Abstract Synchrotron X-ray imaging was used to study the microstructural evolution of solidification cracking for an Al-Cu alloy at the weld crater without applying an external force. The distributions of strain, strain rate, Cu concentration in the liquid and solid fraction during solidification were evaluated using a quantitative analysis of the image sequences. The initiation of solidification cracking was identified by the combination of the radiographic images and the measurement of the transmitted X-ray intensities. The initial crack occurred at the local tensile strain of 1.4%, local tensile strain rate of 0.34 s−1 and solid fraction of 81% in the center of weld pool where columnar dendrites growing from the opposite sides impinged in the parallel to the growth direction. The solidification cracking evolved along the liquid film via the coalescence of small initial cracks. In addition, the solidification cracking propagated to the interdendritic region through the triple junction where the high shear strain was localized. Both the tensile and shear stresses contributed to the cracking formation at the weld crater.

中文翻译：

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Al-Cu合金焊缝处凝固裂纹的时间分辨X射线成像

摘要 利用同步辐射X射线成像技术研究了Al-Cu合金在不施加外力的情况下焊缝处凝固裂纹的显微组织演变。使用图像序列的定量分析来评估凝固过程中应变、应变速率、液体中的铜浓度和固体分数的分布。凝固开裂的开始通过射线照相图像和透射X射线强度的测量来确定。初始裂纹发生在局部拉伸应变为 1.4%、局部拉伸应变速率为 0.34 s-1 和固相分数为 81% 的焊池中心，其中从相对两侧生长的柱状枝晶平行于生长方向碰撞. 通过小的初始裂纹的聚结，凝固裂纹沿着液膜发展。此外，凝固裂纹通过三联结传播到枝晶间区域，在那里高剪切应变是局部的。拉应力和剪应力都会导致焊缝裂纹的形成。