Nie Kaibo, Guo Yachao, Deng Kunkun, Wang Xiaojun, Wu Kun
College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China.
Shanxi key laboratory of advanced magnesium-based materials, Taiyuan University of Technology, Taiyuan 030024, China.
Materials (Basel). 2018 Jan 13;11(1):126. doi: 10.3390/ma11010126.
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 MgAl 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.
在本研究中，通过半固态搅拌和超声振动相结合的方式将碳化硅纳米颗粒添加到基体合金中，同时通过不同温度下的多道次锻造获得第二相的动态析出。在本复合材料的单道次锻造过程中，随着变形温度的升高，再结晶程度增加，由于弥散分布的碳化硅纳米颗粒数量增多产生的抑制作用，晶粒得到细化。在350℃单道次锻造后，在碳化硅纳米颗粒密集区可发现少量孪晶，而在颗粒稀疏区形成了长条状的MgAl析出相和高密度位错的变形带。这表明颗粒稀疏区主要通过位错滑移发生变形，而纳米颗粒密集区可能通过孪晶发生变形。通过将单道次锻造温度从300℃提高到400℃，复合材料的屈服强度和抗拉强度逐渐增强，这表明初始锻造温度较高有助于力学性能的提高。在不同温度下的多道次锻造过程中，随着变形温度降低和锻造道次增加，复合材料的晶粒尺寸逐渐减小，且晶粒尺寸分布趋于均匀。此外，与恒温多道次锻造后的情况相比，析出的第二相数量显著增加。所制备复合材料屈服强度的提高与外加碳化硅纳米颗粒和内部析出第二相的协同作用导致的晶粒细化强化和奥罗万强化有关。
