A combinatorial study of the effect of Al and Cr additions on the mechanical, physical and corrosion properties of Fe

The effects of Al and Cr additions on the mechanical, physical and corrosion resistance of Fe were investigated in a combinatorial approach on a total of 42 alloys with compositions ranging from 0 to 10 wt% of Al together with 0-12 wt% of Cr (in increments of 2 wt%). All alloys were subjected to hardness, tensile, density, Young's modulus and salt-spray testing, along with structural analysis using x-ray diffraction. Selected alloys were additionally analysed with scanning electron microscopy (microstructure) and x-ray photoelectron spectroscopy (corroded surface). Increasing Al additions linearly reduced both density and stiffness, and led to a sudden strengthening above 2 wt% and embrittlement above 8 wt%. Cr additions counteracted the effects of Al on the mechanical and physical properties, and about 4-8 wt% of Cr could be substituted by 8-10 wt% Al for similar protective effects against wet corrosion. A decrease in Cr and increase in Al concentration in the bulk material results in a similar trend within the passive layer, preserving a significant degree of passivity. Evaluation of the comprehensive data by desirability functions allowed to identify most relevant compositions as the basis for the design of lightweight corrosion resistant steels.