Prediction of the Glass Forming Ability and the Composition Range of the Dual Phase Nanocrystalline Aluminum Alloy

Libin Liu¹*, Ligang Zhang¹, Hong Bo²

¹ Central South University, Changsha, Hunan 410083, China

² Yanshan University, Qinghuangdao, Hebei 066004, China

ABSTRACT: Aluminum alloy is an important structural material for aerospace and other light and heavy-duty transportation vehicles due to its light weight, high strength and good welding performance. How to further improve the properties of aluminum alloy has become a research hotspot in the field of structural materials. The strength of aluminum alloy can be improved by controlling the defects that prevent dislocation movement. However, this strengthening effect cannot be expanded indefinitely. Introducing too many defects will change the dominant deformation mechanism from dislocation related process to defect softening behavior, thus limiting the further improvement of material strength.

Amorphous is an effective way to improve the strength of aluminum alloy materials. Recently, IFW Dresden of Germany cooperated with Institute of metals of Chinese Academy of Sciences and Tohoku University of Japan to prepare bulk aluminum alloy with the highest strength so far by combining the methods of atomization preparation of amorphous powder and hot pressing preparation of bulk materials. The yield strength and Young's modulus of the aluminum alloy can reach 1.7GPa and 120GPa respectively at room temperature. The strength of the alloy can reach more than 1GPa at 250 ℃. The reason for the high strength of the aluminum alloy is that there are no grain boundaries and dislocations in the amorphous structure. However, due to the softening effect of shear band caused by shear stress concentration during deformation, the maximum stress that the amorphous alloy can bear can only be limited to 2% strain.
The dual phase nanostructure may further improve the strength of Al-TM-RE alloy. LV Jian et al.  obtained magnesium based ultra nano size biphasic materials with amorphous / nanocrystalline dual phase structure by magnetron sputtering, which combined and strengthened the advantages of nanocrystalline materials and amorphous materials, and showed mechanical properties close to ideal strength at room temperature. The recent development of a series of dual phase alloys (steel, high entropy alloy, etc.) has further supported the development of nano size dual phase structure, which may be one of the key technologies to improve the strength of alloys. These research results also provide a new idea for the design of high-strength aluminum alloy, that is, to improve the strength of aluminum alloy by using amorphous / nanocrystalline dual phase structure. Parshanth et al. obtained high-strength Al85Nd8Ni5Co2 dual-phase alloy by additive manufacturing method, which still has strength of nearly 1 GPa at high temperature. The strength of the nanocrystalline Al88Ni9Ce2Fe amorphous alloy obtained by Inoue et al. can reach 1.5 GPa. The nanostructured phase in these alloys is Al₁₁RE₃ phase which is not coherent with the aluminum matrix. In Al-TM-RE alloy, a kind of AuCu₃ structure (L1₂) Al₃RE phase will be precipitated. This phase can form a coherent or semi coherent interface with the aluminum matrix, which has the characteristics of high melting point and good stability L12 amorphous aluminum alloy was used to further improve the strength of the dual phase nano alloy.
    In recent years, we used the equilibrium alloy method and thermodynamic calculation method of phase diagram to study the multi-component phase diagram of Al-TM-RE, and established the thermodynamic database of phase diagram. On this basis, we predicted the amorphous forming ability of each alloy system and the precipitation range and composition of L1₂ structure nanocrystalline, which provided basic data for the design of high strength dual phase nanostructured aluminum alloy.

 Figure 1. Prediction of amorphous forming ability of Al-Cu-Zr system

Keywords: aluminum alloy; metallic glass; dual phase nanostructured material; thermodynamic calculation.