Analytical electron microscopy of lamellar precipitates in AlZnTi alloys

A technique of analytical electron microscopy was used in order to determin e the changes of chemistry of the phases formed in the microstructure of th e Zn-25 wt.% Al cast alloy modified with Ti. The presence of the Ti (Al, Zn ), compound was detected as well as two kinds of lamellar structures of the alpha and beta-phases having different partitioning of Al and Zn and vario us amount of Ti. It was suggested that the first kind of lamellar precipita tes was formed during monotectoid transformation at the conditions far away from the equilibrium state while the second kind was a result of a discont inuous precipitation beginning after a longer cooling time of casting. Tita nium appeared only within the alpha and beta lamellae of monotectoid and it came from the Ti gradient adjacent to the Ti (Al, Zn)(3) compound. Therefo re, the amount of Ti decreased along increasing distance from the compound.