Effect of Amount of Gd and Y Contents on Precipitation in Mg–Gd–Y Alloys Aged at 473 K

Precipitation in Mg–Gd–Y (Gd : Y = 3 : 1) alloys without Zr were investigated by HRTEM and SAED technique, and calculation of HRTEM images and electron density using DV-Xα to understand the relationship between precipitation in these alloys and HRTEM images. The diffuse scattering was obtained in as-quenched samples in each alloy by SAED and the mono-layer zones have been confirmed by HRTEM observation. The β′-phase was confirmed in the 2.9Gd–0.8Y alloy by HRTEM, although the β′′-phase was confirmed in the 2.1Gd–0.6Y alloy before the β′-phase. The β′-phase became predominant after prolonged aging. Zigzag lines were observed at the same time when the β′-phase appeared in the sample. HRTEM images obtained for these precipitates were compared with calculated HRTEM images. The contrast of atomic columns of the matrix in HRTEM image was calculated simplified model of cluster based on the Mg-matrix including one or some atomic columns of RE. This is also corresponded the distribution of electron density of the cluster.