| SiC/Al composites have been widely applied in aeronautic, aerospace, automotive and electronic applications due to their high specific strength, high specific stiffness, high Young’s modulus, light weight and low coefficient of thermal expansion. As the main raw material of composite materials, the size and purity of SiC particles make an important role on the performance of the composite. SiC particulates reinforced aluminum matrix composites are produced directly by ex-situ SiC particles into the molten aluminum alloys using ex-situ techniques, such as melt-stirring method, ingot metallurgy (IM), powder metallurgy (PM), rheocasting technique perform infiltration and spray deposition. In this case, the ex-situ techniques mainly problems confronted with are the size of ex-situ SiC relatively great and easy reunited. It results in the nonuniform distribution. Meanwhile, The weak wettability between SiC particles and aluminum matrix due to surface contamination of ex-situ SiC powders. It is easy to cause the badly interface binding force between SiC particles with the Al matrix and decrease the enhanced performance. In the present research, a new in-situ processing technique has been developed for fabrication of aluminum based composites, in which the reinforcements are synthesized in metal matrix by in situ reaction method. The in-situ formed SiC particles are not only small size, but also homogeneous dispersed in matrix compared with ex-situ method. Moreover, the in-situ formed reinforcements are free from contamination, leading to strong interfacial bonding between the reinforcements and the matrix and improve the enhancing effect. However, there were rarely researches about SiC particles and reaction mechanism by in situ reaction method. The basic research of the SiC particles and mechanism by in situ reaction method in Al matrix alloys in this work. The synthesis temperature of SiC powders under different circumstances and the reaction process of SiC were discussed. The influences of the proportion of Al with other metal element and synthesis temperature to the microstructure, phases and production of SiC powders were mainly analyzed. And, the SiC/Al composite by in situ reaction were researched. The main studies contain the following parts.(1) The SiC particles are synthesized by graphite, Si and Al powders. The experiment results showed that the synthesis temperature of SiC was lower than 750℃, the content of SiC increased as the increase of temperature and Al contents. The SiC particles and Al martix have a better interface bonding. The residual Si and Al in synthesized SiC were removed with HF solution to the analysis of microtopography. The results indicated that the two different microtopographies of SiC were sheeted and clubbed SiC and the size of SiC particles was 100-500 nm. The size of SiC decreased with the increase of Al contents.(2) The SiC particles are synthesized by graphite, Si and Mg-Al alloy powders. The experiment results showed that the synthesis temperature of SiC was lower than 750℃. The content of SiC increased as the increase of temperature and Mg-Al alloys contents. The microtopography analysis results showed that the two different microtopographies of SiC were sheeted and clubbed SiC and the size of SiC particles was 50-200 nm. The size of SiC decreased with the increase of Mg-Al alloys contents. The size of SiC particles synthesized in Mg-Al alloys was decreased compared with its in Al melts. It indicated that the size of SiC particles was decreased by adding Mg element.(3) The SiC particles synthesized by graphite, Si in Al melt adding a small amount of Cr. The experiment results showed that the size of SiC particle add a small amount of Cr was decreased compared with its in Al. A plenty of (Si, Al)2Cr alloys were synthesized by adding mass Cr element to the disadvantage synthesis of SiC.(4) The reaction mechanism of SiC was researched in Al matrix alloys by in situ reaction. The experiment results show that the graphite reacted with Al to form AI4C3 rather than with Si to form SiC below 750℃. And with the temperature increasing, the intermediate product of Al4C3 reacted with Si in the Al-Si alloy formed SiC. In short, the reaction mechanism of situ synthesis could be divided into two parts:first process is to produce A14C3, and the second process is the intermediate product of Al4C3 reacted with Si to form SiC,(5) SiC/Al composites prepared by in situ hot pressing. Microstructural analysis showed that the synthesized SiC particles are uniformly distributed in the Al matrix. Under the same conditions of SiC content, the flexure strength test results showed that the SiC/Al composites performed better behavior prepared in 500℃ with 2.0 MPa than that prepared in 300℃ with 2.0 MPa. |
PDF Full Text Request