In situ electron microscopy investigation of void healing in an Al-Mg-Er alloy at a low temperature

Using in situ transmission electron microscopy and electron tomography, we have studied the healing process of submicron-scale voids embedded in a cold-rolled Al-Mg-Er alloy. The results show that voids are healed successfully within 50 min at a relatively low temperature of 453 K. Quantitative analysis of the in situ micrographs reveals that the void-healing process involves several stages: an initial fast-healing stage, then a slow-healing stage, and finally a rapid healing near the end. The different healing rates are likely related to varying surface curvatures due to the evolution of void geometry during the healing process. Because the voids are embedded inside Al alloy grains, lattice diffusion is considered to dominate the entire healing process. Mg enrichment was observed at the healed voids immediately after the healing. This indicates that the faster diffusion of Mg atoms in the Al matrix enhances void healing in the Al-Mg-Er alloy. Post-mortem experiments verify that voids in bulk cold-rolled Al-Mg-Er alloy can also be healed by 1 h of annealing at 473 K, consistent with the in situ experiments. The fatigue crack growth resistance and plasticity of the cold-rolled Al alloy are improved significantly after annealing at 473 K.