| With the rapid development of electronic information industry,traditional electronic packaging materials are difficult to meet the requirements of heat dissipation and lightweight of modern electronic products.The electronic information industry urgently needs a new generation of electronic packaging materials with excellent comprehensive performance,such as low coefficient of thermal expansion,high thermal conductivity,low density and simple preparation process.High silicon aluminum alloy is a new type of Al-Si composite with high Si content.Its thermal conductivity is high.The coefficient of thermal expansion and other properties of the composite can be adjusted by changing the Si content.It has low density,high specific strength,good coating performance,easy to weld with the substrate,and is suitable for precision processing.It has a broad application prospect in the field of electronic packaging.In this project,Al-Si alloy with Si content not less than 40%was prepared by powder metallurgy process.The room temperature pressing process,liquid phase reaction sintering process,microstructure and thermophysical properties of the alloy were studied.Al/Si mixed powders with different Si contents were compacted at room temperature to study the densification mechanism of the powders.Huang Peiyun's compaction equation was used to analyze the compaction characteristics of the powders.The results show that the densification behavior of powder can be divided into three stages:particle rearrangement stage,elastic-plastic deformation stage and powder bulk deformation stage.With the increase of Si content,the hardening index m and the pressing modulus m increase gradually.For Al-70Si Powder,m is 2.553,M is353.183MPa.The compaction pressure affects the deformation behavior of powder particles,and the height diameter ratio affects the friction force of cold pressed billet,which affects the densification process of powder.Al Si alloy cold pressed billets with different Si content were sintered in liquid phase at 700?for 1h.The effects of Si content on microstructure,fracture morphology and properties of the sintered billets were studied and compared with the theoretical model.The results show that with the increase of Si content,the growth of fine Si particles along the{111}crystal plane is changed to lath shape and precipitates on the surface of large-size Si particles.Further,the Si particles will grow up in contact with each other.Instead,Si particles precipitate on the surface of large-size Si particles,and further Si particles will contact and grow up.The fracture of high silicon aluminum alloy is composed of ductile fracture of Al matrix and brittle cleavage fracture of Si particles.The increase of Si content reduces the ductile fracture and increases the proportion of brittle fracture of Si particles.With the increase of Si content,the thermal conductivity first increases and then decreases,which is smaller than the theoretical model.The thermal conductivity of Al-50Si is the closest to the theoretical value.With the increase of Si content,the coefficient of thermal expansion decreases gradually,and the Si content with low expansion rate increases,which limits the expansion of high Si aluminum alloy.The liquid phase sintering of Al-50Si alloy was carried out at different sintering temperature for 1h and 750?for different time.The effects of sintering process on the microstructure and properties of sintered billets were studied.The results show that the liquid phase sintering process of Al-Si can be divided into three stages:initial liquid phase formation stage,particle rearrangement and rapid densification stage,and slow densification stage.At the liquid reaction sintering temperature,Si atoms diffuse and eutectic with Al matrix to form Al(Si)(L)liquid phase.With the increase of temperature,the diffusion rate of Si atoms increases,the formation rate of liquid phase increases,the viscosity of liquid phase decreases and the wettability of Si particles improves.The atoms of the smaller Si particles tend to dissolve in the Al(Si)(L)liquid phase and diffuse to the surface of the larger Si particles,resulting in the passivation and growth of the larger Si particles until the overlapping network structure is formed.According to the comparison of microstructure and properties of Al-50Si alloy with different Si content,sintering temperature and holding time,it is found that the morphology of Si particles in Al-50Si alloy prepared at 750?for 1h is nearly spherical and dispersed,and the comprehensive properties are the best,with the density of 98.46%,thermal conductivity of 136.1W/(m·K)and thermal expansion coefficient of 10.7×10-6K-1.The micro Vickers hardness is 159.7. |
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