Study On Properties Of Lower Silver Brazing Filler Used To Electrical Vacuum Devices

In this paper, for the more silver content in B-Ag72Cu28 brazing filler used to the vacuum devices have confined sustainable development of noble metal resources. It's worthy of designing a new silver based filler with lower silver content to substitute B-Ag72Cu28 in order to save product cost. Ag(40-45wt%)-Cu-Sn-Ni alloy foil with the size of 15-60μm thickness and 3-5mm width were prepared by rapid solidified technology. The solidus and liquidus temperature, wettability, electrical resistivity performance, mechanical properties of brazing alloys and brazing process were analysed, and the stannum and nickel elements influence on properties of brazing filler were studied, meanwhile, the mechanical properties of joint were also tested and measured. The results indicated as follows:The microstructure of regular solidified Ag-Cu-Sn alloy are composed of face-centered cubic (Ag),α-Cu and little Cu13.7Sn; in the structure of regular solidified alloy, rough dendrite isα-Cu phase appearing first, and the white and gray alternate ((Ag)+α-Cu) eutectic distribute in the interdendritic space. Ag-Cu-Sn-Ni alloy foil is constituted of face-centered cubic (Ag),α-Cu and little Cu13.7Sn,Ni17Sn3, the microstructure of rapid solidifying alloy is fine and homogeneous equiaxed crystal.With stannum content in(Ag-Cu)100-xSnx(x=12.23,12.94,13.65)increasing, temperature of solidus and liquidus of alloy foil becomes lower, the value range of which are Ts=590-616℃and Tl=615-622℃respectively, temperature interval△T is bigger; Electric resistivity and tensile strength of alloy foil are larger, but elongation ratio is smaller, the value range of which areσb=280-360MPa andδ=2.8-5% respectively. With nickel content in (Ag-Cu-Sn)100-xNix (x=0.4,0.6,0.8,1.0) increasing, temperature of solidus and liquidus of alloy foil becomes higher, the value of which are Ts=690-718℃and Tl=715-727℃respectively, but temperature interval△T is smaller; the tensile strength of alloy foils becomes stronger but elongation ratio is smaller, the value range of which areσb=345-515MPa andδ=3-6% respectively. In the conditions of heating up to 800℃and holding for 30s, (Ag-Cu-Sn)100-xNix brazing alloy foil displays good wettability on Kovar alloy, and with the nickel content increasing, spread areas are smaller gradually but the wetting angle is bigger, the value ranges are S=0.8634-1.4033cm2 andθ=9.4-23.3°respectively; otherwise, the brazing alloy have better wettability on Kovar by rapid solidified technology than regular solidified technology.Using Ag42CuSn10Ni0.4 brazing alloy foil brazed the stainless steel by high-frequency induction brazing technology, the microstructure of brazing seam is mainly made up of (Ag),α-Cu, and, little Cu13.7Sn,Ni17Sn13 andγ-Fe phases distributed into them; the value of tensile strength of joint is up to 189.29MPa, under the conditions of heating time for 15s and holding for 10s and the heating current is 25A during experimental process.