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The influence of minor SiC

The influence of minor SiCp on the dynamic recrystallization (DRX) and dynamic precipitation behaviors of the Mg-5Zn matrix were investigated through the hot compression test. The results showed that the addition of SiCp improved the DRXed ratio of Mg-5Zn matrix, but the recrystallized grains in 1 vol.% 5 μm SiCp/Mg-5Zn material were mainly formed by the “bulging” nucleation of the grain boundary at a low compressive strain (~0.05, ~0.1 and ~0.35), and PDZ (particle deformation zone) around SiCp had little effect on the recrystallization nucleation. However, the fine recrystallized grains appeared around the particles when the compressive strain reached ~0.7, which was attributed to the promotion effect of PDZ on recrystallization nucleation. This shows that PDZ around particles can promote DRX nucleation under large strain. Meanwhile, compared to the Mg-5Zn alloy, the volume fraction and size of the secondary phase in the SiCp/Mg-5Zn material increased due to the influence of SiCp on the recrystallization behavior of Mg-5Zn matrix.

In this paper, the Mg-9%Al alloy reinforced by 5 wt.% SiC nanoparticles was fabricated by hot pressing of powder with ultrasonic vibration under a semi-solid state. The influence of hot-pressing temperature on the microstructure and mechanical properties of the n-SiCp/Mg-9%Al composite was investigated. The results indicated that the density of the composite was increased significantly and the agglomeration of SiC nanoparticles was evidently reduced with the increase in the hot-pressing temperature from 450 to 510 °C. Additionally, the elevated hot-pressing temperature resulted in remarkable grain refinement. However, as the hot-pressing temperature increased to 530 °C, the density decreased and the average grain size increased, which caused a decline in the mechanical properties. The study of the interface between the n-SiCp and the matrix in the nanocomposite suggested that n-SiCp bonded well with the matrix without interfacial activity. The ultimate tensile strength, yield strength and elongation to fracture of the nanocomposites were simultaneously enhanced compared with that of the Mg-9%Al alloy. This improvement could be attributed to obvious grain refinement and the Orowan strengthening mechanism.

In this work, Mg-xAl alloys with an Al content ranging from 10 to 20 wt.% were subjected to equal channel angular pressing (ECAP). The effects of the high Al content on the microstructure and mechanical properties of the alloy before and after ECAP were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis and tensile testing. The results demonstrated that as the amount of Al in the as-cast Mg-xAl alloys increased, the grain size of the as-cast Mg-xAl alloys decreased, whereas the amount of the Mg17Al12 phase with network structure increased. After ECAP, the network β-Mg17Al12 phase was significantly broken into fine pieces. The fine β-Mg17Al12 granules were precipitated from the α-Mg matrix. The broken β-Mg17Al12 phase in the Mg-15Al alloy exhibited a relatively homogeneous distribution. As the Al content increased, the grain size in the α-Mg-rich area decreased. However, the β-Mg17Al12 size in the α+β two-phase area of the ECAPed Mg-15Al alloy was the smallest among the three alloys. The yield strength of the Mg-xAl alloys increased, whereas the elongation to fracture significantly decreased.