Effects Of Ga On Properties Of Cadmium-free Silver Filler Metal

Silver filler metal with cadmium has been used in aerospace field, household appliance and so on, for its excellent processing property. But, EU and China has banned the materials with cadmium applicated in household appliance. R&D of cadmium-free silver filler metal has been focused by foreign and domestic brazing field.Melting characterization experiments and spreading tests of silver filler metals with different content of gallium on pure copper and brass were carried out in this paper, effecting rule of gallium on melting property and spreading were illustrated in detail. The results indicate that 1wt.% Ga addition decrease the solidus of Ag-Cu-Zn filler metals by 53℃, and the liquidus by 45℃;When filler metals with gallium spread on pure copper, the effect of a little In and Ga is not as well as Sn; When they are used on brass, the effect of Ga to spreadability of Ag-Cu-Zn is great, just like the spreading-area of Ag-Cu-Ga-Sn filler metal with 2wt.% Ga addition to Ag-Cu-Zn-Sn filler metal is 50% larger than Ag-Cu-Zn-Sn filler metal.Using brass as base metal, brazing with flame method, the mechanical properties of the joints brazed with lap-joint and butter-joint were analyzed exactly. The results indicate that, the fractures of two kinds of brazed joints all happened on the base metal, which shows good mechanical properties of the joints brazed with the silver filler metals bearing cadmium.The changing rule of brazed joints strength and microstructure of silver filler metal bearing different content of gallium were studied by way of analyzing microstructures of brazed joints. The results indicate that gallium can make great effects to the microstructure of silver filler metal, and the silver filler metals with Ga have the similar microstructures.It is found from brazed joints microstructures of silver filler metal bearing Ga that brazed with flame method, the microstructures of silver filler metals with Ga exhibit tense net structure, which is similar with silver filler metal with high silver content. And the similarity accords with the mechanical test of joints with lap-joint and butter-joint. The results of Energy Spectrum Analysis indicate that, the Cu solid solution is the main phase in brazing joints with Ga and low silver, which guarantee the mechanical properties of silver filler metal with low silver.As a matter of the experimental data, all the results of this paper have provided effective supporting theoretically and practically for the application of cadmium-free brazing filler metal.