The effect of cooling rate on the quench sensitivity of 2618 Al/Al2O3 MMC

Metal matrix composites (MMCs) are materials consisting of metal alloys reinforced with fibers, whiskers, particulates, and wires. Due to their superior mechanical properties, such as low coefficients of thermal expansion and high specific stiffness, they are attractive for many structural and non-structural applications. The most notable production applications are found in the aerospace, automobile, and sports equipment industries. Despite the great potentials possessed by MMCs, there are some concerns regarding the effect of the reinforcements, which are mostly ceramics, on the properties of the matrix alloys. One such property is the quench sensitivity of the matrix material. Heat treatable aluminum alloys are quench sensitive (i. e. their properties and precipitation behavior change with cooling rate or quenchant). The rate of cooling or the type of quenchant used during the fabrication process or the subsequent solution heat treatment affects the mechanical properties of these materials. Therefore, any modification that can alter the quench sensitivity significantly could have important consequences on the heat treatment of the alloys. Thus, the quench parameters may have to be more tightly controlled than for the unreinforced alloy in order to maintain consistent as-quenched properties. In the present study, the quench sensitivity of 2618 Al alloy and its composite containing 10 vol. % Al2O3 particles was investigated using hardness measurements and differential scanning calorimetry (DSC). Although 2618 Al is quench sensitive, its quench sensitivity was significantly increased by the addition of Al2O3 particles. Also, cooling rate affected the precipitation kinetics and the volume fraction of the precipitate phases formed in both materials.