Study on Precipitation Phenomena during Aging of Aluminium-Silver Alloy in Thin Evaporated Films

Precipitation phenomena during aging have been observed on aluminium-20 wt. per cent silver alloy in thin evaporated films by electron microscopy and electron diffraction. A super-saturated solid solution has successfully been obtained in thin films by a new quenching method. In a preprecipitation stage aggregates composed of random clusters have been found in electron micrographs, no appreciable diffraction effect having been perceived. In a true precipitation stage precipitates have been found in electron micrographs to change from a needle-like to a three dimensional shape with increasing aging, the axial ratio obtained from diffraction patterns changing from 1.63_3 to 1.59 passing 1.61_2. It is a merit of the present study that a hexagonal precipitate with the ideal axial ratio has been detected in the course of aging. Except this point, the results obtained confirm generally those reported by X-ray studies. So-called "equal-thickness interference fringes" have been found in images of precipitates aged at 250℃.