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Effects Of Ga/In And Rare Earth Ce On Microstructures And Properties Of Brazed Joint Of Ag30CuZnSn Filler Metal

Posted on:2012-07-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z M LaiFull Text:PDF
GTID:1111330362458283Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
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.
Keywords/Search Tags:Silver filler metals, rare earth element, Ga, In, spreadability, mechanical properties, microstructure
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