Study On Heat Treatment Process Of Semi-Solid Forming Hypereutectic Al-Si-Cu-Mg Alloy

The hypereutectic Al-Si-Cu-Mg alloy has the characteristics of high specific strength,high hardness,small linear expansion coefficient,good wear resistance and good thermal stability,and is an ideal vehicle engine piston material.Coarse primary Si and lamellar eutectic Si have a split effect on the matrix in the conventional gravity casting of hypereutectic Al-Si-Cu-Mg alloy,which affects the performance of the alloy.Therefore,improving the morphology of eutectic Si and primary Si to improve the properties of the alloy has become the focus of research on the application of hypereutectic Al-Si-Cu-Mg alloys at home and abroad.Semi-solid forming and heat treatment methods are used to improve the microstructure of the alloy,thereby improving the mechanical properties of the alloy.Ultra-ultrasonic treatment of hypereutectic Al-Si-Cu-Mg alloy was conducted to study the effect of ultrasonic vibration on the microstructure and mechanical properties of the alloy.The research shows that the primary Si angular passivation in the alloy after the ultrasonic vibration treatment,the ultrasonic vibration produces a strong convection,so that the temperature field and the concentration field of the melt are uniform,so that the growth rate of primary Si in all directions is basically the same.Si grows in the form of particles,but also plays a certain role in inhibiting the aggregation of primary Si,which weakens the macro-segregation and micro-segregation of primary Si and makes the structure even.After ultrasonic vibration,the mechanical properties of semi-solid-formed hypereutectic Al-Si-Cu-Mg alloys are improved than those of alloys without ultrasonic vibration treatment.The tensile strength of the alloy after ultrasonic melt treatment reached 140 MPa,the elongation reached 2.32%,and the hardness reached 109.3 HBThree different slurry temperatures of 560°C,580°C,and 600°C were selected for semi-solid extrusion.As the temperature of the slurry increases,the size of the primary Si phase gradually decreases and gradually disappears;the eutectic Si phase is also significantly refined and distributed uniformly,and the?-Al dendrite in the microstructure is significantly increased and becomes more and more developed.When the slurry temperature was 600°C,the mechanical properties of the alloy were the best.The tensile strength of the alloy reached194 MPa,the elongation reached 2.60%,and the hardness reached 120.2 HB.The effect of heat treatment on the microstructure and mechanical properties of semi-solid formed hypereutectic Al-Si-Cu-Mg alloys was investigated.The effects of solid solution time and aging temperature on the microstructure and mechanical properties of semi-solid-formed hypereutectic Al-Si-Cu-Mg alloy were discussed.With the change of solid solution time,Si phase gradually grew at the corners and grooves.Dissolution,granulation,massive primary Si phase gradually refined,spheroidized,angular and tip passivation,solid solution time is too coarse when the Si phase phenomenon.At the same time,the quaternary Al₂Cu and Al-Si-Cu-Mg precipitated in the aging process also changed significantly.The alloy phase ablation phenomenon in the heat treatment,reducing the splitting effect on the substrate,heat treatment of hypereutectic Al-Si-Cu-Mg friction and wear properties have a greater impact,improving the wear resistance of the alloy.The short-term solid solution 1h alloy at525?has good mechanical properties,tensile strength of 323MPa,hardness of 148.8HB,elongation of 2.96%,and minimum wear.