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.　(C)　2014　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.