Role of Aluminum in Magnesium Alloys: Effects on Strength , Corrosion Resistance , and Microstructure

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Role of Aluminum in Magnesium Alloys: Effects on Strength , Corrosion Resistance , and Microstructure

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Role of Aluminum in Magnesium Alloys: Effects on Strength , Corrosion Resistance , and Microstructure

Role of Aluminum in Magnesium Alloys: Effects on Strength, Corrosion Resistance, and Microstructure

Understanding Aluminum Content Limits and Future Directions of Magnesium Aluminum Alloys

Aluminum Alloys

I. Introduction: Why Aluminum Is Critical in Magnesium Alloys
Magnesium alloys are among the most promising lightweight structural materials, with a density approximately two-thirds that of aluminum and only one-quarter that of steel. Thanks to their excellent specific strength, thermal conductivity, vibration damping capacity, and electromagnetic shielding performance, magnesium alloys are widely studied and increasingly adopted in

automotive, robotics, aerospace, and electronic applications.
However, the industrial application of magnesium alloys has long been limited by several inherent weaknesses, including low room-temperature strength, poor corrosion resistance, and rapid softening at elevated temperatures. Among all alloying elements, aluminum plays the most critical role in addressing these limitations. In commercial magnesium aluminum alloys, especially AZ series magnesium alloys, aluminum significantly enhances mechanical strength, corrosion resistance, and castability, making large-scale

industrial production feasible.
This article systematically reviews the role of aluminum in magnesium

alloys, focusing on strengthening mechanisms, corrosion behavior, aluminum content limits, and future development directions for high-performance

magnesium alloy materials.

II. Effect of Aluminum on Magnesium Alloy Microstructure and Strengthening Mechanisms
1. Solid Solution Strengthening in Magnesium Alloys
Aluminum atoms dissolve into the α-Mg matrix to form a solid solution. Due to the atomic size mismatch between Al and Mg, lattice distortion is introduced, which effectively hinders dislocation motion. This solid solution strengthening mechanism can increase the room-temperature yield strength of magnesium alloys by approximately 40–60 MPa, forming the foundation of strength improvement in AZ series alloys.

2. Precipitation Strengthening by Mg17Al12 Phase
During aging treatment at 180–250°C, a supersaturated Mg–Al solid solution precipitates the Mg17Al12 (β phase). These precipitates interact with dislocations through cutting or bypassing mechanisms, providing significant precipitation strengthening. Proper aging treatment can further increase yield strength by 70– 100 MPa, making precipitation control a key strategy for high-strength magnesium alloys.
3. Corrosion Resistance Improvement by Aluminum Addition
In magnesium aluminum alloys, the β-Mg17Al12 phase has a higher electrochemical potential than the α-Mg matrix. When distributed continuously along grain boundaries, the β phase can effectively reduce the active corrosion area of magnesium, lowering the overall corrosion rate by one to two orders of magnitude. This mechanism is particularly important for corrosion-resistant magnesium alloys used in humid or salt-containing environments.
4. Improved Castability and Fluidity of Magnesium Alloys
Aluminum significantly improves the casting performance of magnesium alloys by reducing melt surface tension and narrowing the solidification temperature range. Alloys such as AZ91D, one of the most widely used die casting magnesium alloys, can be produced with thin-wall sections as fine as 0.8 mm, making them ideal for complex structural components.

III. Aluminum Content in Casting vs. Wrought Magnesium Alloys
Cast Magnesium Alloys (AZ91D, AM60B)
Cast magnesium alloys typically contain 7–9 wt.% aluminum, resulting in a β phase volume fraction of approximately 12–15%. These alloys offer an excellent balance of strength, corrosion resistance, and castability. However, due to β- phase coarsening, mechanical strength decreases rapidly above 120°C, limiting their high-temperature service capability.
Traditional Wrought Magnesium Alloys (AZ31, AZ61)
Wrought magnesium alloys generally contain 3–5 wt.% aluminum, leading to reduced β phase formation and improved ductility. Alloys such as AZ31 and AZ61 magnesium alloy sheets and plates exhibit good formability and stable processing behavior during rolling and extrusion, with typical yield strengths of 180–220 MPa.
High-Strength Wrought Magnesium Alloys (AZ80 and Modified Systems)

New-generation high-strength wrought magnesium alloys with 8–9 wt.% aluminum, such as AZ80, can achieve refined microstructures through advanced processing techniques like severe plastic deformation or heavy rolling. These alloys can reach room-temperature yield strengths close to 300 MPa, although post-processing heat treatment is often required to mitigate surface defects.

IV. Challenges of High Aluminum Content in Magnesium Alloys

Despite its benefits, excessive aluminum introduces several critical challenges:

Stress Corrosion Cracking (SCC)

At aluminum contents above 7 wt.%, the β/α interface may act as a hydrogen trap, significantly reducing the stress corrosion cracking threshold. This limits the application of high-aluminum magnesium alloys in load-bearing environments. High-Temperature Softening
The Mg17Al12 phase has a relatively low melting temperature (~460°C). At service temperatures above 150°C, precipitate coarsening leads to rapid strength degradation, restricting high-temperature applications.
Texture Formation and Surface Defects
High aluminum content can intensify basal texture during extrusion, causing uneven current density distribution during surface treatments such as plasma electrolytic oxidation (PEO), which may result in surface appearance defects.

V. Strategies to Optimize Aluminum-Bearing Magnesium Alloys 1. Microalloying Approaches

Rare Earth Elements (Ce, La, 0.3–0.5%) refine β-phase morphology and improve SCC resistance.
Tin (Sn, 0.5–1.0%) forms thermally stable Mg2Sn particles, increasing high- temperature strength by up to 30%.
Calcium (Ca, 0.2–0.4%) promotes β-phase spheroidization and forms Al2Ca, extending service temperature limits to 180°C.

2. Advanced Microstructure Engineering

Rapid solidification techniques, spray forming, and powder metallurgy can significantly refine grain size and β-phase distribution. Such approaches enable magnesium alloys with ultra-high strength (>400 MPa) while maintaining acceptable corrosion performance.

3. Surface Treatment and Heat Treatment Synergy
Optimized T4/T6 heat treatment, combined with PEO and secondary coatings, can significantly enhance corrosion resistance. Salt spray resistance exceeding 1000 hours has been achieved in high-aluminum magnesium alloys with engineered surface systems.

VI. Future Directions for Magnesium Aluminum Alloys
Ultra-High Aluminum Magnesium Alloys with RE/Ca Synergy
Advanced alloys such as Mg–Al–RE–Ca systems leverage synergistic strengthening from LPSO phases and Al2Ca compounds, targeting room- temperature strengths above 450 MPa with improved creep resistance. Aluminum-Gradient Magnesium Alloys

Emerging additive manufacturing technologies enable aluminum content gradients, combining corrosion-resistant surfaces with ductile cores, offering a novel solution to traditional performance trade-offs.
Biomedical Magnesium Alloys

For biodegradable medical applications, aluminum content is controlled at 2–3 wt.%, combined with Zn or Sr additions to ensure mechanical integrity while minimizing biological risk.

VII. Conclusion
Aluminum plays a decisive role in determining the mechanical properties, corrosion resistance, and processing behavior of magnesium alloys. While the Mg17Al12 phase enables significant performance enhancement, excessive aluminum content introduces challenges such as high-temperature softening and stress corrosion cracking.

Through controlled aluminum composition, microalloying strategies, advanced processing, and surface engineering, magnesium aluminum alloys continue to evolve toward higher strength, improved durability, and broader industrial applicability. These developments position magnesium alloys as key materials for the future of lightweight engineering solutions.

As a magnesium alloy material supplier, Hilbo continuously focus on aluminum-controlled alloy design, magnesium alloy sheet and plate production, and surface protection technologies to support demanding applications in automotive, robotics, and industrial sectors. Through optimized alloy composition

and process control, high-performance magnesium alloys are becoming increasingly viable for next-generation lightweight structures.

For technical inquiries: scm@hilbo-mg.com

Pub Time : 2025-12-18 17:55:10 >> News list

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