選擇性雷射燒熔之AlSi10Mg錳酸根化成處理之研究

Abstract

積層製造製程，如選擇性雷射燒熔或熔融沉積成形，能夠製造具有前所未有的超高自由度的任意三維結構，被稱為新工業革命的技術，為科學和工業領域開拓了一系列潛在的應用，許多行業也正在使用積層製造技術來製造複雜結構，以實現輕量化、增加功能性和減少零件數量等目標，也能在降低成本和設計到製造時間方面滿足需求。鋁合金是選擇性雷射燒熔研究中受到關注的主要材料之一，其所能應用的環境和適用的表面處理也是需要多加研究的。 本研究主要在探討選擇性雷射燒熔之AlSi10Mg經腐蝕測試後，是否化成處理會對材料的微結構或是電化學分析有實質上的腐蝕行為差異，利用如SEM影像分析、橫截面TEM觀察以及動電位極化曲線等來研究並討論。在SEM影像中發現選擇性雷射燒熔之AlSi10Mg有相當獨特和尺寸極細的胞狀結構，並且看到為數不少的含鐵二次相，在6小時的氯化鈉溶液腐蝕測試中，發現此類含鐵二次相會和鋁基地引發伽凡尼效應，產生局部陰陽極，導致伽凡尼腐蝕的發生，鋁基地作為局部陽極受到嚴重腐蝕攻擊，大量鋁基地溶解，此一現象可能讓AlSi10Mg的結構產生裂紋，若裂紋持續擴大或增長，可能對AlSi10Mg材料的性能有不少的影響。 本實驗用0.1 M之過錳酸鉀來進行化成處理，希望能改善AlSi10Mg的抗腐蝕能力，結果顯示經過化成後，在原先含鐵的二次相上會生成膜層，且再經相同時間的腐蝕測試後，含鐵的二次相周圍的鋁基地溶解情形減緩許多，代表此處的伽凡尼腐蝕被抑制，而在動電位極化曲線中也可發現化成處理20分鐘後的AlSi10Mg有很好的陽極抑制能力，抗蝕性獲得良好的提升。然而，錳酸根化成在AlSi10Mg材料表面上的成膜機制還是需更進一步的實驗才有可能得知。

Additive Manufacturing(AM) processes‚ such as selective laser melting (SLM) or fused deposition modeling(FDM)‚ enable the fabrication of complex 3D structures with unprecedented levels of freedom. This technology, known as the new industrial revolution, has opened up a wide range of potential applications in scientific and industrial sectors. Many industries are utilizing additive manufacturing techniques to create intricate structures, aiming to achieve objectives such as lightweighting, increased functionality, and part consolidation. Additive manufacturing also holds promise in reducing costs and design-to-manufacture time. Aluminum alloys are among the main materials of interest in SLM research, and further research is needed to explore their applicability in different environments and suitable surface treatments. This research focuses on investigating the effect of conversion coating on AlSi10Mg‚a commonly used selective laser melting in aluminum alloy.The study aims to determine if the conversion treatment induces significant differences in material microstructure or electrochemical behavior. Various techniques such as scanning electron microscopy (SEM) image analysis, cross-sectional transmission electron microscopy (TEM) observation, and potentiodynamic polarization curves are employed for research and discussion. SEM analysis reveals a unique and fine cellular structure in AlSi10Mg fabricated through selective laser melting, along with the presence of the iron-containing second phases. During a 6-hour corrosion test in sodium chloride solution, it is observed that the iron-containing second phases initiate galvanic corrosion with the aluminum matrix, leading to the formation of localized anodic and cathodic regions. As a result, severe corrosion attack occurs on the aluminum matrix, leading to significant dissolution. This phenomenon can potentially induce cracking in the AlSi10Mg structure, which could have a detrimental effect on its mechanical properties. To improve the corrosion resistance of AlSi10Mg, a conversion coating using a 0.1 M potassium permanganate solution is applied. The results demonstrate that after the conversion coating, a protective film forms on the pre-existing iron-containing second phases. Additionally, after an equivalent corrosion test duration, the dissolution of the aluminum matrix surrounding the iron-containing second phase is significantly reduced, indicating the suppression of galvanic corrosion. The potentiodynamic polarization curves also show that the AlSi10Mg treated for 20 minutes with the conversion coating exhibits excellent anodic inhibition capability, resulting in improved corrosion resistance. However, further experiments are required to elucidate the film formation mechanism of potassium permanganate conversion coating on the surface of AlSi10Mg. Overall, this study aims to contribute to the comprehensive understanding of the corrosion behavior and microstructural characteristics of AlSi10Mg fabricated through selective laser melting and investigate the potential of conversion treatments to enhance its corrosion resistance. However, further experiments are necessary to understand the film formation mechanism of permanganate conversion coating on the surface of AlSi10Mg.