Abstract
The microstructure of an aluminum alloy containing 53 wt% Zn, 2.1 wt% Mg and 1.3 wt% Cu as main alloying elements has been studied with the focus on the precipitation behavior during the spark plasma sintering process. The starting material was an atomized Al-Zn-Mg-Cu powder with the particle size below 50 mu m.
The particles showed a solidification microstructure from cellular to columnar or equiaxed dendritic morphology with a large fraction of the alloying elements segregated in form of intermetallic phases, mainly (Zn, Al, Cu) 4 9 Mg 3 2 and Mg 2 (Zn, Al, Cu) 1 1, at the cell and dendrite boundaries. The microstructure of the sintered specimens followed the microstructure of the initial powder.
However, Mg(Zn, Al, Cu) 2 precipitates evolve at the expense of the initial precipitate phases. The precipitates which were initially continuously distributed along the intercellular and interdendritic boundaries form discrete chain-like structures in the sintered samples.
Additionally, fine precipitates created during the sintering process evolve at the new low-angle boundaries. The large fraction of precipitates at the grain boundaries and especially at the former particle boundaries could not be solved into the matrix applying a usual solid solution heat treatment.
A bending test reveals low ductility and strength. The mechanical properties suffer from the precipitates at former particle boundaries leading to fracture after an outer fiber tensile strain of 3.8%.