磁控濺鍍CrAlN與AlN/CrAlN薄膜提升ZE53鎂合金抗磨耗及耐腐蝕性質之研究

Abstract

鎂合金因其優異的綜合性能，在各種應用領域中逐漸受到重視，目前廣泛應用於電子穿戴裝置、車用輪圈、輕量化無人載具與國防應用等領域。本實驗所使用的材料為ZE53鎂合金，主要合金元素包括鋅、鋯與稀土元素，能有效提升其機械強度與耐腐蝕性，同時賦予良好的鑄造及加工性能。然而，鎂合金本質上耐磨耗性不足，即使透過合金設計與熱機處理對於耐磨耗性的提升仍然有限。因此本實驗進一步採用磁控濺鍍法於表面沉積具有耐磨耗性質薄膜，期望能有效補足鎂合金原有磨耗性能的不足，同時也兼顧其耐腐蝕性能，以因應更加嚴苛的使用環境，拓展其在工程上的應用。 本實驗主要分為四個部分。首先，針對不同熱軋延程度之ZE53熱軋材(10 mm與2mm)進行顯微結構、機械、磨耗以及腐蝕性質分析，探討再施加一道較高程度之熱塑性變形製程於10 mm熱軋材對於各項性質之影響。由結果來看，再施加一道較高程度的熱塑性變形製程可促進析出物細化與動態再結晶，改善結構均勻性並提升整體性能，但對磨耗性質的改善仍有限。 第二部分透過DC磁控濺鍍在2 mm熱軋材上沉積CrAl/CrAlN薄膜，並改變基板偏壓(-50V、-75V、-100V)，探討其對機械與磨耗性能之影響。結果顯示，-100V條件下薄膜結構更緻密、柱狀晶尺寸更小，具有最佳的機械、磨耗性質以及耐腐蝕性質。然而，因鎂與鉻之間有明顯電位差，導致伽凡尼腐蝕加劇，使得CrAl/CrAlN薄膜沉積在鎂合金基材上之腐蝕性能反而劣於基材。 為解決此問題，第三部分採用DC磁控濺鍍在2 mm熱軋材表面沉積Al/AlN中介層，以阻隔CrAlN與基材直接接觸，降低伽凡尼腐蝕的發生。藉由調整Ar/N2流量比(5/15、10/10、15/5)與功率(100、150、200W)優化鍍膜參數。結果指出，當流量比為10/10、功率150W時，可形成最緻密結構，展現最佳電化學表現。 最後，第四部分於最佳參數之Al/AlN中介層上再濺鍍CrAlN薄膜，並探討不同偏壓對其性質之影響。觀察結果，Al/AlN中介層具良好阻隔效果，能有效抑制腐蝕反應，且與僅有Al/AlN層或無鍍膜基材相比，整體電化學性能大幅提升。機械與磨耗性質則維持與第二部分相近，同樣也是在-100V條件下的CrAlN薄膜有最佳機械與磨耗性質的表現，顯示改變中介層後CrAlN仍具有良好的耐磨耗性質。 綜合以上分析，藉由DC磁控濺鍍沉積Al/AlN/CrAlN多層薄膜於ZE53鎂合金表面，能兼顧其耐磨耗與耐腐蝕性能。在磨耗方面，即使增加磨耗荷重至4N，也不會使薄膜產生剝落；在腐蝕方面，Al/AlN中介層阻隔CrAlN與鎂合金基材的直接接觸，降低伽凡尼腐蝕的發生，進一步提升整體耐腐蝕性質。

Magnesium alloys have drawn increasing interest for industrial applications including wearable electronics, automotive wheels, lightweight unmanned systems, and defense technologies. In this study, ZE53 magnesium alloy, primarily alloyed with zinc, zirconium, and rare-earth elements, was selected for its superior mechanical strength, corrosion resistance, and castability. Nevertheless, magnesium alloys inherently suffer from poor wear resistance, and enhancements via alloy design or heat treatment remain limited. To address this, magnetron sputtering techniques were employed to deposit wear-resistant coatings onto the alloy surface, aiming to simultaneously improve wear and corrosion resistance and thereby extend the alloy’s applicability in service environments. This study comprised four main parts. Firstly, ZE53 magnesium alloy sheets with different hot-rolling reductions (10 mm and 2 mm in thickness) were analyzed in terms of microstructure, mechanical properties, wear resistance, and corrosion behavior. The results showed that applying an additional severe hot-rolling process to the 10 mm sheets promoted precipitate refinement and dynamic recrystallization, which enhanced microstructural uniformity and mechanical performance. However, the improvement in wear resistance remained limited. Secondly, DC magnetron sputtering was employed to deposit a CrAl/CrAlN bilayer coating on 2 mm hot-rolled ZE53 alloy samples under varying substrate biases (-50V, -75V, and -100V), aiming to investigate the effect of bias voltage on mechanical and wear properties. The coating deposited at -100 V exhibited a denser microstructure, finer grain size, and superior mechanical performance. However, a significant electrochemical potential difference between magnesium and chromium induced severe galvanic corrosion, leading to poorer corrosion resistance compared to the uncoated substrate. To mitigate the issue of galvanic corrosion, the third part of this study employed DC magnetron sputtering to deposit an Al/AlN intermediate layer on the 2 mm hot-rolled alloy surface, aiming to prevent direct contact between the CrAlN layer and the magnesium substrate. Sputtering parameters, including Ar/N2 gas flow ratios (5/15, 10/10, and 15/5) and power (100W, 150W, and 200W), were optimized. The optimal conditions were identified as an Ar/N2 ratio of 10/10 and power of 150W, which resulted in the densest coating structure and superior electrochemical performance. In the final part, CrAlN coatings were subsequently deposited on the optimized Al/AlN intermediate layers, and the effect of varying substrate biases was further examined. Results indicated that the Al/AlN intermediate layers provided effective barrier protection, reducing galvanic corrosion. Compared to bare ZE53 alloy and samples coated only with Al/AlN, the Al/AlN/CrAlN coatings exhibited enhanced corrosion resistance. The mechanical and wear properties of these coatings were comparable to those observed in the second part, confirming that changing the intermediate layer did not compromise the wear resistance of the CrAlN coatings. In summary, the DC magnetron sputtering methods to fabricate Al/AlN/CrAlN coatings on ZE53 magnesium alloys successfully improved both wear and corrosion resistance. Even under increased wear loading conditions up to 4 N, no significant coating delamination occurred. Furthermore, the Al/AlN intermediate layers effectively prevented galvanic corrosion by separating the CrAlN coatings from direct contact with the magnesium alloy substrate, thus significantly enhancing overall corrosion resistance.