本論文以AZ91鎂合金使用鋁酸鹽基電解液在定電流直流雙極脈衝模式下進行電漿電解氧化實驗。本實驗建立了各項電性參數(包含電流密度J(mA/dm2)[(J+=43.48/ J-=-50.72) (mA/dm2)~( J+=54.35/ J-=-61.59) (mA/dm2)]、正負電荷比(Q+/Q-, Charge Ratio, CR)[0.89~2.22 ; 0.35~0.86]以及正負電流比(I+/I-, Current Ratio, IR)[0.89;1.13]與PEO過程中放電行為及伴隨膜層特性之關聯並建立PEO過程中的soft regime(s.r.)現象與氧化物性質的關聯。在固定CR(~0.87)下調整電流密度大小[(J+=43.48/ J-=-50.72) (mA/dm2)~( J+=54.35/ J-=-61.59) (mA/dm2)]; 固定IR=0.89下藉由調整陽極工作時間[TON+= 200~500(μs)]並固定陰極工作時間[TON-= 200(μs)]來改變CR[0.89~2.22]; 固定IR=1.13下藉由調整陽極工作時間[TON+= 200~500(μs)]並固定陰極工作時間[TON-= 650(μs)]來改變CR[0.35~0.86]過程中放電行為伴隨的膜層性質，將在本論文中探討。
本實驗結果顯示:固定CR、IR下，電流密度(J)將影響放電過程中噴發物質的多寡，電流密度越大平均膜厚越高。從瞬時電壓、流圖中脈衝電壓與脈衝電流間的延遲，可知脈衝電壓代表生成膜層的崩潰電壓，其越高放電現象越強; 隨後的脈衝電流代表放電過程中噴發物質獲得的能量，其越大噴發物質越多。脈衝電流會隨電流密度越高而增加，然而脈衝電壓卻沒有此趨勢，由此可知電流密度非主導放電強度的因素。放電強度與CR的關聯性於本文中建立，CR(正負電荷比)代表偏極化程度，主導放電強度，高陰極極化(較小CR)，放電強度高。從B組(IR=0.89,CR=0.89~2.22)陽極脈衝電壓比較可知，CR越大陽極脈衝電壓越小，表示放電強度越低。無論IR=1.13或IR=0.89，製程中陽極電壓皆隨CR增加而明顯下降。IR(正負電流比)影響放電過程中物質噴發後被氧化的比率，提升氧化比率可使較多噴發物轉化為氧化物。從膜層成分分布分析結果可知，在高氧化比(IR=1.13)條件下外部膜層明顯較低氧化比(IR=0.89)厚，IR越大，外膜成膜速率較高。
PEO過程中的s.r.現象與氧化物電性改變有關，s.r.現象的產生是由於膜中導電缺陷改變氧化物絕緣特性所造成，而PEO過程中的氫可能是關鍵。由不同電流密度J1(I+=1.2/I-=1.4)~J3(I+=1.5/I-=1.7), 12min之瞬時電壓圖中的陽極休息期間(TOFF+)殘餘正電壓變化可知，越接近s.r.現象發生時間點，TOFF+殘餘正電壓越小，這代表膜層絕緣特性變差、導電性提升; Mott-Schottky分析結果顯示，有發生s.r.現象之膜層載子濃度相較於沒有發生的高了10~105倍; 基材中β-phase(Mg17Al12)的消失可證明PEO過程中的氫擴散，此外文獻顯示氫佔據氧化物中氧空缺時為一施體(donor)，根據Mott-Schottky分析可知膜層載子類型為N-type，由此推論s.r.現象與PEO過程中的氫導致膜層導電度提升有關。
s.r.現象發生時主要仰賴氧擴散機制成膜成長，且期間微弱的放電行為導致外部膜層成膜速率極低，膜層主要向內成長，此外s.r.現象並無助於消除多孔特徵。提升CR可抑制PEO過程中會破壞已生成膜層的過大放電現象，消除膜層中放電通道，無論IR=1.13 or 0.89皆可觀察到相同現象，由此證明CR為一獨立參數，需與IR分開討論。在IR>1的情況下獲得的膜層相較於IR<1有較厚的外部膜層，由膜層成分元素分布分析結果可知，IR=1.13相較於IR=0.89有更厚的外部膜層。在高氧化比(IR>1)可承受較強放電現象(較小CR)，而沒有明顯多孔特徵，這是由於高氧化比能提供較多氧化物填補放電通道。比較(IR=1.13, CR=0.35)與(IR=0.89, CR=0,89)外部膜層多孔分布可知，在(IR=1.13, CR=0.35)條件下雖放電強度較高(CR較小)，然而放電通道明顯少於(IR=0.89,CR=0.89)，這是因為IR較可提供較多氧化物填補大型放電通道。

關鍵詞: 電漿 電漿電解氧化法 微弧氧化 鋁酸鹽 鎂鋁尖晶石 鎂合金 AZ91

In this experiment, the plasma electrolytic oxidation experiment was carried out on the AZ91 magnesium alloy using an aluminate-based electrolyte in a constant current DC bipolar pulse mode.In this experiment, various electrical parameters (including current density J (mA/dm2) [(43.48/-50.72) ~ (54.35/-61.59)], positive and negative charge ratio (Q+/Q-, Charge Ratio, CR) [ 0.89~2.22; 0.35~0.86] and positive and negative current ratios (I+/I-, Current Ratio, IR) [0.89; 1.13] correlate with discharge behavior and accompanying film properties during PEO and establish a soft regime during PEO The relationship between the (sr) phenomenon and the nature of the oxide. Adjust current density under fixed CR (~0.87) [(43.48/-50.72) ~ (54.35/-61.59) (mA/dm2)]; Fixed IR = 0.89 by adjusting anode working time [TON+ = 200~500 (μs)] and fix cathode working time [TON-= 200 (μs)] to change CR [0.89 to 2.22]; fixed IR=1.13 by adjusting anode working time [TON+= 200~500 (μs)] and fix Cathode working time [TON-= 650 (μs)] to change the film properties accompanying the discharge behavior during CR [0.35~0.86] will be discussed in this paper.The correlation between discharge intensity and CR has been established in this paper. Increasing CR (positive and negative charge ratio = degree of polarization) can inhibit the excessive discharge phenomenon of the formed film layer during the PEO process and eliminate the discharge channel in the film layer. The s.r. phenomenon in the PEO process has a significant correlation with the electrical properties of the oxides. The s.r. phenomenon is caused by the defect in the film layer that changes the oxide insulation properties, and the hydrogen in the PEO process may be the key. When the s.r. phenomenon occurs, it mainly depends on the oxygen diffusion mechanism to form a film and grow. At a fixed CR, the current density will affect the output of the material during discharge, so the greater the current density, the smaller the difference in thickness between the center and edge layers. The IR (positive and negative current ratio = oxidation rate) will affect the rate of oxidation after the material is ejected during the discharge process. Increasing the oxidation rate allows the material to rapidly form oxides after eruption, filling the pores after discharge, so IR>1 The film layer obtained in the case has a thicker outer oxide film than IR<1.

Keywords: Plasma electrolytic oxidation(PEO) Plasma Aluminate AZ91

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