Directionally controlled precipitation on twin-boundaries in Mg-Zn-Y alloys

Precipitation strengthening in Mg-Zn-Y alloys occurs via the formation of a fine dispersion of β’₁ (Mg₄Zn₇) rods aligned parallel to the hexagonal axis. In this study, texture and controlled deformation have been used to control the directionality and morphology of the precipitates and their effect on the ageing response. The resulting precipitates were studied via conventional and high-resolution transmission electron microscopy.Texture was developed through extrusion at 300°C, followed by controlled room-temperature deformation to generate microstructures where yield occurred either with, or without, twinning. The ageing response was monitored using hardness testing. Both compressive and tensile deformation accelerated the ageing response. Compression parallel to the extrusion axis generated a high volume fraction of twins. Precipitates on the twin boundaries assumed a low aspect-ratio morphology different from the usual high-aspect ratio rods.