B4C/5083 Al Composite Prepared by Cryomilling

In the present investigation, the composite powder with 20wt.% particulate B4C and 80wt.% nanocrystalline 5083 Al was fabricated using mechanically milling at cryogenic temperature (cryomilling). After this, the cryomilled composite powder was homogeneously blended with an equal amount of unmilled coarse-grained 5083 Al. The blended powder was consolidated with hot-pressing at 500°C, followed by hot extrusion at 410°C. The consolidated composite consists of 10wt.% B4C, 50wt.% coarse grain 5083 Al and the balance nanocrystalline 5083 Al. The microstructure evolution of the composite during cryomilling and consolidation was investigated by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The results show that the particle size of the cryomilled composite powder became smaller and then bigger with milling time longer. This demonstrates the course rely mainly on broken first, and then rely mainly on cold welding with milling time longer. B4C particles can be distributed in 5083 Al matrix uniformly. In addition, the presence of oxygen and nitrogen in cryomilled powders has been demonstrated in this paper.