The Preparation Of 6066Al/SiC_P Graded Composites Using Spray Deposition And Study On Their Densification

Functionally gradient materials (FGMs), a new class of advanced and innovative materials which are capable of providing superior and reliable performance, are actively being sought for engineering devices that are subjected to two distinct service conditions on two opposite sides across the thickness direction. In a functionally graded material the properties change gradually with position. The property gradient in the material is caused by a position-dependent chemical composition, microstructure or phase composition. The processing techniques developed for preparing FGMs include powder metallurgy, centrifugal casting, thermal spraying, infiltration processing, electromagnetic separation, etc.This thesis explored the feasibility of spray deposition in preparing functionally graded composites. The 6066Al/SiC_P graded composites were successfully prepared via the spray deposition system. This system was developed by our research team. The microstructure and mechanical properties of the preform were characterized. The results revealed that the SiC_P weight fraction of the as-deposited preform from the top to the bottom ranges almost continuously from 0 to 30%. This result indicated that spray deposition is a reliable approach in producing the FGMs.Densification was conducted on the spray deposited graded composites in this thesis. A novel technique named as stepped force plug pressing was developed. The optimized processing parameter appropriated for 6066Al/SiC_P was obtained through experiments. The results showed that the relative density of the composites was above 99% after densification with the stepped force plug pressing in the processing parameter of 580℃, 220MPa and 10min pressure retaining. The stepped force plug pressing showed excellent perfermence in eliminating the porosity in the preform and improve the interface between the matrix and the reinforcement particles. It is applicable to densify larger preform with less pressure. The SiC particles in the preform still presented a graded feature after densification. The tensile strength of the graded composite varied with different SiC percentage and achieved a peak value 428MPa at 15mass% SiC weight percentage. The results and discussions were given about the different structures and properties between the spray deposited preform and densified composites. The mechanism of the stepped force plug pressing and the stress of the preform during the densification were simply analyzed. The advantages of this novel densification technique were presented, which laid a foundation for its further development.There was no similar report in researchs about SiC_P reinforced aluminum matrix graded composites preparing via spray deposition. Compared with graded composites preparing by other techniques, spray deposited graded composites have advantages of fine grain and easy in controlling. Spray deposition was especially suitable in preparing large graded composites.