- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Mechanism study on the effects of power modulation on energy coupling efficiency in infrared laser welding of highly-reflective materials
摘要： High-reflectivity of materials, such as magnesium, copper and aluminum, results in low thermal efficiency of their infrared laser welding processes. AZ31 magnesium alloy was selected to study the effects of power modulation on energy coupling efficiency in laser welding of highly-reflective materials. A model for the relationship between energy coupling efficiency and modulation parameters was obtained. The energy coupling efficiency in optimized modulated-power laser welding was about 1.58 times that in constant-power welding. The mechanism was explored by analyzing keyhole evolution and the resulted pressure distribution along keyhole wall during welding. The keyhole evolutions in laser continuous welding of common material (Q345 steel, reflectivity of 65%) and highly-reflective material (AZ31, reflectivity of 85%) were observed through high-speed imaging by utilizing a half sandwich method. The results indicated that the secret of improving energy coupling efficiency of laser welding process of highly-reflective materials through power modulation was the formation of a deep keyhole and its long life. When instantaneous power decreased from the peak, there was still enough recoil pressure at the bottom of keyhole to resist surface tension and hydrostatic pressure of liquid metal, which was the fundamental reason for the long time existence of keyhole with a large depth.
关键词： laser welding,magnesium alloy,recoil pressure,keyhole,highly-reflective materials,power modulation
更新于2025-11-28 14:24:20
-
Simulation of evaporation and propulsion of small particles in a laser beam
摘要： The technique of numerical simulation of laser surface evaporation of small particles ranging in size from tens to several millimeters falling into the field of laser radiation is developed. The interaction of a laser beam with solid or liquid particles freely flying in a gas-dispersed stream is accompanied by heating and evaporation of the material, which occurs only from the irradiated part of the particle surface. The result is a reactive force created by the laser, which depends on the characteristics of the radiation and the physical properties of the particle material. The technique allows describing the pre-threshold, near-threshold and super-threshold modes of evaporation and is designed to calculate the light propulsion force due to the vapor recoil pressure arising from the irradiated part of the particle surface in the range of Mach numbers to unity. The Meshcherskii equation is used to simulate the reactive acceleration of particles. It is shown that, in the case of a pulsed laser effect, the theory is in good agreement with experimental data on reactive acceleration of aluminum, corundum, and graphite particles. A distinctive feature of the technique is the ability to calculate the gas dynamic parameters of steam and recoil pressure in a wide range of the power density of the absorbed laser radiation from 10 to 10,000 GW/m2.
关键词： laser surface evaporation,reactive force,vapor recoil pressure,small particles,Meshcherskii equation
更新于2025-09-23 15:19:57
-
An investigation of recast behavior in laser ablation of 4H-silicon carbide wafer
摘要： 4H-silicon carbide (SiC) is a suitable semiconductor material for high-speed power devices but also a typical difficult-to-process and hard-brittle material. Laser ablation is an efficient approach to process SiC. However, recast layer is an inevitable thermal damage during laser ablation. The present study experimentally and numerically investigated the recast behavior in laser ablation of 4H–SiC. The recast humps are with height of 1.4–3.3 μm and width of 12–22 μm, consist of SiC, Si, and SiO2, where 15.08 wt% of oxygen is detected. Microcracks and pore clusters are observed on the recast humps under SEM. Recoil pressure and surface tension in the molten pool dominate the process of recast hump formation. The recoil pressure of Si vapor is 2.27 MPa at 5000 K, as high as 22 times of atmospheric pressure. The simulation results show that the fluid in the middle flows around while the surrounding fluid flows upwards. The upward flow is almost laminar while the flow at the bottom of the molten pool is turbulent entertaining air and forming bubbles. The vaporization-induced keyhole in the molten pool becomes deeper and the sidewall becomes more inclined over time, accompanying with the “growing” of the recast hump. There are mainly three reasons causing the increase of recast height and recast width with the increased average laser power: (a) increase of recoil pressure; (b) increase of temperature gradient in the molten pool, enhancing the Marangoni convection; and (c) enlarging the molten pool and leading to more materials melting. With the decrease of the laser scanning speed, more liquid molten material is evaporated in the molten pool instead of being ejected outward to form recast humps. The increase of the laser pulse frequency decreases the peak laser intensity and hence results in the decrease of the recoil pressure. Besides, it also leads to the weakening of the heating ability of laser and lessening of the liquid molten material that could be ejected.
关键词： Marangoni convection,Recoil pressure,4H-silicon carbide,Recast layer,Laser ablation
更新于2025-09-11 14:15:04