Xiaoshi Hu

Graphene nanoplatelets induced heterogeneous bimodal structural magnesium matrix composites with enhanced mechanical properties.

In this work, graphene nanoplatelets (GNPs) reinforced magnesium (Mg) matrix composites were synthesised using the multi-step dispersion route. Well-dispersed but inhomogeneously distributed GNPs were obtained in the matrix. Compared with the monolithic alloy, the nanocomposites exhibited dramatically enhanced Young’s modulus, yield strength and ultimate tensile strength and relatively high plasticity, which mainly attributed to the significant heterogeneous laminated microstructure induced by the addition of GNPs. With increasing of the concentration of GNPs, mechanical properties of the composites were gradually improved. Especially, the strengthening efficiency of all the composites exceeded 100%, which was significantly higher than that of carbon nanotubes reinforced Mg matrix composites. The grain refinement and load transfer provided by the two-dimensional and wrinkled surface structure of GNPs were the dominated strengthening mechanisms of the composites. This investigation develops a new method for incorporating GNPs in metals for fabricating high-performance composites.

A Novel Method to Fabricate CNT/Mg–6Zn Composites with High Strengthening Efficiency

A novel method was developed to fabricate carbon nanotubes (CNTs)-reinforced Mg matrix composites. The method consists of two steps: CNTs pre-dispersion by ball-milling and the ultrasonic melt processing. Mechanical ball-milling effectively pre-dispersed CNTs on Zn flakes with suitable rotational speed and ball-milling time. Serious CNT entanglements were dispersed by the ball-milling. However, ball-milling for a long time at high speed would damage the morphology of CNTs. The ultrasonic overcame the poor wettability between Mg melt and CNTs and then dispersed pre-dispersed CNTs in the Mg melt. CNTs were distributed well in the composites and maintained integrated structure. CNTs significantly improved the mechanical properties of the matrix. The strengthening efficiency reached to 37.1, which proves the superiority of this novel method. Besides grain refinement, load transfer may make a great contribution to the improvement of the strength for the composites.

Effects of Reinforced Particles on Dynamic Recrystallization of Mg Base Alloys during Hot Extrusion

Abstract SiC particles reinforced Mg base composites were extruded at different temperatures and extrusion ratios. The effects of particles on dynamic recrystallization (DRX) of Mg matrix during hot extrusion were investigated. The results reveal that particle deformation zone (PDZ) is formed near a particle during hot deformation, and the PDZ is a characteristic of fine DRX grains in the composites extruded at lower temperatures. Particles promote DRX nucleation of Mg matrix during hot extrusion which may be attributed to high density dislocations and large orientation gradients in PDZ. Particles promote the growth of fine DRX grains until PDZ is consumed by DRX grains. On the contrary, at the stage when DRX grain boundaries contact with particles, particles pin grain boundaries and then retard grain growth.