Macroscopic kinetics of discontinuous precipitation in a Mg-8.5 wt% Al alloy

The macroscopic kinetics of discontinuous precipitation in two Mg-8.5 wt% Al alloys with different initial average grain sizes has been studied at 220°C by quantitative optical metallography, hardness measurements and integrated intensity measurements of the precipitate peaks during in situ X-ray experiments. The kinetics observed can be described by Johnson-Mehl-Avrami's law, which indicates that a reaction front stops when it meets an …