Microstructural development of Zn–40Al alloy during aging

Abstract

The microstructure development of a Zn–40 wt-%Al alloy during aging was studied using transmission electron microscopy and electron diffraction. The supersaturated solid solution α′_s phase was formed after solution quenching treatment, which exhibited a substructure with a structure factor contrast in some areas after aging for shorter times at ambient temperature. Electron diffraction results show that there are satellite reflections in the 〈110〉 _α′s direction. The α′_sphase decomposes during aging, forming an (α+η) lamellar structure by the discontinuous reaction or cellular decomposition and an equiaxed fine grained structure by the continuous reaction, which are α″_m and α″ or α′_m and α′ with twin relationships to each other. A very fine tweedlike structure was observed to spinodally decompose ahead of the cellular zone. The value of the modulation wavelength λ is about 70–85 nm. The bowing and migration of the grain boundary would occur in the evolution of the discontinuous precipitates. Precipitate free zones of the vacancy denuded type were found in the vicinity of the grain boundary and within grains. It has been observed that the formation of the metastable R phase is always associated with dislocations.