| Zinc-coated steel is used extensively in the automobile industry because of itsdurability and high corrosion resistance and formability. Laser welding technologyplays an important role in welding field of galvanized steel due to its high weldingspeed, narrow welding seam, small heat affected zone, small welding deformation andgood mechanical properties of joint. However the zinc layer is vaporized and ionizedeasily during laser welding of galvanized steel, causing weld defects such as pores,splashes, cave and incomplete fusion. The laser induced plasma produced during theprocess of laser deep penetration welding has a significant relationship with thestability of welding process and welding quality. In this paper, copper powder wasadded to reduce the zinc vapor and the zinc plasma produced in the welding process.Furthermore, the mechanism of zinc behavior control in laser welding of galvanizedsteel with powder feeding was studied, and the corresponding correlation between theweld defects and the spectrum signals in the process was analyzed.Firstly, a test platform based on multi-channel spectrum signal acquisitionsystem was established. During the process of laser welding tests, the multi-channelspectral measurement system was used to obtain the spectra signal of laser inducedplasma. Secondly, the spectral lines was selected to calculate the temperature ofplasma, the effect of adding copper to temperature variation of plasma was analyzed,it has shown that the oscillation amplitude and the average value of temperature of theplasma is reduced when copper powder is added. The electron density and the inversebremsstrahlung absorption coefficient of plasma were calculated: energy decrementinduced by inverse bremsstrahlung absorption of plasma was analyzed when laserwelding galvanized steel with different copper addition, the results show that theaddition of copper can reduce the inverse bremsstrahlung absorption coefficient andthe energy decrement. Thirdly, elements distributions in longitudinal section, crosssection of the welds and around a pore were analyzed. The analysis results show that:the contents of Cu and Zn are basically in the same change trend; Copper-Zinc solidsolution alloy is generated by Zn and added Cu, which reduced zinc evaporation andzinc plasma in the welding process, and inhibited the behavior of zinc to a certainextent. Finally, the characteristic spectral lines of different elements and the weldpores were analyzed, and the corresponding correlation between weld pores and spectrum of Cu â… 324.8nm was established.The results will provide the theoretical basis for the future control of zincbehavior and real-time monitoring of weld quality in the process of weldinggalvanized steel with powder. |
