Microstructural changes in welded Zn-Al alloy

Extruded eutectoid Zn-Al alloy was welded by a melt of the same eutectoid alloy. Two different microstructures were observed in the joint part and in the bulk of the welded alloy. Typical dendritic structure of as-cast Zn-Al alloy was observed in the joint part of the welded alloy. The bulk of the welded Zn-Al alloy appeared as fine grain structure. Two different metastable phases, eta'(T) decomposed from eta'(s) of the chilled as-cast state and eta'(E) of the extruded state, were found to be unstable during the early stages of aging. A four-phase transformation occurred after the decompositions of these two metastable phases of eta'(T). Microstructures of both the joint part and bulk of the welded alloy were investigated simultaneously during the aging processes.