The Manufacture Of Short-Carbon-Fiber Reinforced Aluminum Matrix Composites By Stirring Melt Casting

In this paper, the short carbon fiber reinforced 2024 matrix composites with different volume fraction of carbon fiber were fabricated by stirring melt casting method. The influence of short carbon fiber volume fraction, heat treatment and hot extrusion processes on the microstructure, density, compactness and mechanical properties of composites were tested by the technologies such as Optical Microscope(OPM), Scanning Electron Microscope, Vickers Hardness tester, MTS Tensile Tester, immersion oil technology and Archimedes principle.By using chemical copper process of carbon fiber, the problems about wetting and interfacial reaction between fiber and 2024 alloy matrix was improved and avoided respectively. By using immersing pretreatment of fiber in 1% boracic acid solution, the oxidization of carbon fiber appeared during the composites fabrication was avoided.By redesigning the strirrer and crucible furnace structure, fiber adding velocity into melt was speeded, the distribution of fiber in aluminum melt was improved and the dangers such as scald and splash of melt droplet were avoided. By analyzing the effect of stirring melt casting process parameters on the microstructure and microdefects, it is been that the stirring speed, stirring temperature, stirring time and holding time at melt has an important influence on the microstructure, physical properties and mechanical properties of composites. An optimal fabrication process was determined:adding temperature of short carbon fiber:760℃, strirrer stirring speed is 2500r/min, stirring time is 10min, holding time of fiber in melt is 10min and casting temperature of composites is in the temperature range of 690℃to 720℃. The short carbon fiber reinforced 2024 alloy matrix composites produced with this process shows homogeneous fiber distribution in aluminium alloy matrix and excellent bonding between carbon fiber and aluminium alloy matrix.The casting microstructure of Cf-2024 composites have high volume fraction of micropore and low density and compactness. The hot extrusion can't change the caibon fiber distribution in matrix and also can't destroy the bonding between fiber and aluminium alloy matrix. But the microdefects in composites decrease obviously. The small size of micropores was welded while large size of micorpores were collapsed. The density of composites is closed to 2024 alloys matrix while the compactness of composites were obvious improved and the influence of volume fraction carbon fiber on the compactness of composites is obviously decreased.The increase of carbon fiber volume fraction always increases the reinforcing effect of carbon fiber on the composites whether or not it was treated with heat treatment process. The hardness of composites increase firstly then decreases with increasing the volume fraction of carbon fiber. The composites has the highest hardness and strength when it contains 1% carbon fiber. The reinforcing of carbon fiber can improve the elastic modulus of composites. The elastic modulus of composites is always higher than that of 2024 matrix and increases with increasing volume fraction of carbon fiber.