Fabrication, Reaction Mechanism And Property Of Aluminum Matrix Composites In The Al-ZrO₂ And Al-ZrO₂-C Systems

In this article, the Al-ZrO₂ and Al-ZrO₂-C systems aluminum matrix composites were successfully fabricated by means of the Exothermic Dispersion (XD), its preparation technology was explored, thermodynamic of reaction process was analysed, and the reaction process dynamics model was founded combining with DSC. The reaction outcome and microstructures of composites were analysed by modem means such as optical microscope(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD) and so on, I has tested the normal temperature mechanical performance and the dry sliding fi'iction attrition performance of composites, and discussed its strengthening mechanism and wear mechanism respectively.It was found that liquid aluminum reacted with ZrO2 grains firstly and resulted in active Zr atoms and stabilizedα-Al2O₃ grains. Due to the non-wettability ofα-Al₂O₃ with liquid Al, theα-Al₂O₃ were segregated at grain interface of the matrix, the active Zr atoms could diffuse from the reaction interface to the liquid matrix and then reacted with Al atoms to form Al₃Zr or ZrC with C atoms. In the processing of the reaction, generated Al₃Zr transformed into thermodynamic stable ZrC gradually.As for the mechanical properties of the composites, the results of experiments showed that the tensile strength of composites remarkablely enhanced with the increasing of reinforcement volume fractions, but the trend of elongation declined. When reinforcement volume fi'action was 30%, C/ZrO₂ molar ratio was 0, the reinforcements wereα-Al₂O₃ and Al₃Zr particles, tensile strength and elongation were 215MPa and 3% respectively, and now the cross section surface were made up of fine tensile pits and cleavage crack in the Al₃Zr. The Al₃Zr rod reduced with the increasing of C/ZrO₂ molar ratio, when C/ZrO₂ molar ratio was 1, Al₃Zr basically disappeared, the reinforcements wereα-Al₂O₃ and ZrC particles, tensile strength and elongation rised to 245MPa and 8% respectively, and now it was all the f'me tensile pits in the cross section surface. The strengthening mechanism of composites mostly included dispersion strengthening, fine-grained strengthening, dislocation strengthening, and melting strengthening.The dry sliding wear tests showed that when reinforcement volume fraction was 30%, under the condition that the sliding distance was 300m, the sliding velocity was 0.5m/s, the wear rate of composites enhanced with the increasing of the load, and along with the increasing of C/ZrO₂ molar ratio, this tendency changed quite slowly. Under the condition that the load was 40N, the sliding distance was 300m, the wear rate of composites reduced with the increasing of the sliding velocity. The observation of wear surface and subsurface by SEM discovered that, when has not added the C powder, the sample has many Al₃Zr particals, whose brittleness become big. Ruptured to form the abrasive easily with the function of the shearing force and stress. Simultaneously, the plastic deformation of subsurface layer leaded to produce dislocation in the interface of Al₃Zr and matrix, arousing stress concentrates, and the brittle Al₃Zr breaked to form the crack core, expanded in the horizontal direction, gradually formed the thin layer which separated with the matrix, flaked off under the stress function, and then formed many grind crumbs after rubbing. And now the abrasive grains wear would take the role in the wear and the others such as oxidadion and adhesion were subordinated to it. With the increasing of C/ZrO₂ molar ratio, the brittle Al₃Zr reduced gradually, the intensity and hardness of composites were improved, and the anti-flaking ability enhanced, the abrasive grains coming off also reduced relatively, and now the adhesion wear would take the role in the wear and the others were subordinated to it.