1. Introduction
Laser welding is recognized as an effective process to weld metals with a laser beam of high-power, high-energy density. In fact, the power density of a laser beam is much higher than that of arc or plasma. Consequently, a deep narrow penetration weld can be effectively produced. These properties have made laser welding a suitable technology for weldments that are made from metals of different compositions and properties [
1,
2]. A dissimilar joint is as strong as the weaker of the two metals being joined, i.e., possesses sufficient tensile strength and ductility so that the joint will not fail in the weld, has good fatigue behavior [
3].
Among them, Al/Ti dissimilar joints are of major interest in aeronautics and automotive applications, where weight reduction, coupled with high mechanical strength and corrosion resistance, are paramount. Between the different Al/Ti welding processes laser welding offers numerous advantages. Especially in aluminum alloys when used in keyhole mode improves the absorption of the beam due to the multiple reflections in the cavity [
4]. Moreover, high energy density, high cooling and heating rate allow for reducing the importance of mixing and diffusion phenomena, and thus reduce the formation of intermetallic compounds in the case of dissimilar joints. An Al/Ti joint has a remarkably lower elongation due to the high residual stresses, which facilitate the crack ignition and propagation. Therefore, the quality depends heavily on the process parameters, which determine the magnitude of thermal stresses [
5].
The selection of the welding parameters is crucial for obtaining a satisfactory quality weld. Residual stresses and temperature field in laser welding joints can be predicted by numerical analysis such as a finite element one. The Finite Element Method has been one of the performing techniques to predict the joint properties in the welding process, which involves thermal, metallurgical and mechanical phenomena.
The computation of thermal field relies strongly on the heat source model. Rosenthal was the first researcher who proposed a model for the heat source in welding [
6]. He proposed an analytical solution considering a punctual or a line heat source. Since then, other more realistic models have been proposed. For arc welding, several heat source configurations have also been proposed. Two and three-dimensional approaches can be used. Zeng et al. described the thermal elastic-plastic analysis using finite element techniques to analyze the thermos-mechanical behavior and evaluate the residual stresses and welding distortion on the AZ31B magnesium alloy and 304L steel butt joint in laser-TIG hybrid welding [
7]. A modified three-dimensional conical heat source was used for performing the simulation in arc welding [
8,
9]. In certain cases, the finite element model is integrated with other computational techniques like artificial intelligence to establish an automated and iterative optimization algorithm [
10]. Zeng et al. calculated the thermal cycles and temperature distribution of MIG welding of 5A06 aluminum alloy structure during discontinuous welding. The finite element method transient heat transfer analysis was used to save computing time and improve calculation accuracy [
11].
For the fiber laser, Casalino et al. [
12] developed and applied a stationary process with a surface heat source model based on thermal load through several specific elements next to the welding line. Other researchers [
13] proposed the combination of Gaussian distribution on the surface and distribution along the thickness to consider 3D distribution by applying the conical Gaussian heat source model. They found that 3D conical Gaussian heat distribution can obtain better results with high depth to width ratio (defined as the ratio between the weld penetration evaluated on the axis of fused zone, and the width of the welded seam in the horizontal direction on the sample surface). Nagel et al. [
14] proposed some strategies for the optimization of the laser welding of high alloy steel sheets using two different heat sources.
In this paper, two-dimensional and three-dimensional heat distribution was used for welding laser simulation of dissimilar Al/Ti button joint. The objective of this study is to compare the two approaches to establish the best model. The simulated fusion zone was compared with the macrograph obtained from the experiment to calibrate the model. Then, the validation is based on the comparison of the temperature profile measured with thermocouples during the welding cycle.