AZ31 Magnezyum Alaşımlarında Nadir Toprak Elementleri Etkisi: Mikro Yapı, Korozyon ve Birleştirme Analizi

Abstract

Magnezyum alaşımları, hafif mühendislik uygulamaları için her geçen gün daha fazla önceliklendirilmektedir; ancak bu alaşımların endüstriyel kullanım alanları genellikle mikroyapısal kararlılık ve korozyon hassasiyeti gibi faktörlerle sınırlanmaktadır. Bu çalışmada, neodimyum (Nd) ve lantan (La) gibi farklı konsantrasyonlardaki nadir toprak elementleri ile modifiye edilmiş AZ31 magnezyum alaşımlarının mikroyapısal özellikleri, korozyon davranışları ve birleştirilebilirliği kapsamlı bir şekilde incelenmiştir. AZ31-0.5Nd-0.2La ve AZ31-0.5Nd-0.5La olmak üzere iki spesifik bileşim, indüksiyon ergitme yöntemiyle sentezlenmiş ve ardından 1,5 mm kalınlığında levhalar elde etmek amacıyla sıcak haddeleme işlemine tabi tutulmuştur. Hazırlanan alaşımların yapısal entegrasyon potansiyellerini değerlendirmek üzere, bu levhalar mekanik kenetleme (clinching) yöntemi kullanılarak ara yer atomu içermeyen (IF) çelik ile başarıyla birleştirilmiştir. Detaylı mikroyapısal karakterizasyon işlemleri, taramalı elektron mikroskobu (SEM) ve enerji dağılımlı X-ışını spektroskopisi (EDX) kullanılarak gerçekleştirilmiştir. Analizler; temel olarak Al-Mn-Nd ve Al-La-Nd bakımından zenginleşmiş ikincil intermetalik fazların, her iki alaşım varyantında da ağırlıklı olarak tane sınırları boyunca dağıldığını ortaya koymuştur. Deney tutarlılığını sağlamak amacıyla, %3,5 NaCl çözeltisi içerisinde üç farklı kesit (S1, S2 ve S3) üzerinde potansiyodinamik polarizasyon testleri yürütülmüştür. Kantitatif veriler, AZ31-0.5Nd-0.5La alaşımının, belirgin şekilde daha düşük icorr ve mpy değerleri ile kanıtlandığı üzere, AZ31-0.5Nd-0.2La alaşımına kıyasla üstün korozyon direnci sergilediğini göstermiştir. Uzun süreli daldırma korozyon testleri de bu bulguları doğrulamış; metal kaybının süreyle birlikte genel olarak artmasına karşın, AZ31-0.5Nd-0.5La alaşımının 16 saat sonunda en düşük metal kaybına (0,79 g) ulaştığı gözlemlenmiştir. Sonuç olarak elde edilen veriler, artan lantan içeriğinin AZ31 magnezyum alaşımlarının mikroyapısal kararlılığını ve korozyon direncini iyileştirmede oldukça etkili olduğunu kanıtlamaktadır.

Keywords

• AZ31 magnesium alloy
• Rare earth elements
• Corrosion behavior
• Potentiodynamic test
• Immersion test
• SEM analysis.

Influence of Rare Earth Element Additions on the Microstructure, Corrosion Resistance, and Joinability of AZ31 Magnesium Alloys

Abstract

Magnesium alloys are increasingly prioritized for lightweight engineering applications; however, their industrial utility is often limited by microstructural stability and corrosion susceptibility. In the present study, the microstructure, corrosion behavior, and joinability of AZ31 magnesium alloys modified by varying concentrations of rare earth elements, specifically neodymium (Nd) and lanthanum (La), were comprehensively investigated. Two specific compositions, AZ31-0.5Nd-0.2La and AZ31-0.5Nd-0.5La, were synthesized via induction melting and subsequently processed through hot rolling to produce sheets with a precise thickness of 1.5 mm. To evaluate their structural integration potential, these processed alloys were successfully joined with interstitial-free (IF) steel through a mechanical clinching process. Detailed microstructural characterization was performed utilizing scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The analysis revealed that secondary intermetallic phases, primarily enriched with Al-Mn-Nd and Al-La-Nd, were predominantly distributed along the grain boundaries in both alloy variants. Potentiodynamic polarization tests were executed in a 3.5% NaCl solution across three distinct cross-sections (S1, S2, and S3) to ensure experimental consistency. Quantitative data indicated that the AZ31-0.5Nd-0.5La alloy exhibited superior corrosion resistance compared to the AZ31-0.5Nd-0.2La alloy, as evidenced by significantly lower icorr and mpy values. Long-term immersion corrosion tests further confirmed these findings, showing that while metal loss generally increased with duration, the AZ31-0.5Nd-0.5La alloy achieved the lowest metal loss (0.79 g) after 16 hours. Ultimately, the results demonstrate that an increased lanthanum content is highly favorable for enhancing the microstructural stability and corrosion resistance of AZ31 magnesium alloys.

Keywords

• AZ31 magnesium alloy
• Rare earth elements
• Corrosion behavior
• Potentiodynamic test
• Immersion test
• SEM analysis.

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