PRECIPITATION BEHAVIOR OF BETA-PHASE IN 5 083-ALUMINUM-ALLOY

A commercial 5083 aluminum alloy was aged at 453 K for an extended tim e in order to study the changes in the microstructures. In this alloy, the mechanical properties generally deteriorate with the variation in the microstructure; e. g. the precipitation of beta-phase and/or decr ease in solute Mg concentration in the matrix. This paper dealt with t he changes in the microstructure during aging treatment at 453 K for t imes up to about 10(7) s. Variation in the solute Mg concentration was estimated by electrical resistivity measurement, X-ray diffraction an d electron probe microanalysis. Precipitation of the beta- and/or beta '-phase was also investigated by means of microscopic strain measureme nt, differential scanning calorimetry and microstructural image analys is. The specimens aged for times longer than 10(6) s show decreases in electrical resistivity and lattice constant in relation to the format ion of precipitates. Microscopic strain, which is induced by the forma tion of precipitate having a partially coherent interface with the mat rix, shows a peak value for the aging time of about 10(6) s and then d ecreases.