Deformation characteristics and strengthening-toughening mechanisms of heterostructured 2024Al alloy with various heterogeneity levels

Heterostructured (HS) 2024Al alloys with various heterogeneity levels, consisting of soft domains (CGs) and hard domains (FGs, Al3Tip, and eutectic compounds), were fabricated via adjusting the mold temperature of powder thixoforming. The results reveal that increasing the mold temperature leads to a decrease in microhardness discrepancy between soft and hard domains from 2.12 to 1.08 GPa, and in volume fraction from 0.08 to 0.02, indicating a decrease in heterogeneity level. The alloy thixoformed at 250 °C exhibits a moderate heterogeneity level (the discrepancies in microhardness of 1.23 GPa and volume fraction of 0.04), which endows this alloy with the prominent comprehensive mechanical properties (ultimate tensile strength: 455 MPa, yield strength: 291 MPa, and elongation: 8.65 %). Furthermore, the deformation process of HS alloys occurs in a progressive order, starting from CGs, to FGs, then followed by eutectic compounds, and finally Al3Tip, i.e., the soft domains begin to deform first and then hard domains. The excellent ductility originates from the high hetero-deformation induced (HDI) hardening caused by the largest ability of dislocations accumulation at the interfaces of soft/hard domains. Additionally, the densified microstructure, relatively homogenized stress concentration after thixoforming, and the dislocations emitted from the submicro-Al3Tip also contribute to the strain hardening, and thus enhancing the ductility. In view of the heterogeneous structure, this work proposes a complex calculation model to predict the strength of the HS 2024Al alloys. The findings offer valuable insights into achieving optimal strength-ductility combination in HS alloys by the design of heterogeneous structure and fabrication technology.