Two-stage aging treatment to accelerate aging kinetics without impairing strength in B4C/7A04Al composite

Aging treatments are the key process to obtain satisfactory strength for 7xxxAl alloys and their composites. However, traditional single-stage (SS) aging is time-consuming to reach a peak strength condition. In this study, an efficient 120°C + 160°C two-stage (TS) aging treatment was proposed on a B₄C/7A04Al composite fabricated via powder metallurgy (PM) technology, which could acquire similar peak-aging strength but only took about 15% of the time compared to traditional 120°C SS aging. The evolution of precipitation during the TS aging was investigated, as well as those of the 7A04Al alloys for comparison. In the second stage aging process, the higher aging temperature accelerated the nucleation of η′ phases inside the grains and thus increased the density of precipitates. Moreover, the short aging time limited the coarsening of precipitates and the broadening of precipitate-free zones. The above factors were beneficial for quickly obtaining satisfactory precipitation strengthening effects. The B₄C/7A04Al composite exhibited slower aging kinetics than the 7A04Al alloy in the TS aging. Mg elements consumption by the chemical reaction between B impurities introduced by B₄C particles and the Al matrix was considered to potentially retard the aging kinetics of the B₄C/7A04Al composite. Nevertheless, the precipitation sequence was not affected.