Effect of evaporation and temperature-dependent material properties on weld pool development
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I.
INTRODUCTION
UNDERSTANDING the development of the weld pool during welding is of considerable practical significance, since conduction and convection heat transfer in the weld pool can significantly influence the weld bead geometry, weld quality, and productivity. ]1-41 There have been a number of attempts t5-22] to predict the effect of processing conditions on the final properties of the weldment by mathematically modeling the transport phenomena that occur during welding. As a result, considerable progress has been made in the development of computational models and algorithms for studying weld pool development during fusion joining. The earlier models of welding processes, t5-1~ which involved conductive heat transfer only, are now superseded by more appropriate models in which allowance is made for convective effects, as driven by a combination of buoyancy, electromagnetic, and surface tension forces. ~1-22] Initially, most or all of the computational modeling involved the representation of two-dimensional (2-D) systems. Recently, however, three-dimensional, steadystate, tt8,191 and transient 12~ models have been developed for simulating the flow and heat-transfer conditions associated with welding processes. These models were applied to a variety of weld pool fluid flow and heat flow problems associated with stationary and nonstationary gas tungsten arc (GTA) welding of regular and irregular geometries. The aforementioned studies have contributed significantly to our understanding of the development of the weld pool during welding. However, the predictions of these models have to be considered as qualitative in nature, largely due to a number of idealizations involved in their development together with inadequate verification of their predictions. Although vaporization heat flux is important during welding, ]23]most studies Y~1'13-221of convective heat transfer in weld pools have ignored the vaporization heat flux T. ZACHARIA, Research Staff Member, S.A. DAVID, Group Leader, and J.M. VITEK, Research Staff Member, are with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. Manuscript submitted August 1, 1990.
METALLURGICAL TRANSACTIONS B
from the energy balance at the free surface. It has been shown t231 that weld pool evaporation results in an important cooling effect that limits the maximum temperature in the weld pool surface. To a limited extent, Thompson and Szekely t241 have incorporated the effect of vaporization by prescribing a vaporization temperature and not allowing the free surface temperature to exceed the vaporization temperature. However, this approach, in some cases, can alter the convective heat transfer in the weld pool by altering the surface tension gradient-driven flow, thereby influencing the development of the weld pool. In computational modeling of welding, the thermophysical properties of the alloys, together with the processing parameters, are of prime importance. The effect of processing parameters on the development of the weld pool was the
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