Mechanical properties and fracture of Al-15 vol.-%B4C based metal matrix composites

The present work was performed on three aluminium metal matrix composites (MMCs) containing 15 vol.-% B4C particles. The matrix in two of these materials is pure aluminium, whereas the matrix of the third material was an experimental 6063 aluminium alloy. All composites were homogenised at elevated temperatures for 48 h before being quenched in warm water. The quenched samples were aged in the range of 25-400 degrees C for 10 h, at each temperature. Hardness and tensile tests performed on the aged MMCs show that the presence of Zr (with or without Ti) resulted in a noticeable hardening due to the precipitation of a Zr rich phase. Maximum strengthening was obtained from the 6063 based MMC due to the precipitation of Mg2Si phase particles. The present technique used to produce the MMCs examined proved capable of manufacturing composites with a uniform distribution of B4C in the matrix with a strong degree of matrix/particle bonding. When the MMC samples were deformed to failure, the B4C was fractured transgranularly without debonding from the matrix. The addition of Zr and Ti resulted in the formation of protective layers around the B4C particles that were retained after fracture; these protective layers were not affected by the B4C particle size (0.15-20 mm). Stacking faults were commonly observed in fractured Al 6063/B4C/15p samples. The precipitation of zirconium-titanium compounds during aging contributed to the composite strength.