Microstructure And Properties Of Particulate Reinforced Composites Synthesized By The Reaction In The System Al-Zr-O-B

A novel in-situ reactive system of Al-Zr-O-B is developed. New in-situ (Al₃Zr+Al₂O₃+ZrB₂ ) p/Al and (Al₃Zr+Al₂O₃+ZrB₂) p/Al-4Cu composites are fabricated successfully by reaction in melt technique. The solidification microstructure, reactive thermodynamics and kinetics and influencing factors on the particulate size and distribution have been investigated by some modern analyzer equipments, for example, optical microscope (OM), scanning electron microscope (SEM), electron-probe microanalyzer (EPMA), X-ray diffractometor (XRD), differential thermoanalyzer (DTA) and so on. The mechanical properties and wear-resisting properties of (Al₃Zr+Al₂O₃+ZrB₂) p/Al and (Al₃Zr+Al₂O3+ZrB₂) p/Al-4Cu composites are tested. The fracture behavior, strengthening mechanism and wear-resisting mechanism have been analyzed.The technical optimal parameters of the formed composites in the Al-Zr(CO₃)₂-H₃BO₃ system are that initial reactive temperature is 850 ℃, reactive time is 25 minutes, the mass fraction of the adding reactant is 20wt% of the melt aluminum. The XRD and SEM analyses indicate that the synthesized particles are Al₂O₃. Al₃Zr and ZrB₂. The size of these particles is finer and well-distributed in the aluminum matrix. Adding magnetic field in the in-situ synthesized progress can make in-situ particles smaller and nodular.The reactive thermodynamics and kinetics of in-situ synthesized (Al₂O₃+Al₃Zr+ZrB₂)p/Al composites are researched. Results indicate that Al-Zr(CO₃)₂-H₃BO₃ reactive system can proceed in the aluminum melt spontaneously. The reaction mechanism is the model of reaction-crack-diffusion mechanism. The reactive kinetic model has been established. The influencing factors of chemical reaction and diffusion resistance in the process of reaction are analyzed. When the initial reactive temperature is higher and the concentration of reactant is bigger, the reactive velocity is more quicklyThe ultimate tensile strength and yield strength of (Al₂O₃+Al₃Zr+ZrB₂)p/Al and (Al₂O₃+Al₃Zr+ZrB₂)p/Al-4Cu composites are improved with the increasing of particulate volume fraction, and are markedly higher than the matrix. When the particulate addition content of reactant is 20wt%, the tensile properties of (Al₂O₃+Al₃Zr+ZrB₂)p/Al composites are σb=152.3MPa, σs=112.3MPa, increased separately by 95.2% and 167.3% than that of the matrix pure aluminum. The tensile properties of the (Al₂O₃+Al₃Zr+ZrB2)p/Al-4Cu composites are σb=393.9MPa,as=316.7MPa, increased separately by 72% and 53% than that of the matrix Al-4Cu alloy. After T6 heat treatment, the tensile strength and yield strength of (Al2O3+Al3Zr+ZrB2)p/Al-4Cu composites are increased separately by 11.2% and 23% than that of these composites before 16 heat treatment.The tensile fracture morphology and mechanism of (Al2O3+Al3Zr+ZrB2)p/Al and (Al2O3+Al3Zr+ZrB2)p/Al-4Cu composites are observed and analyzed. Results indicate that the strengthening mechanism of in-situ A^Zr> AI2O3 and ZrB2 particles reinforced aluminum matrix composites include Orowan strengthening, match strengthening and dislocation strengthening.The dry sliding wear tests of in-situ synthesized composites in the system Al-Zr-O-B show that the wear resistance of (Al2O3+Al3Zr+ZrB2)p/Al and (Al2C>3+Al3Zr+ZrB2)p/Al-4Cu composites is superior to that of its matrix, and is greatly enhanced with the increasing of the particulate volume fraction. The wear-resisting extent is obvious with the increasing of the load. The observation of wear surface and subsurface by SEM shows that the wear feature of the matrix Al-4Cu alloy, (Al2O3+Al3Zr+ZrB2)p/Al-4Cu and (Al2O3+Al3Zr+ZrB2)p/Al composites is respectively adhesive wear, abrasive wear and the mixed wear of adhesiveness and abrasiveness.