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Development of functionally graded aluminum matrix composite materials for defense industry applications

Yılmaz, Taha
Functionally graded materials (FGMs) are advanced class of composite materials that have a gradual change in composition and structure over the entire material and many different properties can be obtained by altering the structure. Therefore, they have many different application areas. This study aims to develop functionally graded aluminum matrix composite materials for defense applications. Firstly, porous ceramic pellets and preforms, made of alumina (Al2O3) and olivine ((Mg,Fe)SiO4), were produced with conventional pressing and sintering processes for frontal layer of FGM. Effect of different sintering temperatures, different particle size fractions (for olivine) and different amount of metal powder addition (for alumina) on relative densities of pellets were measured. Secondly, porous ceramic preforms were infiltrated with high strength aluminum alloy AA7075 (Al-Zn-Cu-Mg) by using metal infiltration method. Thirdly, metal matrix composites (MMCs) were produced by melt stirring and squeeze casting methods for backing layer of FGMs using AA7075 (Al-Zn-Cu-Mg) as matrix material and olivine 5-7.5-10 wt. % as reinforcement material. Some of MMCs were T6 heat treated to observe the effect of heat treatment on mechanical properties. All samples were characterized mechanically, physically and microstructurally. Density measurements of pellets showed that from 38 % to 87 % relative densities were achieved with different sintering temperatures, particle fractions and metal alloy addition. T6 heat treatments increased both hardness and flexure strength properties of MMCs. Maximum hardness was measured from 10 wt.% olivine reinforced MMC as 183 HB and maximum flexure strength was measured as 636 MPa from 5 wt.% olivine reinforced MMC. In melt infiltrated preforms maximum hardness was measured as 458 HB from melt infiltrated alumina preforms sintered at 1400 °C and maximum flexure strength was measured as 487 MPa from melt infiltrated olivine preforms sintered at 1250 °C. Olivine as a reinforcement material in MMC and as a preform in melt infiltration process was used successfully with this thesis study for the first time in the literature. By changing process and material parameters preforms with different densities were produced for FGM layers.