The influences of Ca addition on the microstructures and damping capacities of AZ91-(0~2)%Ca casting alloys were investigated, on the basis of the results of X-ray diffractometry, optical microscopy, scanning electron microscopy and vibration tests in a single cantilever mode. The amount of intermetallic compounds decreased with increasing Ca content up to 0.5%, above which it increased; the average cell size showed the opposite tendency. All alloys exhibited similar damping levels in the strain-amplitude independent region. Considering the very low solubility of Ca in the matrix, and that most of the Ca elements are consumed by the formation of the Al 2 Ca phase and incorporation into the Mg 17 Al 12 phase, this would be ascribed to the almost identical concentrations of Ca solutes distributed in the matrix. In the strain-amplitude dependent region, however, the AZ91-0.5%Ca alloy possessed the maximum damping capacity. From the viewpoint of microstructural evolution with Ca addition, the number density of compound particles is considered to be the principal factor affecting the damping behavior in the strain-amplitude dependent region.

The influences of a small amount of CaO addition on the microstructure and corrosion behavior of AZ81 casting alloy have been investigated by means of optical microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, immersion and electrochemical tests. The added CaO led to the refinement of α-Mg grains and the decrease in β precipitate content by the formation of an Al 2 Ca phase. The AZ81-CaO alloy had a better corrosion resistance than the AZ81 alloy. The microstructural characterization on the corroded surface revealed that the enhanced corrosion resistance of the CaO-containing alloy may well be ascribed to the increased barrier effect of precipitates formed more continuously along the grain boundaries and the incorporation of Al and Ca elements into the corrosion film, by which it became more protective.

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Effects of Zn addition on the microstructure and corrosion behavior of Mg-8%Al-(0-1)%Zn casting alloys were investigated. With increasing Zn content, the amount of β(Mg 17 Al 12 ) phase increased, while α-(Mg) dendritic cell size became reduced. The corrosion rate decreased continuously with the increase in the Zn content. The evaluation of the microstructural evolution indicates that the improved barrier effect of β particles formed more continuously along the dendritic cell boundaries and the incorporation of more ZnO into the surface corrosion product, by which the absorption of Cl − ions is impeded, are responsible for the better corrosion resistance in relation to the Zn addition.

The study is intended to investigate the effect of solution treatment on microstructure and corrosion behavior of AZ91(Mg-9%Al-1%Zn-0.3%Mn)-2%Ca casting alloy. In as-cast state, the AZ91-2%Ca alloy consisted of intermetallic β(Mg 17 Al 12 ), Al 8 Mn 5 and Al 2 Ca phases in α-(Mg) matrix. After the solution treatment, Al within the α-(Mg) matrix was distributed more homogeneously, along with the slight decrease in the total amount of intermetallic compounds. The corrosion resistance of the AZ91-2%Ca alloy was improved after the solution treatment. The microstructural examinations for the solution-treated samples revealed that the better corrosion resistance may well be related to the incorporation of more oxides and hydroxides such as Al 2 O 3 , Al(OH) 3 , CaO and Ca(OH) 2 into the surface corrosion product without dissolution of the intermetallic phases along the grain boundaries.