Fabrication of green and sintered Al: Al2O3 composites using gel-casting and powder metallurgy technique

Abstract

An effort had been made to fabricate composite of (1-x) wt% Al: x wt % Al2O3 (where x = 0, 10, 20 30, 40, and 50) using both gel casting and powder metallurgy techniques To the best of our knowledge, there was no such literature available on Al-Al2O3 composites prepared through gel-casting technique. Prior to gel-casting zeta-potential, concentration of deflocculating agent, and viscosity were optimized. A mould was designed and fabricated and a new processing route was employed to produce a homogeneous green body which was successful. Microstructure implies that the sintered body was highly porous which could not provide enough mechanical strength. However, the green product was easily machinable. XRD analysis shows no sign of oxidation of aluminium. It has to be further studied before using it for the production. In powder metallurgy, to attain proper mixing aluminium and alumina in their powdered form are milled for 1h in a planetary milling machine with isopropyl alcohol as the wetting agent. Powders were pressed to samples of different shape and were sintered under vacuum. Normally such composites are sintered at nitrogen or argon atmosphere. Some attachments for were designed and manufactured that could be used in the tubular furnace to obtain vacuum. The design was successful and was able to produce a vacuum pressure of 5.6E-6 mbars inside the tube. It had been found that by reinforcing with 20% alumina the hardness of aluminium was increased to 35 HV. Bending test gives the indication that the plasticity is reduced slowly by the addition of alumina into aluminium matrix. It was also found that the tribological properties can be improved by adding 20 weight % of alumina into the metal. Microstructure indicates that the alumina was well dispersed in the aluminium matrix. The composite is easily machinable with HSS tool with minimum tool wear. Therefore it can be used to replace materials in various automotive, aerospace, and automobile industries.