In laser welding, the welding material is an important factor that affects the welding effect. Therefore, the analysis of welding characteristics of welding materials is particularly important. Common welding materials are: galvanized plate, stainless steel (austenitic stainless steel, ferritic stainless steel, martensitic stainless steel), alloy steel, aluminum alloy, titanium and titanium alloy, copper. Here is a brief introduction of these common welding materials and their welding characteristics.
1、 Laser welding material -- galvanized sheet
The vaporization temperature of zinc (903 ℃) is much lower than the melting point of steel (1535 ℃). During the welding process, the vaporization of zinc causes serious porosity and undercut. When the thickness of the galvanized layer in the overlap area is less than 5-10 μ m, laser welding can be used. Only when the thickness of the zinc coating reaches 10-20 μ M can the corrosion resistance be guaranteed.
2、 Austenitic stainless steel as laser welding material
Generally, austenitic stainless steel has better welding performance. The thermal conductivity of austenitic stainless steel is only 1 / 3 of that of carbon steel, the absorption rate is slightly higher than that of carbon steel, and the welding penetration is about 5-10% of that of ordinary carbon steel. Laser welding is very suitable for welding Cr Ni series stainless steel because of its small heat input and high welding speed. The thermal deformation and residual stress of laser welding austenitic stainless steel are relatively small. When other conventional welding methods are used, the thermal expansion of austenitic stainless steel is 50% larger than that of carbon steel.
3、 Ferritic stainless steel as laser welding material
Toughness and ductility are higher than other welding methods. In the process of fusion welding, martensite transformation and grain coarsening reduce the joint strength and corrosion resistance, but relatively speaking, the influence of laser welding is lower than that of conventional welding. Compared with austenitic stainless steel and martensitic stainless steel, laser welding of ferritic stainless steel has the least tendency to produce hot and cold cracks.
4、 Martensitic stainless steel as laser welding material
In stainless steel, the weldability of martensitic stainless steel is the worst, the welded joint is usually hard and brittle, and has the tendency of cold cracking. When welding stainless steel with carbon content more than 0.1%, preheating and tempering can reduce the tendency of crack and embrittlement.
5、 Alloy steel of laser welding materials
In many applications, including aircraft engine and automobile transmission, laser is often used for welding, and many applications can be welded at room temperature. Due to the characteristics of alloy steel, it is easy to produce cold cracks. Therefore, the influence of low impurity and carbon content on welding quality is very important.
6、 Aluminum alloy as laser welding material
Laser welding of aluminum alloy requires relatively high energy density: high reflectivity of aluminum alloy; high thermal conductivity of aluminum alloy.
Series 1 to 5 aluminum can be laser welded, but there are some differences in process due to different alloy elements. Due to the volatile elements in aluminum alloy, such as silicon and magnesium, there are many pores in the weld. Liquid aluminum has low viscosity and low surface tension, so it is necessary to pay close attention to the weld pool when welding aluminum to prevent the overflow of liquid aluminum in the pool, which can be solved by joint design or non penetration method.
7、 Titanium and titanium alloy of laser welding materials
High quality and good plasticity welding joint can be obtained by laser welding. Titanium is very sensitive to the embrittlement caused by oxygen, hydrogen, nitrogen and carbon atoms. Pay special attention to joint cleaning and gas protection. Titanium starts to absorb hydrogen at 250 ℃, oxygen at 400 ℃ and nitrogen at 600 ℃. Hydrogen is the main reason for the delay crack in the heat affected zone of the joint. Reducing the source of hydrogen and vacuum annealing can reduce the hydrogen content of welded joints.
Porosity is a major problem in titanium and titanium alloy welding. The main ways to eliminate porosity are: a) welding with high purity argon, with purity higher than 99.9%; b) cleaning before welding; c) proper welding specification.
8、 Copper -- the material of laser welding
Copper is a highly reactive material. Copper is generally divided into brass and copper. If the content of zinc in brass exceeds the allowable range of laser welding, zinc is easy to vaporize, which may lead to defects such as porosity and faulty welding. The reflectivity of copper is very high, so it needs high energy density to weld. Impurities such as sulfur and carbon contained in copper will damage the weld. The absorption rate of laser beam is improved by surface treatment. leapion