Effect of Ball-Milling Process on Microstructures and Mechanical Properties of Heterostructured 2024Al Alloy Prepared by Powder Thixoforming

In this work, several heterogeneity-improved heterostructured 2024Al alloys by introducing in-situ Al₃Ti particles were prepared by using powder thixoforging (PTF) with different high-energy ball-milling methods, and the microstructures and mechanical properties of the resultant alloys were investigated. The results indicate that all the alloys have a heterogeneous structure (HS) composed of two domains, i.e. the soft domains consisting of primary α-Al grains and the hard domains consisting of Al₃Ti particles and secondarily solidified structures (SSSs). The alloy prepared by low-speed ball milling (LSBM) has a microstructure in which spheroidal and elongated primary α-Al grains uniformly distribute within SSSs, while the others, especially the alloy fabricated by segmented ball milling (SMBM), possess texture-like structures that flat-shaped primary α-Al grains are embedded layer-by-layer within SSSs. It is found that the former alloy renders an excellent synergy of strength and ductility, an ultimate tensile strength of 430 MPa, yield strength of 275 MPa and fracture elongation of 8.03%, which are 36.14%, 41.91% and 10% higher than that of matrix alloy, respectively. The enhancement of tensile strength is due to the good coordinate deformation of different grains and uniform distribution of Al₃Ti. The good ductility is contributed to the long uniform-elongation period with a large strain hardening rate due to the increased heterogeneities in grain size caused by refining of SSSs and hardness caused by introducing Al₃Ti particles between the two domains.