Key Takeaways & Executive Findings
- •• Er addition promotes grain refinement during solidification by increasing nucleation rate and forming Al3Er secondary phase. • A dense MgO/Er2O3 composite oxide layer is formed, suppressing loose magnesium hydroxide/basic magnesium carbonate. • Mn interacts with Fe impurities to form AlFeMn phase, reducing micro-galvanic corrosion driving force. • The corrosion rate of AZ31Mn-1.2Er in 3.5% NaCl solution decreased from 10.46 mm/a to 0.44 mm/a, approaching the 0.2–0.5 mm/a target for bone-repair implants.
Abstract
Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications. The microstructure and corrosion behavior of AZ31Mn-xEr (x=0.1, 0.5, 1.2) alloys were systematically investigated using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), combined with Tafel polarization and electrochemical impedance spectroscopy (EIS) analyses. The findings showed that the alloying element Er refined the grain structure during solidification by increasing the nucleation rate and forming a secondary phase of Al3Er with Al. The Er and Mg in the matrix co-oxidize to form a dense MgO/Er2O3 composite oxide, preventing the formation of loose magnesium hydroxide/basic magnesium carbonate. The trace alloying element Mn interacts with impurities Fe in the magnesium matrix to form an AlFeMn second phase, reducing micro-galvanic corrosion driving force. Electrochemical testing in a 3.5% NaCl solution demonstrated a marked reduction in corrosion rate from 10.46 mm/a (AZ31Mn alloy) to 0.44 mm/a (AZ31Mn-1.2Er alloy). This research offers a reference for searching for corrosion-resistant magnesium alloy and degradable medical magnesium alloy materials.
1. Introduction
Magnesium is widely recognized as a metal of abundant reserves, and magnesium alloys are characterized by their high specific stiffness, specific strength, excellent machinability, outstanding casting performance, efficient thermal conductivity, and superior recyclability. These properties establish magnesium alloys as environmentally friendly and high-performance lightweight structural materials, leading to extensive utilization in aerospace, transportation, and electronics industries [1−4].
As an essential element in the human body, magnesium is the fourth most abundant metallic ion after potassium, sodium, and calcium. Approximately two-thirds of the total body magnesium is deposited in skeletal tissues, while the remaining one-third is distributed within cellular compartments. Magnesium ions enhance bone mineralization and play a critical role in the maintenance of bone density, contributing to the excellent biocompatibility of magnesium-based materials in biological systems [5,6].
Through advanced processing and strategic alloying, the mechanical properties of magnesium alloys can be tailored to match human bone tissue, minimizing stress-shielding effects associated with conventional metallic implants [7]. Their inherent biodegradability eliminates the need for secondary implant-removal surgeries [8]. Furthermore, magnesium alloys possess beneficial biological properties, including anti-inflammatory effects, antibacterial activity, and osteoinductive capabilities [9−12]. For bone repair applications, the optimal corrosion rate for implant materials is established at 0.2–0.5 mm/a [13]. Therefore, controlling and reducing the corrosion rate of magnesium alloys is a critical step toward their clinical application.
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Ma Wei, Ma Zheng-qing, Chen Bai-hua (2025). Effects of Er on microstructure and corrosion resistance of degradable Mg-Al-Zn-Mn magnesium alloy. Journal of Central South University. https://doi.org/10.1007/s11771-025-6021-4
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Frequently Asked Questions
What alloy was studied in this paper?
The study investigated AZ31Mn-xEr magnesium alloys (x = 0.1, 0.5, and 1.2 wt.%) as degradable biomedical implant materials.
How does erbium improve the corrosion resistance of AZ31Mn magnesium alloy?
Erbium refines the grain structure by increasing nucleation and forming Al3Er phase. It also co-oxidizes with Mg to form a dense MgO/Er2O3 composite oxide, which prevents formation of loose Mg(OH)2 or basic magnesium carbonate.
What was the corrosion rate reduction achieved?
Electrochemical tests in 3.5% NaCl solution showed the corrosion rate decreased from 10.46 mm/a for AZ31Mn to 0.44 mm/a for AZ31Mn-1.2Er alloy, a reduction of approximately 96%.
Why are magnesium alloys used for medical implants?
Magnesium alloys are biocompatible, biodegradable, and have mechanical properties close to human bone. They avoid stress shielding and eliminate the need for second removal surgery, while promoting bone mineralization.
Which experimental methods were used in the study?
The researchers used optical microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Tafel polarization, and electrochemical impedance spectroscopy to characterize microstructure and corrosion behavior.
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