Regulating the Heterogeneity Level and Tensile Properties of Powder-Thixoformed 2024Al Alloy Via T6 Heat Treatment

Abstract

Heterostructured (HS) 2024Al alloy composed of Al3Ti-free coarse grains domains (CGs) and Al3Ti-reinforced fine grain domains (FGs) was fabricated via powder thixoforming, and its heterogeneity level (the microhardness difference between CGs and FGs) was regulated through T6 heat treatment for further improving tensile properties. The results indicate that for the peak-aged alloy, the numbers of Guinier-Preston-Bagaryatsky (GPB) zone and fine S′′ phase in the FGs are higher than those in the CGs, leading to a moderate heterogeneity level (1.50 GPa), and thus endowing prominent tensile properties (ultimate tensile strength of 539.8 MPa, yield strength of 342.7 MPa, and elongation of 11.14%). Small localized strain regions were formed during deformation, which could efficiently enhance the ability to co-deformation between the CGs and FGs. The improved hetero-deformation induced (HDI) hardening due to the promoted dislocation accumulation at the CGs/FGs interfaces, as well as the mobile dislocations that cut the GPB zones and shearable small-sized S′′ phases, contributed to the excellent ductility. The good strength was mainly ascribed to the HDI strengthening besides precipitation strengthening. This work provides a promising way for optimizing the heterogeneity level and fabrication technology of HS alloys with excellent properties.

Keywords: Al alloy, Heterogeneity level, Powder thixoforming, T6 heat treatment, Strengthening and toughening