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Influence of brazing filler metal on vacuum brazing of titanium alloys
Brazing of titanium alloys has the advantages of small deformation, high precision and good mechanical properties, but brazing of titanium alloys is also prone to form intermetallic compounds, resulting in low fatigue resistance and impact strength of joints. Therefore, the selection of suitable brazing filler metal is of great significance to the quality of TC4 titanium alloy brazed joints. Titanium-based solder has high welding strength, excellent corrosion resistance, good fluidity and wetting properties, and has become the first choice for titanium alloys.
Experimental Materials and Methods
The brazing filler metals selected in the experiment are B-Ti57CuZrNi, B-Ti37ZrCuNi, and B-Ag72Cu. The specific chemical composition and melting point are shown in Table 1. The brazing base is TC4 titanium alloy.
The butt brazing of TC4 titanium alloy was carried out in a vacuum brazing furnace with three kinds of brazing filler metals, and the vacuum degree was required to be no less than 5×10-2Pa. Before brazing, the TC4 bar is cut into two pieces, both end faces are finely ground, and the cut bar is cleaned and degreasing to keep the surface to be welded clean. The brazing temperature of B-Ti57CuZrNi solder is 930℃, the brazing temperature of B-Ti37ZrCuNi solder is 880℃, and the brazing temperature of B-Ag72Cu solder is 830℃, and the holding time is 15min.
The microstructure of the brazing interface was analyzed by TG3000 metallographic microscope, the distribution and diffusion of elements in the brazing interface were tested by the energy spectrum tester attached to the Hitachi S4300 scanning electron microscope, and the tensile test was carried out by MTS-SANSCMT500 tensile testing machine. The surface morphology of the tensile fracture was observed and analyzed with a Hitachi S4300 scanning electron microscope.
Results and Analysis
Wettability of Solder and TC4 Titanium Alloy
In order to analyze the wettability between the brazing filler metal and TC4 titanium alloy, the brazing temperature spreading experiment was carried out on the surface of TC4 titanium alloy for these three brazing filler metals. Weigh 0.2 g of the three kinds of brazing filler metals respectively, put them on a TC4 titanium alloy plate of 40 mm × 40 mm, and place them in a vacuum furnace for a holding time of 5 min.
The figure below shows the macroscopic morphology of the surface of TC4 titanium alloy spread by three kinds of brazing filler metals. It can be seen that the three kinds of solders have interface reactions with the surface of TC4 titanium alloy, the wetting angles are all less than 10°, and the spreading is good. This shows that B-Ag72Cu, B-Ti37ZrCuNi and B-Ti57CuZrNi can all be brazed to TC4 titanium alloy.
The brazing of TC4 titanium alloy, but its interface effect is relatively weak, and the welding stability is relatively poor, so its mechanical properties at room temperature and high temperature are relatively weak; The high temperature performance of the solder itself is better, so the high and low temperature performance of the welded joint is better.
In order to further analyze the effect of brazing filler metal on the mechanical properties of TC4 titanium alloy joints, three brazing filler metals were brazed at 930℃/15min, and the mechanical properties of the welded joints were tested. The test results are shown in the following table. It can be seen from the table below that when the B-Ag72Cu and B-Ti37ZrCuNi solders are welded at 930℃/15min, due to the increase of the welding temperature, the effect of the solder on the interface of the TC4 titanium alloy is enhanced, and the high-temperature properties of the welded joints are increased, but the joint strength at room temperature decreased. Through the comparative analysis of the mechanical properties of TC4 brazing by three kinds of brazing filler metals, B-Ti57CuZrNi brazing filler metal is the most suitable for TC4 titanium alloy.
(1) The three brazing filler metals B-Ti57CuZrNi, B-Ti37ZrCuNi and B-Ag72Cu can all be used for brazing TC4 titanium alloy.
(2) Compared with B-Ti57CuZrNi and B-Ti37ZrCuNi solder, B-Ag72Cu solder has weaker brazing strength at low temperature. During high temperature brazing, the solder reacts violently with the TC4 titanium alloy matrix, and the corrosion resistance of the weld is biased. weak.
(3) Compared with B-Ti57CuZrNi solder, B-Ti37ZrCuNi solder has weaker mechanical properties at room temperature, and the mechanical properties of brazed joints are weaker and more dispersed.
(4) B-Ti57CuZrNi brazing filler metal brazing TC4 titanium alloy, its comprehensive performance is relatively good.
After mastering the corresponding process, it is necessary to select a suitable vacuum furnace for operation to ensure sufficient yield. At present, the most suitable product series of SIMUWU is RHVB high temperature vacuum brazing furnace. It has the characteristics of high temperature accuracy, high vacuum degree and good temperature uniformity in the heating area. It is an ideal equipment for vacuum brazing of titanium alloys.
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