Early stage of Al3Zr precipitation in a rapidly solidified Al-Cr-Zr alloy

Abstract

Early stages of A1₃Zr precipitation have been studied in detail in the ternary Al-2.4 at.% Cr-1.1 at.% Zr alloy. A supersaturated solid solution of Zr in the asrapidly solidified state decomposes during subsequent heat treatment at 400°C. This decomposition leads to a homogeneous precipitation of very small Al₃Zr (LI₂) particles in the grain interior, but this homogeneous precipitation is not stable in the vicinity of mobile grain boundaries and is progressively consumed, giving rise to a fan-shaped precipitation of Al₃Zr (Ll₂), often coexisting with very small interlamellar particles of Al₃Zr (LI₂). All these precipitation modes are analysed in the light of the current theory of discontinuous reactions.