Mechanical Responses of Cold‐Rolled AM350 Under Tension: Microstructure, Phase Transformation, and Fracture Mechanism

In this paper, the tensile mechanical properties, deformation characteristics and microscopic deformation and fracture failure mechanisms of AM350 are systematically investigated by using experimental means such as material testing machine, Digital Image Correlation (DIC), Transmission Electron Microscope (TEM), X-ray Diffraction (XRD). The results show that the cold-rolled AM350 sheet exhibits a dual-phase structure, which consists of body-centered cubic (BCC) ferrite (α-Fe) and face-centered cubic (FCC) austenite in a nearly 1:1 ratio. During tensile deformation, a phase transition from FCC to BCC occurs, resulting in a single-phase BCC structure in the deformed specimen. Additionally, deformation-induced dislocation rearrangement leads to the formation of subgrain structures and an increase in severely deformed grains. After deformation, the area of large Grain Reference Orientation Deviation (GROD) greater than 5° accounted for about 33.2%, an increase of 444.3% compared to the pre-deformation state. This suggests that ​a fraction of the recrystallized grains participated in the tensile deformation.​ The plastic deformation mechanisms of AM350 mainly consist of dislocation features such as high-density dislocations, dislocation loop, dislocation tangle, dislocation arrays, and dislocation pile-up, as well as the precipitation of the Laves phase (Fe2Mo), by comparing the dislocation features near the phase boundary, finding that the precipitation does not exist in isolation, strongly interacts with dislocations during deformation, this interaction effectively alleviates stress concentration, thereby suppressing crack nucleation and preventing premature brittle fracture of the material. Subsequently, it is found that fracture in AM350 alloy initiates at grain boundary weak zones, then propagates and coalesces under external loading, ultimately leading to catastrophic failure.