Effect of ball-milling time on microstructures and mechanical properties of heterogeneity-improved heterostructured 2024Al alloys fabricated through powder thixoforming

Abstract

In this study, several heterogeneity-improved heterostructured 2024Al alloys were fabricated by forming in situ Al3Ti particles through powder thixoforming. The results indicated that the inter-soft-domain distance (the size of primary grains) decreased and reached its minimum at the ball-milling time of 8 h, and then, slightly increased. The boundary density of primary-grain/secondarily solidified structure (SSSs) domains reached the maximum at this time. The resulting alloy exhibited the ultimate tensile strength, yield strength, and elongation to failure of 430 MPa, 275 MPa, and 8.03%, showing an enhancement of 41.9%, 36.1%, and 10%, respectively, compared with those of the 2024Al matrix alloy without Al3Ti particles. This alloy exhibited an excellent synergy of strength and ductility. Heterogeneity between the primary-grain and SSS domains of the alloy was considerably higher than that of the matrix alloy but slightly lower than that of the alloys prepared with the milling times of 2 and 10 h. This finding indicated that the alloy prepared at the milling time of 8 h exhibited a reasonably increased heterogeneity. Strength enhancement was attributed to the hetero-deformation-induced (HDI) strengthening, solution strengthening, grain refinement strengthening, and load transfer strengthening. The excellent ductility was mainly ascribed to the large strain partitioning due to the high boundary density of primary-grain/SSS domains, which led to an increase in the uniform elongation plateau with a high work hardening rate.