| Because of the hexagonal close packed (hcp) crystal structure, Mg alloy usually shows a pretty strong texture after deforming, which greatly limites the formability of Mg alloys at room temperature. Particle reinforcing magnesium matrix composites (PMMCs) can be seen as an enhanced version for Mg alloys and draw much attention in recent years. More importantly, the reinforcement particles can weaken the texture of Mg alloys. In this paper, the distribution behaviour of TiB2 particles under different coupled-fields was firstly compared, and then the effect of reinforcement particle distribution on the microstructure, texture and mechanical properties of TiB2/AZ31 composites was investigated. In addition, the application of Al-Ti-B in Al-free Mg-6Zn alloy was explored via Y alloying. At last, the effect of Al on microstructure and properties of Mg-Zn-RE alloy sheets was investigated. The main results are summarized as follows:During the preparation process of TiB2/AZ31 composites, the introduction of the coupled-field (electromagnetic and ultrasonic fields) indirectly enlarged the action range of ultrasonic field by the flow-controlling effect of electromagnetic field, and then effectively reduced the size of particle cluster and improved the utilization rate of particles. Comparing with the rotating and traveling electromagnetic fields, the effect of spiral electromagnetic field on the improvement of particle distribution and utilization rate was the best. Microstructure analysis showed that the shear bands in AZ31 alloy sheet were made up with pretty coarse DRXed grains. However, due to the PSN effect of TiB2 particles, the DRXed grains in shear bands of TiB2/AZ31 composites were obviously refined. In addition, as the distribution of TiB2 particles was improved, the number of the shear bands and twins was increased, the texture intensity was weakened, and the composite showed a comprehensively improved mechanical performance.Y reacted with the Al produced from the Al-Ti-B SHS system by generating Al2Y and Al11Y3 phases. The addition of Y reduced the size of TiB2 particle clusters and refined the microstructure of the composites. In rolling process, the A12Y and Al11Y3 phases, as well as the TiB2 particles, worked as nucleation sites for the DRX, which contributed to the finer microstructure and the formation of a weaker double peak texture. In addition, strength and elongation of TiB2/Mg-6Zn composite were simultaneously improved after the addition of Y. More importantly, the addition of Y played a role in consuming the residual Al, which solved the problem that Al-Ti-B SHS system can not be used in Al-free Mg alloys.The addition of Al significantly changed the solidification and precipitation behaviour of the Mg-5Gd-2.5Y-2Zn alloy:(a) reduced the content of the W phase, (b) promoted the formation of two useful phases (Al11(Y, Gd)3 and Al2(Y, Gd)). The transform of the as-cast microstructure improved the rollability and ductility of Mg-5Gd-2.5Y-2Zn alloy. Especially, the elongation of the alloy with 1.0wt.% Al addition was about 16.4% which reached about 4 times as high as the as-rolled Mg-5Gd-2.5Y-2Zn alloy.The effect of Al alloying on the microstructure and properties of Mg-8Gd-5 Y-2Zn alloy with a high content of rare earth was also obvious. Micro-texture tests showed that the Mg-8Gd-5Y-2Zn alloy sheet exhibited a strong double-peak texture (maximum pole intensity: 15.1). After adding 1.0wt.% Al, the texture showed a characteristic of multi-peak and wider orientation distribution of basal poles, in addition, its maximum pole intensity was remarkable weakened to 3.9. EBSD test indicated that the Mg-8Gd-5Y-2Zn alloy sheet had a not full DRXed microstructure, and misorientations between these grains were not evident. In addition, the proportion of low-angle grain boundaries in Mg-8Gd-5Y-2Zn alloy sheet was high. After the addition of 1.0wt.% Al, the microstructure of the sheet was consisted of homogeneous and fine DRXed grains, and the content of high-angle grain boundaries were increased. |
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