The influence of composition and natural aging on clustering during preaging in Al–Mg–Si alloys

Abstract

This work provides a detailed atom probe tomography study of clustering in the Al–Mg–Si system. Focus is on separating and understanding the influence of natural aging, preaging, and alloy composition on the clustering behavior of solute atoms. Two dilute alloys with the same total solute content have been studied, one Mg-rich and one Si-rich. The detrimental effect of natural aging for these alloys is investigated by comparing directly preaged samples to samples stored at room temperature before the preaging treatment. Clusters were identified in the atom probe datasets by the maximum separation method employing heuristically determined input parameters. It was found that seven days of intermediate natural aging gave a five times lower number density of clusters as compared to direct preaging for both alloy types. The clusters were of comparable size but their compositions depended on heat treatment history. Preaging promoted the formation of clusters with an Mg:Si ratio close to 1 in both alloys, while natural aging produced clusters with Mg:Si ratios more similar to those of the alloys.

An Extended Age-Hardening Model for Al-Mg-Si Alloys Incorporating the Room-Temperature Storage and Cold Deformation Process Stages

“…[7] the k 1 parameter is characteristic of the material under consideration, whereas k 2 , which determines the rate of dynamic recovery during plastic deformation, depends on the actual solute content in the alloy. Appropriate input data for k 1 and k 2 , which can serve as default values in the numerical code, have been reported elsewhere.…”

“…[4][5][6] In addition, the chemical composition and atomic structure of the clusters and hardening precipitate which form have been studied in detail by means of various high-resolution experimental techniques along with atomistic modeling. [7][8][9][10] Obviously, some of these works must be said to be at the leading edge of international materials research, which gives aluminum a competitive advantages compared to other structural and functional materials that are not so thoroughly examined.…”

Design strategy for controlled natural aging in Al–Mg–Si alloys

“…9a) corresponds to fewer trapped vacancies and thus more untrapped vacancies; second, in alloys with higher Si content the vacancy diffusion distances to nearby Si atoms are reduced for untrapped and detached vacancies (compare ref. [38]). A more detailed analysis of the mechanisms involved is the subject of on-going research.…”

Thermal migration of alloying agents in aluminium

“…The Si:Mg ratio within the grains will be influenced by surface migrations, and is very important for the formation of the nanosized precipitate phases during hardening. Low Si:Mg ratios typically suppress the formation of the phases promoting strength, and the alloy becomes softer than in regions with higher Si:Mg ratios 24 . Li depletion also leaves less solute available for the precipitation of hardening phases, rendering the material softer than in regions with more Li 8 .…”