Key Takeaways & Executive Findings
- •• The CRE Al-Ti-V-B master alloy achieves a 89.62% reduction in grain size of A356 alloy, from coarse dendrites to 151.8 μm, significantly enhancing mechanical properties. • Optimal refinement parameters are 0.3wt.% master alloy addition and 20 min holding time, yielding tensile strength of 196.11 MPa and elongation of 5.75% in as-cast state. • After T6 heat treatment, the refined alloy exhibits tensile strength of 290.1 MPa and elongation of 3.09%, demonstrating improved ductility and strength. • The refined grains promote crack path deflection and localized plastic deformation, reducing brittle fracture tendency and enhancing energy dissipation.
Abstract
Based on thermodynamic calculations and continuous rheological extrusion (CRE) technology, Al-Ti-V-B master alloys were designed and prepared. The morphology and the distribution of the refined phases in the master alloys were analyzed by XRD, SEM, and TEM. The effects of master alloy addition and holding time on the microstructure and mechanical properties of A356 alloy were investigated. Under the optimum refiner addition of 0.3wt.% and the holding time of 20 min, the average grain size of the refined A356 alloy is 151.8±9.11 μm, 89.62% lower than that of original A356 alloy. The tensile strength and elongation of as-cast A356 refined alloy are 196.11 MPa and 5.75%, respectively. After T6 treatment, the tensile strength and elongation of A356 refined alloy are 290.1 MPa and 3.09%, respectively. The fracture morphology is characterized by a predominance of along-crystal fracture with a small amount of through-crystal fracture, attributed to the refined grains. Finer grains promote crack path deflection and localized plastic deformation, enhancing energy dissipation and reducing the tendency for brittle fracture. This study provides a novel approach to improving the mechanical properties of A356 alloy through grain refinement using CRE Al-Ti-V-B master alloy.
1. Introduction
A356 alloy is a hypoeutectic Al-Si alloy with low density, superior castability, and high strength, which is widely used in aerospace, transportation and other fields. The rapid development of industry puts forwards the higher demands on the properties of A356 alloy. However, the coarse α-Al dendrites of the alloy adversely affect its mechanical properties [1, 2]. Grain refinement is indispensable for the manufacture of aluminum alloy [3-5].
Common methods of aluminum alloy refinement include adding grain refiner [6-8], applying ultrasonic field [9] or electromagnetic field [10], increasing subcooling [11], and pressure machining [12, 13]. Among them, adding grain refiner is the most cost-effective method. The grain size is refined due to high nucleation rate and inhibition of grain growth [14]. Various theories, including the carbide-boride theory [15, 16], component supercooling theory [17], peritectic theory [18], dual nucleation theory [19], and solute theory [20, 21], are usually adopted to describe the mechanism of grain refinement.
Common grain refiners are Al-Ti-B and Al-Ti-C based master alloys, in which TiB2 and TiC particles are used as substrate for heterogeneous nucleation of α-Al grains [22, 23]. However, TiB2 tends to aggregate into clusters and settle into the Al melt [24], while TiC is destabilized in a portion of the Al melt to generate Al4C3 [25]. The Al-V-B master alloy containing VB2 and VAl3 particles can significantly refine the aluminum alloy, and VB2 particles are the effective nucleation cores for the refinement of Al-7wt.% Si alloy [26]. Furthermore, its refining effect is significantly better than the traditional Al-Ti-B and Al-Ti-C master alloys [27]. Research has shown that V can refine the spacing between secondary dendrite arms [28]. In recent years, scholars have refined Al-Si and Mg-Al alloys by adding Al-V-B master alloy. As stated by Ruan et al. [29], the refinement effect of Al-V-B master alloys was more excellent than the Al-Ti-B master alloy, and the Al-(Ti+V)-B significantly reduced the grain size of Al-7Si from 854.6 to 136.93 μm. Allen et al. [30] found that, the combination of V and Al-Ti-B promoted heterogeneous nucleation in commercial ingots. Zhang et al. [31] prepared Al-3V-1.28B alloy containing VAl3 and VB2 particles, which reduced the size of Al-7Si alloy to 280 μm. Al-V-B and Al-5V-B refiners prepared by Li et al. [32] significantly reduced the grain size of Al-10Si alloy from 1,736 μm to 184-245 μm. Based on above literatures, Al-V-B master alloys can provide effective nucleation particles such as VB2 and VB. However, master alloys that can provide both TiB2 and VB2 are rarely studied. Continuous rheological extrusion (CRE) technology, as an advanced material processing technique, is highly necessary for the production of grain refiners [24]. By integrating the advantages of plastic wo
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Hong-fei Jia, Guang-zong Zhang, Shuo Zhang, Da Teng, Qing He, Jun-wen Li, Ren-guo Guan (2025). Refinement of A356 alloy using continuous rheological extrusion Al-Ti-V-B master alloy. China Foundry. https://doi.org/10.1007/s41230-025-3135-0
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Frequently Asked Questions
What is the optimal addition amount and holding time for the CRE Al-Ti-V-B master alloy in refining A356 alloy?
The optimal addition is 0.3wt.% with a holding time of 20 minutes, resulting in a grain size reduction of 89.62%.
How does the CRE Al-Ti-V-B master alloy improve the mechanical properties of A356 alloy?
It refines the grain structure, leading to increased tensile strength and elongation. As-cast tensile strength reaches 196.11 MPa and elongation 5.75%; after T6 treatment, they are 290.1 MPa and 3.09%, respectively.
What are the key phases in the CRE Al-Ti-V-B master alloy responsible for grain refinement?
The master alloy contains TiB2 and VB2 particles, which act as effective heterogeneous nucleation substrates for α-Al grains.
What is the fracture behavior of the refined A356 alloy?
The fracture morphology shows predominantly along-crystal fracture with some through-crystal fracture, attributed to refined grains that promote crack deflection and localized plastic deformation, reducing brittle fracture tendency.
How does the CRE Al-Ti-V-B master alloy compare to traditional Al-Ti-B refiners?
The CRE Al-Ti-V-B master alloy provides both TiB2 and VB2 particles, avoiding issues like TiB2 clustering and TiC instability, and shows superior refining efficiency compared to traditional refiners.
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