| 其他摘要 | Aluminum alloy has been widely used in daily life due to its excellent properties. In recent years, as the environmental problems deteriorate and the environmental protection consciousness enhances, developing new high strength Al alloys becomes one of the hottest issue in the field of materials science. As a brand-new kind of Al alloys, the atomic structure of Al-based metallic glasses (MGs) is distinguish from that of the conventional alloys, leading to the outstanding physical and chemistry properties. However, their industrial application is greatly limited by the poor glass forming ability (GFA). The effort in improving GFA of Al-based MGs is not rewarded. At present, most of Al-based MGs have been prepared into the samples with a size in a micron scale. But the present investigations tell us that the melt of glass forming alloy is of dense randomly packed atomic configurations and high thermal stability. These features of the melt will obviously affect the solidification process and microstructure formation. Thus, a space is left to prepare materials with good performance with the aforementioned features of the melt. In this work, Al-based bulk MG (BMG), MG matrix composite (MGMC) and high strength Al alloy (HSAA) are synthesized with this view by melt treatment, liquid phase transformation and rapid solidification. Through studying the dependence between local ordering clusters in the melt of Al alloys and the temperature, a two-step melt treatment is established that the alloy is firstly heated to a temperature 1.4 times as high as liquidus temperature (Tl), and then cooled down to a lower temperature of about 100K higher than Tl. The results show the melt treatment effectively eliminates the high-melting-temperature phase in the melt, stabilizes the supercooled liquid, and eventually improves GFA and thermal stability of the alloy. The critical size of the amorphous samples was improved from micron to millimeter for Al-Ni-La alloy and Al-Ni-Y alloy. The Al-based BMGs show excellent mechanical properties. The compressive strengths of the Al85.5Ni9.5La5 and Al84.5Ni5.5Y10 are 1180MPa and 1150MPa, respectively, and the plastic strain is 3% for the Al85.5Ni9.5La5 BMG. Both of the alloys display the typical shear deformation and the vein pattern as most monolithic BMGs do. MGMC has been developed by the addition of the second phase into MG matrix. As the saltation of the structure, energy and composition, the interface greatly influences the properties of materials. In this work, a MGMC of In nano-particles embedded in Al-based amorphous matrix has been synthesized in immiscible system. The influence of interface on the thermal properties of the composite was systematically studied. The disordered structure of the amorphous matrix induces the change of the interfacial energies, which leads to the melting temperature depression of the In nano-particles and the multistage crystallization behaviors of MG matrix. A simple physical model of interface structure was built to calculate the interfacial energy. The calculated results not only well explain the experimental result stated above, but also are coincident with the results in some systems reported previously. Considering the coherence of the characteristics of solidification structure of the glass forming melt and the strengthening mechanisms operating in Al alloys, it is expected that using glass forming melt to synthesize new high strength Al alloy. In this paper, Al-Ni-La system is chosen to serve this purpose. The microstructures of the studied alloys are Al, Al11La3 and Al3Ni phases. The structure and mechanical properties were dependent on the composition of the alloy. The highest strength is up to 1127MPa among the alloys with a considerable plasticity. Through the experiments and simulations, the deformation mechanisms of the alloys were studied. The Al3Ni phases with different direction have great strengthening effect and deformation coordination function. Compared to the Al3Ni phase, the Al11La3 phase is a little more brittle. When the stress level becomes high, the Al11La3 phase is broken and serves the origin of the crack. All these results will provide a new way to develop the new type of high strength Al alloy. |
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