Phase transformations in Zn-22%Al-2%Cu and Zn-22%Al-2%Cu-X (X=1, 2 and 3%Ag) alloys during aging treatments

The study of phase transformations that take place in Zn-22% Al-2% Cu and Zn-22% Al-2% Cu-X (X = 1, 2 and 3% Ag) alloys was carried out using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Alloys were homogenized at 350 degrees C during 10 days and quenched at similar to 2 degrees C. Subsequently, samples were aged at 200 degrees C for different times. The initial microstructure consists in a matrix of fine equiaxial grains of alpha and eta phases for all the alloys. Besides isolated particles of epsilon and Phi were observed without and with Ag addition, respectively. During the aging, the four phase reaction, alpha + epsilon ->eta + tau', takes place to obtain the equilibrium eta, alpha and tau phases. However, the Ag addition promotes the formation of the Phi phase, which retards or inhibits the four phase reaction. The stability of the Phi phase is obtained with 3% Ag, which could improve the dimensional stability of the alloy for future industrial applications.