Composition Design And Application Of Al-Si Cast Aluminum Alloys With High Thermal Conductivity

Al-Si cast aluminum alloys are widely used in the production of thin-walled heatdissipating devices in the communication field.With the advent of the 5G era,the heat consumption per unit volume of electronic product and communication equipment continues to increase,placing higher requirements on the thermal conductivity of materials.The die-casting aluminum alloy represented by ADC12 has low thermal conductivity(only about 96 W/(m·K)),which limits its application in 5G communication heat dissipation thin-walled devices.Therefore,the development of die-cast aluminum alloys with high thermal conductivity and excellent mechanical properties is imminent.In this paper,the multi-alloying and composite modification were used to design the compositions of two typical casting aluminum alloys,hypoeutectic Al-7Si-based and Al-2Si-based with low Si content.The effect of structure modification(the eutectic Si and Fe-rich phase)on thermal conductivity and the interaction mechanism were mainly investigated to develop high thermal conductivity casting aluminum alloy.The effect of alloy elements(22 types)on the electrical conductivity of industrial pure aluminum was systematically studied.The alloy elements would lead to varying degrees of decrease in the electrical conductivity of industrial pure Al.Among them,the electrical conductivity of pure Al decreased exponentially with the increase of Si content,while the electrical conductivity of pure Al decreased linearly with the increase of Fe,Cu and Ni contents.The addition of transition group elements such as Mn,Cr and V could reduce the electrical conductivity of pure Al largely.Alloy elements such as Zn and Co,and modified elements such as Sr,B and RE had little effect on the electrical conductivity of industrial pure Al,and even a small amount of addition could improve the electrical conductivity of pure Al.By comparison,it is found that a few alloy elements existed in Al in the form of solid solution atoms,resulting in a larger "specific electrical resistivity" and thereby a rapid decline in the electrical conductivity of pure Al.However,most alloy elements and Al that are tending to form different second-phase structures,have little effect on the electrical conductivity of pure Al.As the addition contents of Fe and Cu increased,the electrical conductivity of hypoeutectic Al-7Si alloy decreased linearly.The addition of modified elements Sr,B,RE and Sb could significantly improve the electrical and thermal conductivities of Al-7Si alloy.With 0.05% Sr modification,the electrical and thermal conductivities of the alloy could be increased to 24.27 MS/m and 169.9 W/(m·K).The modified elements could change the coarse plate-like eutectic Si in the alloy into coral and short-pieces structure,increase the continuity of the Al matrix,reduce the lattice distortion of the alloy,thereby significantly improving the electrical and thermal conductivities of the Al-7Si alloy.Based on Sr-B-RE composite modification,the thermal conductivity of Fe-containing hypoeutectic Al-7Si based alloy could be significantly improved,up to 165.6 W/(m·K).And its mechanical properties were also excellent,with the Brinell hardness of 62.2 HB,the tensile strength of 189.6 MPa,and the elongation of 13.8%.At the same time,the multi-alloying had obtained a high thermal conductivity alloy system(Al-2Si-2Zn-0.8Fe)with low Si content of only 2% and containing Mg and Co.After being modified by Sr-B,the thermal conductivity of the as-cast alloy was as high as 176 W/(m·K).The fluidity of the alloy was 85% of ADC12.And it had excellent mechanical properties,with the Brinell hardness of 61.6 HB,the tensile strength of 239.6 MPa,and the elongation of 9.2%.The production verification of Al-7Si-based high thermal conductivity aluminum alloy showed excellent die casting moldability.The thermal conductivity of die-casting alloy was 160.4 W/(m·K),and the tensile strength and elongation were 200.2 MPa and 10.5%.After further low-temperature annealing heat treatment,its thermal conductivity could reach 178.9 W/(m·K),meeting the current 5G industry's requirements for the high thermal conductivity thin wall heat dissipation die castings.Based on the results of the influence of alloying elements on the electrical conductivity of pure Al,this study designed the composition of Al-Si casting alloys.It was deeply disclosed that the relationship between multi-alloying and microstructure control by composite modification on the improvement of the alloy's thermal conductivity.The Al-7Si based and Al-2Si based high thermal conductivity casting aluminum alloy system were developed and successfully implemented.This study provided a certain theoretical and experimental basis for the development of high thermal conductivity and high strength Al-Si cast aluminum alloy under the background of 5G.