Geometric and Chemical Composition Effects on Healing Kinetics of Voids in Mg-bearing Al Alloys

The healing kinetics of nanometer-scale voids in Al-Mg-Er and Al-Mg-Zn-Er alloy systems were investigated with a combination of in situ transmission electron microscopy and electron tomography at different temperatures. Mg was observed completely healing the voids, which were then rejuvenated to the alloy composition with further aging, in the Al-Mg-Er alloy. On the contrary, Mg51Zn20 intermetallic compound was formed in voids in the Al-Mg-Zn-Er alloy, which leads to complete filling of the voids but not rejuvenation for the material. For voids with different geometrical aspects, different evolution processes were observed, which are related to the competition between bulk and surface diffusion of the alloys. For voids with a large size difference in their two ends, a viscous flow of surface atoms can be directly observed with in situ electron microscopy, when the size of one end becomes less than tens of nanometers. (C) The Minerals, Metals & Materials Society and ASM International 2016