The lattice type, melting point, thermal conductivity, linear expansion coefficient and chemical composition of copper and titanium plates are very different, so it is very difficult to weld. Let's take a look with the titanium tube manufacturer.
1. The weld is easy to form pores
(1) Copper and titanium high temperature hydrogen absorption capacity is very strong, hydrogen in liquid copper and titanium solubility is larger.
(2) Gas is produced in the high-temperature metallurgical reaction pool.
(3) Oxygen and nitrogen gas around the welding zone are immersed into the molten pool. During the crystallization process of the molten pool, the gas cannot escape from the surface of the molten pool and remains in the weld to form pores.
2, welding joint crack tendency is large
During the welding of copper and titanium, eutectic crystals and hydrides can be formed on the metal sides of the two base materials, and cracks are easy to occur under the welding stress.
(1) Copper and bismuth form (Cu+Bi) eutectic crystal at 270℃.
(2) Copper and aluminum form (Cu+Pb) eutectic crystal at 326℃.
(3) Copper and ferrous sulfide form (Cu+Cu2O) eutectic crystal with a eutectic point of 1067℃.
(4) Sheet hydride TiH2 is formed on the metal side of the titanium base metal, resulting in hydrogen embrittling.
(5) The linear expansion coefficient of copper and titanium is more than 1 times the difference, welding will produce greater stress.
3. The mechanical properties of welded joints are low
(1) The oxide film can weaken the intergranular bonding between copper and titanium. For example, when the oxygen content in the weld reaches 0.38%, the joint bending Angle decreases from 180° to 120°.
(2) A large number of eutectic crystals and hydrides significantly reduce the ductility and toughness of welded joints.
(3) The miscibility of copper and titanium is very small, and it is easy to form intermetallic compounds at high temperature. Such as Ti2Cu, TiCu, Ti3Cu4, Ti2Cu3, TiCu2, TiCu4, increase brittleness, reduce plasticity, and make weld metal corrosion resistance significantly reduced.
Vacuum diffusion welding, argon arc welding, plasma arc welding, brazing and electron beam welding can obtain excellent welding joints between copper and titanium or titanium alloy.
For example, vacuum diffusion welding is used. The characteristics of vacuum diffusion welding are no oxidation of joints, beautiful weld appearance and good product quality. The main operation process is: before welding, copper base metal (such as T2) is cleaned with trichloroethylene to remove oil stains and other sundries. Then it was etched in 10% sulfuric acid solution for 1min, washed with distilled water, and then annealed at 820~830℃ for 10min.
After the titanium base metal (TA2) was cleaned with trichloroethylene, the oxide film was removed by vibration etching for 4min in 2% HF and 50% HNO3 aqueous solution, and then cleaned with water and alcohol.
(4) Assemble the two cleaned base metal according to the technological requirements, and then put them into the vacuum furnace for welding. The welding parameters are as follows: the welding temperature is 810℃±10℃, the pressure is 5~10MPa, the time is 10min, and the vacuum degree is 1.3332×10-8~ 1.3332× 10-9mpa. An intermediate diffusion layer can be added between the two base metals, usually niobium metal is selected as the diffusion layer material, or no intermediate diffusion layer can be added. Clean the surface of the joint carefully after welding.
If argon arc welding is used to weld copper and titanium, the use of cerium tungsten electrode can improve the welding quality and benefit human health. For example, when welding copper alloy (QCr0.5) and titanium alloy (TC2), niobium can be used as the transition layer material, argon purity of 99.8% can obtain high quality joint.