Abstract
In this research, the microstructures and mechanical properties of similar and dissimilar autogenous joints of 3 mm thick commercially pure titanium (CP-Ti) and Ti-6Al-4V welded by ytterbium fiber laser (Yb:YAG) were investigated. Two sets of laser power and welding speed were selected in such a way that the heat input remained constant. Microstructural characterization of the joints was investigated by an optical microscope, and mechanical properties were determined by hardness and tensile tests. The only defects found were porosity and underfill, and no signs of lack of penetration and solidification cracks were observed in any of the joints. Microstructural evaluation of the fusion zone (FZ) showed that in similar Ti-6Al-4V joint, a supersaturated nonequilibrium α′ martensite was formed due to rapid cooling associated with laser welding. In similar CP-Ti, coarse equiaxed grains were observed in the FZ. Unlike the similar joints, a clear interface was observed between the heat-affected zone (HAZ) and the FZ in both the CP-Ti and Ti-6Al-4V sides in dissimilar joints. Among all the joints with different weld parameters, similar Ti-6Al-4V showed the highest strength and the lowest ductility. In similar CP-Ti and dissimilar joints, fractures took place in the CP-Ti base metal, but all the Ti-6Al-4V similar joints failed in the FZ. Significant changes in the strength and hardness with varying laser power and welding speed implied that the mechanical properties of the weld fusion zones were not entirely governed by the heat input but were also affected by individual welding parameters.
Highlights
In the past few decades, titanium alloys have gained considerable popularity in several engineering industries due to their remarkable strength-to-weight ratio [1]
Volume percentage of porosities were 200 from three different cross sections and were calculated found to be 2.37% and 0.32% for 3 and 4 kW, respectively, which indicates that the keyhole was much 0 more stable at higher laser power despite the fact that0 the heat input was constant in both12cases. 0
A clear interface was observed between the heat-affected zone (HAZ) and the fusion zone (FZ) in both the commercially pure titanium (CP-Ti) and Ti-64 sides, which can be explained by sudden changes in the prominent microstructure
Summary
In the past few decades, titanium alloys have gained considerable popularity in several engineering industries due to their remarkable strength-to-weight ratio [1]. Fusion welding processes, such as laser and electron beam welding in dissimilar titanium alloys, have still not been explored in detail Conventional welding methods, such as gas tungsten arc welding (GTAW), can be used to join Ti alloys, but the high heat input during arc welding can significantly reduce ductility and formability, partially due to grain coarsening in the fusion zone (FZ) and heat-affected zones (HAZs) [11]. Froend et al [25] investigated the shape and morphology of welded seam as well as the presence and form of defects in dissimilar T-joints between CP-Ti and Ti-64 welded by ytterbium fiber laser They identified 13 process parameters, including laser power, welding speed, gas shield, and angle of laser, which had strong influences on the weld quality. Weld quality of similar and dissimilar butt joints were studied by analyzing the microstructure, defects, and mechanical properties
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