| The melt-stirring process is one of the main method for preparing the SiC particulate reinforced A1 matrix composites (noted as SiCp/Al). In order to solve the problem about uniform distribution of SiC particles, it is necessary to improve the interfacial reaction and wettability to achieve the controllable preparation of SiCp/Al composites. In this paper, the process and mechanism of the surface oxidation treatment of SiC were primarily investigated. The contact angle between Al and SiC oxidized at different temperature was measure by using the high vacuum contact angle meter. The surface tension, adhesion work and immersion wetting work were calculated. The relationship between the contact angle and oxidation time was investigated during the wetting process. The composite material was prepared by mechanical stirring method. The blade structure was optimized by the hydraulic simulation model. The SiCp/Al composites were synthesized by innovatively design and the two-step method. The influence of process parameters on the micro structure and mechanical properties of the composites was studied. The major results in the present study were as follows:(1) When the SiC particles were oxidized above the 850℃, the oxidation weight gain of SiC and the volume fraction of the oxidized layer firstly increased and then tended to be steady with the increase of high temperature holding time. The oxidation weight gain and the volume fraction of the oxidized layer increased with the increase of the oxidation temperature. The thickness of oxide layer of SiO2 was about 252 nm when the SiC particles were oxidized for 4h at 1100 ℃. Therefore, the oxidation temperature of SiC should be controlled above 1100℃ and The oxidation time was more than 2 h. When the oxidation time ranged from 2 h to 4 h, the SiC surface taken place the transformation from the amorphous structure of SiO2 to crystalline state, which corresponded to the high cristobalite. While the crystal form of SiO2 attached to the SiC surface had no change when the SiC oxidized at high temperature cooled to the room temperature under the different cooling rate. This indicated that the cooling rate has no effect on the crystal structure of the oxidized SiC surface.(2) The wettability was obviously improved after the SiC particles were oxidized at the high temperature. The contact angle has no change when the SiC particles were oxidized at 850℃ for 6h. While the wettability was improved at 1100℃ for 6h and the contact angle decreased by 30.64°. This was ascribed to the substantial presence of the crystalline state SiO2 above the SiC surface. There was three stages. Firstly, the contact angle was larger. Then, the contact angle decreased rapidly during the reaction stage. Finally, the contact angle had no changed during the steady stage. This suggested that the reactive wetting could achieve when the contact time between SiC and A1 was at least 7 min.(3) The optimal process about the preparing the Al matrix composites by melt-stirring process was obtained. The stirring temperature should be controlled at about 680℃, the stirring speed was 950r/min, the use of two-stage blade pitch was H=30 mm, silicon carbide was added in an amount of 5% to 10%, which promoted that a combination of SiC particles and aluminum matrix composites was easily achieved. However, in the high speed stirring process, when the speed stirring was of 6000 r/min, stirring temperature was about 700℃ and stirring time was of 5 min, the prepared SiC particles in the composites uniformly distributed. The results of analysis showed that the interface of A1 matrix composites reinforced by SiC particles prepared by oxidation treatment formed a interface organizations about SiC/SiO2 and MgAl2O4/Al, which achieved the good wettability combination of SiC particles and Al interface. |
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