Synchrotron X-ray microtomography was used to observe the shrinkage and annihilation behaviors of hydrogen micropores in three dimensions during hot and cold plastic deformation of an Al-Mg alloy. It was examined, by exposing the material to a high temperature after plastic deformation, whether complete healing of micropores is achieved after plastic deformation. Although micropores generally show a pattern of shrinking and closing, closer inspection of a single specimen revealed a variety of geometrically variable behaviors. It is noteworthy that some of the micropores are reinitiated in positions identical to those before their annihilation, even after an 8 ~ 22 % macroscopic strain has been further applied after annihilation. We attribute local variations such as these to significant local strain variation, which we measured in a series of tomographic volumes by tracking microstructural features.

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In commercial aluminum alloys, Zr is recognized as an important additional element improving their properties such as strength, corrosion resistivily, and so on. It forms very fine particles of the metastable Al3Zr phase with L12 ordered configuration, in the case of alloys without Si. On the other hand, the DO22-type (Al, Si)3Zr phase besides the L12-type Al3Zr phase is precipitated in alloys including large amounts of Si, such as 6000 series. In this study the main stress falls on precipitation behavior of these Zr compounds in a Zr bearing Al-Mg-Si alloy. The Al-0.67Mg-0.97Si-0.37Zr alloy was cast into a metal mold and hot-rolled to a 5 mm thick plate. A lot of fine L12-type Al3Zr particles were coherently precipitated in the matrix by aging the plate at 673K. The aged plate was cold-rolled to a 1 mm thick sheet and annealed at 553-813K, and then microstructure was investigated by using a transmission electron microscope. It was realized that fine coherent L12-type Al3Zr particles are transformed to incoherent and coarse DO22-type (Al, Si)3Zr particles through recrystallization. The DO22-type (Al, Si)3Zr particles reduced recrystallized grain size owing to their pinning effect.