Aluminum alloy is widely used to make building panels, doors and windows, curtain walls, automobile decorative parts and aircraft skin due to its corrosion, surface treatment, beauty and durability. There is usually a dense oxide film on the surface of aluminum alloy. The oxide film has many pores, and the pore size becomes larger from the inside to the outside. It has good adsorption capacity and strong adhesion with the substrate. Therefore, it is necessary to pretreat and clean the oxide film of aluminum alloy. Compared with the traditional cleaning method, laser cleaning is an advanced environmental protection cleaning technology. Laser cleaning method has the characteristics of less environmental pollution, no contact, less wear on the substrate, high flexibility and stability, which can realize automatic cleaning, wide application range and good cleaning effect. But the key problem of cleaning is to determine the laser cleaning threshold and damage threshold. Firstly, the experiment of laser cleaning aluminum alloy oxide film was simply carried out, and the cleaning threshold and damage threshold were roughly determined by the morphology characteristics. In the theoretical part, the cleaning threshold is obtained by heat conduction model and numerical calculation analysis. Finally, it is found that the theoretical calculation results are consistent with the experimental results.
In the industrial field, in order to protect the metal, the metal surface is painted. However, when metals need to be welded, coating becomes a problem. Since the solid polymer coating sublimates during the high temperature welding process, pores are generated in the weld bead[1] .So removal coating is very importance in industry and there have numerous ways to removal coating. Paint removal by laser ablation is favoured among cleaning techniques due to its high efficiency. How to predict the optimal laser parameters without producing damage to substrate still remains challenging for accurate paint removal [2] .In this paper, based on the laser ablation morphology, combined with experiments and numerical simulations, the mechanism and optimal conditions of laser ablation for paint removal are deeply studied. Our studies suggest that laser removal have many physics and chemistry phenomenon including the redox reaction, carbonization, melting and gasification. The threshold value of laser paint removal is 30W obtained from the laser cleaning experiment. The model of laser temperature rise is established, and it is found by numerical simulation that the theory is in good agreement with the experiment
As a common alloy material, aluminum alloy has a good application prospect in the fields of construction, automobile, electric power and aerospace.There is a layer of high melting point oxide film on the surface of aluminum alloy, which will hinder the laser energy transfer, lead to poor welding stability, and easily lead to welding defects such as porosity and inclusion in the weld; the surface of aluminum alloy has high reflectivity of laser, which makes the utilization rate of laser energy low, which is easy to cause welding defects such as incomplete penetration and incomplete fusion. Therefore, the surface of aluminum alloy should be pretreated before laser welding. Laser cleaning is an advanced and environmentally friendly cleaning technology. A Nd: YAG laser with 1064 ns pulse width was used to study the morphology of aluminum alloy under the action of nanosecond laser pulse cleaning.The laser-treated surfaces were characterised using metallurgical microscope. Successful oxide removabove certain thresholds that defined the lower end of the process operating window for pulse operation . The ablationechanisms involved in the removaloxide firom 1064nm and found to combineboth thermal and mechanical effects , the surface melting first occurring at fluences lower than those at which cleaning is initialised.In the process of laser cleaning, new oxide layer is formed.
In this paper, the temperature and damage morphology of silicon induced by ms-ns combined-pulse laser with different pulse delay are investigated. The small holes and trapped bubbles were formed on the center of damage morphology when the pulse delay is 0.8ms -1ms. The temperature of target exceeds the melting point and the molten pool begins to be formed before the irradiation of ns laser. It was found that the process of droplet ejection and phase explosion might occurred after the irradiation of ns laser. The relationship between temperature and damage morphology induced by ms–ns combined-pulse laser with different pulse delays was discussed. The results in this paper can provide foundation for ms-ns combined-pulse laser processing of semiconductor materials in the future.
In this paper, we established a two-dimensional spatial axisymmetric finite element model to simulate the laser-supported absorption wave(LSAW) induced millisecond pulsed laser on aluminum alloy, obtained the relationship among velocity of LSAW, laser energy density and pulse width. And the finite element analysis software, COMSOL Multiphysics, was utilazed in the research. we simulated the generation and propagation procedure of LSAW based on hydrodynamic theory. All the important physical process were considered in the model which were inverse bremsstrahlung, thermal radiation, heat conduction and thermal convection. We simulated aluminum alloy irradiated by long pulse laser with different energy densities and pulse widths, the results showed that the time when the velocity reached maximum was increased with the growth of laser energy density, after laser irradiation, the velocity of LASW decreased immediately to zero, and the velocity of LSAW become slower by increasing the pulse width while the laser energy density was unchanged, moreover, the velocity of LSAW increased by increasing the laser energy density while the pulse width was unchanged. The results of the study can be applied in the laser propulsion and laser enhancement technology, etc.
In this paper, we established a two-dimensional spatial axisymmetric finite element model to simulate the laser-supported absorption wave(LSAW) induced millisecond multiple pulsed laser on aluminum alloy, made theoretical investigation. And the finite element analysis software, COMSOL Multiphysics, was utilized in the research. we simulated the generation and propagation procedure of LSAW based on hydrodynamic theory. All the important physical process were considered in the model which were inverse bremsstrahlung, thermal radiation, heat conduction and thermal convection. We simulated aluminum alloy irradiated by long pulse laser with 35J energy, 1ms pulse width and 1mm spot radius in the case of different pulse number, we first obtain the simulation result of velocity fields and temperature fields of LSAW, the results showed that there was a certain temperature cumulative effect near target material; Aiming at obtaining the relationship between the generation time of LSAW and laser pulse number. We keep the laser pulse width, energy density and pulse frequency unchanged, the pulse number was 3, 5, 10 respectively; the results showed that the generation time of LSAW become shorter by increasing the laser pulse number. The results of the study can be applied in the laser propulsion and laser enhancement technology, etc.
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