低温高应变量衬板控轧高固溶Al-Mg合金高强塑性与高热稳定性机制

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

通过大变形技术制备的高强Al-Mg合金具有广阔应用前景,但其塑性低和高温稳定性差的缺点严重限制其进一步发展。本工作采用低温高应变量衬板控轧(cryogenic high-reduction hard-plate rolling,CHR-HPR)制备了兼具高强塑性(抗拉强度约597 MPa、延伸率约7.7%)和高热稳定性的高固溶Mg含量Al-9Mg合金。利用EBSD、TEM、硬度测量和拉伸实验等方法系统研究了Mg含量对CHR-HPR Al-Mg合金微观组织和力学性能的影响。结果表明:CHR-HPR Al-9Mg合金中高含量固溶Mg原子与低温变形促进合金中形成了高密度位错及小角晶界,显著提高合金的屈服强度;高含量固溶Mg原子与可动位错交互作用引起的动态应变时效导致合金加工硬化能力提高,进一步提高了合金的抗拉强度和塑性。此外,在再结晶退火过程中,高含量固溶Mg原子有效地抑制位错滑移、钉扎晶界,延缓回复与再结晶的发生。因此,CHR-HPR Al-Mg合金热稳定性随固溶Mg含量增加而显著提高,其中CHR-HPR Al-9Mg合金再结晶温度达到400℃。

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 alloys 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(~597 MPa),decent elongation(~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 EBSD,TEM,microhardness measurements,and tensile tests.The high yield strength is derived from highdensity 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℃.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.