Laser processing technology of the hottest magnesi

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Laser processing technology of magnesium alloy

the density of magnesium is 1.78 × 103kg/m3, which is 2/3 of aluminum and 1/4 of steel. Magnesium alloys have high specific strength, specific stiffness, thermal conductivity, machinability and recyclability, and are known as "green" engineering materials in the 21st century. In recent years, magnesium alloy materials have been widely used in various casings, "land, sea and air" transportation vehicles, national defense industry, etc. with the development of magnesium refining and deep processing technology, magnesium alloy materials have become the third largest category of metal materials after steel and aluminum, and have developed rapidly all over the world

based on the review of laser cutting, laser welding and laser surface modification of magnesium alloys at home and abroad, the laser processing technology of magnesium alloys is studied in this paper

1 mechanism of laser and magnesium alloys

laser processing of magnesium alloys is a thermal processing based on photothermal effect, on the premise that the laser is absorbed by magnesium alloys and converted into heat energy. From the analysis of atomic structure theory, the effect of laser on metal materials is the effect of high-frequency electromagnetic field on free electrons in materials. Free electrons in materials vibrate at high frequency under the action of laser induction. Through bremsstrahlung, part of the vibration energy is transformed into electromagnetic wave outward radiation, and the rest is transformed into the average kinetic energy of electrons, and then into heat energy through the relaxation process between electrons and lattice

different materials have great differences in the absorption of lasers with different wavelengths. The absorption rate an is expressed as:

where: C0 is the speed of light, c0=3 × 108m/s is the wavelength of the incident laser; Is the conductivity of metal materials. It can be seen from formula (1) that when the processed material is certain, the shorter the wavelength of the laser, the more the material absorbs the laser. Due to the skin effect, a large number of free electrons in the metal prevent the laser energy from penetrating into the interior of the material, so that most of it is reflected away. Therefore, general materials are sensitive to CO2 gas laser( λ= ten point six μ m) Absorption ratio of YAG solid laser( λ= one point zero six μ m) The absorption of is low. When the laser wavelength is a constant value, the absorptivity of the material to the laser beam depends on the conductivity of the material. The greater the conductivity, the less the material absorbs the laser. Therefore, the laser absorption of magnesium alloy materials is lower than that of general metal materials, which is one of the difficulties in laser processing of magnesium alloy materials

2 laser cutting technology of magnesium alloy

cutting is the primary link of magnesium alloy material deep processing, and good cutting quality is the guarantee of material deep processing. Compared with traditional cutting methods, laser cutting has higher cutting accuracy, lower roughness and higher production efficiency. At present, the research on laser cutting of magnesium alloy at home and abroad is still rare

we studied the cutting process of 4mm thick AZ31B magnesium alloy plate with 500W solid pulsed nd:yag laser. The laser cutting seam is narrow, with the upper seam width of 0.45mm, the middle seam width of 0.22mm, and the lower seam width of 0.35mm. The perpendicularity of the cutting seam is approved by the AQSIQ to prepare for the establishment of the national printed circuit board quality inspection center of 0.05mm, with small section ripple and regular distribution. The heat affected zone is not obvious, and the overall width of the cutting seam is about 1/4 of that of air plasma arc cutting. However, there is slight oxidation (now fatigue resistance) on the lower surface of the slit, and the section is 80 μ The microstructure of m thick is the remelted layer of equiaxed crystal. The new module is about 20% lighter than the previous process. The conclusion of the process research is that the slit width increases with the increase of discharge voltage, pulse width and pulse frequency, and the cutting speed and auxiliary gas have little effect on the slit width. Figure 1 shows the macro morphology and microstructure of AZ31B magnesium alloy after laser cutting

Fig. 1 laser cutting macro morphology and microstructure of AZ31B magnesium alloy

3 laser welding technology of magnesium alloy

poor welding performance of magnesium alloy is one of the technical prerequisites restricting the application of magnesium alloy. Compared with traditional welding methods, laser welding has the characteristics of fast welding speed, low heat input and small welding deformation. The research on laser welding technology of magnesium alloys is in its infancy. The research on laser welding of magnesium alloys at home and abroad mainly focuses on two fields: continuous CO2 laser welding of magnesium alloys and solid pulse YAG laser welding

e1H in Germany. Coelho welded 2mm thick AZ31B magnesium alloy with a 2.2kw nd:yag laser. The weld with good surface forming, less pores, small HAZ area and no obvious particle growth was obtained. Canadian kazzaz and others successfully welded the 2mm-6mm thick ze41a with 4kw nd:yag laser. Too high or too low laser power in the welding process will lead to the reduction of the power density of the machined surface. The welding mode changes from small hole focusing to partial focusing, and finally to heat conduction mode

laser combined heat source welding as a new welding technology has attracted more and more attention. Song Gang and others used 400W solid pulse YAG laser and paraxial TIG as the welding combined heat source, and successfully welded 2.5mm thick AZ31B magnesium alloy plate for the first time. The penetration of the combined welding can reach 2 times that of TIG alone and 4 times that of laser alone, and the tensile strength of the weld is equivalent to that of the base metal (240mpa). In order to improve the laser absorption rate of magnesium alloy materials in the welding process, SUN Hao and others used a 500W solid-state pulsed YAG laser to study the effect of active agent on the laser welding process of magnesium alloy. Oxides and chlorides can increase the penetration and depth width ratio of magnesium alloy laser welding, because the active agent fine powder increases the absorption of laser energy in the initial stage of laser action

we have carried out laser welding and laser hybrid welding of magnesium alloy thin plates. At present, we are studying laser welding of medium and heavy plates to provide theoretical support for engineering practice

4 laser surface modification technology of magnesium alloys

with the continuous improvement of laser surface modification technology, the application of laser surface treatment of magnesium alloys in the corrosion resistance, wear resistance and other aspects of magnesium alloy surface has attracted more and more attention of researchers at home and abroad. Laser surface modification technology is divided into laser surface remelting, laser surface alloying and laser surface cladding

4.1 laser surface remelting

laser surface remelting of magnesium alloys refines the grain structure on the surface of the material, reduces micro segregation, and generates non-equilibrium phases, which leads to surface strengthening and increases the wear resistance of the alloy surface

ghazanfar Abbas of Pakistan and others used a 1.5KW semiconductor laser to conduct surface melting treatment on AZ31 and AZ61 magnesium alloys. The hardness of AZ31 was increased from 65hv of the matrix to 120hv of the melting layer, and the hardness of AZ61 was increased from 70hv of the matrix to 140hv of the melting layer. The wear amount was reduced by half, improving its wear resistance

Gao Yali et al. Used an 800W CO2 laser to conduct laser surface melting treatment on AZ91HP Magnesium alloy. Compared with the original magnesium alloy, the hardness of the fused layer is increased by about 90%, the wear resistance is increased by 78%, and the corrosion resistance is significantly improved. This is the joint effect of dendrite refinement and melting layer. We studied the laser melting technology of AZ31B with a 5kW transverse flow CO2 laser. The microstructure is shown in Figure 2. It can be seen that the grains in the melting zone are significantly smaller than the base metal

Fig. 2 laser melting microstructure of AZ31B magnesium alloy

4.2 laser surface alloying

there are few studies on alloying treatment of magnesium alloy surface at home and abroad, and the main research is to improve the wear resistance of alloying layer by injecting hard particles. Majurndar J D of India used a 10kW continuous CO2 laser to carry out surface alloying treatment on mez with al+mn, SiC and al+al2o3 alloy powders. The hardness was increased from 35hv of the matrix to 270hv of the alloying layer. Due to the existence of hard phase SiC, the wear resistance was improved at the same time

Chen Changjun and others used a 5kW CO2 laser to alloying ZM5 with Al-Y powder on the surface. The hardness of the coating can reach 250hv-325hv, while the hardness of the substrate is only 80hv-100hv. Compared with the base material, Sandvik is also one of the few manufacturers in China that can produce high-quality U-tubes. The corrosion resistance of the coating after laser treatment has been significantly improved

4.3 laser surface cladding

compared with laser melting and laser alloying, the research on laser cladding of magnesium alloys at home and abroad is relatively active. Laser cladding of magnesium alloys mainly focuses on improving the wear resistance and corrosion resistance of magnesium alloys

German Maiwald T and others used al+cu, al+si and AlSi30 alloy powder to laser cladding az91e and nez210. The corrosion resistance of al+si cladding layer is better than that of al+cu cladding layer, and the corrosion resistance of AlSi30 cladding layer is the best. German bakkar a laser cladded Al-S powder on the surface of carbon fiber reinforced AS41, and obtained a cladding layer with a good interface with the base Hugh, and the corrosion resistance of the cladding layer was improved

Huang Kaijin and others used a 3.5kw laser to effectively cladding amorphous composite powder Zr Cu Ni Al/TiC on the surface of az9id. Under the action of amorphous and intermetallic compounds, the hardness of the cladding layer was increased from 100hv0.1 to 850hv0.1 of the substrate, and the hardness was increased by about 7 times. After adding tic, the hardness was increased by about 9 times, and the wear resistance of the cladding layer was increased by 16 times compared with the substrate

improving the structural service performance of magnesium alloys through surface modification is an important means, and will become one of the important directions of magnesium alloy research. However, this work is far from enough, and the research that can be used for practical reference is even fewer

Further research on laser processing of magnesium alloys

magnesium alloy materials have attracted the interest of research and development all over the world, but about 70% of magnesium alloy materials are mainly used in the form of castings or die castings, and only about 10% are processed into thick plates, thin plates, bars and profiles, forgings and die forgings by pressure processing. Therefore, the development of deep processing of magnesium alloys is an inevitable trend

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