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Effects Of Rare Earth Pr On Microstructure And Properties Of Ag30CuZnSn Brazing Filler Metal

Posted on:2017-04-26Degree:MasterType:Thesis
Country:ChinaCandidate:M K QianFull Text:PDF
GTID:2271330503468008Subject:Materials engineering
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Silver-based brazing filler metals are widely used in automobiles, home appliances and aerospace industry for its excellent processing property, and silver brazing metal with cadmium is the most outstanding among silver-based brazing filler metals. However,because of the toxicity of cadmium and the promulgation of relevant policies, cadmium-free silver brazing filler metal research has become the current hot topic.In this study, the properties of AgCuZn with different Ag contents and Sn, and the Ag30 CuZnSn with different addition of rare earth Pr were studied.The spreading test results shows that with the increase of Ag content, the spreadability of the AgCuZn filler metals is gradually improved and 2wt.%Sn addition also can improve the spreadability greatly; with the addition of rare earth Pr, the spreadability of the Ag30 CuZnSn filler metals with 0.15 wt.% Pr additon has the best spreadability on copper/brass. When the amount exceed suitable range, the spreadability deteriorated.The melting temperature tests results shows that with the increased of Ag content, the solid/liquid phase temperature of AgCuZn brazing filler metal declined in different degrees;2wt.%Sn addition can significantly reduce the solid-liquid phase temperature but increase the solid-liquid phase temperature range; the addition of rare earth Pr(≤0.3wt.%) doesn’t make an obvious impact on Ag30 CuZnSn brazing filler metal.The mechanical result indicates that except for the lap-joint of brass, the fracture positions of two kinds of joints happen on the base metal, which shows outstanding mechanical properties of the brazed joints with the silver filler metal. For Brass butt joint,the addition of Sn and Pr can improve the tensile strength of the brazed joint and with increased of Pr additon, the mechanical properties of the brazed joints is improved and brazing filler metal reflect the best mechanical properties with 0.15 wt.% Pr additon.However, if the Pr addition continued, the mechanical properties of the joints is declined.By analysing the microstructure of silver filler metals and the fracture morphology,combining the energy spectrum and XRD analysis, the result shows that the silver brazing filler metal microstructure is mainly composed of Cu based solid solution, Ag based solidsolution and Cu-Zn compound and Sn dissolved in Cu and Ag based solid solution; the rare earth Pr mainly enriched in grain boundaries and nearby area to purify grain boundaries and refine grains; with the addition of Pr, the original needle structure transformed to granular structure and on the basis of 0.15 wt.% Pr, the microstructure and grain size of silver filler metal were refined further; The corresponding fracture surfaces of Ag30 CuZnSn joints have shown the characteristics of ductile fracture, which indicate that the joints have excellent mechanical properties and the dimples are small and dense, and with the addition of Pr, the dimple shape become more larger and deeper which indicates excellent plasticity and toughness. While by adding Pr continued, the characteristic of fracture changed from ductile fracture to quasi-cleavage fracture and can find the existence of tear ridges and hard alloy particles which declines the properties of silver brazing filler metals.
Keywords/Search Tags:silver filler metals, rare earth Pr, mechanical property, microstructure
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