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.

中文翻译：

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CP-Ti和Ti-6Al-4V相似和不相似的光纤激光焊接接头的组织和力学性能

在这项研究中，研究了3光纤激光器（Yb：YAG）焊接的3mm厚商业纯钛（CP-Ti）和Ti-6Al-4V相似和不相似的自生接头的组织和力学性能。选择两组激光功率和焊接速度，以使热量输入保持恒定。用光学显微镜研究了接头的微观结构特征，并通过硬度和拉伸试验确定了机械性能。发现的唯一缺陷是气孔和底部填充，在任何接头中均未观察到缺乏渗透和凝固裂纹的迹象。熔合区（FZ）的显微组织评估表明，在相似的Ti-6Al-4V接头中，由于激光焊接的快速冷却，形成了过饱和的不平衡α'马氏体。在类似的CP-Ti中，在FZ中观察到了粗等轴晶。与类似的接头不同，在不同接头的CP-Ti和Ti-6Al-4V侧面的热影响区（HAZ）和FZ之间观察到清晰的界面。在所有具有不同焊接参数的接头中，相似的Ti-6Al-4V表现出最高的强度和最低的延展性。在相似的CP-Ti和不相似的接头中，CP-Ti母材发生了断裂，但所有Ti-6Al-4V相似的接头在FZ中均失效。强度和硬度随激光功率和焊接速度的变化而发生显着变化，这意味着焊缝熔合区的机械性能并不完全受热量输入的影响，还受到各个焊接参数的影响。在不同接头的CP-Ti和Ti-6Al-4V侧面的热影响区（HAZ）和FZ之间观察到清晰的界面。在所有具有不同焊接参数的接头中，相似的Ti-6Al-4V表现出最高的强度和最低的延展性。在相似的CP-Ti和不相似的接头中，CP-Ti母材发生了断裂，但所有Ti-6Al-4V相似的接头在FZ中均失效。强度和硬度随激光功率和焊接速度的变化而发生显着变化，这意味着焊缝熔合区的机械性能并不完全受热量输入的影响，还受到各个焊接参数的影响。在不同接头的CP-Ti和Ti-6Al-4V侧面的热影响区（HAZ）和FZ之间观察到清晰的界面。在所有具有不同焊接参数的接头中，相似的Ti-6Al-4V表现出最高的强度和最低的延展性。在相似的CP-Ti和不相似的接头中，CP-Ti母材发生了断裂，但所有Ti-6Al-4V相似的接头在FZ中均失效。强度和硬度随激光功率和焊接速度的变化而发生显着变化，这意味着焊缝熔合区的机械性能并不完全受热量输入的影响，还受到各个焊接参数的影响。类似的Ti-6Al-4V表现出最高的强度和最低的延展性。在相似的CP-Ti和不相似的接头中，CP-Ti母材发生了断裂，但所有Ti-6Al-4V相似的接头在FZ中均失效。强度和硬度随激光功率和焊接速度的变化而发生显着变化，这意味着焊缝熔合区的机械性能并不完全受热量输入的影响，还受到各个焊接参数的影响。类似的Ti-6Al-4V表现出最高的强度和最低的延展性。在相似的CP-Ti和不相似的接头中，CP-Ti母材发生了断裂，但所有Ti-6Al-4V相似的接头在FZ中均失效。强度和硬度随激光功率和焊接速度的变化而发生的显着变化表明，焊接熔合区的机械性能并不完全受热量输入的影响，还受各个焊接参数的影响。