The age-hardening ability of B 4 C/6061Al composites, fabricated by powder metallurgy technique, were systematically investigated through varying B 4 C contents (0–30wt%), hot-pressing temperatures (560–620°C) and holding times (30–120min). The results showed that the quantity of Mg 2 Si precipitates formed in the composites after T6-treatment decreased with increasing B 4 C content and hot-pressing temperature, attributable to the consumption of Mg resulting from interfacial reactions. The main interfacial reaction products were MgAl 2 O 4 and Al 3 BC. The formation of MgAl 2 O 4 was determined to be the primary factor degrading the age-hardening ability of the composites. Reducing the hot-pressing temperature and holding time and increasing the Mg content were beneficial to improving the age-hardening ability of the composites. It was experimentally verified that 580°C and 30min were the optimal hot-pressing temperature and holding time, and the amount of additional Mg should be less than 1.5wt%, when considering both the age-hardening ability and comprehensive properties of the composites.