  The age-metallicity relation is a fundamental tool for constraining the
chemical evolution of the Galactic disc. In this work we analyse the
observational properties of this relation using binary stars that have not
interacted consisting of a white dwarf - from which we can derive the total age
of the system - and a main sequence star - from which we can derive the
metallicity as traced by the [Fe/H] abundances. Our sample consists of 46
widely separated, but unresolved spectroscopic binaries identified within the
Sloan Digital Sky Survey, and 189 white dwarf plus main sequence common proper
motion pairs identified within the second data release of Gaia. This is
currently the largest white dwarf sample for which the metallicity of their
progenitors have been determined. We find a flat age-metallicity relation
displaying a scatter of [Fe/H] abundances of approximately 0.5 dex around the
solar metallicity at all ages. This independently confirms the lack of
correlation between age and metallicity in the solar neighbourhood that is
found in previous studies focused on analysing single main sequence stars and
open clusters.
