Effect Of Sr And B Composite Treatment On Thermal Conductivity And Mechanical Properties Of Hypoeutectic Al-Si Alloy

Hypoeutectic Al-Si alloy is often used in communication industry because of its high thermal conductivity and low cost.With the rapid development of 5G technology,the power consumption of base station increases greatly.As a common material of base station radiator,hypoeutectic Al-Si alloy requires higher performance.Only by obtaining high thermal conductivity and good mechanical properties of hypoeutectic Al-Si alloy can we meet the needs of practical applications.At present,the main ways to enhance the mechanical properties of hypoeutectic Al-Si alloy are alloying,refinement modification and heat treatment.No matter which kind of treatment,the purpose is to improve the mechanical properties of the alloy,but there are few investigations on the thermal conductivity of the alloy at the same time.In as-cast hypoeutectic Al-Si alloy,eutectic silicon is large and flaky,and primary ?-Al is coarse dendrite,which is easy to cause stress concentration and uneven microstructure distribution.The size,morphology and distribution of eutectic silicon can be changed by modification.Combined with boron treatment,fine eutectic silicon and fine primary ?-Al can be obtained at the same time.Through microstructure control,the alloy has good thermal conductivity and mechanical properties,and its action rule and mechanism are explored.Therefore,the investigation on the effect of modification combined with boron treatment on the microstructure and properties of hypoeutectic Al-Si alloy has both material research and practical application significance.In this paper,based on Al-8Si alloy,the effects of eutectic silicon with different morphology,size and distribution on the microstructure and thermal conductivity of Al-8Si alloy after Sr,Sb modification and T6 heat treatment are investigated,and their action rules and mechanisms are analyzed.On this basis,the effects of single Sr modification and Sr modification combined with boron treatment on the microstructure and properties of Al-8Si-0.6Mg-0.1Cu alloy are investigated.The main results are as follows:(1)When Sr or Sb is added to Al-8Si alloy,the fibrous eutectic silicon modified by Sr significantly increases the thermal conductivity of the alloy,while the effect of Sr content on the thermal conductivity of the alloy is relatively small.The fine flake eutectic silicon which aggregates after Sb modification reduces the thermal conductivity of the alloy.After T6 treatment,the fracture of flake eutectic silicon modified by Sb and the disappearance of aggregation phenomenon can improve the thermal conductivity,but the coarsening of fibrous eutectic silicon modified by Sr is not conducive to the improvement of thermal conductivity.(2)When Sr is added to the Al-8Si-0.6Mg-0.1Cu alloy,when the content of Sr is0.04 wt.%-0.12 wt.%,the Sr element is adsorbed on the Si phase,thus the eutectic silicon is transformed into fiber.The size of eutectic silicon decreases with the increase of Sr content.When the content of Sr reaches 0.08 wt.%,the eutectic silicon size is uniformly distributed within 1 ?m.Correspondingly,the secondary dendrite arm spacing of ?-Al is the smallest at0.08 wt.% Sr,and the thermal conductivity and electrical conductivity of the alloy are 166.8W/(m·K)and 39.3% IACS,respectively,which are 13.5% and 13.3% higher than those of the unmodified alloy.The tensile strength of the alloy is 218.1 MPa,the elongation is 6.45%,which is 7.8%,35.9% higher than that of the unmodified alloy,respectively.(3)Eutectic silicon is transformed into fibrous,?-Al is transformed from dendrite to equiaxed dendrite,and the grain size decreases obviously after 0.08 wt.%Sr modification and boron compound treatment of Al-8Si-0.6Mg-0.1Cu alloy.When composite treated with 0.025 wt.% B,the average grain size decreases from unmodified 270.29 ?m to the minimum of112.21 ?m,and the thermal conductivity and electrical conductivity of the alloy are 164.6W/(m·K)and 39.0% IACS,respectively,which are 12.0% and 12.4% higher than those of the unmodified alloy.The tensile strength of the alloy is 233.4 MPa,the elongation is 8.23%,which is 15.4%,73.3% higher than that of the unmodified alloy,respectively.After Sr modification combined with B treatment,the thermal conductivity,electrical conductivity and mechanical properties of the alloy have been comprehensively enhanced.