Hot-Press Sintering,Microstructure And Properties Of C/(Al-Cu) System Composites

The Al-Cu matrix composites are widely used in automotive,aerospace,national defense and other high-tech fields due to their excellent properties,which are a combination of light weight,high specific strength,good corrosion resistance of Al,and high conductivity,thermal conductivity,good ductility of Cu.C is a composite reinforcement element having been commonly used.In the preparation processes of C/?Al-Cu?composites in the past,Al and Cu were prone to form brittle intermetallic compounds,and the wettability between C and matrix was low,the interface bonding was not good either.To solve the problem memotioned,the C/?Al-Cu?composite was prepared by in-situ formation of C by pyrolysis of organic polymer and combined with hot pressing sintering.In this paper,the metal powders and the organic additives were firstly mixed.Different ratioes of Al and Cu powder were adjusted to prepare uniform mixed slurries,followed by the vacuum dry process and obtained precursors before the pyrolysis process.The research shows that the maximum temperature of the pyrolysis precursor was 520°C.After the pyrolysis process,the organic polymer was basically removed,and pyrolysis C was in-situ generated in the matrix along with a small amount of short-chain polymer.The C/?Al-Cu?composites with different compositions were prepared by vacuum hot pressing sintering of pyrolysis C/?Al-Cu?composite powders.The results showed that the composites with uniform phase distribution and good particle bonding could be obtained under the hot pressing sintering condition of 490°C-300MPa-1.5h.The densities of the composites were all above 94%.In the C/?Al-Cu?composite,the main phases were the matrix Al and Cu phases,and the content of pyrolysis C generated in situ was about 1.2%.Part of the Al and Cu particles reacted to form some intermetallic phases,mainly Al₂Cu and Al₄Cu₉.Finally,the carbon-free Al-Cu composites were used as the reference to analyze the existence of in-situ pyrolysis carbon in the matrix and its effect on the structure and properties of the composite.The results showed that the pyrolysis C formed by pyrolysis of organic polymer existed between the grain boundaries of Al and Cu particles,and the content of intermetallic compound formed in C/?Al-Cu?composites reduced evidently compared with carbon-free Al-Cu composites.This indicated that the C species at the grain boundaries of Al and Cu hindered the reaction between Al and Cu to a certain extent,and reduced the formation of intermetallic compounds.The hardness of C/?Al-Cu?composites increased with the increase of Cu content,and the hardness of C/?40%Al-Cu?and C/?60%Al-Cu?composites increased sharply.C/?60%Al-Cu?composite had a maximum of 210 HV because the Al₂Cu and Al₄Cu₉phases were hard and brittle,which effectively improved the hardness of the composite.When the Cu content was between 0 and 60%,the variation of the wave velocity and the wave impedance of the composite material were basically consistent with the predicted value.When the Cu content was increased to 80%and 95%,the difference of the experimental value and prediction value increased,and the wave impedance decreased by a maximum of 21.9%when the Cu content was 95%.