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Laser Welding Part 12

Tham khảo tài liệu 'laser welding part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 214 Laser Welding Fig. 14. a A typical spectrum of weld metal A15754 using a long pulse Nd YAG with 7ms pulse duration and 15Gw m2 power density b the emission characteristic lines of Al 396.1nm and Mg 285.2 nm for laser welding with different pulse duration 3and 5msec Mean Intensities of Al and Mg emission lines for various conditions of the laser welding process 3-7msec pulse duration are revealed in table 7. Pulse duration of laser welding process 3msec 4msec 5msec 6msec 7msec mean Intensity 285.2 nm MgI 211 202 197 193 190 RSD 285.2 nm MgI 2 1.3 1.5 2.2 1.9 mean Intensity 396.1 nm AlI 2563 2993 3021 3205 3421 RSD 396.1 nm AlI 1.9 1.8 2.1 2.2 1.9 Table 7. Mean Intensities of Al and Mg emission lines in LIBS analysis for 3-7msec pulse durations of laser welding The generated plasma in the laser ablation process is assumed to be in local thermodynamic equilibrium LTE . The LTE condition is given by 30 Ne 1.6 X1012T1 2AE3 36 Where Ne ascertains the electron density T K denotes the plasma temperature and AE eV is the largest energy transition for which the condition holds. Electron density is known as an important plasma parameter which gives indications about the thermal equilibrium. A common method for spectroscopic determination of Ne is based on the Stark effect of the atomic or ionic lines whereas for typical LIBS the contribution of ion broadening could be negligible. Therefore the Stark broadening AẰs of the neutral line expressed as the FWHM in nanometers is simplified as 13 31 Estimation of composition change in pulsed Nd YAG laser welding 215 N AZ 2W I 37 y 1016 Where W is the electron impact parameter. Therefore the line width AẶ. corresponding to the typical characteristic NII line was determined to estimate the electron density. The experiment satisfies equation 36 to emphasize the validity of LTE condition. Thus Boltzmann equation is used to relate the population of an excited level to the number density of the species within the plasma. The typical .