Abstract
High-strength aluminum alloy (mainly refers to the 7xxx series) is the optimum material for lightweight military equipment. However, this type of aluminum alloy is a wrought aluminum alloy. If it is directly formed by traditional casting methods, there will inevitably be problems such as coarseness, unevenness, looseness, and hot cracking in the structure, which will greatly affect the final performance of the part. Based on the internal cooling with annular electromagnetic stirring (IC-AEMS) method, a new technology of rheological die forging is developed in this paper, and the scale-reduced parts of a brake hub of Al-6.54Zn-2.40Cu-2.35Mg-0.10Zr aluminum alloy were prepared. The influence of IC-AEMS and the addition of rare element Sc on the structure and mechanical properties of the parts was studied. An optical microscope and scanning electron microscope (SEM) were used to observe the microstructure evolution, energy dispersive spectroscopy (EDS) was used to analyze the phase distribution and composition, and the mechanical properties of the parts were tested by uniaxial tensile tests. The results show that the addition of Sc element can effectively refine the grains and improve the strength and elongation of the material; the application of IC-AEMS improves the cooling rate of the melt, increases the effective nucleation rate, and the grains are further refined. Through process optimization, scale-reduced parts of a brake hub with good formability and mechanical properties can be obtained, the ultimate tensile strength is 597.2 ± 3.1 MPa, the yield strength is 517.8 ± 4.3 MPa, and the elongation is 13.7 ± 1.3%.
Highlights
High-strength aluminum alloy (7xxx series deformed aluminum alloy) has the characteristics of low density, high strength, and good processing performance
Sc element to the melt and applying electromagnetic stirring, the scale-reduced parts of a brake hub with different microstructure characteristics were successfully prepared by rheological die forging process
After the Two-stage solution treatment (TST)-T6 heat-treatment, part of the T phase transforms into the S phase and remains between grains; The addition of 0.15 wt.% Sc to the Al-6.54Zn-2.40Cu-2.35Mg-0.10Zr aluminum alloy can significantly reduce the grain size and transform the grain morphology from dendrites to equiaxed cellular grains without producing an Al3 (Sc, Zr) primary phase, improving the strength and plasticity of the material at the same time; internal cooling with annular electromagnetic stirring (IC-AEMS) melt-treatment can further enhance the Sc refinement effect, and can reduce the micro-segregation of solute elements between the grains, which reduces the formation of intergranular eutectic phases; Through rheological die forging technology, the Al-6.54Zn-2.40Cu-2.35Mg-0.10Zr(-Sc) aluminum alloy scale-reduced parts of brake hub was successfully prepared, the structure is compact and defect-free, and well-formed
Summary
High-strength aluminum alloy (7xxx series deformed aluminum alloy) has the characteristics of low density, high strength, and good processing performance. It is widely used in aerospace and civil industries. Scholars around the world have conducted a lot of research on the composition, processing technology, the heat treatment process, and their effects on the performance of high-strength aluminum alloys [2], and have made certain progress, greatly promoting the application of this type of material. High-strength aluminum alloys are mainly based on Al-Zn-Mg-Cu alloys. Al-Zn-Mg-Cu alloys were developed based on the research of Al-Zn-Mg alloys by German scientists W. Sander and Materials 2020, 13, 5591; doi:10.3390/ma13245591 www.mdpi.com/journal/materials
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