Abstract: This paper examines the effect of Fe addition on the microstructure characterized by scanning electron microscopy/electron backscattered diffraction, neutron diffraction, and synchrotron X-ray tomography and the mechanical properties of Al-Mg-Mn-Fe-Cu alloys. The findings reveal that the microstructures of the alloys consisted of an Al matrix, Al₆(FeMn), and Al₂CuMg phase particles. The addition of Fe significantly increased the yield strength (YS), and ultimate tensile strength (UTS) of the alloys, while reducing elongation. The transformation of the 3D morphology of the Al₆(FeMn) phase from separated and fine particles with Chinese-script morphology to interconnected rod-like structure as Fe content increased from 0.1 % to 0.8 %. This strengthening effect was attributed to the slip lines being blocked at the vicinity of the interconnected Fe-rich phase, leading to grain rotation and dislocation density increment around the Fe-rich phase, ultimately improving the strength of the alloys. However, the Fe-rich phases and Al₂CuMg phases were found to be prone to cracking under tensile stress, resulting in decreased elongation of the alloys. This study provides a potential application in the design and manufacturing of new non-heat-treatable Al alloys for the automotive industry.

Key words: Al alloy, Fe-rich phase, Synchrotron X-ray tomography, Neutron diffraction, In-situ EBSD, Strengthening