| As a heat treatmentable high-strength aluminum alloy, excellent mechanical properties,and good formability have7075aluminum alloy very popular application, but poor wearresistance limits its wide use in aerospace, aviation and automotive industries. This thesispresents the study of7075aluminum alloy matrix composites layer reinforced withmixtures of SiC and MoS2particles by friction stir processing (FSP), which can improvethe anti-wear property without influencing its intrinsic mechanical properties.The microstructure of7075aluminum alloy can be changed by heat treatment, in whichthe insoluble phase and second phase will be partially dissolved into the matrix. Themechanical properties and corrosion resistance of materials were enhanced with increasingsolid solution temperature, which is below480degree, and incubation time ranging from0to3h. The hardness of7075aluminum alloy is191.62HV after ageing for24h. Afteraging for36h,7075aluminum alloy exhibits the highest corrosion resistance in3.5%NaClsolution. Although the hardness, strength and corrosion resistance of7075aluminum alloycan be effectively improved by solution-aging treatment, but the effect on wear resistanceis slight.7075aluminum alloy matrix composites layer reinforced with mixtures of SiC andMoS2particles has been got through friction stir processing technology. The resultsindicate that further FSP passes leads to significantly more homogenous dispersion of theadditive hybrid particles and less defects. Moreover, the hardness of friction stir zone ishigher than that of the matrix and heat affected zone. The effect of process parameters onthe hardness of friction stir zone is as follows: number of FSP pass, rotational speed,traverse speed, tilt angle, and volume ratio of additive particles. The impact fracturemorphology shows that the more homogenous dispersion of the additive hybrid particles,the greater is the adhesive force between the substrate and composite layer and impacttoughness. The effect of process parameters on the impact toughness of friction stir zone isas follows: traverse speed, volume ratio of additive particles, rotational speed and tiltangle.Compared with7075aluminum alloy, the addition of hybrid particles deteriorates thecorrosion of composite layer. Pitting corrosion occurs mainly around the second phase in7075aluminum alloy, whereas pitting corrosion is easily formed around SiC particles incomposite layer, which is influenced by the size of SiC particle in composite layer. The smaller SiC particle size, the higher is the corrosion resistance of composite material layer.The results of dry wear tests indicate that the wear resistance is markedly enhanced for7075aluminum alloy matrix composites layer, and the wear modes change from adhesivewear to abrasive wear. The effect of process parameters on the wear resistance of frictionstir zone is as follows: number of FSP passes, volume ratio of additive particles, traversespeed, rotational speed, and tilt angle.In this study, the orthogonal test design has been adopted to study the optimal FSPparameters. The results shows that, as far as all properties are concerned, the optimal FSPparameters to prepare the7075aluminum alloy matrix composites layer reinforced withmixtures of SiC and MoS2particles are as follows: the SiC and MoS2volume ratio is2:1,the rotational speed of stirring head is750rpm, the traverse speed is67.5mm/min, the tiltangle is2°, the number of FSP passes is4. When only the wear resistance and corrosionresistance are concerned, the best optimal FSP parameters are as follows: the volume ratio(SiC/MoS2) is2:1, the rotational speed of stirring head is750rpm, the tilt angle is1°,traverse speed is47.5mm/min, and the number of FSP passes is4. |
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