Key Takeaways & Executive Findings
- •• WAAM significantly refines the Mg2Si phase and grain size, leading to a 36.6% increase in microhardness and 63.4% improvement in room-temperature tensile strength compared to as-cast Mg-6Si alloy. • The granular Mg2Si phase becomes finer and more uniformly distributed, while the detrimental acicular Mg2Si phase is reduced, contributing to enhanced mechanical properties. • The rapid cooling inherent in WAAM promotes a homogeneous microstructure, offering a promising route for producing high-performance Mg-Si alloys for engineering applications. • This study provides practical guidance for optimizing additive manufacturing parameters to control intermetallic phase morphology in magnesium alloys.
Abstract
Si-containing Mg alloys solidified at conventional rates often contain coarse and sharp Mg2Si phases, which can result in inferior material properties. In this study, Mg-6wt.% Si (Mg-6Si) alloy was prepared by wire arc additive manufacturing (WAAM), employing the gas tungsten arc welding technique with rapid cooling. The microstructures and mechanical properties of the WAAM alloy were investigated and compared with those of the as-cast samples produced using a metal mold. The results indicate that the WAAM Mg-6Si is harder and stronger than the as-cast samples. The microhardness of the WAAM Mg-6Si increases by 36.6% in comparison to that of as-cast Mg-6Si alloy. Furthermore, the average tensile strengths at room temperature and 150 °C increases by 63.4% and 21.3%, respectively. WAAM refines both the Mg2Si phase and the overall grains, resulting in a homogeneous morphology and improved mechanical properties. The granular Mg2Si phase, characterized by fine particles with a diffused distribution, shows a significant increase in concentration. The acicular Mg2Si phase is distributed along the grain boundaries, and its concentration significantly decreases. The average grain size of the Mg2Si phase is about 9.20 μm, about 5 times smaller. The refinement and distribution of the granular Mg2Si phase, as well as the reduction in the amount of needle-like Mg2Si particles, are the key factors for improving the mechanical properties of WAAM Mg-6Si alloy.
1. Introduction
Mg alloys are promising lightweight materials owing to their low density (approximately 1.74 g·cm-3), high specific strength, excellent damping and vibration reduction properties, and outstanding electrical and thermal conductivities. They have a wide range of applications in various sectors including aerospace, automotive, rail transportation, and consumer electronics (3C products) [1, 2]. Numerous Mg alloys have been developed, including those containing Si in the Mg2Si reinforced phase. This phase is known for its high hardness (4.5 GPa), high elastic modulus (120 GPa), low density (1.93 g·cm-3), high melting point (1,085 °C), and low coefficient of thermal expansion (7.5×10-6 K-1) [3, 4].
However, the morphology of the primary phase of Mg2Si under solidification conditions is highly sensitive to the solidification rate. It tends to coarsen when solidified by conventional casting, which degrades mechanical properties and limits engineering applications of the Mg alloys [5]. For achieving a desirable morphology of the Mg2Si phase, there are two main approaches: (1) adding elements such as P, Sb, Sr, Zn, Ca, and Re to modify the Mg2Si phase [6-11], and (2) achieving higher solidification rates via process control to refine the Mg2Si phase [12-14].
Additive manufacturing technology is becoming increasingly mature and has industrial applications in the small-batch manufacturing of complex-shaped parts. Wire arc additive manufacturing (WAAM), as a rising additive manufacturing method, has unique safety advantages for Mg alloys owing to the use of wires rather than powder as the raw material [15, 16]. In wire arc additive manufacturing, an electric arc is employed as the heat source to facilitate layered clad formation. The characteristics of this process, namely the small melt-pool sizes and rapid melting and solidification [17, 18], are well-suited to the material and process properties of Mg-Si alloys. Consequently, the combination of Mg-Si alloys with wire arc additive manufacturing presents a promising avenue for engineering applications.
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Peng-cheng Zhou, Guo-qiang You, Jin-yu Feng, Lei Wang, Xiao Lin, Bin Jiang (2025). Mechanical properties and microstructures of Mg-6Si alloys fabricated using the tungsten-inert-gas arc additive manufacturing. China Foundry. https://doi.org/10.1007/s41230-025-4070-9
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Frequently Asked Questions
What is the main advantage of using WAAM for Mg-Si alloys?
WAAM provides rapid cooling and small melt pools, which refine the Mg2Si phase and grain structure, leading to improved mechanical properties compared to conventional casting.
How does WAAM affect the Mg2Si phase morphology?
WAAM transforms the coarse, sharp Mg2Si phase into a finer granular morphology with a more uniform distribution, while reducing the detrimental acicular phase along grain boundaries.
What are the improvements in mechanical properties of WAAM Mg-6Si alloy?
The WAAM Mg-6Si alloy shows a 36.6% increase in microhardness, a 63.4% increase in room-temperature tensile strength, and a 21.3% increase at 150°C compared to as-cast alloy.
Why is the refinement of Mg2Si phase important?
Refinement of Mg2Si phase reduces stress concentration and improves the homogeneity of the microstructure, which enhances the overall mechanical performance of the alloy.
What is the significance of this research for industrial applications?
This research demonstrates that WAAM can produce high-performance Mg-Si alloys with refined microstructures, offering a viable manufacturing route for lightweight components in aerospace, automotive, and electronics industries.
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