The processing and characterization of aluminum boride flake-reinforced aluminum matrix composites

AlB{dollar}sb2{dollar} flakes in an aluminum matrix offer the potential for greatly increased composite mechanical and wear properties because of their high aspect ratio, very high mechanical properties and good wetting to the aluminum matrix. This thesis describes, for the first time, an approach to the processing of AlB{dollar}sb2{dollar} flake reinforced aluminum alloy composites in the absence of any other Al-B phase. The processing route is presented and then the crystallization and growth behavior of the flakes are described. Specifically, a high temperature heat treatment is discussed which produces a homogeneous distribution of AlB{dollar}sb2{dollar} flakes in the absence of AlB{dollar}sb{lcub}12{rcub}{dollar} cuboidal impurities. The production of high aspect ratio 10v/o and 20v/o AlB{dollar}sb2{dollar}/Al-Cu composites along with the resultant composite mechanical properties is then described. The randomly oriented AlB{dollar}sb2{dollar} flake reinforced aluminum matrix composites show a significant enhancement of the strength and modulus over the aluminum alloy both at room and elevated temperatures. Increased planar alignment of the flakes is demonstrated to further increase the mechanical properties of the composites. Wear, thermal conductivity, and thermal expansion data of the composites are then presented. The incorporation of AlB{dollar}sb2{dollar} flakes in aluminum is shown to increase the wear resistance and decrease both the thermal conductivity and thermal expansion coefficient in the longitudinal direction.