Study On Zn-based Filler Metal Of Medium Temperature

There are mainly two kinds of filler metals used to braze Cu or steel, one is the solderingfiller metal which liquidus is lower than300℃, and another is the brazing filler metal whichliquidus is higher than650℃, there is barely filler metal of medium temperature. The meltingpoint of Zn is419℃, and the melting temperature can be adjusted between400℃and450℃with the addition of right alloy metal. The interactions of Zn and Cu or steel are strong, so Znis choosed to be the matrix, and study on the Zn-based filler metal.Zn is the matrix, and through the analysis of phase diagrams, foreign patents and otheracademic researches, Cu and Sn are added in the Zn-based filler metal to improve the strengthand toughness of Zn-based filler metal. In order to further improve the processing propertyand refine the grains of Zn-based filler metal, this paper contrasts the effects of Bi, Ag, Al, Mg,Ti and Ni alloy elements on the wettability and shear strength of joints. The result is that thespread area of BZn90Sn5Cu3Bi2is182mm2, higher than that of any other filler metals, thestrength of it is28.4MPa, higher than that of any other filler metals, too. So Bi is choosed tobe one of alloying elements in Zn-based filler metal. The microstructure of BZn90Sn5Cu3Bi2is fine and close, and many intermetallic compounds inset in the base metal, the thickness ofthe reaction layer is17.8μm. The fracture of the joint is in the filler metal, and the mode of thejoint is intercrystalline fracture.The weight percent of Cu, Sn and Bi are considered as the natural factors to code, and themethod of the second-order regression orthogonal design is used to make schemes. To get thecomposition of the best filler metal, the spread area, the shear strength of joint and thethickness of reaction layer are considered as the indexes to build regression equations to studythe effects of Cu, Sn and Bi, the software of Matlab is used to get the optimal Zn-based fillermetal. This paper applies modern methods to analysis BZn89.38Cu1Sn6.94Bi2.72, themicrostructure of it is fine and close, the microhardness of it is54HV, the spread area of it is3.98cm2, and the shear strength is36.8MPa, they are close to the predicted value. The strengthof the joint is high, and the mode of the joint is intercrystalline fracture and some microscopictoughening nests.