Research On Microstructure And Mechanical Properities Of Cast Al-Si-Mg-Cu-Zr-Ti Alloy

Due to its low density,excellent thermomechanical properties,excellent castability,better mechanical properties and air tightness,aluminum-silicon casting alloys are suitable for various casting methods and are subjected to high loads in the aviation field as aircraft and missile cabins.Parts have widely replaced cast iron in the automotive industry.As a structural material,high-strength aluminum alloy is required to have a higher modulus of elasticity to improve mechanical stability.At the same time,there are requirements for lighter weight and high strength and toughness in the aerospace field,and higher requirements for its strength are required.Therefore,it is necessary to continue Improve the mechanical properties of aluminum-silicon alloys.Firstly,the crystal model of Al-Si-Mg-Cu-Zr-Ti alloy was established by virtual crystal approximate method.The structural,elastic,and plastic properties of the Al-Si-Mg-Cu-Zr-Ti alloy varying with the single element content of the Si,Ti,Zr were calculated using the first-principle computing software Castep.The calculation results show that the alloy with many kinds of elements contained in the alloy has a small lattice constant and a high density.The Young's modulus,bulk modulus and shear modulus are calculated by VRH approximation method.The results show that with the increase of Si,Ti,Zr element content,the Young's modulus and shear modulus increase,but the bulk modulus does not change.The effect of Ti and Zr on the modulus of elasticity is greater than that of Si.The thesis studied the effects of element content and cooling conditions on the microstructure and mechanical properties of Al-Si-Mg-Cu-Zr-Ti alloys.The composition of 10 Al-Si-Mg-Cu-Zr-Ti alloys with varying contents of single elements is designed.The results show that as the Si content increases,the eutectic structure gradually increases and the?(Al)phase grains gradually refinement.Eutectic silicon has changed from coarse lamellae to fine lamellae or needles.The tensile strength and yield strength of the alloy increase with the increase of Si element content.The heat treatment process for the alloy is:solution treatment at 520?×13h,water quenching at 25?after solution treatment,and finally aging at 175?×32h.After heat treatment,the Si phase undergoes fusing and spheroidization.The tensile strength and yield strength increase with the increase of Si element content,but the increase is small.The elongation rate decreases with the increase of Si element content,and when the Si content is 7.3wt.%,the alloy exhibits a great elongation rate of 13.95%.When the Si content is in the range of 7.8-8.3wt.%,as the Si content increases,the elastic modulus of the alloy increases,and the yield strength and tensile strength decrease.With the increase of Ti content,the?(Al)phase is obviously refined,but a coarse Al₃Ti phase is formed,which reduces the strength and plasticity of the alloy.Therefore,the optimal Ti addition amount obtained in this paper is 0.15wt.%.As the Zr content increases,the ductility of the alloy decreases,and the yield strength and tensile strength of the alloy gradually increase with the increase of the Zr content,which is related to the increase in the number of smaller-sized Zr phases.When the Zr content is 0.6 wt.%,an alloy with an elongation of more than 8%can be obtained.Different cooling conditions have a great influence on the morphology of eutectic silicon.Under the metallic cooling condition,the eutectic silicon has the best modification effect.The eutectic silicon has a fine and uniform lamellar shape.Under the sand cooling condition,the modification effect is the worst,with a large amount of coarse acicular eutectic silicon.Different cooling conditions have a great influence on the morphology of?(Al)phase.Under the metallic cooling condition,the?(Al)phase crystal grains are the smallest,and under the sand cooling condition,the?(Al)phase is coarse equiaxed crystals.Under the three cooling conditions,the yield strength,tensile strength and elongation of the metal castings reached the highest at the same time.After T6 treatment,alloy metal mold castings with alloy composition of Al-7.8Si-0.6Mg-0.2Cu-0.6Zr-0.15Ti have the best mechanical properties.The mechanical properties are:E?76Gpa,?_0.2?290MPa,?_b?335MPa,?₅?8%.