Strengthening Mechanism And High Temperature Oxidation Behavior Of Magnesium Alloy

Many kinds of magnesium alloys were prepared by casting technique. The relationship between tensile strength and microstructure of magnesium alloy and the high temperature oxidation behavior of magnesium alloy were studied by the techniques of scanning electron microscope (SEM), optical microscopy, X-ray diffraction (XRD) and WAW-500C stretcher in this paper. Proper quantities Sb can refine the morphology, better the shape and distribution of Mg₁₇Al₁₂, and form a new strengthening phase Mg₃Sb₂ in AZ91D magnesium alloy, which causes the strength of magnesium alloy to increase 44MPa. However when the content of Sb exceeds 0.7%, the strength of AZ91D magnesium alloy begins to decrease because granular Mg3Sb2 phase turns into needle-shaped. The strength of RE ignition-resistance magnesium decreases with increasing RE content due to a large number of long needle-shaped phases Al11RE3 occur. The strength contribution of Sb in RE ignition-resistance magnesium alloy comes from the decreasing of long needle-shaped A111RE3 phase and the formation of a new granular CeSb phase. So the strength of RE ignition-resistance magnesium alloy is improved. There are two kinds of surface damage forms in magnesium alloy from high temperature oxidation experiment. They are pitting damage and grain-boundary damage. Grain-boundary damage is mainly related to low melting second-phase on grain boundary. The capability of high temperature oxidation of RE ignition-resistance magnesium alloy is better than as-cast AZ91D magnesium alloy and the ignition point of the former is 70℃ higher than that of the latter. It is analyzed that the action mechanism of rare earth in different temperature stages is different. During the low temperature stage, rare earth can decrease the amount of low melting second-phase on grain boundary and prevent oxygen from entering the matrix of magnesium alloy; with the temperature rising, the effect of surface-active element which rare earth can display gradually enhanced. In addition, the capability of high temperature oxidation AZ91D magnesium alloy can also be improved by solution treatment because the low melting second-phase on grain boundary is removed.