Effect Of Si, Ce On The Micro Structure And Mechanical Property Of Magnesium Alloy

The most commonly used magnesium alloys are those based on the Mg-Alsystem. Three series of magnesium alloys are designed on the base of the Mg-Alsystem. The effect of Si, Ce on the microstructure and mechanical property ofmagnesium alloy was investigated by using the optical microscopy, the scanningelectron microscope and the X-ray diffraction. The important results are summarizedas follows:The microstructure of the as-cast Mg-7Al-2.5Ca-0.4Mn-0.25Sr-xSi（x=1,2,3）alloys are mainly composed of α-Mg matrix, AlMn phase, Mg₂Ca phase, Al₂Ca phaseand CaMgSi phase, the volume fractions of CaMgSi phase increases with the Sielement. The addition of Si ranging from1%to3%results in the eutectic（Mg₂Ca+Al₂Ca） decreasing and CaMgSi phase increasing. The morphology of theCaMgSi phase gradually changes from hollow block shape to needle script shape, andthen evolves into Chinese script shape. At the same time, the dendritic α-Mg phasestructure become large.The addition of rare earth Ce element can promote significantly themicrostructure and mechanical property of the Mg-5Al-3Zn-3Si-xCe（x=0.5,1,1.5,2）alloy. When the Ce content is2%, the mechanical property of the alloy reaches itsmaximum. The tensile strength and elongation of Mg-5Al-3Zn-3Si-2Ce alloy are175.17MPa and5.0%. The heat treatment process for Mg-5Al-3Zn-3Si-2Ce alloy issolution16h at420℃and then aging6h,12h and24h at200℃. The tensile strength,yield strength and elongation of Mg-5Al-3Zn-3Si-2Ce alloy are183.83MPa,191.15MPa,181.85MPa and5.3%,5.6%,5.1%respectively after heat treatment. Themechanical properties of the alloys have been significantly improved after heattreatment.Mg-5Al-3Zn-3Si-2Sr alloy is obtained by adding3%Zn and3%Si to AJ52alloy.Compared with AJ52alloy, the strength of the alloy has been significantly improved.The tensile strength and elongation of Mg-5Al-3Zn-3Si-2Sr alloy are194.39MPa and5.9%. Based on Mg-5Al-3Zn-3Si-2Sr alloy, Ce element instead of Sr element can result in the microstructure coarsening and strength reducing. While the most suitableheat treatment process for Mg-5Al-3Zn-3Si-2Sr alloy is solution24h at420℃andthen aging12h at200℃. The tensile strength, yield strength and elongation ofMg-5Al-3Zn-3Si-2Sr alloy are228.57MPa,169.42MPa and6.4%respectively afterheat treatment.