| Cu-Al joint, benefiting from its merits, such as light weight, material saving, low price, excellently comprehensive properties and so on, has been widely used in the manufacture of motors and the spare parts of transformers. However, there are obvious differences in physical and chemical properties between pure copper and aluminum, such as melting temperature, latent heat of fusion, linear expansion coefficient etc. Besides, there is a high chemical affinity between them, and it is easy to produce brittle intermetallic compounds. So there are serious difficulties in realizing reliable connection between copper and aluminum.In this thesis, based on Zn-10 Al binary alloy,brazing T2 copper plates and 1060 aluminum plates in electric resistance furnace, adding Sn and Cu elements in different quantity. The microstructure, mechanical and welding performance of brazing alloy and brazed joint are studied by using optical microscopy, scanning electron microscope, energy dispersion spectrometry, X-ray diffraction and differential scanning calorimeter. The main conclusions are presented as follows.The proper addition of Sn and Cu elements can refine the microstructure of zinc-based filler metal as cast and improve its uniformity. When the additive quantity of Sn elements is 12.0wt.%, dendrite structure disappears. On this basis, a small amount of Cu Zn4 phase is formed after adding 2.0wt.% Cu elements. With continuously increasing of Cu element, the phase of Cu Zn4 becomes coarse and distributes in dendritic, which increases uniformity of microstructure and weakens the toughness of filler alloy.Sn can make the endothermic peak of filler metal shift to the left, which implies that the melting temperature of filler alloys decrease. When the addictive quantity of Sn is 16.0wt.%, the peak of solder alloy decreases 22℃. Cu has little effect on solidus temperature of filler alloy, but it can make the liquid temperature rise. Adding 4.0wt.% Cu, the solidus and liquid temperatures of solder alloy are 325.2℃ and 383.6℃respectively. The liquid temperature has been improved by 10℃. Both Sn and Cu elements will cause the melting range of filler alloys increase.The spreading areas of filler alloy on aluminum plate are gradually improved with the content of Sn and Cu increasing. The spreading areas of filler alloy on copper plate rise first and then decrease with the content of Sn increasing, but the spreading areas are gradually decreased with the content of Cu increasing. The spreading areas of filler alloy on copper plate are 122mm2 and 91.99mm2 when the additive quantities of Sn and Cu are 12.0wt.% and 4.0wt.% respectively.Sn and Cu can refine dendrite in weld, and improve metallurgy combination between the solder alloy and copper base. The tensile strength of the brazing lap rises first and then decreases with the addictive quantities of Sn and Cu increasing. The shear strength reaches a peak value of 53 MPa, when the addictive quantity of Sn is 12.0wt.%, increased by 35%. The shear strength is 60.49 MPa, When the addictive quantities of Sn and Cu are12.0wt.% and 2.0wt.% respectively.Fracture of brazing join shows as brittle fracture. There are dimples in local area of fracture, when the addictive quantity of Sn is 12.0wt.%. On this basis, there are more ductile fractures zone in fracture, adding Cu by 2.0wt.%, and dimples are deeper and distribute uniformly. The fracture occurred intergranular fracture, and the fracture is smooth with the continuous addition of Cu element.In summary, the best comprehensive properties of filler mental can be attained, when Zn-10 Al filler alloy with 12.0wt.% Sn and 2.0wt.% Cu. |
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