Microstructure Observation of Naturally Aged Thixoforming ZA27 Alloy

The microstructure of the thixoformed ZA27 alloy naturally aged for 5 years has been observed and analyzed. The results indicate that most of the original β + η laminar eutectics have changed into the structures that small α particles uniformly distribute in η phase matrix. Both the β phase and α’ phase have also decomposed. It is suggested that a continuous or dot-line α phase first precipitates in the β phase close to the eutectic η phase layer. Then eutectoid η phase nucleates or directly grows up from the eutectic η phase, which promotes the nucleation of eutectoid α phase or...