The welding method of titanium and titanium alloys is best to use tungsten electrode inert gas shielded welding and molten electrode inert gas shielded welding, collectively referred to as hydrogen arc welding. The welding materials used are mainly titanium and titanium alloy welding wires, argon gas and tungsten electrodes.
The composition of titanium and titanium alloy argon arc welding wire should be the same as that of the base metal, that is, the filler wire should generally be made of homogeneous material. In order to improve the plasticity of the joint, a medium wire with a slightly lower alloying degree than the base metal can be used, such as TA1 welding wire when welding TA2. The impurity content of the wire should be much lower than that of the base metal. The titanium welding wire is supplied in vacuum annealed state, and the surface shall not have defects such as burnt skin, crack, oxidation color, metallic or non-metallic inclusions, etc.
Titanium alloys need to be protected with inert gas during welding. Argon, helium or a mixture of argon and nitrogen can be used as protective gas. In my country, only hydrogen is usually used as the shielding gas, so it is called argon arc welding.
Argon is denser than air, has lower specific heat capacity and thermal conductivity than air, and hardly has any chemical interaction with any metal, nor does it melt into metal. These physical and chemical properties enable it to play a good protective role in titanium argon arc welding and to stabilize the welding arc.
The argon gas used for welding titanium and titanium alloys is first-grade argon gas, and the technical requirements of argon gas for welding are stipulated in the national standards GB/T4842-2006 and GB/T10624-1995. The main technical requirements for argon are: purity, argon ≥99.99%; moisture <0.002mg/L; relative humidity not greater than 5%; residual pressure in the hydrogen bottle should not be less than 0.2MPa.
If the purity of argon is unqualified, it means that there are excess impurities such as oxygen, nitrogen and hydrogen in it. Among them, oxygen and nitrogen will melt into the welding pool to make the weld metal brittle, and excess hydrogen will form weld porosity defects. Other impurities will reduce the breaking length of the welding arc,
The purity of argon can be easily identified by observing the color of the weld surface. The specific method is to first use a tungsten electrode to ignite the arc on the titanium plate, and keep it fixed. When a melting zone is formed on the titanium plate, immediately extinguish the arc (still argon gas at this time) to observe. If the solder joint shows bright white dots, it means that the argon gas is of high purity. You can also observe the color of the heated tungsten wire to determine the purity of argon. If the tungsten wire is oxidized under the protection of argon after heating, that is, it is not silver-white, it means that the purity of the bottle of argon is not enough.
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