Al-based glassy alloys (metallic glasses) have been of great scientific and technological interest as a high specific strength and high corrosion resistant materials. However, the low glass-forming ability (GFA) is still a choke point that greatly influences the applications. In order to further comprehend the glass formation mechanism and investigate the possibility of enhancing the GFA, it is important to obtain the definite information on the atomic scale glassy structures in correlation with properties and to study the composition dependence of crystallization and properties of Al-based metallic glasses. The purpose of this paper is to summarize the structure characteristics and crystallization behavior in conjunction with alloy component in Al-based metallic glasses and to investigate the possibility of synthesizing an Al-based bulk metallic glass with better engineering performances. This may assist to learn the structural features systematically and understand the development and current status for Al-based metallic glasses.

Metallic glasses (amorphous alloys) have grown from a singular observation to an expansive class of alloys with a broad range of scientific interests. Their unique properties require a robust understanding on the structures at the atomic level while alloys in this class have a similar outlook on the microstructure. In this review, we went through the history of the majority studies on the structure models of metallic glasses, and summarized their historical contributions to the understanding of the structure metallic glasses and the relationship between their structures and properties.

This paper reviews the features of alloy components, structure and mechanical properties, physical and chemical properties of metastable Al-based alloys developed by use of various liquid or vapor quenching-induced phases such as amorphous, quasicrystalline, nanocrystalline, nanocomposite, supersaturated solid solution and structure gradient phases. As advantages of the metastable Al-based alloys, one can exemplify a high tensile strength of 1500 MPa for amorphous alloys, high elevated temperature strength of 364 MPa at 573 K for nanoquasicrystalline alloys, high strength of 1000 MPa at room temperature and 520 MPa at 473 K for nanocrystalline alloys, relatively high strength of 596 MPa with large elongation of 16% for nanocomposite alloys and high strength of 900 MPa and distinct elongation of 5% for supersaturated fcc-Al solid solution. These highly functional properties, which have not been obtained for conventional crystalline Al-based alloys, have enabled the commercialization of metastable Al-based alloys as structural, machinery and sporting goods materials. Owing to the significant increase of various fundamental properties caused by the essential differences in the structures, the engineering importance of the metastable Al-based alloys is expected to increase steadily in the future low carbon and nature harmonious society.