Effects of microalloying tin and combined addition of silver and tin on the formation of precipitate free zones and mechanical properties in Al-Zn-Mg alloys

Abstract

The additions of microalloying tin and (silver and tin)-combination were performed to modify the precipitate microstructure in the vicinity of grain boundaries with precipitate free zones (PFZs) and mechanical properties in Al-Zn-Mg alloys. In the Sn-containing alloy, TEM observation showed that some precipitates were sparsely formed within the region of PFZs of the Al-Zn-Mg ternary alloy. The quantitative analysis of the chemical compositions in precipitates showed that tin mainly contributes to nucleation in the vicinity of grain boundaries through the suppression of the vacancy depletion. This is well explained by the favorable interaction of tin with vacancies. The (Ag+Sn)-containing alloy formed a very narrow PFZ width and corresponding tensile properties were remarkably improved, which shows that tin enables to reduce the amount of microalloyed silver in Al-Zn-Mg alloys. © 2011 The Japan Institute of Light Metals.