Study On Preparation Technology And Property Of B₄Cp Reinforced AZ91 Magnesium Matrix Composites

In this paper, B₄Cp/AZ91 composite was fabricated by the semi-solid stirring method (the AZ91 magnesium alloy as matrix and the 125 urn B4C particle as the reinforced phase). The metallographs of the composites were treated by Photoshop and Digital Micrograph softwares, then to edit feasible programs by using LinGo software and quadrat method. The parameters were optimized (the radial and longitudinal distribution uniformity of particles as the evaluation criteria) to analyse the relationship between distribution uniformity of particles and some influencing factors, which were the percentage of adding particles, heating temperature, cooling time, stirring speed and stirring time. The B₄Cp/AZ91 composite was hot extruded, then its microstructure, properties, interface and wear-resisting property were analyzed. The testing results indicated that B₄Cp/AZ91 composites had radial and longitudinal distribution uniformity of particles, high interfacial bond strength, which could be fabricated effectively by the semi-solid stirring method.There were some optimized parameters as follows: the percentage of particles was 8wt.%, heating temperature was 604℃, cooling time was 20.5 minutes, stirring speed was 700 rpm, and stirring time was 13.5 minutes. The parameter (ζ) of distribution uniformity of particles was 0.53004, longitudinal Brinell hardness (SD) was 0.48824 on the basis of above processing parameters. Processing parameters were optimizated could led to the distribution uniformity of particles and interfacial bond strength between B₄C particles and matrix were improved greatly.These relationship curves between mixed particles number and processing parameters were quadratic function. It showed the maximal influence between stirring time and mixed particles number, the minimal influence between heating temperature and mixed particles number. In addition, other processing parameters also had some influences in mixed particles number. Because the B₄Cp/AZ91 composites was hot extruded, the materials' surface became smooth, the distribution of internal particles became uniformity, the interfacial bond strength was higher, the casting tissues' shrinkage was reduced, and the density of materials was improved. The parameters of hot-extrusion as follows: preheating temperature of die was 300℃, temperature of hot extrusion was 370℃, extrusion ratio was 10 and extrusion speed was 10mm/s.The hardness of composite was improved on the method of adding the B₄C particles into AZ91 alloy. However, the compressive strength and bending strength were decreased. The hardness, the compressive strength and the bending strength were improved obviously by B₄Cp/AZ91 composite was hot extruded.At the same time, the wear-resisting property of AZ91 alloy was improved greatly by adding B₄C particles. The wear-resisting property was further improved when B₄Cp/AZ91 composite was hot extruded.