Numerical and experimental investigation of magnesium/aluminum laser welding with magnetic field

A three-dimensional numerical model for thermal-fluid-metallurgical coupling was established to inspect the effect from a stable longitudinal magnetic field on molten pool of magnesium/aluminum laser welding. Magnetic field-assisted laser welding platform was built to test the morphology and spectrum of the metal vapor/plasma. The scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) were used to determine the morphology and element distribution of molten pool cross section. Simulation results showed that temperature gradient of molten pool was reduced, heat distribution became uniform, and keyhole area was enlarged. In addition, the flow velocity of molten pool was increased, the vorticity of molten pool was improved, and the flow region of liquid metal was enlarged. Experimental results showed that penetration of molten pool was deeper, the shape of welding pool tended to be symmetrical and the density of Al element distribution in welding pool was increased by magnetic field. Thus, heat and mass transfer in welding pool was promoted due to the application of magnetic field, the elements exchange and the convection of liquid metal were accelerated, and the distribution of Mg-Al compounds should be dispersed under the agitation of Lorentz force. It’s predicted that the distribution of Mg-Al compounds in magnesium/aluminum laser welding would be positively affected by magnetic field, which was beneficial to control the weld quality. Hence, numerical results and experimental verification shared good consistency.

Simulation on the Thermal Behavior in Vacuum Electron Beam Welding of Magnesium Alloy

The thermal behavior during electron beam welding on magnesium alloy were analyzed and simulated. According to the thermal effect of the electron-beam-generated keyhole, a mathematic model of rotary Gaussian body heat source with incremental power-density-distribution was developed. This model can be useful for simulating the thermal effect of metal vapor plasma on the surface of the workpiece and the deep-penetrating effect of the electron beam. By the action of thermal model, the characteristics of temperature field during vacuum electron beam welding on AZ61 magnesium alloy were studied by the method of finite element analysis. And then, the influence of welding parameters on the temperature distributions and the weld contours were analyzed. The simulations and experiments showed that the different deep-penetration effects and temperature distributions were achieved with the varying welding energy inputs, and the metal vapor plasma has a significant impact on the weld contour of magnesium alloy.

Ways to discharge-based soft X-ray lasers with the wavelength λ<15 nm

Two basic ways to amplification of spontaneous emission in the soft X-ray region are described. The first is based on the electron-collisional recombination pumping scheme, which uses recombination of fully stripped ions into hydrogen-like ions to create (in the case of sufficiently fast cooling) a population inversion on energy levels belonging to the Balmer-alpha transition. We test this scheme on nitrogen, for which the lasing wavelength is 13.4 nm. The second way to amplification of spontaneous emission is based on the electron-collisional excitation pumping scheme: this uses for creation of population inversion a fast excitation of Ne- or Ni-like ions. However, for wavelength below 15 nm it is necessary to use Ni-like ions of some metal vapors. Feeding metal vapors into a capillary is difficult, and if being fed they deposit on the capillary wall and significantly reduce the capillary lifetime. That is why we prepare metal vapor plasma in a capillary with liquid wall – by wire explosion in water. For slowdown of the plasma-channel expansion a local-water-compression by linearly focused shock wave is being developed.