Microstructural development of Zn-40Al alloy during aging

The microstructure development of a Zn-40 wt-%Al alloy during aging was stu died using transmission electron microscopy and electron diffraction. The s upersaturated solid solution alpha(s)' phase was formed after solution quen ching treatment, which exhibited a substructure with a structure factor con trast in some areas after aging for shorter times at ambient temperature. E lectron diffraction results show that there are satellite reflections in th e (110)(alpha s') direction. The a(s)' phase decomposes during aging, formi ng an (alpha + eta) lamellar structure by the discontinuous reaction or cel lular decomposition and an equiaxed fine grained structure by the continuou s reaction, which are alpha(m)" and alpha " or alpha(m)' and alpha' with tw in relationships to each other. A very fine tweedlike structure was observe d to spinodally decompose ahead of the cellular zone. The value of the modu lation wavelength lambda is about 70-85 nm. The bowing and migration of the grain boundary would occur in the evolution of the discontinuous precipita tes. Precipitate free zones of the vacancy denuded type were found in the v icinity of the grain boundary and within grains. It has been observed that the formation of the metastable R phase is always associated with dislocati ons, MST/4411. (C) 2000 IoM Communications Ltd.