Study On Microstructure Regulation And Performance Of Al-Fe Based Alloys With High Thermal Conductivity

The communication technology represented by 5G is developing rapidly.With the rapid increase of wireless signal frequency and integration,higher requirements are put forward for the heat dissipation of communication devices.Generally,the communication heat sinks are formed by die-casting Al-Si-based alloys,but their thermal conductivity is relatively low.Si-free Al-Fe-based alloys with high thermal conductivity are one of the important future development directions.However,their mechanical properties are relatively poor,which hinders their applications.The present study intends to use elemental modification and rolling deformation to control the microstructures of Al-2Fe eutectic alloy and Al-1.75Fe-1.25Ni eutectic alloy to obtain the Al-Fe-based alloys with high strength and high thermal conductivity and corresponding preparation technology.The main conclusions are as follows:The influence of limited solid solution elements(such as Fe,Co,Ni)in Al solution on the thermal conductivity of pure aluminum is much smaller than that of Si element.With the increasing in the adding content of elements,the microstructures of these binary alloys have evolved from dots and strips to continuous network.When the second phase exists in the form of dots and strips,the Modified Series model can better describe the relationship between alloy thermal conductivity and composition.When it exists in a continuous network form,the predicted value of the Modified Maxwell model agrees well with the experimental results.Based on the influence of low solid solubility elements on the thermal conductivity of pure aluminum,two Al-Fe-Co/Ce and Al-Fe-Ni-Yb eutectic alloy systems with high strength and high thermal conductivity were designed and prepared.Co/Ce elements modification and rolling deformation can significantly improve the microstructure of Al-2Fe eutectic alloy,which simultaneously increased their conductivity and mechanical properties.The thermal conductivities of the as-rolled Al-2Fe-0.3Co and Al-2Fe-0.1Ce alloy were 225 W/(m·K)and228 W/(m·K),respectively.Their ultimate tensile strengths were improved to 185 MPa and 180MPa,exhibiting the excellent comprehensive properties.The Modified Maxwell model was used to estimate the thermal conductivity of the Al-2Fe eutectic alloy.The dot-and stripe-like Co/Ce-rich phases were distributed in the?-Al matrix.The Series model was conducted to describe the thermal conductivity of the Al-2Fe alloy after Co/Ce element modification.The fitting result of the thermal conductive structure model was consistent with the thermal conductivity of the experimental test.The Al-1.75Fe-1.25Ni eutectic alloy has the most potential to be developed into a new generation of high thermal conductivity aluminum alloy,but coarse eutectic structure(?-Al+Al₉Fe Ni)is detrimental to its mechanical properties.The rare earth element Yb was optimized to significantly refine the eutectic structure by changing the growth mode of the Al₉Fe Ni phase.Consequently,thermal conductivity and mechanical properties were simultaneously improved the for the Al-1.75Fe-1.25Ni eutectic alloy.The thermal conductivity,ultimalte tensile strength and elongation of rolled Al-1.75Fe-1.25Ni-0.3Yb alloy were 223 W/(m·K),210 MPa and 13%,respectively,exhibiting both the high strength and good thermal conductivity.Since the microstructure of Al-1.75Fe-1.25Ni alloy was a typical eutectic morphology,the thermal conductivity estimated by Series and Parallel model was consistent with the measured value.The introduction of vibration during the solidification of the Al-1.75Fe-1.25Ni eutectic alloy can promote the formation of fine and uniformly?-Al grains.strengthening and toughening of Al-1.75Fe-1.25Ni alloy with high thermal conductvity were suscessfully realized.In this study,based on the element modification and deformation strengthening,we have achieved the simultaneous improvement of thermal conductivity and mechanical properties of Al-Fe-based alloys.The alloys can not only be produced by die casting,but also can be plastically formed.This research results obtained in the present study have important reference value and theoretical guiding significance for the development of high thermal conductvity aluminum alloys.