Alloying element vaporization and weld pool temperature during laser welding of AlSl 202 stainless steel
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I.
INTRODUCTION
THE importance of element vaporization phenomena during laser welding process has been emphasized in recent studies. 1,2,3The vaporization process is particularly important in the laser welding of alloys containing one or more volatile components because of the potential loss of elements from the laser melted pools. The principal factors that govern the rates of vaporization of different elements are the temperature distribution at the surface of the molten pool and the composition of the melt. The temperature distribution, in turn, is governed by several factors including the rate of absorption of beam energy by the workpiece and convection in the molten region driven by surface tension gradients and the natural convection. The rate of absorption of the beam energy is dependent on the plasma composition which again is influenced by the temperature distribution at the surface of the molten pool. The complexity in the understanding of the element vaporization process arises from the interdependence of various physical phenomena that are involved in the process. Because of these complexities, no basic formalism is available at present to predict either the composition or the temperature of the plasma. Even the measurement of pool temperature is a formidable task since the molten pool is surrounded by hot plasma. Calculation of the pool temperature distribution by mathematical modeling would require prescription of the energy density distribution at the surface of the molten pool. Since the extent of the attenuation of the beam energy in the vicinity of the molten zone is dependent on the amount and composition of the plasma, determination of the energy density distribution at the surface of the workpiece with a reasonable degree of trustworthiness is not a straightforward task. If approximate calculations of pool temperature are made with several simplifying assumptions, the predicted value of pool temperature must be compared with experimentally determined values to examine the reliability of the prediction scheme. Therefore, the need to obtain experimental data on the pool temperature and plasma composition cannot be overemphasized. P. A. A. KHAN, Graduate Assistant, and T. DEBROY, Associate Professor of Metallurgy, are with the Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802. Manuscript submitted March 29, 1984. METALLURGICALTRANSACTIONS B
In this paper a new technique for the determination of weld pool temperature is demonstrated. Experimental data on the alloying element vaporization rates, plasma composition, and the changes in the weld composition during laser welding of AISI 202 stainless steel are discussed.
II.
EXPERIMENTAL PROCEDURES
A schematic diagram of the experimental set-up is presented in Figure l. A carbon dioxide laser, Coherent Model Everlase 525-1, capable of producing a maximum output power of 575 watts in the continuous wave mode, was used. Samples were placed on a remotely controlled, electrically operated tab
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