The best brazing method of titanium alloy pipe

Titanium and iron, aluminum, vanadium, molybdenum and other metal elements made of alloy, with high strength, high heat resistance, good corrosion resistance and other excellent physical and mechanical properties, is widely used in chemical, Marine engineering, transportation, medical, construction and aerospace, military and other high-tech fields, is a very important lightweight structural materials, among them, aerospace is its important downstream application field.

Titanium alloy tube is an active metal, which is widely used in aerospace, petrochemical and atomic energy industries. The main problems in titanium and titanium alloy brazing are as follows:

① The surface oxide film is stable, titanium and its alloy have a large affinity with oxygen, and the surface is easy to generate a very stable oxide film, which prevents the wetting and spreading of the solder, so it must be removed during brazing.

② Titanium and its alloys have a strong tendency to absorb hydrogen, oxygen and nitrogen during the heating process, and the higher the temperature, the more serious the absorption, so that the plasticity and toughness of titanium metal are sharply reduced, so brazing should be carried out in a vacuum or inert atmosphere.

③ Easy to form intermetallic compounds, titanium and its alloys can chemically react with most needles to produce brittle compounds, resulting in brittle joints. Therefore, brazing brazes used for brazing other materials are basically not suitable for brazing active metals.

④ The structure and properties are easy to change. Titanium and its alloy will undergo phase transformation and grain coarsening when heated, the higher the temperature, the more serious the coarsening, so the temperature of high temperature brazing should not be too high.

In short, attention must be paid to the brazing heating temperature when brazing titanium and its alloys. In general, the brazing temperature should not exceed 950 ~ 1000 ℃, the lower the brazing temperature, the smaller the impact on the base metal performance. For quench-aged alloys, brazing can also be carried out under conditions that do not exceed the aging temperature.

In order to prevent the oxidation of the brazing head and the oxygen absorption and hydrogen absorption reaction, titanium and titanium alloy brazing is carried out in a vacuum and an ambient atmosphere, and generally does not use flame brazing. When brazing in vacuum or chlorine gas, high frequency heating, furnace heating and other methods can be used, the heating speed is fast, the holding time is short, the compound in the interface area is thin, and the joint performance is better. Therefore, the needle welding temperature and holding time must be controlled so that the filler metal can fill the gap.

Titanium alloy pipe manufacturers said: The reason why titanium and titanium alloy is best brazed in vacuum and argon, because in vacuum brazing, although titanium has a great affinity for oxygen, titanium can get a smooth surface at 13.3Pa vacuum degree, which is due to the surface of the oxide film can be dissolved in titanium.

Brazing under the protection of argon, when the brazing temperature range is 760 ~ 927 ℃, in order to prevent titanium discoloration, high purity argon is required, and liquid argon in refrigeration storage containers is generally used because it has a high purity.

When brazing titanium and titanium alloys, brittle compounds are often formed on the interface or in the brazing seam, which reduces the performance of the brazing joint. Therefore, diffusion welding can be used to improve the performance of brazed joints. During brazing, 50μm thick copper foil, nickel foil or silver foil is placed between titanium alloys, and Cu-Ti, Ni-Ti and Ag-Ti eutectic are formed depending on the contact reaction between titanium and these metals. Then these brittle intermetallic compounds are diffused away, and the diffusion-brazed joint has quite good performance at a certain temperature and time.

In addition, a+B phase titanium alloys can be used in annealing, solution treatment or aging state. If annealing is required after brazing, there are three options to choose from: brazing at or below the annealing temperature after annealing; The annealing structure is obtained by brazing at a temperature above the annealing temperature and taking a step cooling process in the brazing cycle. Braze at a temperature above the annealing temperature and then anneal.