| With the rapid development of electronic information,communication and other industries,electronic communication products such as base stations,inverters and radiators are gradually developing in the direction of high integration,miniaturization and lightweight,and the requirements for material heat dissipation performance are getting higher and higher.Therefore,high thermal conductivity materials have become the key to improving the heat dissipation capacity of equipment and reducing system temperature.However,the thermal conductivity of common cast aluminum alloys is generally less than 150 W/(m·k),such as ADC12,A356,A380,etc.,which is difficult to meet the requirements of parts for heat dissipation capacity.Taking commercial Al Si12 Fe alloy as a reference,under the premise of ensuring its mechanical properties casting performance,this paper designs and prepares high thermal conductivity Al Si Ni Fe die-cast aluminum alloy by changing the content of Si and Ni elements,melt sonication and heat treatment process,and discusses the influence law and interaction mechanism of alloy microstructure control(eutectic Si and iron-rich phase)on thermal conductivity.By reducing Si elements and increasing Ni content,the influence of composition changes on the thermal conductivity,mechanical properties and casting properties of alloys was studied,and the influence mechanism was analyzed,which provided theoretical support for the design and development of high strength and high thermal conductivity cast aluminum alloy components.The results show that with the decrease of Si element content and the increase of Ni element content,the yield strength of the alloy gradually increases,and the elongation change is the opposite,compared with the mechanical properties of the original Al Si12 Fe alloy,the thermal conductivity of the alloy shows a trend of first decreasing and then rising.The addition of Ni improves the subcooling of the solid/liquid interface,promotes nucleation,inhibits the growth of α-Al phase,and refines the grains.When the silicon-nickel content in the alloy is Al-10Si-0.8Ni and Al-8Si-1.2Ni,some long needle-like Al-Fe-Ni-Si phases penetrate deep into the α-Al,which seriously cuts the matrix,which leads to low thermal conductivity of the alloy at this time.When the alloy composition is adjusted to Al-4Si-2Ni,compared with the original Al Si12 Fe alloy,the comprehensive mechanical properties are increased by about 27%,the thermal conductivity is increased by about 19.4%,and the fluidity of the alloy is reduced by 23% compared with the original commercial Al Si12 Fe alloy.By changing the ultrasonic temperature and ultrasonic power,the effects of melt sonication on the mechanical and thermal conductivity properties of Al-4Si-2Ni-0.8Fe-0.4Mg alloy were studied.The results show that at lower ultrasonic temperature,the alloy has finer grain structure,higher thermal conductivity and mechanical properties,and the mechanical properties of the three alloys after ultrasound are increased by 5.0%,7.6% and 64.7%,respectively,compared with non-ultrasound.The thermal conductivity has been improved from 160 W/(m·k)to 170W/(m·k),an increase of approximately 5.5%.At the same time,with the increase of ultrasonic power,the alloy grain size gradually decreases,and when the ultrasonic power changes from 0to 900 W,the alloy grain size decreases by about 61.1%.As the power continues to increase,the grain size decreases slowly,and the thermal conductivity remains basically unchanged with the increase of ultrasonic power.The tensile strength,yield strength and elongation of the alloy at2100 W power are 216 MPa,142MPa and 6.3%,respectively,and the thermal conductivity is169W/(m·k).The ultrasonic action in the solidification process of sub-eutectic Al-Si alloy is manifested by the transformation of dendrites to equiaxed crystals,and the grain refinement and eutectic phase dispersion refinement realize the synchronous improvement of the thermal conductivity and mechanical properties of cast aluminum-silicon alloy with high Fe.By changing the aging time,the influence mechanism of aging time in heat treatment on the microstructure and thermal conductivity of alloy was studied.The results show that the thermal conductivity of the alloy after heat treatment is greatly improved compared with the casting state,and the thermal conductivity is increased from 169 W/(m·k)to 194W/(m·k),which is increased by 14.7%.After heat treatment,the alloy structure changed significantly,and the dendritic eutectic silicon changed into short rods and granular,uniformly dispersed in the grain boundaries,and added channels to the transport of electrons.This is the main reason for the increase in thermal conductivity of alloys after heat treatment.After heat treatment,the thermal conductivity is 193W/(m·K)and the strength is 326 MPa,which is a new low-Si cast aluminum alloy material with high strength and thermal conductivity. |
