Precipitation in Mg-(4-13)%Li-(4-5)%Zn ternary alloys

Precipitations in Mg-Li-Zn ternary alloys containing 4 to 13%Li and 4 to 5%Zn (in mass%) with alpha or beta single phase, or with (alpha + beta) dual phases were investigated using a micro-Vickers hardness measurement and transmission electron microscopy. Age hardening in the alpha phase alloy was found to occur, which was attributed to the precipitation of the stable theta (MgLiZn) phase with the following orientation relationships: [ 1010](alpha) \\ [110](theta'), (0001)(alpha) \\ (1 (1) over bar(1) over bar)(theta'). In the (alpha + beta) phases alloy, the precipitation of the alpha phase together with the metastable theta' (MgLi2Zn) phase occurred at grain boundaries between the alpha and beta, and also beta and P grains. The orientation relationships between the alpha and theta' were as follows; (0001)(alpha) \\ (01 (1) over bar)(theta'), [0 (1) over bar 10](alpha) \\ [111](theta'). Age hardening in the beta alloy was caused by the precipitation of the theta' phase and over-aging was attributed to the precipitation of the alpha and theta phases.