Due to their diverse properties, iron-aluminium alloys have a high potential to replace steel in various applications. The good availability of the two material components, the excellent recyclability, lower density with increasing aluminium content and the high corrosion resistance in sulphide- and sulphur-rich environments are just some of the advantages. However, with increasing aluminium content, the ductility of the FeAl alloys decreases, which is particularly due to the hydrogen embrittlement at room temperature. As a result, iron-aluminium alloys have been excluded from potential applications, particularly in the structural application area.
Investigations on powder metallurgical produced iron-aluminium alloys have shown that a fine-grained microstructure can lead to a significant improvement in ductility. Assuming the same grain diameter, a higher toughness is expected in the case of metallurgical ingot production followed by hot forming.
The present work deals with the adjustment of fine-grained microstructure in iron-rich iron-aluminium alloys using the ECAP process (Equal Channel Angular Pressing). Due to the limited formability of Fe-Al alloys with increased aluminium content, high forming temperatures and low forming speeds are required. Therefore, tool temperatures above 800 °C are permanently needed to prevent cooling of the workpieces, which makes the design of the ECAP process very challenging.
For the investigation, the Fe-Al workpieces were heated to the respective hot forming temperature in a chamber furnace and then formed in the ECAP tool at a constant punch speed of 5 mm/s. Besides the chemical composition (Fe9Al, Fe28Al and Fe38Al (At.% - Al)), the influences of a subsequent heat treatment, the number of forming cycles and the recovery time on the microstructure development were investigated. For this purpose, the average grain size of the microstructure was measured using the AGI (Average Grain Intercept) method and correlated with the aforementioned parameters.