Microstructure And Mechanical Properties Of Al-8Mg-xSi Alloy Squeeze Casting

Lightweight is the development direction of future automobiles.And materials are one of the most important ways to reduce the weight of automobile s.At present,high-strength lightweight materials such as high-strength steel,aluminum-magnesium alloy,and carbon fiber have been widely used in automobile lightweight.Aluminum alloy is the best material for lightweight cars due to its excellent properties such as low density,high specific strength,high specific rigidity,and good corrosion resistance.Although the eutectic Al-Si alloy has better fluidity and fillability,it has a wide range of applications in the manufacture of auto parts.However,due to its low mechanical properties,its popularization in automotive structural parts is limited.Therefore,the development of a lightweight,high-strength aluminum alloy has become a current research hotspot in automotive lightweight.In this paper,Al-8Mg alloy is used as the basic research material,and the content of silicon in the alloy is adjusted by adding Al-18Si master alloy to the base alloy.Direct reading spectroscopy,X-ray diffractometer,optical microscope,scanning electron microscope,electronic universal tensile testing machine were used to study the influence of different silicon content on the microstructure,phase composition and mechanical properties of Al-8Mg as-cast alloy.Explore the changes in microstructure and mechanical properties of alloys with optimal silicon content under different squeeze casting process conditions.At the same time,the influence of heat treatment process parameters on the evolution of the microstructure and mechanical properties of the castings was stud ied.The specific research results are as follows:The microstructure of the base alloy is composed of?-Al phase and irregular block Al₃Mg₂ phase.When silicon is added to the alloy,a Chinese character-shaped Mg₂Si phase appears in the microstructure.With the increase of silicon content,the volume fraction of Al₃Mg₂ phase gradually decreases,and the volume fraction of Mg₂Si phase gradually increases.And the size of Mg₂Si phase gradually becomes smaller.Its tensile strength and yield strength show a t rend of increasing first and then decreasing.When the silicon content reaches the peak value of 1.19wt.%,the tensile strength and yield strength are 233.7MPa and193.5MPa,respectively.With the increase of silicon content,the number of dimples in the fracture morphology gradually decreases,the area of the cleavage surface gradually increases,and the alloy exhibits a quasi-cleavage fracture mode.The Al₃Mg₂ phase in the microstructure of the alloy is completely dissolved into the matrix after solution treatment.At the same time,the Mg₂Si phase has changed from elongated to nearly spherical or granular.After aging treatment,the Al₃Mg₂ phase in the alloy microstructure was precipitated and dispersed near the grain boundaries.At the same time,as the aging time increases,the crystal grains show a growing trend.When the aging time is 10h,the mechanical properties are the best,the tensile strength is 291.7MPa,the yield strength is 237.3MPa,the hardness is 110.1HV,and the elongation decreases with the increase of the aging time.A large number of dimples appeared in the morphology of tensile f racture.With the increase of aging time,the number of dimples increased and their size became smaller,and the fracture mode gradually changed to brittle fracture.