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首先深入研究了电子束扫描焊接对钛合金焊缝金属凝固组织细化的影响,发现模拟凝固前沿电子束扫描焊接才能细化焊缝凝固组织,提出了电子束扫描焊接细化凝固组织的机理。 其次,研究不同凝固组织的焊缝金属腐蚀性能发现,当电子束扫描频率为0～200Hz时,粗大柱状晶焊缝金属的阳极极化曲线中出现活化电流密度峰值,与母材的腐蚀电位差小于零,维钝电流密度显著高于母材,发生焊缝优先腐蚀。当电子束扫描频率为300Hz时,150μm等轴晶焊缝金属的阳极极化曲线与母材几乎重合,为焊缝和母材耐腐蚀的最佳匹配,由此提出焊缝与母材均等耐腐蚀的理论。当电子束扫描频率为400Hz时,100μm等轴晶焊缝金属的阳极极化曲线中未出现活化电流密度峰值,维钝电流密度低于母材,与母材的腐蚀电位差大于零,母材有优先腐蚀的倾向。 同时发现柱状晶微观组织中粗大的晶内组织及α相中均匀条形密排位错造成的应力场会加速均匀腐蚀,而亚稳β相分解成两相组织与点蚀有关,提出了钛合金焊缝金属均匀腐蚀和点蚀的机制。 最后得出焊缝金属凝固组织化学不均为性与母材化学不均匀性程度的差异,制约腐蚀反应的方向,是腐蚀发生的热力学判据,而焊缝金属凝固组织的化学不均匀性,是腐蚀反应的驱动力,为腐蚀反应的动力学判据。
Firstly, the effect of electron beam scanning welding on the microstructure refinement of the weld metal of titanium alloy was studied in depth. It was found that the solidification microstructure of weld metal could be refined by electron beam scanning before simulated solidification. The mechanism of electron beam scanning welding refinement solidification structure was proposed. Secondly, the study of the corrosion properties of the weld metal in different solidified microstructure shows that when the scan frequency of the electron beam is 0 ~ 200Hz, the peak value of the activation current peak appears in the anodic polarization curve of the coarse columnar crystal weld metal, which is different from the corrosion potential difference Less than zero, dimension obtuse current density is significantly higher than the base metal, weld priority corrosion occurred. When the scanning frequency of electron beam is 300Hz, the anodic polarization curve of 150μm equiaxed weld metal almost coincides with the base metal, which is the best match of the corrosion resistance between the weld and base metal, Corrosion theory. When the scanning frequency of electron beam is 400Hz, the peak value of activation current density does not appear in the anodic polarization curve of 100μm equiaxed grain weld metal. The current density is lower than that of base metal and the difference of corrosion potential between base metal and base metal is more than zero. Preferential corrosion tendency. At the same time, it is found that the coarse intragranular microstructure of columnar grains and the stress field caused by dislocation of dense strip in the α phase accelerate the uniform corrosion, while the metastable β phase decomposes into two phases and pitting corrosion is proposed. Mechanism of uniform corrosion and pitting of alloy weld metal. Finally, the difference between the chemical heterogeneity of the solidified microstructure of the weld metal and the chemical heterogeneity of the base metal is obtained, the direction of the corrosion reaction is constrained, and the thermodynamic criterion for the corrosion occurs. The chemical heterogeneity of the solidified microstructure of the weld metal, It is the driving force of corrosion reaction and the kinetic criterion of corrosion reaction.