Effects of latent heat of fusion on thermal processes in laser welding of aluminium alloys

Abstract

Based on the Green's function method, a mathematical model allowing for the latent heat of fusion and solidification is developed to describe the steady state, two-dimensional heat flow during welding of thin plates. It is demonstrated that the latent heat has a pronounced effect on shape and size of the weld pool and mushy zone. The thermal efficiency of base metal fusion by a line heat source g t can exceed 0 . 4839 considerably if the latent heat is taken into account. It is shown that the known simplified approaches for considering the latent heat can introduce large errors into the estimation of g t . The calculated and experimental weld pool shapes are compared.A L cross-sectional area of fused metal, m 2 a thermal diffusivity, m 2 s 21 c specific heat capacity of liquid and solid phases, J kg 21 K 21 c ma maximum specific heat capacity including latent heat, J kg 21 K 21 d diameter of constant density heat source, m D hs heat source area, m 2 D mz mushy zone area, m 2 f Green's function, K W 21 f L liquid fraction h plate thickness, m H enthalpy per unit mass, J kg 21 DH latent heat of fusion and solidification, J kg 21 i, iz1 iteration levels K 0 modified Bessel function of second kind of zero order L total latent heat of fusion and solidification, J kg 21 Pe Peclet number Pr Prandtl number q 2 net heat flow density, W m 22 q net net heat input (net power), W Ste Stefan number T temperature, K T 0 initial temperature, ambient temperature, K T L liquidus temperature at which solid formation commences, K T S solidus temperature at which full solidification is achieved, K v welding speed, m s 21 W weld width, m x, y Cartesian frame travelling with source, m a coefficient of heat transfer from plate to ambient air, W m 22 K 21 b dimensionless heat transfer parameter e 1 , e 2 dimensionless heat input j, g coordinates of reference point for Green's function g t thermal efficiency of base metal fusion l thermal conductivity, W m 21 K 21 l ma maximum thermal conductivity including latent heat, W m 21 K 21 L dimensionless latent heat of fusion and solidification r density, kg m 23 v iteration parameter IntroducionIn analysis of thermal processes, the known functionanalytical solutions of the heat conduction problem, which do not include the latent heat of phase transformations, are usually used. 1-4 The major advantage of these solutions is the ease of implementation; the major disadvantage is a large calculation error for the high temperature region. Whereas the latent heat of solid-solid transformation is relatively low and can be neglected, the energy stored in the latent heat of fusion for aluminium alloys can be as much as 40% of the energy required to bring the material to its melting

Residual stresses in gas tungsten arc welding: a novel phase-field thermo-elastoplasticity modeling and parameter treatment framework

“…Thus, by utilizing the phase-field approach, it is possible to account for the effect of energy release or absorption in the shape of latent heat during the phase change. Furthermore, this term has a prominent effect on the temperature evolution in the weld pool, which was also observed in, e.g., [56,97]. The impact on the temperature profile is shown in Fig.…”

Influence of Latent Heat of Fusion on the Melt Pool Shape and Size in the Direct Laser Deposition Process

“…Let us use the iterative method presented in [ 26 , 27 ]. Then, the essence of the method is as follows: The multiplier is determined according to the known distribution of the field H f (Θ) k at the k iteration; Temperature Θ k is calculated according to Equation (14); Calculate H f (Θ) k+1 for the next iteration as subject to the constraint 0 ≤ H f k+1 ≤ L , where Θ( H ) is the inverse function, L —value of latent heat of fusion.…”

“…In this case, the elongation degree can be completely different up to zero, as in the case of an aluminum alloy. However, it should be noted that if the function H ( T ) is non-linear and increases sharply towards the end of the temperature interval, it can then lead to a greater elongation of the melt pool tail than with a linear dependence [ 27 ].…”

“…The procedure works on a fixed grid and does not require the implementation of the Stefan condition at the solid–liquid interface. The implementation of the phase transition phenomenon for the laser welding process calculation based on the analytical approach is described by Karkhin [ 27 ]. It is shown that latent heat has a pronounced effect on the shape and size of the weld pool and the mushy zone; namely, the molten pool takes on the typical elongated and tear drop shape.…”

Characterization of Temperature Fields in Laser Beam Welded Hollow-Cylindrical Cold Crack Samples from High Strength Steel 100Cr6

“…The heat input during welding leads to a local temperature increase, which varies depending on the specific enthalpy h and density ρ of the material. The resulting temperature gradient generates a directional flow depending on the thermal conductivity λ. Karkhin [15] uses the example of laser welding of aluminum to describe the effects of latent heat on thermal processes. He shows that considering latent heat of fusion and solidification reduces the weld width and affects the geometric course of the mushy zone (solid/liquid interface).…”