Effect Of Modification And Hot Rolling On Microstructure And Properties Of High Silicon Aluminum Alloy

High-silicon aluminum alloys have broad application prospects in the automotive.electronic packaging,aerospace and other fields because of their small specific gravity,high strength,low coefficient of thermal expansion,and good wear resistance.Its excellent performance mainly depends on the size,morphology and distribution of the Si phase in the alloy structure.In this paper,aiming at the difficulty of Si phase refinement in high-silicon aluminum alloys,Al20Si4Cu alloy is used as the target component,and rapid cooling,modification,heat treatment and rolling are used to improve the microstructure of the alloy.Using OM,SEM,EDS,XRD and other major testing methods,the influence of different preparation processes on the microstructure and properties of A120Si4Cu alloy was studied.The results show that increasing the cooling rate can effectively refine the primary Si phase in the A120Si4Cu alloy and can significantly increase the tensile strength of the alloy.Under the non-metamorphic condition,when the cooling rate increases from 11.75℃/s to 172.94℃/s,the average primary Si size of the alloy is reduced from 98.63μm to 41.32μm,and the tensile strength is increased from 113MPa to 192MPa.The modification results show that the average primary Si size can be refined from 55.26μm to 12.65 μm and the tensile strength by up to from 183 MPa to 255 MPa under the optimum modification conditions of 0.08%of P addition and 80 minutes of modification.The mathematical relationship between the primary Si average size D and the cooling rate V of the A120Si4Cu alloy under non-deforming and optimum P modification conditions is:D=220.95*V-1/3 and D=57.11*V-1/3.This shows that at the same cooling rate,P modification can significantly refine the primary Si grains of the alloy.Explains that the alloy must be P-modified even under rapid cooling conditions.The heat treatment results showed that the primary Si phase in the A120Si4Cu alloy was passivated at the 525℃ for 3h and 175℃ for 9h aging,and the eutectic Si phase changed from long needle to short rod.The massive 0 phase transforms into a diffusestrengthening phase.At the same time,after heat treatment,the tensile strength of the alloy increased by 255 MPa by 350 MPa.The results of the rolling treatment show that the primary Si phase in the alloy structure is circularized and the eutectic Si phase changes from a long needle to a matte shape under the optimal hot rolling process of 525℃ for 3 hours and 10%for rolling deformation.The irregular θ phase transforms into a punctiform strengthening phase uniformly distributed in α-Al matrix.At this point,after rolling,the tensile strength of the alloy was increased from 255 MPa to 297 MPa.The friction and wear test results show that the increase of cooling rate,P modification,heat treatment and rolling process can improve the wear resistance of A120Si4Cu alloy to some extent,and make the alloy wear rate,average friction coefficient and friction coefficient fluctuation relatively reduced.In the friction and wear test process,A120Si4Cu alloy mainly has wear mechanisms such as peel wear,abrasive wear,adhesive wear and oxidation wear.