Key Takeaways & Executive Findings
- •• Multidirectional forging (MDF) for six passes effectively refines α-Al grains and improves TiB2 particle distribution in in-situ TiB2/Al–Cu composites. • Grain refinement is driven by mechanical fragmentation and dynamic recrystallization, including discontinuous, continuous, and particle-stimulated nucleation mechanisms. • MDF significantly enhances tensile properties: ultimate tensile strength and yield strength increase by 51.2% and 54%, respectively, compared to as-cast composites. • The strengthening is primarily attributed to grain refinement and dislocation strengthening, offering a scalable approach for high-performance aluminum matrix composites.
Abstract
In-situ TiB2/Al–Cu composite was processed by multidirectional forging (MDF) for six passes. The microstructure evolution of the forged workpiece was examined across various regions. The mechanical properties of the as-cast and MDFed composites were compared, and their strengthening mechanisms were analyzed. Results indicate that the grain refinement achieved through the MDF process is mainly due to the subdivision of the original grains through mechanical geometric fragmentation and the occurrence of dynamic recrystallization (DRX). DRX grains are formed through discontinuous DRX, continuous DRX, and recrystallization induced by particle-stimulated nucleation. A rise in accumulated equivalent strain results in finer α-Al grains and a more uniform distribution of TiB2 particles, which enhance the Vickers hardness of the composite. In addition, the tensile properties of the MDFed composite significantly improve compared with those of the as-cast composites, with ultimate tensile strength and yield strength increasing by 51.2% and 54%, respectively. This enhancement is primarily due to grain refinement strengthening and dislocation strengthening achieved by the MDF process.
1. Introduction
Compared with conventional Al alloys, particle-reinforced Al matrix composites (PRAMCs) exhibit improved strength, stiffness, and toughness due to the addition of reinforcing particles [1–2]. Their lightweight and high-performance characteristics make them appropriate for aerospace, automotive, and equipment manufacturing applications [3–4]. Among various matrix alloys, Al–Cu alloys are notable for their high specific strength and modulus [5]. However, their poor castability, which is attributable to thermal cracks, shrinkage porosity, and casting micropores, limits their broader application [6]. TiB2 ceramic particles, which are recognized for their high melting point, hardness, excellent wettability, and superior thermal and chemical stability, serve as effective reinforcement [7]. Furthermore, TiB2 enhances the solidification mechanism and improves the castability of the Al–Cu alloys [6,8]. Plastic deformation processing, such as extrusion, rolling, and forging, has been shown to further enhance the mechanical properties of PRAMCs while reducing porosity [7,9].
Grain refinement is often identified as the main mechanism behind these improvements [10]. Conventional severe plastic deformation (SPD) techniques, including high-pressure torsion (HPT), equal channel angular processing (ECAP), accumulative roll bonding (ARB), and multi-directional forging (MDF), are widely employed to produce ultrafine-grained materials (UFG) [11–13]. Among these techniques, MDF is particularly advantageous for large-scale production due to its simplicity, cost-effectiveness, and efficiency [14]. Prior studies have illustrated the efficacy of MDF in refining the microstructure of aluminum alloys. Manjunath et al. [15] reported a substantial reduction in grain size from 60 to 10 μm in the 7050 alloy through MDF, which resulted in increased compressive strength and Vickers hardness. Kumara and Kumar [16] observed improved fragmentation and uniformity of silicon particles in Al–12Si alloy after MDF for nine passes at room temperature. Zhao et al. [17] studied the recrystallization behavior of Al–Zn–Mg–Cu alloy during MDF at 400 and 450°C, which showed that lower strain rates and higher temperatures promoted recrystallization and microstructural refinement.
Current research on MDF technology mainly addresses the effects of process parameters, such as deformation passes, temperature, and strain rate, on the morphology and properties of materials. However, the deformation behavior within forged workpieces is complex, and understanding microstructural variations across different locations within the workpiece remains limited. Moreover, research on MDF processing of PRAMCs is notably less common than that of Al alloys. This study aimed to investigate the refinement of α-Al and the distribution of TiB2 in in-situ TiB2/Al–Cu composites processed through the MDF method. The mechanical properties of the MDFed composite were also compared with those of the as-cast composite.
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Sen Yang, Zhiren Sun, Zipeng Wang, Shuhui Zhao, Kaikun Wang, Dun Li, Xiaokai Wang (2025). Microstructural optimization and strengthening mechanisms of in-situ TiB2/Al–Cu composite after multidirectional forging for six passes. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3058-6
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Frequently Asked Questions
What is the effect of multidirectional forging on the microstructure of TiB2/Al-Cu composites?
Multidirectional forging (MDF) for six passes refines the α-Al grains through mechanical fragmentation and dynamic recrystallization, and improves the distribution uniformity of TiB2 particles, leading to enhanced hardness and tensile properties.
What are the main strengthening mechanisms in the MDFed TiB2/Al-Cu composite?
The primary strengthening mechanisms are grain refinement strengthening and dislocation strengthening, which result from the severe plastic deformation during MDF.
How much do the tensile properties improve after MDF?
Compared to the as-cast composite, the ultimate tensile strength and yield strength of the MDFed composite increase by 51.2% and 54%, respectively.
What types of dynamic recrystallization occur during MDF?
The dynamic recrystallization during MDF includes discontinuous DRX, continuous DRX, and recrystallization induced by particle-stimulated nucleation.
Why is MDF considered advantageous for large-scale production?
MDF is simple, cost-effective, and efficient, making it suitable for large-scale production of ultrafine-grained materials.
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