Study of precipitates in an aged Mg-3.6wt%Zn alloy by an X-ray method

Abstract

Formation and growth of precipitates in a Mg-3.6wt.%Zn alloy during aging between room temperature and 140°C were examined by means of an X-ray diffraction method. Two different types of G.P. zones as well as intermediate phases were formed during the aging. The precipitation process occurred in the following order: supersaturated solid solution→G.P. [1]→G.P. [2]→β'₁→β'₂→β. The plate-like G.P. [1], formed by the aging below 60°C was parallel to {1120} planes of the magnesium matrix. The G.P. [2] appeared in the form of an oblate spheroid on the basal plane of the matrix below 80°C. The rod-shaped β'₁ was perpendicular to the basal plane, while the β'₂, the other intermediate phase of rod shape, was formed perpendicular to {1010} planes of the matrix. The β'₂ which had the same composition, structure, and shape as the β'₁, was thought to be formed by the transformation stress of the β'₁ phase. Hardening of the present alloy was induced by the precipitation of the β'₁ and β'₂, while it was hardly affected by the formation of the G.P. zones.