A test for diffusional coherency strain hypothesis in the discontinuous precipitation in Mg-Al alloy

Abstract

Discontinuous precipitation (DP) occurs in many alloy systems under certain conditions. Although solute supersaturation is the chemical driving force for DP, this has to be coupled with another driving force for grain boundary migration. This was identified to be diffusional coherency strain ahead of the moving boundary in the case of diffusion induced grain boundary migration (DIGM) and liquid film migration (LFM). In the present work, the validity of diffusional coherency strain hypothesis is verified in Mg-Al alloy, which exhibits discontinuous precipitation. Samples were tested with an applied stress simultaneously with discontinuous precipitation and it was found that the velocity of the boundaries both parallel and transverse to the stress axis obeys the model for diffusional coherency strain. This work can be used as a conclusive evidence for diffusional coherency strain hypothesis for the occurrence of discontinuous precipitation in Mg-Al alloys.