Precipitation and grain boundary internal friction peaks in AlMgSi

Abstract

Polycrystalline specimens of Al–1% Mg2Si (0.2% excess Si), annealed at temperatures between 443 and 650 K after solution treatment and water quench show an internal friction peak at 480 K (1 Hz). It is proposed as a Si precipitate grain boundary peak. In macrocrystals, another peak appears during the first cooling from 620 K. It is located at 465 K (1 Hz), but under long aging it shifts to higher temperatures and increases its height. From this and other characteristics, it is concluded that this peak originates in a relaxation mechanism in which dislocations as well as precipitates in volume could participate.