Effect Of External Field Treatment And Heat Treatment On Microstructures And Properties Of Al-25% Si Alloy

Hypereutectic aluminum-silicon alloy,with high wear resistance,heat resistance,and reduce the density of linear shrinkage overall performance,are widely used in automotive,marine,military,and other fields.However,due to the high silicon content,low strength and high brittleness,traditional processes often cannot meet the performance requirements of various fields,which restricts the development and application of hypereutectic aluminum alloys.Pulsed magneto-oscillation and ultrasonic treatment are regarded as effective techniques to improve material structure and mechanical properties in recent years.Therefore,Al-25%Si alloy is taken as the research object in this paper.By applying pulsed magneto-oscillation technology and ultrasonic treatment to Al-25%Si alloy melt,the effects of pulsed magneto-oscillation frequency,pulse peak current and ultrasonic power treatment on the solidification structure and properties of the alloy and the effects of pulsed magnetic induced oscillation and ultrasonic treatment on the kinetics of the dissolution and crystallization of primary silicon and the microstructures and properties of solid solution treatment were studied.The following main conclusions are obtained:(1)Pulsed magneto-oscillation treatment can refine the primary silicon structure of Al-25%Si alloy and improve its performance.When the frequency is constant,the average size of primary silicon of Al-25%Si alloy first decreases and then increases with the increase of peak current.When the pulse peak current is 350A,the effect of microstructure refinement is the best.The average size of primary silicon decreases from 130.2?m to 40.1?m,the pulse peak current is 350A,the Brinell hardness of alloy is about 60.3HB,and the wear rate of alloy is the lowest.When the pulse peak current is constant,as the frequency increases,the average size of the primary silicon continues to increase,and the organization refinement effect is best at a frequency of 20 Hz.The average size of the primary silicon is about 43.3?m,and the Brinell hardness is about 59.6HB,the wear rate of the alloy is the lowest.(2)Ultrasonic treatment can refine the solidification structure of Al-25%Si alloy to improve its properties.With the increase of ultrasonic power,the average size of primary silicon of Al-25%Si alloy decreases first and then increases.When the ultrasonic power is 1200W,the refinement effect of the solidified structure is the best.The average size of the primary silicon is reduced from 130.2?m to 34.2?m,the Brinell hardness is about 65.2HB,and the wear rate of the alloy is the lowest.(3)After the treatment with the peak pulse current of 350A and the ultrasonic power of1200W,the dissolution and crystallization temperatures T_s,T_pand T_eof the primary silicon were changed.The S curve of the dissolution and crystallization process is shifted left compared to the curve of the untreated Al-25%Si alloy.The reason is that the treatment with peak pulse current of 350A and ultrasonic power of 1200W accelerated the dissolution and crystallization kinetics of primary silicon.(4)After 540?solid solution treatment,the eutectic silicon tissue was partially dissolved,which gradually changed from long needles to short rods and even some spherical eutectic tissues,and after 540?+16h solution treatment,the effect was the best,a large number of short rod eutectic structure appeared.At this time,the Brinell hardness of alloys treated with pulse peak current of 350A and ultrasonic power of 1200W were 62.5HB and 66.7HB,respectively.