Tham khảo tài liệu 'laser welding part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 194 Laser Welding determined by laser induced breakdown spectroscopy LIBS for different welding conditions. Keywords Pulsed laser welding Nd YAG Laser Alloying element losses Keyhole formation model Stainless Steel 316 Aluminum alloy 5754 LIBS 1. Introduction During laser beam welding of many important alloys vaporization usually takes place from the weld pool surface. Undesirable vaporization of volatile alloying elements changes the weld metal composition relative to the base metal and resultantly the mechanical and metallurgical properties of the weld metal will change too. To realize a quantitative estimation of the weld metal composition while varying the irradiation parameters a comprehensive model is required. Several authors have used Longmuir equation for the calculation of the changes in weld metal composition due to various welding processes 1 2 .The equation is useful for calculation of relative vaporization rates from different alloying elements in vacuum and it results to a higher absolute rate than actual values 2-5 . Mundra and 2 derived equations for the vaporization rate of various alloying elements in conduction mode laser welding of high-manganese stainless steel with a CW CO2 laser. The model is based on the coupling of the principles of weld pool transport phenomena and vapor phase gas dynamics. In a similar work developed by and 5 the composition changes of stainless steel were estimated during Nd YAG laser welding. Although these models are valid for conduction mode welding but when the laser power density is increased to a level sufficient to evaporate a thin layer of material and the second kind of laser welding mode known as keyhole welding occurs they are not able to evaluate the composition change. By keyhole formation a deep hole is created inside the weld pool which is an effective trap for the laser beam 6 . Therefore creation of keyhole will increase the laser energy coupling to the material. U. Dilthey and .
