The Microstructure And Properties Of Al-Si-Cu-(Sn/In) Alloys For Heat Dissipation

With the rapid development of communication technology,high-speed transmission of large data has become an advantage of the new generation of electronic products.At the same time,the heat generated by the high-power consumption of electronic components has increased dramatically and there is an urgent need to develop lightweight and efficient heatdissipation materials.The heat dissipation components also need to withstand external loads and connections and therefore have high requirements for their heat transfer and mechanical properties.Improving the alloy’s thermal conductivity to ensure its strength has become a key issue for the new generation of heat-dissipation materials for the electronics industry.Compared to other aluminum alloy strengthening elements(Mg,Si,Mn,Fe,Zn,etc.),the influence of Cu elements on the thermal conductivity of Al-Si alloys is relatively small;promoting the precipitation of Cu elements and further regulating the structure of the precipitated phase is the key to harmoniously enhancing the thermal conductivity and strength of Al-Si-Cu alloys.This paper used micro-alloying(trace Sn and In elements)and double-stage aging processes to regulate the precipitation behavior and microstructure of θ’phase to synergistically enhance the strength and thermal conductivity of Al-Si-Cu alloys.Specifically,trace Sn and In elements were added to Al-7Si-3Cu alloys,and all alloys were prepared by water-cooled copper casting in the paper.The microstructure and properties of Al-7Si-3Cu alloys were analyzed by SEM,LFA,and microhardness,and the aging precipitation behavior of Al-7Si-3Cu alloys was investigated by TEM,DSC,and XRD after solid solution and two-stage aging treatment.The effect mechanism of θ’ phase amount,distribution,and morphology on the strength and thermal conductivity was also discussed.Based on the above investigations,the conclusions are as follows:(1)Trace amounts of Sn elements can significantly improve the strength and thermal conductivity of Al-7Si-3Cu alloys.The comprehensive performance of Al-7Si-3Cu-0.13Sn alloy was better with a yield strength of 306 MPa and a thermal conductivity of 161.1 W/m·K at 100℃-3h+160℃-6h.The trace Sn decreased the activation energy of θ’ from 36.84 kJ/mol to 20.16 kJ/mol and promoted its precipitation.Compared to the base alloy,the quantity density of θ’ phase increased and the size decreased in Al-7Si-3Cu-0.13Sn alloy.The lattice constant of the Al-7Si-3Cu-0.13Sn alloy(aged state)was only 0.0007 ? and the difference from pure aluminum was smaller.In conclusion,Sn could promote θ’ precipitation,and improve the lattice distortion.This will benefit the thermal conductivity.(2)The influence of trace In element on θ’ precipitation behavior was similar to that of Sn.When the In content was controlled as 0.41 wt.%,the activation energy of θ’ of Al-7Si3Cu-0.41In alloy was 28.59 kJ/mol(less than the decrease of 0.13 wt.%Sn alloy),and the increase of quantity density of θ’ was small relatively.The precipitation was slightly larger than that of Al-7Si-3Cu-0.13Sn alloy,and further aggregation and growth of the precipitated phase will be more conducive to the improvement of thermal conductivity.The thermal conductivity of Al-7Si-3Cu-0.41In alloy was increased to 166.6 W/m·K after aging and was higher than that of Al-7Si-3Cu-0.13Sn.(3)Due to the high price of In elements,this paper improves the thermal conductivity of Al-Si-Cu alloy by adding Sn and In elements in combination to reduce processing costs.The reaction activation energy of the θ’ phase of the Al-7Si-3Cu-0.13Sn-0.06In alloy was found to be reduced to 27.57 kJ/mol,at which point the number,size,and distribution of theθ’ phase in the alloy were closer to the results of adding the In element alone.The results of the combined study showed that the Al-7Si-3Cu-0.41In alloy exhibited the best overall performance after heat treatment at 500℃-10 h+100℃-3 h+160℃-6 h.The yield strength was 324 MPa and the thermal conductivity was 166.6 W/m·K.Compared with the base alloy(yield strength 209 MPa,thermal conductivity 149.8 W/m·K),the strength and thermal conductivity were increased by 55%and 11%respectively compared to the base alloy(yield strength 209 MPa,thermal conductivity 149.8 W/m·K).