Effect of Sn addition on the microstructure, mechanical properties, and corrosion behaviour of AZ31 magnesium alloy
Year: 2026
Type: article
Abstract: This study systematically investigates the effect of adding tin (Sn) to AZ31 magnesium alloy on its microstructure, mechanical strength, and corrosion behaviour. Alloys with 0, 2, and 4 wt.% Sn were processed and characterized using microscopy, X-ray diffraction, hardness testing, hot compression (at 300 °C), and electrochemical impedance spectroscopy (EIS). Quantitative analysis revealed that Sn addition significantly refined the grain size from 137.8 µm to 23.7 µm and promoted the formation of Mg 2 Sn precipitates. Calculations determined that the total strength gain in the AZ31–2%Sn alloy was overwhelmingly dominated by grain refinement and solid solution effects. In the AZ31–4%Sn alloy, while grain refinement remained the largest component, the sharp increase in overall strength was substantially augmented by the presence of Mg 2 Sn Orowan precipitates. Constitutive analysis of hot deformation yielded strain rate sensitivity exponents (m) between 0.17 and 0.20, identifying dislocation climb as the governing deformation mechanism, with a minor contribution from grain boundary sliding in the fine-grained 4% Sn alloy. Equivalent circuit modeling of EIS data demonstrated a trade-off in corrosion performance: the 2% Sn alloy achieved the highest charge-transfer resistance (R ct ≈ 1.7 ×10^5 Ω). This improvement is specifically attributed to Sn4+-induced modification of the MgO/Mg(OH) 2 passive film, resulting in a denser and more stable barrier. Conversely, the 4% Sn alloy suffered from accelerated degradation (R ct ≈ 2.05 ×10^4 Ω) because excessive Sn forms coarse Mg 2 Sn intermetallics, which act as cathodic sites and drive micro-galvanic corrosion. These findings highlight that moderate Sn alloying (2 wt.%) optimizes the property balance by enhancing strength without compromising corrosion resistance. • Microstructural Refinement: Tin (Sn) addition significantly refined the grain size of the AZ31 alloy from 137.8 µm to 23.7 µm and promoted the formation of Mg₂Sn precipitates. • Strengthening Mechanisms: The total strength gain in the AZ31–2%Sn alloy was primarily dominated by grain refinement and solid solution effects. In the AZ31–4%Sn alloy, the substantial strength increase was augmented by Mg₂Sn Orowan precipitates, in addition to grain refinement. • Hot Deformation: Constitutive analysis of hot compression at 300 °C showed that dislocation climb is the governing deformation mechanism, characterized by strain rate sensitivity exponents (m) between 0.17 and 0.20. • Optimal Corrosion Performance: The AZ31–2%Sn alloy demonstrated the highest corrosion resistance, with a charge-transfer resistance (R ct ) of approximately 1.7 ×10 5 Ω. This improvement is attributed to Sn 4+ -induced modification, forming a denser and more stable passive film. • Corrosion Trade-off: Increasing Sn to 4 wt.% led to accelerated corrosion degradation (R ct = 1.7 ×10 5 Ω), as excessive Sn formed coarse Mg₂Sn intermetallics that acted as micro-galvanic cathodic sites. • Property Optimization: The findings conclude that moderate Sn alloying (2 wt.%) is optimal for balancing properties, as it enhances mechanical strength without compromising the corrosion resistance.
Institution: Bangladesh University of Engineering and Technology
Language: English
Subfield: Biomaterials
Field: Materials Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,540
Award: G8351061378
OpenAlex ID: W7126108642