Nack J. Kim

Fe–Al–Mn–C lightweight structural alloys: a review on the microstructures and mechanical properties

Abstract Adding a large amount of light elements such as aluminum to steels is not a new concept recalling that several Fe–Al–Mn–C alloys were patented in 1950s for replacement of nickel or chromium in corrosion resistance steels. However, the so-called lightweight steels or low-density steels were revisited recently, which is driven by demands from the industry where steel has served as a major structural material. Strengthening without loss of ductility has been a triumph in steel research, but lowering the density of steel by mixing with light elements will be another prospect that may support the competitiveness against emerging alternatives such as magnesium alloys. In this paper, we review recent studies on lightweight steels, emphasizing the concept of alloy design for microstructures and mechanical properties. The influence of alloying elements on the phase constituents, mechanical properties and the change of density is critically reviewed. Deformation mechanisms of various lightweight steels are discussed as well. This paper provides a reason why the success of lightweight steels is strongly dependent on scientific achievements even though alloy development is closely related to industrial applications. Finally, we summarize some of the main directions for future investigations necessary for vitalizing this field of interest.

On the embrittlement of a rapidly solidified Al-Fe-V-Si alloy after high-Temperature exposure

The effects of high-temperature exposure on the mechanical properties and the microstructure of a rapidly solidified Al-Fe-V-Si alloy were examined in order to identify the critical factors controlling the thermal stability of the alloy, particularly at temperatures above 400 °C. Room-temperature (RT) tensile tests were conducted on specimens exposed to temperatures ranging from 150 °C to 482 °C for 100 hours. The microstructure of the extrusion is characterized by a banded structure consisting of a layer containing fine silicide dispersoids and a layer containing coarse silicide dispersoids, which is a replication of the microstructure of the melt-spun ribbon. The alloy did not show any significant change in tensile properties after 100 hours exposure up to 427 °C due to the stability of the microstructure. However, after exposure above 427 °C, tensile elongation decreased significantly and the brittle cleavage regions were observed on the fracture surface. The occurrence of brittle cleavage fracture is due to the presence of coarse equilibrium Al13Fe4 or Al3Fe phase, which forms by the transformation of the coarse silicide dispersoids above 427 °C.