An environment‐friendly phosphate conversion coating free of chromate, fluorides, and nitrite was developed on AZ91D alloy through a facile chemical deposition method. The surface morphology and phase composition of the coating were characterized by field‐emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD). The corrosion resistance of the coating was evaluated by potentiodynamic polarization test in 3.5 wt% NaCl solution. Results indicate that the calcium phosphate coating was composed of a large number of leaf‐like and flower‐like particles. The chemical composition of the conversion coating was CaHPO4·2H2O crystals. The coating can remarkably reduce the corrosion current density of the substrate. Introduction of triethanolamine (TEA) additive into the phosphating bath leads to denser coating and high anticorrosive property of the phosphate coating.

Natural ageing responses of duplex structured Mg-6%Li and Mg-6%Li-6%Zn-1.2%Y alloys have been investigated. Microstructural analyses revealed that the precipitation and coarsening process of α-Mg particles could occur in β-Li phases of both two alloys during ageing process. Since a certain amount of Mg atoms in β-Li phases were consumed for the precipitation of abundant tiny MgLiZn particles, the size of α-Mg precipitates in Mg-6%Li-6%Zn-1.2%Y alloy was relatively smaller than that in Mg-6%Li alloy. Micro hardness measurements demonstrated that with the ageing time increasing, the α-Mg phases in Mg-6%Li alloy could have a constant hardness value of 41 HV, but the contained β-Li phases exhibited a slight age-softening response. Compared with the Mg-6%Li alloy, the age-softening response of β-Li phases in Mg-6%Li-6%Zn-1.2%Y alloy was much more profound. Meanwhile, a normal age-hardening response of α-Mg phases was maintained. Tensile results indicated that obvious ageing-softening phenomenon in terms of macro tensile strength occurred in both two alloys. Failure analysis demonstrated that for the Mg-6%Li alloy, cracks were preferentially initiated at α-Mg/β-Li interfaces. For the Mg-6%Li-6%Zn-1.2%Y alloy, cracks occurred at both α-Mg/β-Li interfaces and slip bands in α-Mg and β-Li phases.