1、鎂合金微弧氧化膜結構及耐蝕性的初步研究劉元剛,張巍,李久青,申磊(北京科技大學材料科學與工程學院,北京100083摘要空氣中由于AZ 91D 鎂合金耐腐蝕性差,影響實際應用。為了弄清腐蝕原因,增加應用效果,作者利用掃描電鏡和X 射線衍射分析了AZ 91D 鎂合金表面微弧氧化膜的形貌、結構和相組成,并對氧化膜的耐蝕性作了初步試驗分析。研究表明,AZ 91D 微弧氧化膜呈3層結構,外層氧化膜存在一些孔洞;中間層氧化膜疏松、具有較大厚度;內層氧化膜與基體金屬結合緊密。氧化膜主要由MgO ,MgS iO 3,MgAl 2O 4,Mg 3(PO 42組成。經1周3%NaCl 溶液浸泡試驗,結果表明微弧氧

2、化膜可以較大程度地提高AZ 91D 鎂合金的耐蝕性,但氧化膜表面富含S i ,P 的顆粒是易發生腐蝕的電化學活性點,導致氧化膜發生局部腐蝕。關鍵詞AZ 91D 鎂合金;微弧氧化膜;耐蝕性中圖分類號TG 174.451文獻標識碼A 文章編號10011560(200401001702收稿日期200308230前言鎂合金具有高的比強度和比剛度、良好的可鑄性、可鍛性和延展性,具有能量衰減系數大以及優良的電磁屏蔽性等特點,被譽為21世紀理想的電子產品殼體和汽車構件的替用材料1。但鎂的化學性質活潑,在空氣中鎂合金表面往往形成一層很薄的氧化膜,膜層多孔且比較脆,對基體金屬沒有保護作用。因此,耐蝕性差成為制約

3、鎂合金發揮優勢的一個主要因素,必須對其表面進行防腐蝕處理。隨著雙階段氧化、脈沖陽極氧化的發展和應用,陽極氧化技術日趨多樣化,近年來興起了微弧氧化技術2,3。微弧氧化是在有色金屬表面原位生長陶瓷層的新技術,又稱微等離子體氧化或陽極火花沉積。它是將Al ,T i ,Mg 等金屬及合金置于電解質溶液中,在熱化學、等離子化學和電化學的共同作用下,使材料表面產生火花放電生成陶瓷層。微弧氧化因可顯著提高上述材料的耐蝕性、耐磨性和硬度而廣泛應用于航空、航天、機械、電子、紡織、裝飾等領域。AZ 91D 鎂合金具有均衡的力學性能、鑄造性能和耐蝕性能,是用于汽車工業的重要鎂合金之一。作者研究了微弧氧化條件下AZ

4、91D 鎂合金表面形成的氧化膜的形貌、結構、相組成及耐蝕性。1材料及試驗方法試驗材料為AZ 91D 鎂合金,化學成分是:Al 9.0%,Mn 0.13%,Zn 0.7%,余量Mg 。圓盤狀試樣的尺寸是40mm 3mm 。微弧氧化使用大功率直流電源,電解液是鈉鹽體系的溶液,采用循環水冷卻并用氣泵攪拌。不同微弧氧化處理時間分別為30min ,60min ,90min ,120min 。利用掃描電鏡(Cambridge S360觀察微弧氧化膜的表面及截面形貌、結構和鹽水浸泡后的氧化膜形貌,用M21X 超大功率X 射線衍射儀(銅靶,K射線研究相組成。2試驗結果與分析2.1處理時間對微弧氧化膜形貌的影響

5、經不同時間微弧氧化處理的氧化膜表面都分布著幾微米到幾十微米的孔洞(見圖1,其成因可以由如下的過程來解釋。隨處理時間的延長,初期生成的氧化膜不斷被擊穿;擊穿導致的瞬間高溫使膜層/溶液界面產生大量的水蒸氣,同時高溫熔融物的表層與溶液直接接觸而先于內層凝固,致使內部氣體的逸出通道被封閉,來不及逸出的氣體在氧化膜下次被擊穿時逸出,形成孔洞4,5。隨著氧化膜厚度的增加,擊穿氧化膜將消耗更多的能量,膜層每次被擊穿釋放的氣體也越來越多,造成孔洞尺寸逐步增大。此外,氧化膜表面有許多微米級顆粒。隨時間延長,顆粒的數量和尺寸都明顯增加。分別對顆粒及整個表面進行E DS 成分分析,結果見表1和表2。比較表1和表2認

6、為 ,圖1不同微弧氧化時間AZ 91D 微弧氧化膜表面形貌材料保護2004年1月第37卷第1期表面顆粒相對富含S i ,而整個膜層相對富含P 。表1氧化膜表面小顆粒的成分與處理時間的關系時間/min 306090120M g 摩爾分數/%48.5455.6334.3240.53S i 摩爾分數/%11.0430.3253.8328.53P 摩爾分數/%表2氧化膜表面的成分與處理時間的關系54.6955.5950.30S i 摩爾分數/%1.98 3.9016.50P 摩爾分數/%2.2微弧氧化膜結構分析圖2為AZ 91D 微弧氧化膜截面形貌 。圖2AZ 91D 微弧氧化膜截面形貌膜層基體對氧化

7、膜(60min 試樣沿垂直于表面方向切割,其截面形貌見圖2a 。由此可見,氧化膜為3層的分層結構,外層存在很多孔洞,是氣體的逸出通道;中間層比較疏松,厚度約占整個氧化膜厚度的60%;內層與基體結合緊密。這與蔣百靈6和薛文斌7等的研究結果相似。此外,在內層氧化膜與基體的結合區域中有大量微裂紋。E DS 分析發現,裂紋內含有大量P ,越接近裂紋尖端的P 含量越低。沿垂直于氧化膜(60min 表面方向切割,超過試樣一半厚度時將其敲斷。氧化膜自然斷口部位的截面形貌見圖2b 。整個氧化膜仍分為內層氧化膜、中間疏松層和外層氧化膜3部分。在表面形貌中所看到的孔洞并不貫穿整個氧化膜,一般始于外層氧化膜,止于中

8、間疏松層。比較圖2a 和圖2b 認為,裂紋可能是試樣在打磨、拋光過程中受機械力和化學作用造成的。此外,內層氧化膜含有P 元素也可能是產生裂紋的原因。2.3微弧氧化膜相成分分析圖3是微弧氧化處理(60min 的AZ 91D 鎂合金的X 射線衍射圖。由圖可知,膜層主要由MgO ,MgAl 2O 4,MgS iO 3和Mg 3(PO 42構成。MgAl 2O 4,MgS iO 3和Mg 3(PO 42的生成是由于電解液成分在鎂合金表面的電化學沉積8。生成MgO 原因為,對試樣進行微弧氧化時發生微區弧光放電并釋放出巨大的能量,使鎂合金中的Mg 原子在高于自身熔點的溫度下發生微區熔融,同時在電解液的冷卻

9、作用下與吸附在合金表面的氧原子迅速結合,生成MgO 并沉積。2.4微弧氧化膜耐蝕性的初步分析將未處理過的AZ 91D 放入3%NaC l 溶液中,幾秒鐘后即產生大量氣泡,表面發生腐蝕溶解。有微弧氧化膜(90min 圖3AZ 91D 微弧氧化膜相成分的X 射線衍射圖的AZ 91D 浸泡5h 后,白色氧化膜表面才開始出現黑色腐蝕斑點。微弧氧化處理(90min 的AZ 91D 浸泡1周后,部分表面僅有腐蝕斑點(見圖4a ,部分表面腐蝕嚴重并產生局部脫落(見圖4b 。表3的能譜分析表明,斑點主要含有Mg ,P 以及少量的S i 和Cl ,氧化膜剝落后基體部分主要由Mg 和P 組成。而P 是氧化膜的重要

10、組成元素。這說明這些部位可能仍殘留內層氧化膜,對基體仍有一定的保護作用。鹽水浸泡試驗表明,微弧氧化處理可顯著提高AZ 91D 鎂合金的耐蝕性 。圖4AZ 91D 微弧氧化膜浸泡1周后的腐蝕形貌表3微弧氧化膜浸泡后腐蝕斑點和氧化膜的能譜分析摩爾分數%M g氧化膜表面富含S i ,P 的顆粒可能是發生腐蝕的敏感部位,它們先被溶解掉,進而是氧化膜中的電化學活性點。膜剝落后基體中存在少量的Cl 是溶液中的Cl -在氧化膜表面吸附造成的。3結論(1AZ 91D 微弧氧化膜表面多孔,分為外層、中間疏松層和內層致密層。隨微弧氧化時間的延長,氧化膜表面富含S i ,P 的顆粒的數量和尺寸都增大。(2AZ 91

11、D 微弧氧化膜由MgO ,MgAl 2O 4,MgS iO 3,Mg 3(PO 42組成。(3微弧氧化處理的AZ 91D 經1周的鹽水浸泡(3%Na 2C l 后,部分表面存在腐蝕斑點,部分表面氧化膜剝落,去除剝落氧化膜后的基體表面仍富含P 。參考文獻1王渠東.鎂合金在電子器材殼體中的應用J .材料導報,2000,6:2224.(下轉第22頁Jan.2004V ol.37N o.1Materials Protection鎂合金微弧氧化膜結構及耐蝕性的初步研究of Nanocrystalline Nickel Produced by E lectrodepositonJ.Nanos2tructu

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26、Protection納米結構鍍層的制備及其應用fied fluororesin provides excellent weatherability and corrosion re2 sistance and high performance index.K ey w ords:low-fluorinated fluororesin;m olecular constitution; coatingPhosphorizing Agent for C athodic Eiectrophoresis CoatingsW ANG Chun-ming1,W U Wen-ping2(1.Shanghai

27、Institute of T echnology,Shanghai200235; 2.Shanghai Zhenhua Scientific T echnology and Industry&T rade C o.Ltd.,Shanghai200439, China.Cailiao Baohu2004,37(1,1416(Ch.Phospho2 rizing agent was studied for cathodic electrophoresis coatings,and a new composite organic accelerant was developed to overcom

28、e the environmental pollution of conventional NaNO2accelerant.The op2 timal process conditions such as acidity and temperature were de2 termined,and the crystalline structure and relevant properties of phosphorizing coating were tested.Results show that the environ2 mental friendly phosphorizing age

29、nt has the characteristics of rapidly phosphorizing,low temperature,little sediment and long life.The phosphorizing coating is thin and compact with granule polyc stalline structure,which has strong alkali proof and corrosion resis2 tance and high adhesion,aside it is suitable for cathodic elec2 tro

30、phoresis coating well.K ey w ords:phosphorizing;cathodic electrophoresis coating;accel2 erant;alkali proof;corrosion resistance;environmental protection Microstructure and Corrosion R esistance of Microarc Oxid a2 tion Film on AZ91D Magnesium AlloyLI U Y uan-gang,ZH ANG Wet,LI Jiu-qing,et al(School

31、of Materials Science&Engineering,University of Science and T ech2 nology Belling,Belling100083,China.Cailiao Baohu2004,37( 1,1718(Ch.C orrosion resistance of AZ91D magnesium al2 loy is weak in air.In order to reveal corrosion mechanism and im2 prove performance,the m orphology,n ficrostructure and p

32、hase composition of microarc oxidation(M AOfilm on AZ91D magne2 sium alloy were studied by scanning electron microscopy(SE M and X-ray diffraction(XRD.Furtherm ore the corrosion resis2 tance of film was tested.Results show that the M Ad film on AZ91D magnesium alloy contains three layers that are ou

33、ter layer,middle layer and inner layer.S ome small discharge pores lie in the outer layer.The middle layer is loose and thick.Inner layer is combined to metal substrate tightly.The M Ad film is mainly composed of MgO,MgS iO3,MgAI2O4and Mg3(PO42compounds.The mi2 croarc oxidation is proved to improve

34、corrosion resistance of AZ91D after three-week immersion in3%NaCI s olutinn.There exist pitting corrosion on the oxide film for ninny small particles contain2 ing S i and P element richly on the surface are electrochen fically ac2 tive sites easy to corrode.K ey w ords:AZ91D magnesium alloys;microar

35、c oxidation film; corrosion resistancePrep aration and Application of N anostrueture CoatingsT AN Jun,X U Bin-shi(S tate K ey Laboratory of Equipment Re2 manu facture T echnology,Belling100072,China.Cailiao Baohu 2004,37(1,1922(Ch.Recent developments of nanos2 tructure coatings by electrodeposition

36、were reviewed.The prepara2 tion,properties and application of nano-crystalline coatings, nano-particle composite coatings and nano multilayer coatings were introduced.K ey w ords:electrodeposition;nano-crystalline;nano-par2 ticle;nano multilayer;preparation of coatingsDetection Stand ards of Organic

37、 Polymer Coatings for Archi2 tectural Aluminum Alloys Seetion in Abroad and ChinaZH U Zu-fang(Belling G eneral Research Institute for N on-Fer2 rous Metals,Belling100088,China.Cailiao Baohu2004,37(1,2326(Ch.Detection purpose and method for organie poly2 mer coatings on aluminum alloy section were ov

38、erviewed.C ompar2 ing Chinese standard with European standard and American stan2 dard,s ome technologies were illuminated on their comm on ground and differentia.S ome opinions were put forward for the testing items and methods and quality distinguishing.K ey w ords:aluminum alloy;spraying coatings;

39、detection;stan2 dardC atalytic Mech anism of Amorphous Ni-P-B ased Coatings for H ydrogen Evolution R eactionLI Y ou-xia,G Ad Cheng-hui,LI N Y ou-xi,et al(Department of Mechanical Engineering,Fuzhou University,Fuzhou350002, China.Cailiao Baohu2004,37(1,2729(Cha Am or2 phous Ni-P-based coatings have

40、remarkable corrosion resis2 tance,and have quite active for the hydrogen ev olution reaction (HERto act as promising cathodic materials,which can decrease the overpotential of the HER and reduce energy losses.The in flu2 ences of P content in Ni-P deposits,fihn thickness,preparation conditions,anoth

41、er adding element,surface oxidation after deposit2 ing,pretreatment and heat treatment were analyzed for controlling the electrocatalytic activity of HER.The catalytic mechanism of am orphous Ni-P-hased coatings was discussed.K ey w ords:am orphous;Ni-P alloy coating;hydrogen ev olution2 reaction(HE

42、R;electrode propertyE lectroless Nickel P lating T echnology for Aluminum AlloysYI N G uo-guang,PAN X iao-fang,CHE N Y an-min,et al (Chemistry Department,Quanzhou N ormal C ollege,Quanzhou 362000,China.Cailiao Baohu2004,37(1,3032(Ch.In order to improve electroless nickel plating technology of alumin

43、um alloys and av oid contamination of zincate conversion process on electroless nickel plating s olution,activation-electroless Ni pre-plating technology for aluminum alloys was investigated.The opti2 mal conditions are determined that pH value in activation process is in the range of9to10and pre-plating time is about4to5min2 utes through coating adhesion and porosity and corrosion resistance tests.The coating quality meets the G B/T1391