Investigation Of High Strength And Toughness Al-Si(Mg) Die Casting Alloy On Microstructure And Mechanical Properties

The light weight of automobiles has become the development trend of the automobile industry to reduce automobile exhaust emissions and improve the recharge mileage of electric vehicles.Therefore,the use of aluminum alloy instead of traditional steel has become an important means of automobile lightweight.As a near-net forming technology,die casting can be directly used to produce complex automotive parts,which can greatly improving production efficiency.However,the domestic research on commercial die-casting aluminum alloy is still in the initial stage and can't meet the requirements of the mechanical properties and die casting properties of the automobile structure.In this study,Al-Si?Mg?alloy was used as the base alloy,the influence of trace elements alloying and main alloying elements Mg/Si mass ratio on the microstructure and properties of the alloy was investigated under the solidification conditions of high pressure,fast cooling and non-equilibrium about die casting process.The experimental results has shown that the weak strengthening effect of eutectic Si in Al-Si alloy.When Si content increased from 5% to 12%,the yield strength of the alloy only increased by 40MPa.The addition of Sr could transformed the morphology of striped eutectic Si into coral,which could improved the elongation of the alloy.The Sr-modified Al-9Si-0.6Mn alloy had the optimum toughness,but the strength was low.Addition of trace amount of Mg could combined with Si to formed hard and brittle Mg₂Si phase which would significantly increased the yield strength of the alloy to 161MPa,but the elongation decreased to 7.8%.The main strengthening method of Al-Mg alloy was solid solution strengthening and dispersion strengthening,So it had excellent comprehensive mechanical properties.However,the casting performance of Al-Mg alloy was poor that needed to added Si for improvement.The mechanical properties of Al-Mg-Si alloy could improved by changing the mass ratio of Mg/Si to control the amount and morphology of?-Al-Mg₂Si eutectic structure.When the excess Mg content was between the complete transformation point of Mn?Cr?-containing phase and the initial formation point of Al₃Mg₂ phase,the amount of?-Al-Mg₂Si eutectic reached the maximum value with the minimum interlayer spacing and the Al-Mg-Si alloy had the optimum toughness.The optimum excess Mg content in this study was ranged from 1.8%to 2.2%.The Al-5.9Mg-2.4Si-0.6Mn alloy had the best comprehensive properties with a yield strength of 163MPa,tensile strength of 335MPa,elongation of 10.3% and excellent die casting performance which could meet the requirements of this research.