Preparation Of High-volume SiCp/6061Al Composites Via Pressureless Sintering

SiCp/Al composites have the important application potentials in the fields of automobiles,power electronics,aerospace and so on,due to their excellent properties such as high specific strength,specific stiffness and thermal conductivity(TC)and low thermal expansion coefficient(CTE)and density.Research on the preparation of the high-volume Si Cp/Al composites via pressureless sintering is developed as a part of the project of low-cost fabrication technology of high-performance SiCp/6061 Al composites,which is more important to amplify the application areas and preferably serve to the national economic construction.In this paper,the powder metallurgies of pressureless sintering with/without ball milling were employed to produce the 30 vol% and 50 vol% SiCp/6061 Alcomposites.Effects of the average size and its distribution of the Si Cp on the microstructures and properties of the composites were studied.The possible negative influence of ball milling on the composites was discussed.And thus,the optimal processing route was put forward and eventually the high-volume SiCp/6061 Al composites of excellent microstructures and great mechanical/thermo-physical properties were well developed.The methods of grain compositing of F500-SiC and F1000-SiC powders,ball milling,annealing at 500 ?,forming at 400 MPa and pressureless sintering at680-750 ? was used to fabricate the even and dense 30 vol% and 50 vol%SiCp/6061 Al composites.During sintering,the Si Cp/Al interfacial reaction takes place to produce Mg2 Si,Si,AlN and Al4C3 and it turns to be more intensive as rising the sintering temperature.Density and bending strength of the SiCp/Al composites increase initially and then decrease with the sintering temperature.These of the 30vol% and 50 vol% SiCp/6061 Al composites are just 96%,364 MPa and 97%,400 MPa,respectively.The reason why the composites cannot be nearly full-dense lies in the segregation of the small SiCp to form lots of pores which cannot be filled by the Al alloy melt and more intersive interfacial reaction between the small SiCp and the Al alloy during sintering.After elutriating,the F500-SiC powder was blended with the 6061 Al alloy powder of an average particle size of 15 um and mixed in a double-roller mixer.After adding1-2 wt% wax plasticizer,the 50 vol% SiCp/6061 Al composite powder was pressedunder 400 MPa and pressureless sintered at 660-700 ?.The 50 vol% Si Cp/6061 Al composites have better microstructures and greater properties than the former.The composite sintered at 680 ? is the densest with a relative density as high as 99%,so,the nearly-full densification of the composites is achieved.The SiCp/Al interfical reaction is weaker than ever,the reaction product of Al4C3 can only be detected in the composites sintered at 700 ?.The density,bending strength and TC of the 50 vol%SiCp/6061 Al composites also increase initially and then decrease as increasing the sintering temperature.The fracture mode of the composites is of the cleavage fracture of the SiCp and plastic tearing of the Al alloy matrix,showing that the SiCp/Al interfacial bonding strength is high.The properties of the 680 ? sintered 50 vol%SiCp/6061 Al composites are: the bending strength of 495 MPa,the TC of 153W/(m�K)and the CTE of 8.1�10-6 K-1(20-100 ?),respectively.They are greatly superior to those of the composites having the similar composition and fabricated via hot pressing and pressure/pressureless infiltration.