Precipitation and grain boundary internal friction peaks in AlMgSi

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.

Precipitation internal friction peak in AlMgSi

“…In a previous work [3], it is found that the effect is also observable in large grained specimens (macrocrystals), but there are definite differences in characteristics and behaviour between this peak and that detected in polycrystalline samples. These facts lead to the conclusion that they are two different effects arising from also different relaxation mechanisms.…”

“…The internal friction experimental curves were analyzed assuming an internal friction background obeying an exponential law and symmetric Debye peaks characterized by height, width, and temperature position as in [3].…”

“…Even if after a preliminary analysis G, can be associated with the internal friction peak P, previously described [3], it is necessary to demonstrate that there is a close correlation between characteristics and behaviour of both effects. Fig.…”

“…As both relaxation peaks [3] seem to arise from mechanisms that involve those microstructural elements considered as critical in relation to the mechanical properties of the alloy, it may be of interest to gain insight into the actual mechanisms originating these peaks.…”

“…Considering the different origin of each internal friction effect, it must be possible to detect both contributions (Pz and P3) in polycrystalline samples aged to produce j3' precipitation, so the first part of the present work follows this aim. In the second part, the study performed on the P, peak in [3] is reviewed and completed; on this basis a quantitative model for the relaxation mechanism is proposed.…”