Key Takeaways & Executive Findings
- •• Increasing Si content from 6.5% to 8.5% promotes eutectic segregation band formation in super-slow-speed die-cast Al-Si-Mn-Mg alloys. • Optimal mechanical properties (quality index) are achieved at different Si contents depending on heat treatment: as-cast (7.5% Si, QI=376.1 MPa), T5 (6.5% Si, QI=373.4 MPa), and T6 (8.5% Si, QI=432.2 MPa). • T6 heat treatment significantly enhances both thermal and electrical conductivities by spheroidizing eutectic silicon and precipitating Mg and Si solutes, reducing electron scattering. • Thermal and electrical conductivities decrease slightly with increasing Si content, indicating a strong correlation with Si content in the alloy.
Abstract
In this study, Al-xSi-0.3Mn-0.3Mg-0.14Fe alloys (x=6.5, 7.5, 8.5, wt.%) were prepared by super-slow-speed die-casting, and the effects of Si content on the microstructure, mechanical, and thermal/electrical conductivities in as-cast, T5, and T6 states (DIN EN 1706:2020) were investigated. It is found that the increase of Si content in the alloy enhances the formation of eutectic segregation band in the casting surface microstructure. Within the Si content range of 6.5%-8.5%, as a comprehensive evaluation criterion of mechanical properties, the quality index (QI) of 376.1 MPa can be obtained in the as-cast state of the alloy with about 7.5% Si content, 373.4 MPa in T5 state of the alloy with 6.5% Si content, and 432.2 MPa in T6 state of the alloy containing 8.5% Si. The heat treatment state significantly affects the thermal conductivity and electrical conductivity of the alloys. The eutectic silicon in the alloy is segemented and further spheroidizaed during the solution process, and the solute atoms of Mg and Si are more adequately precipitated during the aging process. Both of these greatly reduce the probability of electron scattering. Thus, T6 treatment significantly improves the electrical and thermal conductivities. With the increase of Si content, both thermal conductivity and electrical conductivity decrease slightly, demonstrating a strong correlation with the Si content in the alloy.
1. Introduction
With the rapid advancement of science and technology, there is an increasing demand for lightweight new energy vehicles to save energy and reduce emissions. In response to these demands, aluminum alloys have become more and more important in human production and life due to their excellent characteristics [1, 2]. Among them, Al-Si-Mg alloys have good castability, high corrosion resistance, good machinability, and high strength due to the precipitation hardening of Mg2Si transition particles [3, 4].
In addition, due to the rapid development of new energy vehicles (NEVs), the demand for high-performance die-castings of aluminum alloys is increasing. More and more Al-Si-Mg system alloys are being widely used and included in the relevant standards. In the latest European standard DIN EN 1706:2020 [5], the newly included grade EN AC-AlSi7MnMg alloy has a Si content between 6.5% and 8.5%, in which the range of Si content is wider than other AlSi7Mg series alloys (Si content between 6.5% and 7.5%). At the same time, with the rise of electric air conditioning compressors of carbon dioxide refrigerants in NEVs, casting aluminum alloys are required to have higher strength and better thermal conductivity. Therefore, in order to guide production practice, it is necessary to study the influence of Si content on the microstructure, mechanical properties, and thermal/electrical conductivities of AlSi7MnMg alloy by die-casting.
Loading authentic research manuscript (Pages 1–5)...
Lu Zhang, Heng-cheng Liao, Jiang Li (2025). Effect of Si content on microstructure, mechanical, and thermal/electrical conductivities of Al-xSi-0.3Mn-0.3Mg-0.14Fe alloy prepared by super-slow-speed die-casting. China Foundry. https://doi.org/10.1007/s41230-025-4082-5
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the effect of Si content on the microstructure of Al-Si-Mn-Mg alloys?
Increasing Si content from 6.5% to 8.5% enhances the formation of eutectic segregation bands in the casting surface microstructure, as observed in the study.
How does heat treatment affect the mechanical properties of these alloys?
Heat treatment significantly influences mechanical properties. The quality index (QI) varies with Si content and state: as-cast (376.1 MPa at 7.5% Si), T5 (373.4 MPa at 6.5% Si), and T6 (432.2 MPa at 8.5% Si).
What is the impact of T6 treatment on thermal and electrical conductivities?
T6 treatment significantly improves both thermal and electrical conductivities by spheroidizing eutectic silicon and precipitating Mg and Si solutes, which reduces electron scattering.
How does Si content affect thermal and electrical conductivities?
Both thermal and electrical conductivities decrease slightly with increasing Si content, showing a strong correlation with Si content in the alloy.
What is the significance of this study for new energy vehicles?
The study provides guidance for optimizing Si content and heat treatment to achieve high strength and good thermal conductivity in die-cast aluminum alloys, which are essential for lightweight components in new energy vehicles.
Related Technical Papers & Translations
Pull-out capacity and energy absorption of cable bolts under impact loading
This study investigates the performance of high-strength cable bolts under impact loading conditions representative of rock bursts in underground environments. Although widely used, the dynamic behaviour of these cable bolts has received limited experimental attention, and their effectiveness in seismically active zones remains a subject of ongoing debate. To address this gap, a reverse pull-out test machine integrated with a drop hammer rig was employed. Tests were conducted on 70-t SUMO bulbed and non-bulbed cable bolts with encapsulation lengths of 300 and 450 mm, subjected to an impact energy of 14.52 kJ. Results indicate that non-bulbed cables, despite showing lower initial peak loads (average 218 vs. 328 kN for bulbed cables at 300 mm encapsulation), demonstrated superior energy absorption (average 11.26 vs. 8.75 kJ) and displacement capacity (average 48.40 vs. 36.25 mm). Increasing the encapsulation length for bulbed cables led to a reduction in initial peak load but improved displacement and energy absorption. The dominant failure mechanism was debonding at the cable-grout interface, characterised by frictional sliding and cable rotation. These findings provide new insights into the energy dissipation mechanisms of cables and support the development of more resilient ground support systems for dynamically active conditions.
Effect of eutectic content on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys
The 7xxx series aluminum alloys have emerged as a particularly promising class of lightweight structural materials. However, the inherent strength of these materials is primarily influenced by the content and type of alloying elements added during the manufacturing process, as well as casting defects. The present study investigated the effects of eutectics formed by solute atoms (Zn, Mg, and Cu), with equal mass ratios (Zn/Mg=2, Mg/Cu=3) but varying overall contents, on the liquid film thickness, crack propagation depth, and the mechanical properties of the Al-Zn-Mg-Cu alloy after heat treatment. The results from gravity casting indicate that the intergranular liquid film thickness increases with the increase of eutectic content. A thick intergranular liquid film in the casting can accommodate greater strain during grain contraction, thereby preventing liquid film rupture and subsequent hot tearing. Concurrently, during the solution treatment at 475 °C, the residual eutectic fraction in the Al-7Zn-3.5Mg-1.18Cu alloy diminishes from 9.1% at 10 h to 0.35% at 40 h. At 165 °C, the Al-6Zn-3.0Mg-1.0Cu alloy exhibits the optimal mechanical properties, with a peak aging tensile strength of 510 MPa and an elongation of 6.4%. The incorporation of lower concentrations of solute atoms (Zn, Mg, and Cu) serves to reduce the barrier to dislocation precipitation, thereby enhancing alloy plasticity. However, when the proportion of alloying elements exceeds the solubility limit of the α-Al matrix at specific heat treatment temperatures, coarse residual phases remain intergranular, thereby significantly impairing the mechanical properties of the alloy. This study provides a reference for the optimal addition level of the main strengthening elements in Al‑Zn‑Mg‑Cu alloys.
Achieving optimal strength-conductivity balance in cast Al-2.3Fe-Mg-Si alloys via Mg/Si ratio regulation
The Al-2.3Fe eutectic alloy is regarded as a promising substitute for Cu conductors in automotive motors owing to its excellent castability and low resistivity. However, its application is restricted by the mutually exclusive relationship between electrical conductivity and mechanical strength. The microstructure and mechanical properties of Al-2.3Fe alloy were modified through Mg/Si alloying combined with T6 heat treatment in this work, leading to the development of a high-performance cast Al-2.3Fe-Mg-Si alloy. In the Al-2.3Fe-0.40Mg-0.72Si (Mg/Si=0.56) alloy subjected to T6 treatment, an electrical conductivity of (52.5±0.6)% IACS is achieved, while the ultimate tensile strength is significantly enhanced to 309.5±5.6 MPa. The addition of Mg and Si brings about marked changes in the solidification process of the Al-2.3Fe alloy, resulting in considerable variations in both the morphology of the second phase and its phase constitution. The aging behavior of the alloy is governed by second phase and solid solubility. Through optimization of the Mg/Si ratio, the aging response can be effectively enhanced. At the ratio of Mg/Si=0.56, a balance is achieved between solid solubility and precipitation, while simultaneously minimizing the detrimental impact on electrical conductivity and reaching the best mechanical properties and electrical conductivity in peak-aged Al-2.3Fe-xMg-ySi alloy. This work providing valuable insights for developing advanced conductor materials.