头的力学性能。银钎料中单独添加In元素时,钎焊接头的抗拉强度亦随着银钎料中In含量的增加逐渐提高,添加In含量在1.0wt.%范围内,强度值几乎呈直线增长,In含量在1.0 wt.%~1.5wt.%范围内,钎焊接头的抗拉强度呈现抛物线变化趋势,添加In超过1.5wt.%以后,接头强度的变化趋于平缓。研究发现,在Ag30CuZnSn钎料中添加Ga/In元素可以显著提高其铺展性能和钎焊接头抗拉强度的根源是银钎料显微组织的改善。Ga添加量的增加,基体组织由针状组织逐渐转变为规则的细小晶粒组织。当Ga添加量为3.0wt.%时,针状组织被细小的类似蠕虫状的组织取代,基体组织也变得更加细小、均匀;Ga添加量超过3.0wt.%时,基体组织明显粗化。研究发现,添加合金元素In,同样会使银钎料组织显著改变,但是含In的银钎料显微组织与添加Ga的不同,组织分布也缺乏规律性。分析发现,In添加量为1.0wt.%时,基体中有均匀的初晶晶粒形成,另外伴生有小颗粒状和微细条状的共晶组织出现。当In添加量进一步增加,组织明显变得粗大,银钎料共晶组织之间的差别较为明显。分析分别添加Ga、In合金元素的银钎料的SEM组织,结合能谱分析结果可以看出,Ga/In均能均匀地分布于Ag30CuZnSn银钎料中。Ga的添加量为3.0wt.%时,基体组织主要由α-Ag固溶体和α-Cu固溶体组成,纵横交错的固溶体中主干结构为α-Ag构成,在纵横交错的蠕虫状主干的固溶体之间分布的是α-Cu固溶体,性能优良的Ga-Ag与Ga-Cu固溶体填充于主干结构内部。进一步分析钎缝显微组织和断口形貌,发现钎缝组织致密、规则,银钎料钎焊接头的断裂形式为韧性断裂。研究发现,采用复合添加的方式添加Ga/In元素,可进一步改善Ag30CuZnSn银钎料的性能。在添加3.0wt.%Ga的基础上添加1.0wt.%的In,含Ga银钎料的固相线温度从638℃下降到621℃,固相线温度大约下降了17℃,液相线温度从701℃下降到676℃,液相线温度则大约下降了25℃。In添加量增加致使含Ga银钎料的固液相线温度进一步下降,液相线温度降幅增大,固相线温度降幅减小,而固液相线温度变化区间也逐渐减小。当In的添加量为3.0wt.%时,固、液相线温度降幅趋于稳定。实验结果表明,含Ga-In的银钎料铺展性能均优于单独添加Ga或In元素的银钎料,尤其是Ag30CuZnSn-3.0Ga-2.0In和Ag30CuZnSn-3.0Ga-2.5In银钎料的铺展面积较为规则,实验试样表面光亮、边缘整齐,形状近似为圆形。研究发现,在Ag30CuZnSn银钎料中单独添加Ga、In元素时,可以分别提高银钎料在紫铜、黄铜上的铺展性能。同时添加Ga/In元素时,仍然可显著地提高银钎料在紫铜、黄铜上的铺展性能,但是银钎料在黄铜上的铺展性能更好一些。深入研究结果发现,添加稀土元素Ce以后还可以进一步改善含Ga与In的银钎料在紫铜、黄铜上的铺展性能,但是仍然是银钎料在黄铜上的铺展性能更好,铺展面积更大。研究发现,将Ga元素控制在3.0wt.%,改变In的添加量,发现AgCuZnSn-3Ga-2In钎缝具有最佳的力学性能。同时添加Ga和In时,银钎料的钎焊接头强度高于单独添加Ga或In的银钎料钎焊接头强度。理论分析表明,在添加Ga为3.0wt.%的基础上,添加少量的In,基体组织变得更加均匀,呈现“花纹”状共晶组织。对钎焊接头拉伸断口的分析研究发现,AgCuZnSn-3Ga-2In钎焊接头断口具备明显韧性断裂特征,这是由于Ga/In元素在银钎料基体中分布均匀,没有偏析现象,且AgCuZnSn-xGa-yIn钎料基体组织呈现明显的“骨架”状特征。由于Ag30CuZnSn-Ga-In中含有Sn、Ga和In,形成的部分Ga-Ag固溶体和Ga-Cu固溶体弥散分布在钎缝组织的主干网络,故而可以在降低钎料熔点、提高铺展性能的基础上,抑制了Cu6Sn5金属间化合物的产生,因此可以保证钎焊接头具有较高的强度和塑性。在添加Ga/In元素后显著地降低银钎料固溶体组织的熔点,另由于银钎料基体组织生成的固溶体相的弥散作用,因此能够保证银钎料的强度和塑性。研究发现,向含Ga和In的银钎料中加入微量稀土元素Ce具有进一步改善其性能的作用。研究结果表明,添加稀土Ce具有强化晶界、细化晶粒的作用,在含Ga/In银钎料中添加稀土元素Ce,因为稀土Ce在银钎料中不固溶,在银钎料基体中以稀土相的形式存在,并在晶界产生富集现象,充当“异相形核”质点的作用,因而Ce对银钎料的铺展性能和接头力学性能仍然有进一步的改善作用,但是对银钎料的熔化特性几乎没有影响。铺展实验和钎缝抗拉强度实验结果表明,含Ga和In的银钎料中稀土元素Ce的最佳添加量应该控制在0.03wt.%~0.1wt.%范围。更多还原

【Abstract】 Due to the moderate melting point, excellent properties (processing, intensity, toughness, conductivity, corrosion-resistance) of the silver filler metal with cadmium, it has been used in aerospace field, household appliance and so on. However, for the toxicity of cadmium, countries of the world has banned the materials with cadmium using in household appliance, moreover, considering the cost of materials, cadmium-free silver filler metal with lower Ag-containing has been focused in foreign and domestic brazing field.Effects of gallium and indium on melting property were illustrated in this thesis. The results indicate that 3.0wt.% Ga addition can decrease the solidus of Ag30CuZnSn filler metals by 52℃, and the liquidus by 68℃, moreover, 2.0wt.% In addition into Ag30CuZnSn filler metals can decrease the solidus by 23℃and the liquidus by 54℃approximately. When filler metals with gallium and indium spread on copper and brass, spreadability were gradually improved with the increasing of gallium and indium content. When the In was added into the silver filler metals, the more content of In, the better spreadability. When the content of In is up to 1.5wt.%~2.0wt.%, the spreading area is equal to the traditional silver filler metals containing Cd. With the addition of small amount of Ga/In, the spreading areas can be increased by 70%、108%、71%、146% on copper and brass plates respectively. When Ga is added into silver filler metals, the tensile strength of the brazed joints is improved with the increasing of Ga content, and will remain stable when the content of Ga is up to 3.0wt.%, whose tensile strength is 325Mpa, and 75Mpa larger than Ag30CuZnSn without Ga containing. Therefore adding Ga into silver filler metals can improve the mechanical properties of the joints. Effect of In on the property of the silver filler metals is also studied, the tensile strength of the joints is improved with the increasing of In content, and the value shows a linearly development when the In content is within 1.0wt.%. The tensile strength shows a parabolic trend with a further increasing in In content (1.0 wt.%~1.5wt.%), when the In content exceeds 1.5wt.%, the variation tendency of the joint strength tends to stability.The microstructure of Ag30CuZnSn, which was improved by Ga addition, is similar to the matrix of the Ag56CuZnSn filler metals with high Ag content. With the addition of Ga, the acicular structure turned into the fine grains gradually. The acicular phase was disappeared and the wormlike microstructure was found when the Ga content is 3.0wt.%. However, continue to increase the Ga content coarsening the grains of the brazing alloy. The microstructure was also changed by In addition. The fine primary grain and micro-stripy or granular eutectic structure were found in the 1.0wt.% In contenting alloy. The grains coarsened significantly and the difference between the eutectic phases was obvious with the increasing content of In. From the analysis results by SEM and EDS, Ga and In distribute uniformly in the AgCuZn alloy, and the mainly phase are solid solutionα-Ag andα-Cu in the Ag30CuZnSn-3wt.%Ga alloy.α-Cu distributed between the wormlike backboneα-Ag structure, and the Ga-Ag,Ga-Cu solid solution was filled in the wormlike backbone. The characteristics of fracture morphology of the brazing seam were also analyzed. It is found that the microstructure of the brazing seam is dense and regular and the fracture mechanism of the brazing seam is the toughness fracture.In was also added into the alloy on the basis of 3.0wt.% Ga adopted. With the addition of 0.5wt% In, the solidus temperature of the alloy was decreased by about 17°C from 638°C to 621°C , and the liquidus temperature was decreased by 25℃from 701℃to 676℃. With the increasing of In content, both of the solidus temperature and liqudus temperature decrease obviously, and effect of the liquidus was larger than that of solidus. The melting range (liquidus temperature minus solidus temperature) was also reduced. When the content of In is around 3.0wt.%, the decrease magnitudes of the liquidus and solidus were diminished and come to stabilization. It can be found from the results that the spread-ability of the alloy was improved with the addition of Ga and In, the spreading characterization of Ag30CuZnSn-3.0Ga-2.0In and Ag30CuZnSn-3.0Ga-2.5In filler metals is ideal, the shape of spreading filler metals is similar roundness with bright and trim brim. The results indicated that single addition of Ga or In in Ag30CuZn filler metal could improve the spreading performance on copper and brass. Simultaneous addition of Ga and In could improve the spreading behavior as before, and the performance on brass is relatively superior to that on copper. Deeply study showed that with additive minor Ce, the spreading performance could further improved, as the same, the spreading area on brass is larger.On the basis of 3.0wt.% Ga, adding a small amount of In, the microstructures of silver filler metals can be refined further, and the“stripe”shape eutectic microstructures appeared in the filler metal matrix. Based on analysis of microstructures of silver filler metals, the optimal In content is in the range of 1.0wt.%~1.5wt.% for Ag30CuZnSn-3Ga-xIn filler metals. Observing from the tensile fracture of the butt joint brazed with Ag30CuZnSn-3Ga-2In, it can be found that the ductile fracture characteristics, when the content of In exceeds 2.0wt.%, the dissociation morphology fracture will be emerged which have little influence on the tensile property of the brazed joints. When studying the microstructure of the Ag30CuZn-Sn3Ga-2In filler metals by way of SEM, it is found that the elements of Ga and In distribute uniformly, and there are no segregation, and the significant‘framework’structure which can be found in the matrix. Due to the existence of Sn, Ga and In in Ag30CuZnSnGaIn filler metals, the melting point and spreading properties can be improved, and the formation of Cu6Sn5 can be exhibited too, thus the strengthen and plastic properties of joints brazed with silver filler metals can be protected obviously. Therefore, the addition of Sn, Ga and In can decrease the melting points significantly, moreover, since the dispersive distribution of solid solutions, the properties of joints with silver filler metals can also be improved.In the investigation, the addition of rare earth Ce can further improve the properties of silver filler filler metals bearing In and Ga. Based on the experimental results, due to the grain refinement and grain boundary strengthening of rare earth Ce, adding minor amount of rare earth Ce to Ag30CuZnSn-3Ga-2In filler metals can improve the spreading and mechanical properties by an effective way, and has little effect on the melting characterization of original silver filler metals, by analyzing the spreading areas and tensile strengthening synthetically, it is found that the greatest improvement to the properties of Ag30CuZnSn-3.0Ga-2.0In filler metals is obtained with around 0.03wt.%~0.1wt.%. Rare earth Ce plays two roles in the silver filler metals, fine-grain strengthening and grain-boundary strengthening. When the rare earth Ce is added into silver filler metals, it is found that the rare earth Ce does not dissolve into Ag based solid solution and Cu based solid solution, but can form rare earth phase in the filler metal matrix. In addition,“enrichment phenomena”could be confirmed for rare earth Ce in the grain boundary.更多还原