Studies On Nano-Al₂O₃ Reinforced Brass Matrix Composite

A novel materials of nano-Al₂O₃ reinforced brass composite has been developed by the processes mechanical alloying (MA) and sintering under pressure hereafter in the present thesis. The morphology of the composite particles and The structure of transformation of Al\ZnO, Al\CuO and Cu-Zn- Al₂O₃ mixed during mechanical alloying process has been investigated by several methods, i.e. x-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis(DTA).On this basis ,the Cu-Zn- AI2O3 composite are produced.The mechanical alloying process of Al-ZnO\CuO powders is investigated. Results show that the powders of mixed Al-ZnO\CuO undergo severe plastic deformation, cold-welding and fracture due to the collision of balls during mechanical alloying, and composite particles of ZnVCu-Al₂O₃ are formed, in which exists the typical lamellar structure. Prolonged milling time, lamellar structure will be refined, a great deal of internal strain and crystal lattice distortion are accumulated in the powders. The Al₂O₃ particle is formed by a local metathesis reaction during ball milling, and exits a gestating period. Increasing the milling time and the sintering temperature are both advantageous for the formation of Al₂O₃. The distribution of Al₂O₃ particles in matrix is uniform and no micro-or macro-segregation exist. The combination between the reinforced phase of Al₂O₃ and the matrix is strong.Investigation on the Cu-Zn-Al₂O₃ system shows that Al₂O₃ and α-Cu powder can be formed through ball milling. In the gestating period the Zn rich ε-phase are formed firstly, and then transform to Cu rich α -phase . The lattice parameter of α -Cu (Zn) is increased. The grain of α -Cu is refined and the strain increases continually in the ball milling of process of Cu-Zn-Al₂O₃ powders. But after 75 hours Ball milling time, the meta γ -phase is formed, the lattice parameter of α -Cu (Zn) should be decreased. The composite particles with dispersion Al₂O₃ have been prepared after 120 hours milling time. The grain of composite powders is about 22nm in size.The sintering technology and properties of Cu-Zn-Al₂O₃ composite are studied. The results indicate that the best sintering parameters are as below: temperature of 850℃ wintering pressure of 50MPa with the holding temperature and pressure time of 2 hours. The grain of Al₂O₃ and α -Cu is also nano-crystal after sintering. Thedual phase reinforced composite of AI2O3 particles, which with a good properties, can be synthesized through processes of ball milling and sintering with the raw material of Al-ZnCACuO-A^Cb powders.