Quantitative volumetric identification of precipitates in dilute alloys using high-precision isothermal dilatometry

The present case study demonstrates that high-precision dilatometry serves as sensitive tool for quantitatively characterising precipitation processes down to small relative length changes in the range of 10^-5 and covering long time scales exceeding 10⁵ s. For a dilute Al-based Al–Mg–Si alloy, the amount of the metastable coherent β' -phase and the semicoherent β''-phase as well as of the stable β-phase could be determined on an absolute scale from in-situ relative length change measurements upon long-time isothermal annealing. The quantitative analysis allows an assessment on the various contributions of the length change, i.e. the volume excess of the precipitates, the volume change of the matrix upon precipitation of solute atoms, and the length change due to the formation of interfaces.