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High-precision isothermal dilatometry as tool for quantitative analysis of precipitation kinetics: case study of dilute Al alloy

Enzinger, R., Hengge, E., Sprengel, W., Würschum, R.
Journal of materials science 2019 v.54 no.6 pp. 5083-5091
alloys, aluminum, case studies, heat treatment, models, quantitative analysis, temperature
An in-depth case study of precipitation kinetics for alloys is presented utilizing recent progress in high-precision isothermal dilatometry by measuring relative length changes down to the range of [Formula: see text] and covering large timescales exceeding [Formula: see text] s. Using a dilute Al–Mg–Si alloy as model system, the different phases that form during isothermal heat treatment could quantitatively be analyzed both with respect to the absolute amount of precipitates and with respect to the underlying kinetics. Owing to the distinct length change features upon multi-step precipitation processes, the formation of the metastable [Formula: see text]- and [Formula: see text]-phases can unambigously be detected and furthermore can specifically be distinguished and resolved. From the reaction rate analysis of the precipitation-induced relative length change, that was isothermally measured for temperatures between 170 [Formula: see text] and 260 [Formula: see text], the evolution with time of the atomic fraction of both the [Formula: see text]- and the [Formula: see text]-phase was determined. The results were also used to construct the isothermal time–temperature–precipitation diagrams which are important for technologically relevant processes.