Effect of Homogeneous/Heterogeneous Precipitation on Aging Behavior of SiC sub P /Al 2014 Composite

The aging behavior of the matrix in SiC sub P /Al 2014 composite at different aging temperatures was examined and the results with the unreinforced Al 2014 alloy were compared. The reinforced material peak aged much faster than the unreinforced matrix at 195 deg C. The relatively large difference between thermal expansion coefficients of SiC and Al resulted in substantial stresses which generated dislocations at and near the interface on quenching. During aging at 195 deg C, the high density of dislocations would provide a short-circuit path for heterogeneous nucleation and fast growth of S' precipitates resulting in accelerated aging of the matrix. As the aging temperature was lowered, the difference in aging kinetics between the reinforced and the unreinforced materials diminished. This was attributed to the homogeneous nucleation of GP zones and a decrease in growth rate of precipitates at lower aging temperature. The DSC results confirmed that at lower aging temperatures both GP zones and S' precipitates existed in the Al matrix. However, at higher aging temperatures the incidence of GP zone formation decreased and at 195 deg C only S' precipitates heterogeneously nucleated on the dislocations. Graphs. 14 ref.--J.H.