Engineering Solutions to the Four Major Bottlenecks of Magnesium Alloys

Magnesium alloys, recognized for their low density and high specific strength, hold significant potential as next-generation lightweight structural materials. However, their applications are constrained by four intrinsic bottlenecks: poor deformability, limited room-temperature bendability, insufficient corrosion resistance, and inferior weldability. This paper systematically analyzes these fundamental challenges from the perspectives of crystal structure, thermomechanical behavior, and processing pathways. It further proposes engineering-level strategies integrating alloy design, process optimization, and advanced surface and joining technologies to enable comprehensive performance enhancement of magnesium alloys for structural applications.

1. Solutions to the Deformation Limitation

The hexagonal close-packed (HCP) crystal structure of magnesium affords only a limited number of independent slip systems at ambient temperature, leading to intrinsic difficulties in plastic deformation and forming. Engineering strategies to address this fundamental limitation may be categorized into three main approaches.

1.1 Alloying and Microalloying

Adding rare earth (RE) elements—such as Ce, Y, Nd, and Gd—significantly improves the deformability of magnesium alloys. For instance, introducing cerium into AZ91 alloy refines the β-Mg₁₇Al₁₂ phase and promotes the formation of fine, dispersed Al₁₁RE₃ intermetallic compounds. These improve the cooperative deformation of the α-Mg matrix and weaken basal texture development, thereby enhancing isotropic plasticity (Li et al., 2008, Effect of Neodymium on Microstructure and Corrosion Resistance of AZ91 Magnesium Alloy).

1.2 Severe Plastic Deformation (SPD) Processing

SPD techniques develop ultrafine-grained or nanocrystalline structures that simultaneously strengthen and toughen magnesium alloys at low temperatures. Key SPD methods include:

• Equal Channel Angular Extrusion (ECAE) – imparts intense shear strain without changing cross-section, producing ultrafine equiaxed grains. For example, AZ31 alloy processed at 225 °C through three ECAE passes attains a uniform ultrafine structure (Zhang et al., 2016, Grain Refinement of Magnesium Alloys Processed by Severe Plastic Deformation).

• High-Pressure Torsion (HPT) – introduces enormous shear strain under compression, yielding nanocrystalline microstructures.

• Accumulative Roll Bonding (ARB) – repeatedly stacks, rolls, and bonds sheets to generate cumulative strain.

These severe deformation methods promote continuous dynamic recrystallization, introducing dense dislocations and refined equiaxed grains, thereby achieving simultaneous enhancement in strength and ductility (Liang et al., 2019, Research achievements of severe plastic deformation on magnesium alloys).

1.3 Optimization of Temperature and Process Parameters

Temperature critically influences the activation of non-basal slip systems in magnesium alloys. Below approximately 498 K, deformation is dominated by basal slip and twinning, while at higher temperatures, prismatic and pyramidal slip systems are activated, promoting overall ductility. Therefore, plastic forming processes such as extrusion, rolling, and forging are typically conducted within 300–450 °C, using controlled strain rates and multi-pass deformation with intermediate annealing to prevent cracking.

2. Improving Room-Temperature Bendability

The limited room-temperature bendability of magnesium sheets—especially for automotive and electronic applications—originates from strong basal texture formed during conventional rolling. Texture weakening and microstructural optimization are thus essential.

2.1 Texture Weakening via Alloying or Shear Deformation

• Rare Earth Alloying: RE addition reduces basal texture intensity by promoting orientation spreading during hot rolling. This approach, requiring no complex process modification, has proven industrially feasible (通过织构弱化来改善镁合金塑性变形能力的工艺).

• Shear Deformation Technique: Imposing pure shear load using customized dies rotates the c-axis of grains by about 45°, decreasing basal orientation strength. After annealing, partial retention of deviated grains enhances formability (一种提高镁合金板带材塑性变形能力的方法).

2.2 Pre-Deformation and Annealing

Applying a small pre-strain (2–10%) followed by controlled annealing promotes localized recrystallization and abnormal grain growth, generating favorable grain orientations and making greater use of twinning during forming. This approach can increase stamping formability by over 50% (改善镁合金板材冲压成形性能的方法).

2.3 High Strain-Rate Forming

• Electromagnetic Forming: Produces strain rates exceeding 103 s−1103 s−1, thereby increasing twinning fraction and disturbing the strong basal texture. It significantly improves room-temperature formability while maintaining energy efficiency (一种提升镁合金室温成形性能的装置).

• Explosive Forming: Uses pressure waves with extreme strain rates to achieve substantial ductility gains in alloys such as AZ91, unattainable by conventional cold forming (Wang et al., 2015, Study of Forming of Magnesium Alloy by Explosive Energy).

3. Enhancing Corrosion Resistance

Magnesium’s standard electrode potential (-2.37 V) makes it highly reactive, particularly in chloride-rich humid environments. The native oxide layer is porous and non-protective. A multi-tier approach combining purification, alloying, and advanced surface treatments is essential.

3.1 Purification and Alloying Strategies

Ultra-high purity is critical since trace Fe, Ni, and Cu impurities form microgalvanic couples that accelerate corrosion. Techniques such as reversed temperature-gradient refining eliminate such impurities. Alloying with Al and Mn stabilizes intermetallic phases and sequesters harmful elements, while RE additions densify the oxide film and enhance self-healing behavior (Sun et al., 2019, Effect of Gd on Microstructure and Corrosion Resistance of Mg-Gd-Y-Sm-Zr Rare Earth Magnesium Alloys).

3.2 Surface Coating Technologies

• Chemical Conversion Coatings: Chromate (being phased out), phosphate, molybdate, and RE-based (e.g., cerium) conversion films provide adhesion-enhancing and corrosion-suppressive base layers.

• Anodic or Micro-Arc Oxidation (MAO): Produces dense ceramic-like oxide layers with high hardness and corrosion resistance. Porosity necessitates subsequent sealing; hybrid oxide techniques are the latest industry trend (镁合金表面处理技术中,哪些方法可以有效提高耐腐蚀性能?).

3.3 Advanced Protective Architectures

• Superhydrophobic Coatings: Created via laser or chemical texturing and low-surface-energy modification to achieve water contact angles >150°, forming an “air cushion” layer that hinders electrolyte penetration (Luo et al., 2013, Superhydrophobic Magnesium Alloy).

• Composite Coatings: Integrate MAO base layers with electrophoretic or polymeric topcoats to combine the barrier and inhibition mechanisms. Smart composite systems incorporating inhibitor-releasing LDH layers and hydrophobic polymers like U-PDMS demonstrate long-term self-healing protection (Zhou et al., 2019, Superhydrophobic composite coating with active corrosion resistance for AZ31B magnesium alloy protection).

• Laser Surface Modification: High-energy laser re-melting forms dense remelted surfaces and hierarchical microstructures that enhance coating adhesion (一种镁合金材料的耐腐蚀性能增强方法.pdf).

4. Improving Weldability

Magnesium’s low melting point, high thermal conductivity, and high reactivity complicate conventional fusion welding, often causing porosity, hot cracking, and distortion. Effective solutions emphasize selecting appropriate welding techniques and controlling process parameters.

4.1 Suitable Welding Methods

• Friction Stir Welding (FSW): A solid-state process avoiding melting-related defects. The plastically deformed and dynamically recrystallized stir zone exhibits fine grains with high strength and minimal residual stress, achieving joint efficiencies above 80% (Kim et al., 2008, Effect of Axial Force on Microstructure and Tensile Properties of Friction Stir Welded AZ61A Magnesium Alloy).

• Laser and Electron Beam Welding: Offering concentrated heat input and high energy density, they are suitable for precise, thin-walled structures. Proper shielding and reflectivity management are critical.

• Gas Tungsten Arc Welding (GTAW): The most common existing method, requiring AC current for oxide removal and fine parameter control to prevent excessive heat or porosity (Huang et al., 2015, Welding Technology and Microstructure of MIG Welded Magnesium Alloy).

4.2 Parameter Optimization and Auxiliary Techniques

Accurate control of heat input is crucial—too high causes coarse grains and cracking, while too low leads to incomplete penetration. For instance, optimal heat input for a 3 mm AZ31B plate is approximately 369 J/mm (Xu et al., 2016, Effect of Welding Speed on Microstructural Characteristics and Tensile Properties of Gta Welded Az31b Magnesium Alloy). Pre-treatments such as friction stir processing refine grains and mitigate hot cracking (一种改善镁合金局部焊接性的方法).

Applying magnetic fields during welding promotes electromagnetic stirring, refines dendritic structures, and enhances gas escape, improving joint performance (典型难焊接材料焊接技术_七...).

4.3 Hybrid Heat Source Welding

Laser-arc hybrid welding synergistically combines deep-penetrating laser energy with the wide molten pool of arc welding, achieving tripled penetration depth, faster speeds, and fewer defects—an increasingly important approach in high-efficiency magnesium joining (让航空制造更绿色...).

Breaking through the four intrinsic bottlenecks of magnesium alloys is increasingly feasible through integrated material–process innovation. For deformation and bendability, refining grain size and controlling texture via alloy design and SPD or high-strain-rate forming offer key progress. For corrosion and weldability, advances in surface engineering and solid-state or hybrid joining technologies are indispensable.

Future directions emphasize cost-efficiency, environmental sustainability, and system integration—for instance, developing continuous rolling systems that integrate texture control and forming, or designing intelligent self-sensing, self-healing coatings. As these enabling technologies mature, magnesium alloys will fully realize their potential as the cornerstone of lightweight engineering materials.

References 

Kim, H. J., Park, S. H., Kim, W. S., & Kang, S. B. (2008). Effect of Axial Force on Microstructure and Tensile Properties of Friction Stir Welded AZ61A Magnesium Alloy. https://www.aminer.cn/pub/53e9a1f3b7602d9702af80ba

Li, W., et al. (2008). Effect of Neodymium on Microstructure and Corrosion Resistance of AZ91 Magnesium Alloy. https://www.aminer.cn/pub/53e9aeddb7602d970390a7ea

Liang, Z., et al. (2019). Research achievements of severe plastic deformation on magnesium alloys. https://www.aminer.cn/pub/5c755cc7f56def9798a189d3

Zhang, R., et al. (2016). Grain Refinement of Magnesium Alloys Processed by Severe Plastic Deformation. https://www.aminer.cn/pub/56d9165edabfae2eee5c2b5c

Sun, P., et al. (2019). Effect of Gd on Microstructure and Corrosion Resistance of Mg-Gd-Y-Sm-Zr Rare Earth Magnesium Alloys. https://www.aminer.cn/pub/5c7fd0c24895d9cbc668a3da

Luo, Y., et al. (2013). Superhydrophobic Magnesium Alloy. https://www.aminer.cn/pub/53e9b873b7602d970443e87c

Zhou, D., et al. (2019). Superhydrophobic composite coating with active corrosion resistance for AZ31B magnesium alloy protection. https://www.aminer.cn/pub/5c757d8cf56def9798af4eb6

Wang, T., et al. (2015). Study of Forming of Magnesium Alloy by Explosive Energy. https://www.aminer.cn/pub/56d89cb1dabfae2eee44098a

Huang, Q., et al. (2015). Welding Technology and Microstructure of MIG Welded Magnesium Alloy. https://www.aminer.cn/pub/53e99d3db7602d97025f1b48

Xu, L., et al. (2016). Effect of Welding Speed on Microstructural Characteristics and Tensile Properties of GTA Welded AZ31B Magnesium Alloy. https://www.aminer.cn/pub/56d9165ddabfae2eee5c2197