Study of 6061-Al2O3p composites produced by reciprocating extrusion

A reciprocating extrusion process was developed to consolidate 6061-Al2O3p composites from mixed powders. The 6061 alloy powder was first dehydrated i n a vacuum chamber at 450 degrees C and then mixed with 12.5 mu m Al2O3 pow der in various volume fractions: 0, 5, 10, 20, and 30 pet. The mixed powder s were hot pressed at 300 degrees C under a pressure of 300 MPa and finally extruded reciprocatingly 14 times at 460 degrees C. The results show that the composites were fully densified, with no sign of pores or oxide layers observable in the optical microscope. The Al2O3 particles were distributed uniformly in the matrix. As compared with 6061 alloys, the composites demon strated a smaller precipitation hardening and elongation, but exhibited a h igher Young's modulus and a larger work hardening capacity. The degradation of precipitation hardening was due to the loss of Mg, which reacts with Al 2O3 to form MgAl2O4. The large work-hardening capacity is attributable to t he incompatibility between Al2O3 and the matrix, which possibly generates m ore dislocations to harden the matrix. The composites had much higher frict ion coefficients and greater wear resistances than the 6061 alloy against s teel disc surface. The friction coefficient of the 6061-30 vol pet Al2O3p c omposite was double that of the 6061 alloy and the wear resistance was 100- fold. As compared with similar composites reported previously, these compos ites possessed much higher elongation at the same strength level. A 30 vol pet Al2O3p Still displayed an elongation of 9.8 pet in the T6 condition. Al l of these improvements are attributed to the merits, including full densif ication of the bulk, uniform dispersion of the Al2O3 particles in the matri x, and strong binding between the Al2O3 particles and the matrix resulting from reciprocating extrusion.