The influence of alloy composition on precipitates of the Al-Mg-Si system

Abstract

To study how changes in solute elements affect precipitation, six Al-Mg-Si alloys aged at 175 °C were investigated by transmission electron microscopy (TEM). In alloys with 1.3 at. pct solute, when the Si/Mg ratio exceeds 5/6, a sharp hardness peak appears after 3 hours that correlates with a high density of fine Guinier-Preston (GP) zones. A second, broader peak correlates with ␤Љ precipitates and U phases. With high Si/Mg ratios, GP zones survive for long aging times. The ␤Љ-Mg 5 Si 6 phase becomes very stable in the alloy with its Si/Mg ratio closest to 6/5. Deviation from this ratio increases fractions of ␤Ј, U-phases and disordered precipitates. In Mg-rich alloys less GP zones form and the first peak is suppressed. A coarse precipitate microstructure of ␤Љ and ␤Ј develops, the volume fraction being much higher than in Si-rich alloys. The Mg-rich alloys overage faster. Reducing the content of solutes causes alloys with high Si/Mg ratios to have a more Mg-rich behavior.

Probing defects in Al-Mg-Si alloys using muon spin relaxation

“…Similar conditions have been studied extensively using various characterization methods such as atom probe tomography (APT), 25 positron annihilation spectroscopy (PAS), 26 and transmission electron microscopy (TEM). 27,28 Their microstructures are therefore well-known.…”

Microstructure and Low-Cycle Fatigue of a Friction-Stir-Welded 6061 Aluminum Alloy

“…[54] Compared with those in copper bearing 2xxx series alloy, the formation of metastable phases in 6xxx-series alloys required diffusion of both magnesium and silicon. [57,58] It was generally accepted that the precipitation sequence of the Al-Mg-Si alloys was as follows: [43,59] SSSS fi atomic clusters [60] fi initial b¢¢ [4,60] fi {pre-b¢¢ [60,61] /needle-shaped b¢¢ precipitate [54,62,63] } fi {rod-shaped precipitates b¢/ lath-shaped B ¢ precipitates [3,64] /U1, U2 [65] } fi {b-Mg 2 Si [64,66] /Si [65] }, where SSSS represented the supersaturated solid solution. As shown in Figure 2(e) and (f), the fine needleshaped b¢¢ primary strengthening precipitates were visible due to the strain field contrast.…”

Natural Aging in Al‐Mg‐Si Alloys – A Process of Unexpected Complexity

“…Some of REVIEW the phases might not occur at all at too low a temperature or may evolve into others almost instantaneously at too high a temperature and there may be ranges of co-existence of more than one phase. The exact precipitation sequence depends on the alloy composition (excess in Mg or Si, or balanced alloy [6] ) and the possible presence of additional elements (Cu, Mn, Fe, . .…”

“…Such work focuses on: Structural characterization of hardening particles, [6,7,8,9,10] Study of precipitation sequence and transformation pathway, [6,7,11,12] Influence of alloy composition, [13] Interrelationship between hardening particles and mechanical properties, Influence of thermal and mechanical history on hardening, i.e. influence of storage at lower temperatures (often ''negative'' or deleterious) or influence of deformation (mostly ''positive'' or beneficial) on the hardening potential of the alloy.…”