Investigation of Microstructures and Mechanical Properties of Ultra-High Strength Al-Zn-Mg-Cu Alloy Prepared by Rapid Solidification and Hot Extrusion

Al-Zn-Mg-Cu aluminum alloys have the advantages of high specific strength, easy processing, and high toughness, showing great potential application in the aerospace field. However, ultra-high strength aluminum alloys usually contain coarse microstructures, micro-segregation, and casting defects that seriously deteriorate mechanical properties. Here, we report a high-strength aluminum alloy (Al-10.5Zn-2.0Mg-1.2Cu-0.12Zr-0.1Er) prepared by rapid solidification and hot extrusion to explore the microstructure modification of the alloy based on this strategy. The results show that: rapid-solidification technology can significantly refine alloy grains, alloy ribbons were composed of alpha (Al) equiaxed fine grains, and the average grain size was less than 6 mu m. After extrusion, the alloy had partially recrystallized, existing coarse second-phase (T-phase) and needle-shaped precipitates were MgZn2 (eta-phase), and the tensile strength and elongation of the extruded bar were 466.4 MPa and 12.9%, respectively. After T6 heat treatment, the tensile strength of the alloy reached 635.8 MPa, while elongation decreased to 10.5%. According to microstructure analysis and considering the contributions of grain boundary, dislocation, and precipitation-strengthening to the improvement of the mechanical properties, it was found that precipitation-strengthening is the main strengthening mechanism. Our research shows that rapid-solidification and hot-extrusion technology have great potential for improving the microstructures and mechanical properties of aluminum alloys.

Automated summary

This study prepared a high-strength Al-Zn-Mg-Cu aluminum alloy using rapid solidification and hot extrusion, and analyzed the improvement mechanism of the alloy's microstructure. The results showed that rapid solidification technology could significantly refine the alloy grain. After hot extrusion, the alloy partially recrystallized and formed coarse second-phase and needle-shaped precipitates. After T6 heat treatment, the alloy's tensile strength reached 635.8 MPa, but the elongation decreased to 10.5%. It was found that precipitation strengthening was the main strengthening mechanism.