Key Takeaways & Executive Findings
- •• T6-200°C/1h aging produces dense G.P. zones, yielding one order of magnitude lower steady-state creep rate than T6-275°C/8h with Al2Ca phases. • The high stress exponent (~8.2) in T6-200°C/1h indicates power-law breakdown, with creep controlled by cross-slip between basal and prismatic dislocations. • T6-275°C/8h exhibits mixed creep mechanism of dislocation cross-slip and climb, less effective in impeding dislocation motion. • Dense G.P. zones are more effective than Al2Ca phases in blocking dislocation climb and glide, enhancing creep resistance.
Abstract
The effects of artificial aging (T6) on the creep resistance with tensile stresses in the range of 50−80 MPa at 175 °C were investigated for an extruded Mg−1.22Al−0.31Ca−0.44Mn (wt.%) alloy. The Guinier-Preston (G.P.) zones primarily precipitate in the sample aged at 200 °C for 1 h (T6-200°C/1h), while the Al2Ca phases mainly precipitate in the sample aged at 275 °C for 8 h (T6-275°C/8h). The T6-200°C/1h sample exhibits excellent creep resistance, with a steady-state creep rate one order of magnitude lower than that of the T6-275°C/8h sample. The abnormally high stress exponent (~8.2) observed in the T6-200°C/1h sample is associated with the power-law breakdown mechanism. TEM analysis illuminates that the creep mechanism for the T6-200°C/1h sample is cross-slip between basal and prismatic dislocations, while the T6-275°C/8h sample exhibits a mixed mechanism of dislocation cross-slip and climb. Compared with the Al2Ca phase, the dense G.P. zones effectively impede dislocation climb and glide during the creep process, demonstrating superior creep resistance of the T6-200°C/1h sample.
1. Introduction
The magnesium (Mg) alloys have gained considerable interest in response to the increasing need for lightweight materials in the transportation and aerospace industries. This is primarily because of their favorable specific strength and low density [1−3]. However, poor creep performance limits their high-temperature applications [4,5]. In recent years, research has focused mainly on enhancing the creep resistance of Mg-based alloys by adding rare-earth (RE) elements [6−8]. Many Mg−RE alloys with excellent creep performance have been developed, most of which involve Mg−Gd and Mg−Y based alloys. However, the addition of RE elements increases the cost of alloys, making them unsuitable for widespread commercial applications. Therefore, the development of low-cost, heat-resistant Mg alloys is crucial. Among non-RE Mg alloys, the Mg−Al−Ca−Mn alloy system has gained widespread attention owing to its excellent creep resistance and cost-effectiveness [9−11].
Creep is a critical consideration in engineering applications in which components are subjected to prolonged mechanical stress at elevated temperatures. The principal creep mechanisms include atomic diffusion, dislocation glide, and climbing [12−15]. The evolution of the microstructure in Mg−Al−Ca−Mn alloys during the creep, specifically the alterations in the precipitate morphology, distribution, and phase composition, significantly impacts their mechanical properties and resistance to creep. The addition of Ca can result in the formation of thermally stable intermetallic compounds, specifically, Mg2Ca (C14) and Al2Ca (C15) [16]. ZHU et al [17] studied squeeze-cast Mg−Al−Ca alloys and reported that the (Mg,Al)2Ca phases improve creep resistance. SUZUKI et al [18] reported that the Al2Ca phase in a die-cast Mg−Al−Ca alloy poses a significant obstacle to non-basal dislocation slip. Moreover, artificial aging treatments exert a notable influence on the microstructural features of these alloys, consequently affecting their creep behavior. Single-layer ordered Guinier-Preston (G.P.) zones were observed in aged Mg−0.5Al−0.3Ca (wt.%) alloy [19] and Mg−3.6Al−3.4Ca−0.3Mn (wt.%) alloy [20]. HOMMA et al [21] demonstrated that the addition of Mn significantly enhances the creep resistance of Mg−6Al−3Ca (wt.%) alloys, and both the Al2Ca phases and sp
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Ming-yu LI, Zhi-ping GUAN, Jia-wang SONG, Hong-jie JIA, Pin-kui MA, Gang WANG, Wei YAN, Ming-hui WANG, Zhi-gang LI (2025). Effect of different artificial aging treatments on tensile creep behavior of extruded lean Mg−Al−Ca−Mn alloy. SinoTechIntel Verified Research. https://doi.org/10.1016/S1003-6326(25)66952-4
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Frequently Asked Questions
What is the effect of artificial aging on the creep behavior of Mg-Al-Ca-Mn alloy?
The study found that aging at 200°C for 1 hour (T6-200°C/1h) produces dense G.P. zones, which significantly improve creep resistance compared to aging at 275°C for 8 hours (T6-275°C/8h) that forms Al2Ca phases. The T6-200°C/1h sample exhibits a steady-state creep rate one order of magnitude lower than the T6-275°C/8h sample.
What are the dominant creep mechanisms in the differently aged samples?
For the T6-200°C/1h sample, the creep mechanism is cross-slip between basal and prismatic dislocations, associated with power-law breakdown. For the T6-275°C/8h sample, a mixed mechanism of dislocation cross-slip and climb is observed.
Why does the T6-200°C/1h sample show better creep resistance than the T6-275°C/8h sample?
The dense G.P. zones in the T6-200°C/1h sample effectively impede dislocation climb and glide during creep, whereas the Al2Ca phases in the T6-275°C/8h sample are less effective in blocking dislocation motion, leading to inferior creep resistance.
What is the significance of the high stress exponent (~8.2) in the T6-200°C/1h sample?
The high stress exponent indicates power-law breakdown, which is associated with the cross-slip mechanism. This suggests that the creep deformation is controlled by dislocation cross-slip rather than climb, contributing to the enhanced creep resistance.
What are the potential applications of this research?
This research provides insights into developing low-cost, heat-resistant Mg alloys for automotive and aerospace applications, where lightweight materials with good high-temperature creep resistance are required.
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