Aging Characteristics of Short Mullite Fiber Reinforced Al-4.0Cu-1.85Mg Metal Matrix Composite

摘要

Mullite short fiber reinforced Al-4.0Cu-1.85Mg composite and its base alloy were fabricated by squeeze casting. The age-hardening behavior, precipitation procedure, microstructure of dislocation and precipitates, and the interfacial structure have been studied by means of hardness measurement (HB), differential scanning calorimetry (DSC), and analytical transmission electron microscope (ATEM), respectively. The short mullite fiber in the composite induces high dislocation density in the near vicinity of the interface after it is solutionized and quenched in ice water, and suppresses or delays the formation of GPB zones. The aged hardness of the composite is always higher than that of its base alloy, but there appears little difference between the time needed in the composite and in the base alloy to reach the peak hardness, which means that the acceleration effect of mullite fiber in the precipitation of Al-Cu-Mg alloy is not great enough. Mg also reacts with Al and SiO_2, resulting in the formation of spinel (MgAl_2O_4), which depletes Mg in the matrix and finally hinders the aging acceleration in the testing composite.