Effets Of P And Sr On Microstructure And Mechanical Properties Of Mg-Si Alloys

For improveing the heat resistant properties of Mg alloys, and in this paper aiming toimprove the heat resistant properties of Mg alloy by aollying. It was analyzed by usingx-ray diffractometer （XRD）, scanning electron microscopy （SEM）, and energy dispersivespectrometer （EDS）, optical microscopy （OM）， Transmission Electron Microscope（TEM）.In order to study the effects of modification mechanism of P and P/Si ratio on Mg₂Siphase. The phase constituent and microstructure of the as-cast raesultantMg-7Al-1Zn-xSi-yP-3.597Cu （x=1,2,3; y=0,0.5） alloys were analyzed by using x-raydiffractometry （XRD）, scanning electron microscopy （SEM） and mechanical tester. Thiswere used to study the effect of P/Si ratio on precipitate, microstructure and mechanicalproperties of magnesium alloys. The results indicate that when P/Si ratio is0, the largerChinese script shape Mg₂Si phases form in the microstructure of the alloy. While P/Si ratiois0.5and0.25, the morphology of Mg₂Si phase change from Chinese script shape to blockshape. When P/Si ratio decrease to0.17, the effect of P modification on Mg₂Si becomeweakened, so the morphology of Mg₂Si phase appear Chinese script shaped and blockshapes two forms. Modification mechanism of P is that it can provide step defects forMg₂Si crystal lateral growth, and Its growth process is affected by the control of stepdefects.When the morphology of Mg₂Si is block shape, it has better mechanical properties asthe separation effect is little. The tensile strength, yield strength and elongation of theas-cast Mg-6.5Zn-1Si-0.3P-3.597Cu alloy are156MPa,120MPa and5.0%, respectively.The best heat treatment of alloy is that solution24h at400℃and then aging12h at200℃.The tensile strength, yield strength and elongation are224.68MPa,113.45MPa,6.07%,respectively.In order to study the effects of P on microstructure and mechanical property ofMg-6.5Zn-1Si-xP-3.597Cu（x=0、0.1、0.3、0.5）. When P addition is0.3%, Mg₂Si phase is block shape and MgZnCu phase refinement performence is the best.Mg-6.5Zn-1Si-0.3P-3.597Cu alloy has the best mechanical property in as-cast alloys,The tensile strength, yield strength and elongation of the as-cast alloy are208.36MPa,135.42MPa and5.2wt%, respectively. The best heat treatment of alloy is solution24h at400℃and then aging6h at200℃. The tensile strength, yield strength and elongation are235.1MPa,141.00MPa,5.5%.By compare different addition of Sr in Mg-5Sn-2Si-xSr-2Ca （x=0,0.1,0.5,1） that itcan find Sr effects on morphology of CaMgSn phase. when Sr addition is0.5%, it has thebest refinement effects of CaMgSn phase.Mg-5Sn-2Si-0.5Sr-2Ca alloy has the best mechanical property in as-cast alloys, Thetensile strength, yield strength and elongation of the as-cast Mg-5Sn-2Si-2Sr-0.5Ca alloyare165.22MPa,101.27MPa and54.8%, respectively.