Investigation of the precipitation kinetics in an A16061/TiB2 metal matrix composite

The aging kinetics of AA6061 (Al−Mg−Si−Cu) based metal matrix composites (MMCs) containing TiB2-particles were investigated using hardness measurements, texture determination and electron microscopy. The samples were produced by an in-situ process. Two industrially manufactured in-situ composites with an AA6061 matrix and TiB2-particles (3.4 vol.%, 6.8 vol.% TiB2) were studied at two different aging temperatures (160°C, 250°C) and compared to a similarly processed non-reinforced AA6061 alloy. An increasing volume fraction of TiB2 correlated with changes in the aging response of the composites. Samples subjected to three aging times were selected for microstructure analysis in the TEM (10 min, 200 min, 1365 min, aging temperature 250°C). Special emphasis was laid on the investigation of the growth kinetics of metastable needle shaped matrix precipitates, which cause the increase in hardness. The TEM examinations of the MMCs substantiated that precipitate growth was accelerated in the presence of TiB2 particles as compared to the unreinforced AA6061. These differences in kinetics were related to microstructural changes induced by the presence of the ceramic TiB2 particles.