Study On Preparation Of Short Carbon Fiber Reinforced Aluminum Matrix Composites By Mechanical Stirring

It was widely used in practical production that the carbon fiber reinforced aluminum matrix composite material (Cf/Al) for it had good mechanical properties. Al4C3 brittle phase was generated by chemical reaction when carbon fiber contacted with liquid aluminum. The contact angle between the aluminum and carbon fiber was 135-140° when the temperature was below 1000℃, which mad a poor bonding between the aluminum and carbon fiber. It could be improved that the wettability between carbon fiber and the liquid aluminum by the metal coating on the surface of carbon fiber, and metal coating also could prevent the reaction between them. The coating could make liquid aluminum entered into the gap among carbon fibers. The state of carbon fiber surface could be changed through electroplating nickel and chemical plating nickel. The Cf/Al could be prepared by squeeze casting, ultrasonic vibration and vacuum pressure impregnation method etc. Mechanical stirring tech was used to prepare short carbon fiber reinforced aluminum matrix composites in this paper.The properties of composite materials were affected by the quality of metal coating on the surface of carbon fiber. The coating was 100% nickel (Ni) and the average thickness of coating was under 1μm in electroplating by optimizing current, concentration of boric acid in plating solution and time. The chemical plating solution was adjusted by adding plating solution stabilizer (cadmium sulfate) and PH stabilizer (anhydrous sodium acetate), increasing the content of main salt (nickel sulfate) and reducing the content of reducing agent (sodium hypophosphite). Those adjustments can increase the service life of plating solution and it was twice before it was adjusted. The average thickness of coating was 3.7μm when chemical nickel plating time was 40 minutes. It was enhanced with the time increasing that the combination between coating and carbon fiber. The main components of the coating were nickel (Ni) and phosphorus (P), and the mass fraction was 4.78% and 95.22%. The mainly ingredient of coating was amorphous Ni-PIt was found that chemical plating nickel carbon fiber had a better combination with liquid aluminum than electroplating nickel carbon fiber. The wettability has been changed by nickel coating. The coating could also prevent chemical reaction between carbon fiber and the liquid aluminum. Short carbon fiber reinforced aluminum matrix composites was prepared by self-made mechanical stirring device in this paper. Some carbon fibers were dispersed distribution in liquid aluminum and others were aggregated distribution in the surface of liquid aluminum. Some coatings of short carbon fiber were exfoliated. It was for this reason that the thermal expansion coefficient of Ni-P coating was bigger than carbon fiber.It was found that the coating had crystallization when the nickel-coated carbon fiber was put into A356 aluminum alloy in high temperature. Carbon fiber and aluminum matrix were respectively analyzed by XRD after compositing in high temperature, Al3Ni phase was found in the coating of carbon fiber and Al1.1Ni0.9 phase and AlP phase were discovered in aluminum matrix, which proved that the chemical reaction have occurred between the Ni-P coating and liquid aluminum. AlNi5.4Si2 phase and Ni3Si phase were discovered in short carbon fiber reinforced matrix composites by XRD, which also proved the chemical reaction have occurred between them. The chemical reactions occurred between carbon fiber and A356 aluminum alloy. Chemical bond was the main interface binding force.