Key Takeaways & Executive Findings
- •• Direct aging (DA) significantly enhances the strength of LPBF TiB2/AlSi7Mg alloys while preserving ductility, with optimal under-aging at 150°C for 4 h yielding YS of 361 MPa, UTS of 503 MPa, and elongation of 9.1%. • DA promotes the formation of nanoprecipitates (Si and β'-Mg1.8Si phases) within the α-Al matrix without altering the grain size or cellular structure, contributing to strengthening via Hall–Petch and Orowan mechanisms. • Under-aging (UA) results in a balanced work-hardening response, whereas over-aging (OA) leads to rapid saturation of work hardening due to dynamic recovery, limiting uniform elongation. • The study validates DA as an effective post-processing strategy for enhancing the mechanical performance of LPBF Al–Si–Mg alloys for engineering applications, particularly in aerospace and transportation.
Abstract
The effects of direct aging (DA) on the microstructure and mechanical properties of TiB2/AlSi7Mg alloys fabricated via laser powder bed fusion (LPBF) were systematically investigated. DA significantly improves strength while maintaining satisfactory ductility. Optimal performance is obtained through under-aging (UA) at 150°C for 4 h, resulting in a yield strength of 361 MPa, tensile strength of 503 MPa, and elongation of 9.1% in the horizontal direction. DA does not substantially alter the grain size or cellular structure but promotes the formation of nanoprecipitates within the α-Al matrix. Specifically, UA induces dot-like and needle-like Si precipitates, whereas over-aging (OA) additionally generates short rod-like β'-Mg1.8Si phases. The strengthening mechanism is attributed to the Hall–Petch effect associated with grain and cell boundaries, and the Orowan mechanism induced by nanoprecipitates. Work-hardening behavior is governed by interactions between dislocations and nanoprecipitates. The OA sample exhibits rapid saturation of work hardening due to a high initial hardening rate and dynamic recovery of dislocations, resulting in limited uniform elongation. In contrast, the UA sample demonstrates a more balanced work hardening response. These findings provide theoretical and experimental validation of DA as an effective post-processing approach aimed at enhancing the performance of LPBF Al–Si–Mg alloys in engineering applications.
1. Introduction
Additive manufacturing (AM) technology, known as 3D printing, demonstrates considerable potential for application in diverse industrial sectors, including aerospace, military equipment, and transportation industries [1–3]. Notably, laser powder bed fusion (LPBF) metal additive manufacturing technology has garnered significant attention due to its ability to construct intricate three-dimensional structures through the layer-by-layer deposition of metal powders, thereby circumventing the constraints imposed by conventional manufacturing methodologies [3–4]. This technology has significantly promoted innovation in product design, manufacturing efficiency, and material utilization.
Near-eutectic Al–Si alloys, such as AlSi10Mg and AlSi7Mg, are among the few aluminum alloy systems suitable for additive manufacturing and have found successful engineering applications, particularly in LPBF, due to their excellent solidification properties and exceptional resistance to hot cracking under extreme solidification conditions [5–6]. Due to the rapid solidification rate (0.01–1 m/s) and steep temperature gradient (105–107°C/m) generated by LPBF processing, near-eutectic Al–Si alloys tend to develop unique strengthening microstructure, termed continuous three-dimensional dual-phase cellular nanostructure (3D-DPCN) [7], which acts as dislocation cages such that significantly enhances the material’s work-hardening capability and fatigue resistance [7–8]. However, the cellular nanostructure in LPBF Al–Si alloys has not resulted in a significant improvement in yield strength (YS) compared to traditional cast Al–Si alloys [9–11]. A component with high YS is, however, crucial for aerospace applications.
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Yirui Chang, Tingting Chen, Yang Li, Yihao Wang, Yuchi Cui, Wenjun Zhao, Yi Wu, Mingliang Wang, Haowei Wang, Zhe Chen (2025). Effects of direct aging on mechanical properties and microstructure of TiB2/AlSi7Mg alloy fabricated by laser powder bed fusion. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3225-4
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Frequently Asked Questions
What is the optimal direct aging condition for TiB2/AlSi7Mg alloy fabricated by LPBF?
The optimal direct aging condition is under-aging at 150°C for 4 hours, which yields a yield strength of 361 MPa, tensile strength of 503 MPa, and elongation of 9.1% in the horizontal direction.
How does direct aging affect the microstructure of LPBF TiB2/AlSi7Mg alloy?
Direct aging does not significantly alter the grain size or cellular structure but promotes the formation of nanoprecipitates within the α-Al matrix. Under-aging induces dot-like and needle-like Si precipitates, while over-aging additionally generates short rod-like β'-Mg1.8Si phases.
What are the main strengthening mechanisms in direct-aged TiB2/AlSi7Mg alloy?
The strengthening mechanisms are attributed to the Hall–Petch effect associated with grain and cell boundaries, and the Orowan mechanism induced by nanoprecipitates.
Why does over-aging lead to limited uniform elongation?
Over-aging exhibits rapid saturation of work hardening due to a high initial hardening rate and dynamic recovery of dislocations, resulting in limited uniform elongation.
What is the significance of this study for engineering applications?
The study validates direct aging as an effective post-processing approach to enhance the mechanical performance of LPBF Al–Si–Mg alloys, which is crucial for high-strength applications in aerospace and rail transit.
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