Abstract: The ageing behavior of Mg-xAl-Zn alloys with a variation of Al contents (x=3, 5, 7, 9 and 11 wt pct) were investigated. Solid solution treatment and artificial ageing were carried out at 693 and 493 K, respectively. After the solid solution treatment, β-Mg17Al12 was resolved to the α-Mg matrix in the specimens which contained Al up to 9 wt pct and partially resolved in the specimen of 11 wt pct Al. During ageing, the β-Mg17Al12 phase was precipitated at the grain boundary in the form of discontinuous precipitation and grown into the matrix. The volume fraction of β-phase was increased with the Al contents. Tensile strength increased with the volume fraction of precipitated β-phase, which was believed to strengthen the matrix.

Key words: Ageing, Mg alloy, Discontinuous precipitation