Effect of Small Amount of Manganese on the Interdiffusivities in Fe-Al Alloys

Abstract

The ability to weld aluminum and steel sheets depends strongly on the formation of intermetallic phases; a process that is, in turn, controlled by the interdiffusion of iron and aluminum across the welded interface. Understanding the interdiffusion behavior, and how it is influenced by tertiary elements such as manganese, will allow for better prediction of the properties of the spot weld. Hence, interdiffusion coefficients and activation energies for interdiffusion were determined in the α solid solution and B2 intermetallic phases of Fe-Al alloys in the presence of 1.5-2 at.% manganese with pseudo-binary diffusion couples investigated at 900-1095 °C. The interdiffusion coefficients in α were found to increase in the presence of Mn at all temperatures compared with those reported in the binary Fe-Al alloys. The activation energies for interdiffusion in α are correspondingly lower than those in the binary Fe-Al alloys. The increase in the main interdiffusion coefficients in the presence of Mn indicates that diffusional interactions between Fe and Al are increased in the presence of Mn. The expected increase in diffusional interactions of Fe and Al are found to be consistent with the thermodynamic interactions between Fe and Al in the binary Fe-Al and ternary Fe-Al-Mn system as estimated from the literature. The presence of Mn is found to decrease the solubility of Al in the α solid solution, which, in turn, is expected to decrease the growth rate of the intermetallic at the interface between steel and aluminum.