Welding of carbon steel and low alloy steel
(1) When the carbon equivalent exceeds 0.3%, the difficulty of welding will increase, the cold crack sensitivity will increase, and the brittle fracture tendency of the material under fatigue and low-temperature conditions will also increase.
- Preheating or post-heating;
- Double beam welding is adopted, one beam is focused and the other beam is defocused;
- Under the condition of ensuring penetration, lower power and welding speed shall be adopted as far as possible.
(2) When welding high carbon materials and low carbon materials, the use of offset weld is conducive to limiting the transformation of martensite and reducing the generation of cracks.
(3) The laser welding performance of killed steel and semi-killed steel is better, because deoxidizers such as silicon and aluminum are added before pouring, which reduces the oxygen content in the steel to a very low level.
(4) Steel with sulfur and phosphorus content exceeding 0.04% is prone to thermal cracks during laser welding.
(5) For galvanized steel with overlapping structure, it is generally difficult to use laser welding.
Welding of stainless steel
(1) Stainless steel has good laser welding performance.
(2) The thermal conductivity of austenitic stainless steel is only 1 / 3 of that of carbon steel, and the absorption rate is slightly higher than that of carbon steel.
Therefore, austenitic stainless steel can obtain a slightly deeper penetration than ordinary carbon steel (about 5% ~ 10%).
(3) During laser welding of Cr-Ni stainless steel, the material has high energy absorption and melting efficiency.
(4) When welding ferritic stainless steel by laser welding, the weld plasticity and toughness are higher than those by other welding methods.
(5) Laser welding of stainless steel can be used for welding stainless steel tubes and nuclear fuel packages in nuclear power plants, as well as other industrial departments such as the chemical industry.
Laser welding of non-ferrous metals
1. Laser welding of aluminum alloy
Deep penetration welding is often used in aluminum alloy laser welding. The main difficulty in welding is its high reflectivity to laser beam and its high thermal conductivity.
During laser welding of aluminum and aluminum alloys, with the increase of temperature, the solubility of hydrogen in aluminum increases sharply, and there are many pores in the weld. During deep penetration welding, there may be cavities in the root and poor weld bead formation.
When laser welding aluminum and aluminum alloys, in addition to the problem of energy density, there are three important problems to be solved: porosity, thermal crack and serious weld irregularity.
The strong reflection of aluminum alloy on laser makes welding very difficult. High power laser must be used for welding.
2. Laser welding of titanium alloy
Titanium alloy is an excellent structural material with high specific strength, good plasticity and toughness and high corrosion resistance.
Titanium has active chemical properties and is very sensitive to oxidation.
It is also very sensitive to gap embrittlement caused by oxygen, hydrogen, nitrogen and carbon atoms.
Therefore, special attention should be paid to joint cleaning and gas protection.
3. Laser welding of Superalloys
Laser welding can weld all kinds of superalloys, including aging treated alloys with high content of A1 and Ti that are difficult to weld by arc welding, and good joints can be obtained.
The laser generator used for superalloy welding is generally pulse laser or continuous CO2 laser with power of 1 ~ 50KW.
Helium or the mixture of helium and a small amount of hydrogen is recommended as the shielding gas for laser welding.
4. Laser welding of dissimilar materials
Dissimilar metals such as copper nickel, nickel titanium, titanium aluminum and low carbon steel copper can be welded by laser under certain conditions.
The laser can also weld ceramics, glass, composite materials, etc.
When welding ceramics, it is necessary to preheat to prevent cracks. Generally, preheat to 1500 ℃, and then weld in air.
Usually, a long focal length focusing lens is used; In order to improve the joint strength, welding wire can also be filled.
When welding metal matrix composites, brittle phases are easy to produce, which will lead to cracks and reduce the strength of joints.