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After the Mg-Y-Ce magnesium alloy was exposed to air at a temperature up to 1173 K for 0.5 hours, the dense and compact oxide film formed on the surface. Accordingly, oxidation and ignition of magnesium alloys at elevated temperature was successfully retarded by the Y and Ce additions. Thermogravimetric measurements in air revealed that the oxidation dynamics curves measured at 673 and 773 K followed the parabolic-line law and the curve investigated at 873 K followed the complicate quartic law. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicated that the oxide film on the surface of Mg-Y-Ce alloys exhibited a duplex structure, which agreed with the results of thermodynamic analysis. The oxidation film included two layers: the outer layer was a multiple structure of Ce 0.202 Y 0.798 O 1.601 and Y 2 O 3 , and the inner layer mainly consisted of metal Mg and MgO.

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The mechanical properties (σ b , σ 0.2 , and δ) and fracture behavior of tensile specimens of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy under both as-cast and T6 heat-treated conditions. The results show that as the addition level of Al-5Ti-1B master alloy increases from 0.1 wt.% to 5.0 wt.%, the mechanical properties of refined A356 alloys improve steadily and then decrease slightly under both as-cast and T6 heat-treated conditions. Also, they display excellent mechanical properties with σ b = 231.30-258.30 MPa, σ 0.2 =134.00-155.50 MPa, and δ = 8.5%-11.75% at T6 heat-treated state. The excellent mechanical properties of refined A356 alloys are ascribed to the formation of α-Al equiaxed dendrites, the improvement of eutectic structure from needle/plate-like to short-lathy/block-shaped, and the Mg 2 Si aging precipitation phase after T6 heat treatment. The fracture surface examined by SEM exhibits a mixed fracture mode of refined A356 alloys at as-cast state, while it reveals a ductile fracture mode after T6 heat treatment.

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