Enhanced Mechanical Properties and Thermal Stability Mechanism of a High Solid Solution Al-Mg Alloy Processed by Cryogenic High-Reduction Hard-Plate Rolling

Al-Mg series alloys are highly desirable for structural applications, owing to their high specific strength, good formability, and excellent corrosion resistance. However, high-strength Al-Mg al-loys prepared via severe plastic deformation generally exhibit poor thermal stability, which is caused by the high-density grain boundaries (GBs). Achieving simultaneous high strength and thermal stability in binary Al-Mg alloys remains a challenge. In this study, Al-9Mg alloys with a combination of high strength (similar to 597 MPa), decent elongation (similar to 7.7%), and enhanced thermal stability were developed via cryogenic high-reduction hard-plate rolling (CHR-HPR). The effects of solute Mg content on the microstructure evolution and mechanical properties of CHR-HPR Al-Mg alloys were systematically investigated using EB-SD, TEM, microhardness measurements, and tensile tests. The high yield strength is derived from high-density dislocations and low-angle GBs promoted via the high content of solute Mg atoms and low deformation temperature. In addition to the positive roles of Mg atoms and low deformation temperature on work-hardening ability, the simultaneous improvement in the ultimate tensile strength and ductility of CHR-HPR Al-Mg alloys with increasing solute Mg content is partially attributed to the enhanced work hardening induced via the dynamic strain aging. Furthermore, the recrystallization temperature of the CHR-HPR Al-Mg alloys gradually increased with increasing solute Mg content, and the recrystallization temperature of CHR-HPR Al-9Mg could reach 400 degrees C. The enhanced thermal stability of CHR-HPR Al-9Mg alloy is due to the high content Mg solute atoms, which strongly retard recovery and recrystallization by dragging dislocations and pinning GBs.