Accession Number : AD0831164

Title :   INVESTIGATION OF SPINODAL DECOMPOSITION IN ALUMINUM-ZINC ALLOYS.

Descriptive Note : Final rept. 1 Nov 66-31 Jan 68,

Corporate Author : STANFORD RESEARCH INST MENLO PARK CA

Personal Author(s) : Douglass, D. L.

Report Date : MAR 1968

Pagination or Media Count : 70

Abstract : The effect of spinodal decomposition on the mechanical behavior of Al-Zn alloys was studied over the range of 30 to 60 wt % zinc. Two solution treatment temperatures, 365 and 435C, were used; extensive aging studies were carried out at 22 and 100C, and limited tests were made on samples aged at other temperatures, 0, 55, and 200C. The yield and tensile strengths were significantly increased by spinodal transformation, but ductility was seriously impaired. The tensile fracture was intergranular, with but one exception, and was related to grain boundary precipitation and a narrow denuded zone. The nature of the modulated structure was studied by X-ray diffraction, metallography, and electron microscopy. Overaging was investigated by the same techniques. Stability of the structure varied inversely with zinc content but was greater in samples prepared at the higher solution temperature. Spinodal structures were extremely anisotropic to X-rays, the anisotropy disappearing during aging. Calculated yield strengths based on Cahn's analysis did not agree with those derived from the correct dislocation model. The wrong model did give fortuituous agreement. Spinodal hardening appears to offer a promising new hardening mechanism in aluminum alloys if the particular composition and treatment can be found to eliminate the serious lack of ductility. (Author)

Descriptors :   (*ALUMINUM ALLOYS, ZINC ALLOYS), (*ZINC ALLOYS, HARDENING), GRAIN STRUCTURES(METALLURGY), MECHANICAL PROPERTIES, DISPERSION HARDENING, DISLOCATIONS, AGING(MATERIALS), X RAY DIFFRACTION, METALLOGRAPHY, ELECTRON MICROSCOPY, MICROSTRUCTURE.

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE