Development of SiC Nanoparticles and Second Phases Synergistically Reinforced Mg-Based Composites Processed by Multi-Pass Forging with Varying Temperatures

Abstract

In this study, SiC nanoparticles were added into matrix alloy through a combination of semisolid stirring and ultrasonic vibration while dynamic precipitation of second phases was obtained through multi-pass forging with varying temperatures. During single-pass forging of the present composite, as the deformation temperature increased, the extent of recrystallization increased, and grains were refined due to the inhibition effect of the increasing amount of dispersed SiC nanoparticles. A small amount of twins within the SiC nanoparticle dense zone could be found while the precipitated phases of Mg17Al12 in long strips and deformation bands with high density dislocations were formed in the particle sparse zone after single-pass forging at 350 °C. This indicated that the particle sparse zone was mainly deformed by dislocation slip while the nanoparticle dense zone may have been deformed by twinning. The yield strength and ultimate tensile strength of the composites were gradually enhanced through increasing the single-pass forging temperature from 300 °C to 400 °C, which demonstrated that initial high forging temperature contributed to the improvement of the mechanical properties. During multi-pass forging with varying temperatures, the grain size of the composite was gradually decreased while the grain size distribution tended to be uniform with reducing the deformation temperature and extending the forging passes. In addition, the amount of precipitated second phases was significantly increased compared with that after multi-pass forging under a constant temperature. The improvement in the yield strength of the developed composite was related to grain refinement strengthening and Orowan strengthening resulting from synergistical effect of the externally applied SiC nanoparticles and internally precipitated second phases.

Hot Deformation Behavior and Processing Maps of SiC Nanoparticles and Second Phase Synergistically Reinforced Magnesium Matrix Composites

“…As shown in Figure 1b, a mass of bulk and granular precipitated phases of Mg 17 Al 12 were distributed at the grain boundaries. According to our previous research [15], with the decrease of deformation temperature from 673 K to 573 K, the average size of the precipitated phase distributed on the grain boundaries can reach the nanometer scale. These nano-sized precipitates can pin the grain boundaries and refine the grains.…”

“…The fine-grained nanocomposite (denoted as “FN”) was prepared by 12 passes of multi-pass forging, decreasing the temperature from 400 °C to 300 °C as described in detail in Ref. [15].…”

Recent advances in mechanical properties of Mg matrix composites: a review

“…The presence of reinforcements inhibits dislocation movement and leads to the formation of dynamic recrystallisation. 122,123 Chen et al 70 explored the TEM image of the ZK60/ 0.2 wt-% GO composite. The authors stated that the presence of GO was verified by EDS analysis (Figure 16(b)).…”

“…The presence of reinforcements inhibits dislocation movement and leads to the formation of dynamic recrystallisation. 122,123…”

The Comparison in the Microstructure and Mechanical Properties between AZ91 Alloy and Nano-SiCp/AZ91 Composite Processed by Multi-Pass Forging Under Varying Passes and Temperatures

“…When one or more reinforcements are introduced into the magnesium matrix, it usually helps to improve the mechanical properties such as high strength, superior creep and wear resistance at elevated temperature. Therefore, more and more attention has been paid on the magnesium matrix composites with low density and superior specific mechanical properties [ 9 , 10 , 11 , 12 ]. Since the addition of micron-sized ceramic particles deteriorates the ductility of matrix alloy, many attempts have been made to develop magnesium matrix nanocomposites by substituting micron-sized particles by nano-sized particles [ 13 , 14 , 15 , 16 ].…”