Interfacial reaction mechanism between matrix and reinforcement in B4C/6061Al composites

The interfacial reaction mechanism in B4C/6061Al composites, fabricated by the powder metallurgy technique at 560 and 620 °C with various holding times, was subjected to detailed investigations using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and hardness tests. Results showed that complicated interfacial reactions occurred in the B4C/6061Al composites, forming Al3BC, MgAl2O4, MgB7, Mg0.78Al0.75B14, AlB12C2 and Al4SiC4 as the main products, which clearly deteriorated the age-hardening ability of the composites. The interfacial reactions involving Mg and Si could be divided into two series. The oxidation of Mg occurred at both 560 and 620 °C, whereas other reactions only occurred at 620 °C. The existence of the liquid phase at 620 °C activated the reaction between Al and B4C, leading to the generation of free B, and subsequent reactions involving B and Mg occurred. After the reactions involving B and Mg was completed, the reaction involving Al, Si and C took place. It was determined that the reactions involving B and Mg rather than the oxidation of Mg or the reaction involving Si were the main reasons for the consumption of Mg and the deterioration of age-hardening ability of the B4C/6061Al composites at 620 °C.