Effects of Al contents on aging hardening behaviors of Fe-Mn-Al-Cu low-density steels with ultra-high specific hardness

Low-density steels have garnered significant attention due to the demand for lightweight structural materials in aerospace and automobile industries. However, manufacturing low-density steels with different hardness levels poses challenges in composition design, processing optimization, and the application of hardening techniques across various alloy systems. In this work, Fe-35Mn-(15, 17, 19)Al-5Cu (at.%) low-density steels with an ultrawide flexible hardness ranging from 253.4 HV to 965.6 HV through simple aging treatments were developed, attributing to the continuous precipitation of the ultra-hard n-Mn phase. The densities of the Fe-Mn-Al-Cu steels were regulated by varying the Al contents, and the effects of Al contents on the aging hardening behaviors of FeMn-Al-Cu low-density steels were systematically investigated. The results show that the increase of Al content led to the decrease in precipitation kinetics of n-Mn. Moreover, increasing Al content slightly enhanced the intrinsic hardness of n-Mn. However, it also led to the decrease of FCC Cu-rich phase between n-Mn interfaces and the decrease in the fracture toughness of the ultra-hard alloys. This resulted in the decrease in the final hardening effect of Fe-Mn-Al-Cu low-density steels with increasing Al content. Due to the advantages of ultra-high hardness (965.6 HV) and low density, our Fe-35.2Mn-15Al-5.2Cu low-density steel achieved an ultra-high specific hardness of 141 HV & sdot;cm3/g.