Mg对原位自生TiB2/Al-4.5Cu复合材料微观组织及力学性能的影响

采用Al-K₂TiF₆-KBF₄混合盐原位自生反应法，制备了不同Mg质量分数的3wt% TiB₂/Al-4.5Cu复合材料。采用SEM、TEM、HM硬度测试和室温拉伸等方法研究了Mg含量和多级热处理对3wt% TiB₂/Al-4.5Cu复合材料微观组织和力学性能的影响。微观组织观察发现:Mg质量分数为3wt%时，经过多级热处理后，TiB₂颗粒的团聚现象明显改善，反应生成的TiB₂颗粒平均尺寸约为130 nm，基体内伴随有大量弥散分布的纳米级颗粒，且α-Al的晶粒尺寸也明显减小。力学测试结果表明:多级热处理后，3wt% TiB₂/Al-4.5Cu复合材料的硬度和抗拉强度随Mg含量的增加而提高，但过量的Mg (≥4wt%)会造成TiB₂颗粒细化效果下降。分析表明:Mg的加入能够降低TiB₂/α-Al界面能，减少脆性相Al₃Ti、Al₂B的生成，并通过反应生成的MgAl₂O₄使界面结构变成TiB₂/MgAl₂O₄/α-Al，从而有效抑制了TiB₂的团聚，改善了TiB₂颗粒与Al液界面的润湿性，提高了形核率，进一步细化了α-Al晶粒尺寸。 

Effect of Mg on microstructure and mechanical properties of in-situ TiB2/Al-4.5Cu composites

The 3wt% TiB₂/Al-4.5Cu composites with different mass fraction of Mg were fabricated by Al-K₂TiF₆-KBF₄ molten salt reaction method. The influences of Mg and multistage heat treatment on the microstructure and mechanical properties of the 3wt% TiB₂/Al-4.5Cu composite were studied by means of SEM, TEM, HM hardness test and room temperature tensile test. The microstructure observation shows that the agglomeration of TiB₂ particles is obviously improved after multistage heat treatment along with addition of Mg, In particular, with 3wt% Mg, the average size of TiB₂ particles is about 130 nm, accompanied by a large number of dispersed nano particles, and the grain size of α-Al is also significantly reduced. The mechanical test results show that after multistage heat treatment, the hardness and tensile strength of the 3wt% TiB₂/Al-4.5Cu composite are enhanced with the increase of Mg content. However, excess Mg content (mass fraction≥4wt%) will decrease the refinement effect of TiB₂ particles. The analysis reveals that addition of Mg can reduce the interfacial energy of TiB₂/α-Al and block the formation of brittle phase Al₃Ti, Al₂B. Meanwhile, the MgAl₂O₄ formed by reaction makes the interface become into the TiB₂/MgAl₂O₄/α-Al, which could restrain the agglomeration of TiB₂ particles and improve the wettability of the interface between TiB₂ particles and Al liquid, increase the nucleation rate and refine the grain size.