Abstract:Nano-B4CP particulates (n-B4CP) reinforced 2009Al matrix composites with different reinforcement volume fractions (0, 2, 4 and 6vol.%) were fabricated by powder metallurgy combined with hot extrusion. The effects of different volume fractions of n-B4CP on microstructure, solution and aging behavior and mechanical properties of n-B4CP/2009Al composites were studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), vickers hardness measuring instrument and so on. The results show that, the n-B4CP were uniformly dispersed in the composites after hot extrusion process. The best solution temperature and time of the composites were 495℃ and 1 h, the resolution of second phase particles (Al2Cu) were dissolved back into the matrix and only a small amount remaining in the matrix during solution treatment process. N-B4CP/2009Al composites with different volume fractions (0, 2, 4 and 6vol.%) treated at 495℃ for 1h and then ageing at 175℃for 14h almost simultaneously reached the peak hardness, and the aging peak time decreased 2h compared to matrix alloy. After peak aging, the microstructure of composites were observed by TEM, indicating that the growth of precipitation was strongly restrained due to the addition of n-B4CP particulates. Compared to the matrix alloy, the composites with higher density of ?ner precipitates led to an earlier attainment in the peak aging condition. After the optimum heat treatment process, the tensile strength of the composites increases at first and then decreases along with the increasing of n-B4CP volume fraction, while the yield strength always increases. High volume fraction of n-B4CP effectively play the role of pinning dislocations, but the phenomenon of agglomeration of high volume fraction of n-B4CP results in composites’ early cracking.