Microstructure and texture evolution of the β-Mg17A12 phase in a Mg alloy with an ultra-high Al content

In the present study, the effects of equal channel angular pressing (ECAP) on the microstructure and mechanical property of the Mg-20Al alloy were systematically investigated. For the first time, the texture of Mg17Al12 phase and its evolution with ECAP conditions were reported. The results show that increasing the processing temperature and passes generates more uniform distribution and finer size of β-Mg17Al12 phases. The large pieces of β-Mg17Al12 phases are composed of many fine grains with different crystallographic orientations. For the β-Mg17Al12 phase, a preferred distribution of (001) appears at 523 K and 573 K, and hardly varies with temperature. Nevertheless, a random texture is observed at 623 K. The (0002) poles exhibit a preferred distribution at 473 K, but this preferred distribution varies with temperature. A random distribution of (0002) poles is observed when processed at 623 K. Many types of crystallographic planar relationship between β-Mg17Al12 phase and α-Mg matrix are observed and the relationships of {11 2- 3}//{100} or {110} or {111} and {1 2- 11}//{100} or //{110} or {111} have a relatively higher frequency than others. The texture of α-Mg matrix is much different from that of the ECAPed Mg alloys with a relative low Al content, in which a texture with basal poles inclining approximately 45° away from the extrusion direction often develops. The mechanical properties of Mg-20Al alloy are closely related to the temperature and passes of ECAP. A higher temperature often decreases the yield strength, but hardly alters the maximum strength. There is a low plasticity for all the samples and increasing processing temperature slightly enhances the plasticity. The corresponding mechanisms were deeply discussed.