Poisoning of Zr microstructures during casting homogenisation and solution treatment

Abstract

The influence of Al–Ti–B grain refiners on the microstructures of Zr-containing Al–Zn–Mg–Cu alloy was investigated by optical microscopy and scanning electron microscopy, as well as through tensile and hardness tests. A poisoning effect occurred when the grain refiner was added to the Zr-containing alloy, and the grain size increased significantly. The precipitates in the alloy without the grain refiner were finely distributed, while the phases of the alloy with the Al–Ti–B refiner agglomerated at the grain boundaries, decreasing both the hardness and elongation. The addition of the grain refiner to the alloys markedly increased their hardness and elongation, when coupled with slow cooling, although the peak stress also decreased slightly.