The mechanistic contribution of nanosized Al3Fe phase on the mechanical properties of Al-Fe alloy

Al-1Fe (wt%) alloys containing nanosized Al3Fe phase and micrometer-sized Al3Fe phase were prepared by continuous rheo-extrusion and casting, respectively. The yield strength, tensile strength and elongation of Al-1Fe (wt%) alloy containing nanosized Al3Fe phase were 128.2 MPa, 135 MPa and 30%, respectively, while that of Al-1Fe (wt%) alloy containing micrometer-sized Al3Fe phase were 81.6 MPa, 87.1 MPa and 26.8%, respectively. The influence of nanosized Al3Fe phase on the mechanical properties of Al-Fe alloy was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), and compared with pure Al. The results suggested that the improvement of yield strength was 80.6 MPa and the reduction of elongation was 4.2% induced by nanosized Al3Fe phase. However, for the micrometer-sized Al3Fe phase, the increment of yield strength was only 32.8 MPa and the loss of elongation was 6.5%. When Al3Fe phase was refined to nanosize, its number density was increased, and the Orowan strengthening effect was significantly better. Micro-cracks around Al3Fe phase gradually grow and connect to one another with the accumulation of stress concentration and incompatible deformation. The rapid propagation of crack led to failure of the alloy. The crack around the hard Al3Fe phase became smaller once Al3Fe phase was refined, and it took a longer time for crack growth to occur. Thus, alloys containing nanosized Al3Fe phase shown superior plasticity. However, the deformation incompatibility between the matrix and the hard Al3Fe phase could not be completely eliminated even when the Al3Fe phase was refined to nanosize.