Key Takeaways & Executive Findings
- •• Addition of 0.018wt.% TiB2 significantly reduces externally solidified crystals (ESCs) and porosity, improving filling distance from 1,700 mm to 1,833 mm in HPDC AlSi10MnMg alloy. • TiB2 promotes migration of ESCs toward the melt center where temperature and flow velocity are higher, enhancing fluidity and mechanical properties. • At a filling distance of 1,300 mm, 0.018wt.% TiB2 notably increases ultimate tensile strength, yield strength, and elongation. • Increasing TiB2 to 0.036wt.% improves short-distance mechanical properties but degrades performance beyond 1,000 mm due to increased ESCs and reduced filling distance.
Abstract
Optimizing the mechanical properties and fluidity of hypoeutectic Al-Si alloys in high-pressure die casting (HPDC) is critical for manufacturing thin-walled components with large sizes. The performance and fluidity of castings over long flow distances depend on the precise control of solidification behavior during the complex HPDC process. In this study, an AlSi10MnMg alloy was fabricated using a fluidity test mold with three channels of different thicknesses to investigate the influence of varying TiB2 content on the microstructure, mechanical properties, and fluidity of the alloy during long-distance filling in HPDC. Results indicate that the addition of 0.018wt.% TiB2 significantly reduces externally solidified crystals (ESCs) and porosity contents, improving the filling distance from 1,700 mm to 1,833 mm. The reduction in ESCs in the castings by TiB2 is attributed to its ability to promote the migration of ESCs from the shot sleeve toward the melt center, where temperature and flow velocity are higher. At a filling distance of 1,300 mm, the ultimate tensile strength (UTS), yield strength (YS), and elongation increase notably with addition of 0.018wt.% TiB2. When the addition of TiB2 increases to 0.036wt.%, the area fraction of ESCs in the channel increases compared to that with 0.018wt.%, and the filling distance slightly decreases to 1,796.9 mm. The mechanical properties of the alloy with 0.036wt.% TiB2 are better than those of the alloy with 0.018wt.% TiB2 over short distances, but become inferior beyond 1,000 mm. This work reveals the role of TiB2 in regulating solidification and flow during long-range filling, offering new insights into the processability of HPDC Al-Si alloys.
1. Introduction
Due to its high efficiency, high precision, and excellent thin-wall forming capability, high-pressure die casting (HPDC) is widely used for mass production of critical automotive components [1]. Hypoeutectic Al-Si alloys are the preferred materials for lightweight and multifunctional automotive parts due to their good fluidity, excellent castability, balanced strength and toughness, and low cost [2-4]. The increasing demand for energy efficiency requires thinner and more integrated body structural components while maintaining strength and torsional rigidity, leading to a greater structural complexity in thin-walled parts [5]. The manufacture of large, thin-walled castings with complex geometries imposes higher demands on the long-distance fluidity and mechanical stability of alloys in HPDC.
The coupled high-speed flow and rapid solidification in HPDC produce a heterogeneous microstructure in Al-Si alloys, consisting of a fine-grained surface layer, a central zone rich in externally solidified crystals (ESCs), and an intermediate eutectic band [6-8]. Meanwhile, the existence of gas entrapment and incomplete melt filling in the mold cavity can lead to casting defects such as porosity and shrinkage [9, 10]. These defects are highly likely to serve as the origin of cracks. Jiao et al. [11] reported that in low-porosity AlSi10MnMg alloys, cracks initiate mainly in the skin layer, whereas in high-porosity alloys, crack propagation occurs via consolidation and collapse of pores. Fu et al. [12] found that in Al-6Si-Mg alloy castings with long filling distances, cracks originate from the ESC/eutectic Si interface in low-defect conditions, and from porosity in high-defect regions.
Melt fluidity is closely linked to solid phase evolution during filling, as the flow stops once the solid reaches a certain critical fraction. Han et al. [13] suggested that increasing solid content during HPDC causes a pressure drop in the cavity, and filling ceases when the resistance equals the driving pressure. The flow resistance of semi-solid melt depends on solid fraction and grain size, the resistance rising rapidly once the solid fraction reaches a critical value, and finer grains reducing shear resistance [14, 15]. Therefore, understanding the coupled behavior of solidification and flow is essential for modifying microstructure, defect, and fluidity.
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Lei Liu, Wei-xiao Yang, Kai Zhao, Yan-qiang Li, Tao Zhang, Ying Fu, Zhi-rou Zhang, En-yu Guo, Hui-jun Kang, Zong-ning Chen, Tong-min Wang (2026). Effects of TiB2 on microstructure, mechanical properties, and fluidity of AlSi10MnMg alloy fabricated by high-pressure die casting. China Foundry. https://doi.org/10.1007/s41230-026-5150-1
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Frequently Asked Questions
What is the effect of TiB2 on the fluidity of AlSi10MnMg alloy in high-pressure die casting?
The addition of 0.018wt.% TiB2 significantly improves the filling distance from 1,700 mm to 1,833 mm by reducing externally solidified crystals and porosity, thereby enhancing fluidity during long-distance filling.
How does TiB2 influence the mechanical properties of AlSi10MnMg alloy?
At a filling distance of 1,300 mm, 0.018wt.% TiB2 notably increases ultimate tensile strength, yield strength, and elongation. However, increasing TiB2 to 0.036wt.% improves short-distance properties but degrades them beyond 1,000 mm.
What is the mechanism behind TiB2 reducing externally solidified crystals (ESCs)?
TiB2 promotes the migration of ESCs from the shot sleeve toward the melt center, where temperature and flow velocity are higher, thereby reducing the area fraction of ESCs in the castings.
What are the optimal TiB2 addition levels for HPDC AlSi10MnMg alloys?
The study suggests that 0.018wt.% TiB2 is optimal for long-distance filling applications, while 0.036wt.% may be beneficial for short-distance components but not for those requiring long flow lengths.
What are the implications of this research for industrial applications?
This research provides insights into regulating solidification and flow during long-range filling, offering new strategies to improve the processability and mechanical performance of HPDC Al-Si alloys for large thin-walled automotive components.
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