Microstructures and mechanical properties of aluminum-transition metal binary alloys (Al-Fe, Al-Mn, and Al-Cr) processed by laser powder bed fusion

Transition metals added as alloying elements to aluminum improve high-temperature strength. To design heat-resistant aluminum alloys for additive manufacturing, we have focused on the basic transition metals of iron (Fe), manganese (Mn), and chromium (Cr). The present study systematically examined the aging characteristics and the relationship between the microstructures and mechanical properties of aluminum- transition metal alloys, specifically Al-3mass%Fe, Al-3mass%Mn, and Al-3mass%Cr, fabricated by laser powder bed fusion (LPBF). All the LPBF samples were densified by optimizing laser scan parameters, achieving a relative density greater than 99.9%. The hardness values of the LPBF samples, especially Al-3mass%Fe, increased as a result of the aging heat treatment, leading to excellent high-temperature strength. From the extensive microstructural investigation, the peak aged Al-3mass%Fe and Al-3mass%Mn LPBF samples had microstructures with distinct network Al-Fe and granular/platy Al3Mn compounds with high-temperature stability, respectively. The improvement of mechanical properties in the Al-3mass%Fe and Al-3mass%Mn LPBF samples was thus attributed to the microstructural composite and dispersion hardening along with the grain boundary reinforcement. Meanwhile in the Al-3mass%Cr LPBF sample, chromium had a tendency to form a solid solution in the α-Al matrix, leading to solid-solution hardening. These results indicate that the strengthening factors significantly differed depending on the added transition metals.