Advanced Materials Research Vols. 750-752

Abstract: Cu90Zr10 alloy powder was prepared by high-energy ball milling. The microstructure and property evolution of this alloy powder during mechanical alloying (MA) were investigated by using X-ray diffraction and optical microscopy (OM). The alloy powder with an average grain size of 10 - 40 nm was obtained, and the grain size was found to decrease gradually with increasing milling time. The microhardness reached a maximum value (about 295 Hv) after 30 h milling. The internal microstrain and the microhardness of the samples increased due to the grain refinement and solid solution during milling, and 10at.% Zr could be brought into Cu lattice by solid solution during MA. At last, the mechanisms of strengthening were discussed.

Abstract: In this paper, the Al-8.5Fe-1.3V-1.7Si alloys were fabricated by spray forming and extrusion process. The microstructure and mechanical properties of the alloy were investigated by means of metallographic, scanning electron microscope and tensile test. The results indicate that the tensile strength of the extrued alloys can reach 353MPa, the yield strength 300MPa, elongation 19.12%, at room temperature. At 250°C, the tensile strength of the extrued alloys can reach 221MPa, the yield strength 208MPa, elongation 13.33%.

Abstract: Based on the dynamic analysis of beryllium bronze's stress relaxation, the environmental temperature and outside stress which related to its stress relaxation were discussed. The TEM was been used to observe materials micro-structure during the test of stress relaxation. Then the performances regulation of beryllium bronze's stress relaxation and the variation of its microcosmic organization structure were researched. Results showed that the process of stress relaxation is divided into two stages: accelerating stage and smoothing stage. Besides, the materials microscopic mechanism was analyzed and explained.

Abstract: Alloys with different compositions in Mg-rich corner of Mg-Zn-La system at 150°C were prepared, and the phase equilibrium in Mg-Zn-La alloys were determined by scanning electron microscopy (SEM), electron probe microanalysis based on energy dispersive X-ray spectroscopy (EPMA-EDS) and X-ray diffraction (XRD). The stability, compositions and lattice structures of the intermetallic compounds of Mg-Zn-La alloys were identified. The results show that, there exists a ternary compound (T-phase) with constant La (about 8at%) and the changed ratio of Mg/Zn in the Mg-rich corner of Mg-Zn-La system. Though the ratio of (Mg, Zn)/La of T-phase is close to that of Mg/La of Mg₁₂La, the T-phase was not the binary solid solution of Mg₁₂La because of the difference of the lattice structure. It also reveals that T-phase is a stable phase, and it is in two-phase equilibrium of T-phase+Mg at 150°C.

Abstract: The oxidation behavior of beryllium bronze is studied through phase and component analysis, SEM and other methods in the paper. Make a study on oxidation mass gain law of beryllium bronze between 210°C and 300 °C. Results show that the mass of beryllium bonze gains obviously at the initial time, then gains slowly gradually, which follows approximately parabolic rate law in whole. The oxidation of beryllium bronze is a progress of O spreads to interior of alloy while Be and Cu spread outside. The oxidation products are BeO and CuO, BeO is beneath CuO.

Abstract: Effects of the holding time and the stirring time on the microstructure and mechanical properties of A356 alloy modified by Sc are researched. According to the test results, most of the eutectic silicon phases have changed to the shape of creeping point, dispersed in the grain boundary of α (Al) phase while stirring 1 minute, in which case both the tensile strength and elongation reach the highest, resulting in the best modification effect. The results also indicate that microstructure and mechanical properties of the alloy reach are the best modification effect when the melt is held 15 minute. It can be known that the optimal stirring time is 1 minute and the optimal holding time is 15 minute in the experiment condition of the work.

Abstract: The effects of ultrasonic vibration (USV) on the solidified microstructure of AZ61 magnesium alloy were investigated. The experimental results show that the remarkable microstructural refinement is achieved when the USV was applied to the solidification of the AZ61 alloy. The average grain size is decreased from 263 μm without ultrasonic treatment to 98 μm with USV treatment. The microstructure evolution reveals that the primary α-Mg generates and grows in globular shape with USV, contrast with the dendritic shape without USV. The USV causes melt convection during solidification, which makes the temperature of the whole melt homogenized, and produces an undercooling zone in front of the liquid/solid interface, which makes the nucleation rate increased and big dendrites prohibited. In addition, the β-phase in the entire cross-section of the billet is significantly refined and also changed from continuous to discontinuous morphology. Spherical β-phase is formed during the solidification of billet treated with USV.

Abstract: The semi-solid metal (SSM) processing, including thixoforming and rheocasting, offers the opportunity to manufacture net-shaped components with complicated shape and good mechanical properties. More and more researches have been focused on rheocasting in recent years because of its low cost and high productivity [1,. Rheocasting involves stirring the solidifying alloy to prepare non-dendritic semisolid slurry, then shaping the slurry directly. Ultrasonic vibration (USV) has the potential to be a simple and effective process to produce semisolid metal slurry. Previous investigations have revealed that when USV is applied on the solidifying melt, microstructure changes occur involving grain refinement, increased homogeneity, reduced micro-segregation as well as degassing [3-.

Abstract: Cu-La₂O₃ composite was fabricated by internal oxidation method using powder metallurgy. Its sliding behavior was studied under various electrical currents and applied loads. The worn surfaces of Cu-La₂O₃ composite were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to probe the wear mechanisms. The results indicated that applied load has a significant effect on the wear rate of the Cu-La₂O₃ composite pins. The wear rate displayed the minimum value at the load of 50N during electrical sliding processes.

Abstract: The novel high aluminum zinc-based alloy is prepared by changing composition of the alloy and adding 0.05% mixed rare earth with lanthanum-rich. The microstructure, mechanical properties and thermal expansion coefficient are investigated under as casting condition. The results showed that the novel high aluminum zinc-based alloy had fine microstructure, higher mechanical properties and smaller thermal expansion coefficient compared to the ZA27 alloy.