Synthesis of nano-to micrometer-sized B_(4)C particle-reinforced aluminum matrix composites via powder metallurgy and subsequent heat treatment

微/纳双尺寸B_(4)C颗粒增强铝基复合材料的粉末冶金合成及后续热处理

B4C/6061Al composites reinforced with nano-to micrometer-sized B4C particles were fabricated via powder metallurgy route consisting of spark plasma sintering(SPS)and hot extrusion and rolling(HER),followed by T6 treatment.The microstructural evolution and mechanical properties were investigated.Results showed that the status of B4C particles changed from a network after SPS to a dispersion distribution after HER.The substructured grains reached 66.5%owing to the pinning effect of nano-sized B4C,and the grain size was refined from 3.12μm to 1.56μm after HER.After T6 treatment,dispersed Mg_(2)Si precipitated phases formed,and the grain size increased to 1.87μm.Fine recrystallized grains around micro-sized B4C were smaller than those in the areas with uniform distribution of nano-sized B4C and Mg_(2)Si.The stress distributions of as-rolled and heated composites were similar,considering that the T6 heat treatment was only effective in eliminating the first internal stress.The Vickers,microhardness,and tensile strength of as-SPSed composites were greatly improved from HV 55.45,0.86 GPa,and 180 MPa to HV 77.51,1.08 GPa,and 310 MPa,respectively.Despite the precipitation strengthening,the corresponding values of as-heated composites decreased to HV 70.82,0.85 GPa,and 230 MPa owing to grain coarsening.

采用放电等离子烧结(SPS)、热挤压+轧制(HER)、粉末冶金工艺及后续T6热处理制备了微/纳双尺寸B4C颗粒增强铝基复合材料。研究了制备过程中复合材料的显微组织演变和力学性能。结果表明:B4C颗粒分布由SPS状态的网状分布转变为挤压轧制态的均匀分布,平均晶粒尺寸由烧结态的3.12μm细化至挤压轧制态的1.56μm。由于纳米B4C的钉扎作用,亚结构比例达到66.5%。T6热处理后,材料内部析出弥散分布的Mg_(2)Si。微米B4C周围分布明显的动态再结晶晶粒,且晶粒尺寸远小于弥散分布Mg_(2)Si的基体区域。由于T6热处理只能有效地消除第一内应力,因此轧制态和热处理态复合材料的应力分布相似。烧结态复合材料的维氏硬度、显微硬度和抗拉强度分别从HV 55.45、0.86GPa和180 MPa提高到HV 77.51、1.08 GPa和310 MPa。T6热处理后,尽管内部存在着析出强化,但由于晶粒粗化,复合材料的析出强度分别为HV 70.82、0.85 GPa和230 MPa。