鎂合金微弧氧化膜結(jié)構(gòu)及耐蝕性的初步研究_百度文庫(kù)

1、鎂合金微弧氧化膜結(jié)構(gòu)及耐蝕性的初步研究劉元?jiǎng)?張巍,李久青,申磊(北京科技大學(xué)材料科學(xué)與工程學(xué)院,北京100083摘要空氣中由于AZ 91D 鎂合金耐腐蝕性差,影響實(shí)際應(yīng)用。為了弄清腐蝕原因,增加應(yīng)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(jié)構(gòu)和相組成,并對(duì)氧化膜的耐蝕性作了初步試驗(yàn)分析。研究表明,AZ 91D 微弧氧化膜呈3層結(jié)構(gòu),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(nèi)層氧化膜與基體金屬結(jié)合緊密。氧化膜主要由MgO ,MgS iO 3,MgAl 2O 4,Mg 3(PO 42組成。經(jīng)1周3%NaCl 溶液浸泡試驗(yàn),結(jié)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(fā)生腐蝕的電化學(xué)活性點(diǎn),導(dǎo)致氧化膜發(fā)生局部腐蝕。關(guān)鍵詞AZ 91D 鎂合金;微弧氧化膜;耐蝕性中圖分類(lèi)號(hào)TG 174.451文獻(xiàn)標(biāo)識(shí)碼A 文章編號(hào)10011560(200401001702收稿日期200308230前言鎂合金具有高的比強(qiáng)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(shù)大以及優(yōu)良的電磁屏蔽性等特點(diǎn),被譽(yù)為21世紀(jì)理想的電子產(chǎn)品殼體和汽車(chē)構(gòu)件的替用材料1。但鎂的化學(xué)性質(zhì)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(duì)基體金屬?zèng)]有保護(hù)作用。因此,耐蝕性差成為制約

3、鎂合金發(fā)揮優(yōu)勢(shì)的一個(gè)主要因素,必須對(duì)其表面進(jìn)行防腐蝕處理。隨著雙階段氧化、脈沖陽(yáng)極氧化的發(fā)展和應(yīng)用,陽(yáng)極氧化技術(shù)日趨多樣化,近年來(lái)興起了微弧氧化技術(shù)2,3。微弧氧化是在有色金屬表面原位生長(zhǎng)陶瓷層的新技術(shù),又稱(chēng)微等離子體氧化或陽(yáng)極火花沉積。它是將Al ,T i ,Mg 等金屬及合金置于電解質(zhì)溶液中,在熱化學(xué)、等離子化學(xué)和電化學(xué)的共同作用下,使材料表面產(chǎn)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(yīng)用于航空、航天、機(jī)械、電子、紡織、裝飾等領(lǐng)域。AZ 91D 鎂合金具有均衡的力學(xué)性能、鑄造性能和耐蝕性能,是用于汽車(chē)工業(yè)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(jié)構(gòu)、相組成及耐蝕性。1材料及試驗(yàn)方法試驗(yàn)材料為AZ 91D 鎂合金,化學(xué)成分是:Al 9.0%,Mn 0.13%,Zn 0.7%,余量Mg 。圓盤(pán)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(huán)水冷卻并用氣泵攪拌。不同微弧氧化處理時(shí)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(jié)構(gòu)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(yàn)結(jié)果與分析2.1處理時(shí)間對(duì)微弧氧化

5、膜形貌的影響經(jīng)不同時(shí)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(jiàn)圖1,其成因可以由如下的過(guò)程來(lái)解釋。隨處理時(shí)間的延長(zhǎng),初期生成的氧化膜不斷被擊穿;擊穿導(dǎo)致的瞬間高溫使膜層/溶液界面產(chǎn)生大量的水蒸氣,同時(shí)高溫熔融物的表層與溶液直接接觸而先于內(nèi)層凝固,致使內(nèi)部氣體的逸出通道被封閉,來(lái)不及逸出的氣體在氧化膜下次被擊穿時(shí)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(lái)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(jí)顆粒。隨時(shí)間延長(zhǎng),顆粒的數(shù)量和尺寸都明顯增加。分別對(duì)顆粒及整個(gè)表面進(jìn)行E DS 成分分析,結(jié)果見(jiàn)表1和表2。比較

6、表1和表2認(rèn)為 ,圖1不同微弧氧化時(shí)間AZ 91D 微弧氧化膜表面形貌材料保護(hù)2004年1月第37卷第1期表面顆粒相對(duì)富含S i ,而整個(gè)膜層相對(duì)富含P 。表1氧化膜表面小顆粒的成分與處理時(shí)間的關(guān)系40.4214.0511.8530.94表2氧化膜表面的成分與處理時(shí)間的關(guān)系時(shí)間/min 306090120M g 摩爾分?jǐn)?shù)/%54.9245.0843.3340.5133.202.2微弧氧化膜結(jié)構(gòu)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(duì)氧化膜(60min 試樣沿垂直于表面方向切割,其截面形貌見(jiàn)圖2a 。由此可見(jiàn),氧化膜為3層的分層結(jié)構(gòu),外層存在很

7、多孔洞,是氣體的逸出通道;中間層比較疏松,厚度約占整個(gè)氧化膜厚度的60%;內(nèi)層與基體結(jié)合緊密。這與蔣百靈6和薛文斌7等的研究結(jié)果相似。此外,在內(nèi)層氧化膜與基體的結(jié)合區(qū)域中有大量微裂紋。E DS 分析發(fā)現(xiàn),裂紋內(nèi)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(guò)試樣一半厚度時(shí)將其敲斷。氧化膜自然斷口部位的截面形貌見(jiàn)圖2b 。整個(gè)氧化膜仍分為內(nèi)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(gè)氧化膜,一般始于外層氧化膜,止于中間疏松層。比較圖2a 和圖2b 認(rèn)為,裂紋可能是試樣在打磨、拋光過(guò)程中受機(jī)械力和化學(xué)作用造成的。此外,內(nèi)層氧

8、化膜含有P 元素也可能是產(chǎn)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(gòu)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(xué)沉積8。生成MgO 原因?yàn)?對(duì)試樣進(jìn)行微弧氧化時(shí)發(fā)生微區(qū)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(diǎn)的溫度下發(fā)生微區(qū)熔融,同時(shí)在電解液的冷卻作用下與吸附在合金表面的氧原子迅速結(jié)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(guò)的AZ

9、 91D 放入3%NaC l 溶液中,幾秒鐘后即產(chǎn)生大量氣泡,表面發(fā)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(kāi)始出現(xiàn)黑色腐蝕斑點(diǎn)。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(diǎn)(見(jiàn)圖4a ,部分表面腐蝕嚴(yán)重并產(chǎn)生局部脫落(見(jiàn)圖4b 。表3的能譜分析表明,斑點(diǎn)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 是氧化膜的重要組成元素。這說(shuō)明這些部位可能仍殘留內(nèi)層氧化膜,對(duì)基體仍有一定的保護(hù)作用。鹽水浸泡試驗(yàn)表明,微弧氧化處理可顯著

10、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(diǎn)和氧化膜的能譜分析摩爾分?jǐn)?shù)%M g56.0340.54- 3.43氧化膜表面富含S i ,P 的顆?？赡苁前l(fā)生腐蝕的敏感部位,它們先被溶解掉,進(jìn)而是氧化膜中的電化學(xué)活性點(diǎn)。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(jié)論(1AZ 91D 微弧氧化膜表面多孔,分為外層、中間疏松層和內(nèi)層致密層。隨微弧氧化時(shí)間的延長(zhǎng),氧化膜表面富含S i ,P 的顆粒的數(shù)量和尺寸都增大。(2AZ 91D 微弧氧化膜由MgO ,MgAl 2O 4,MgS iO 3,Mg 3(P

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26、威,來(lái)永春,等.鎂合金微等離子體氧化膜的特性J.材料科學(xué)與工藝,1997,5(2:8992.編輯:段金弟Jan.2004V ol.37N o.1Materials Protection納米結(jié)構(gòu)鍍層的制備及其應(yīng)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 Agen

27、t for C athodic Eiectrophoresis CoatingsW ANG Chun-ming1,W U Wen-ping2(1.Shanghai 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 el

28、ectrophoresis coatings,and a new composite organic accelerant was developed to overcome 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 phosphorizin

29、g coating were tested.Results show that the environ2 mental friendly phosphorizing agent 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 an

30、d corrosion resis2 tance and high adhesion,aside it is suitable for cathodic elec2 trophoresis 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

31、tion Film on AZ91D Magnesium AlloyLI U Y uan-gang,ZH ANG Wet,LI Jiu-qing,et al(School 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 r

32、eveal corrosion mechanism and im2 prove performance,the m orphology,n ficrostructure and phase 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.

33、Results show that the M Ad film on AZ91D magnesium alloy contains three layers that are outer 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

34、of MgO,MgS iO3,MgAI2O4and Mg3(PO42compounds.The mi2 croarc oxidation is proved to improve 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 ele

35、ctrochen fically ac2 tive sites easy to corrode.K ey w ords:AZ91D magnesium alloys;microarc 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 Bao

36、hu 2004,37(1,1922(Ch.Recent developments of nanos2 tructure coatings by electrodeposition 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-crystall

37、ine;nano-par2 ticle;nano multilayer;preparation of coatingsDetection Stand ards of Organic 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.Det

38、ection purpose and method for organie poly2 mer coatings on aluminum alloy section were overviewed.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

39、items and methods and quality distinguishing.K ey w ords:aluminum alloy;spraying coatings;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,

40、Fuzhou350002, China.Cailiao Baohu2004,37(1,2729(Cha Am or2 phous Ni-P-based coatings have 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.T

41、he in flu2 ences of P content in Ni-P deposits,fihn thickness,preparation conditions,another 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 coating

42、s was discussed.K ey w ords:am orphous;Ni-P alloy coating;hydrogen ev olution2 reaction(HER;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

43、Baohu2004,37(1,3032(Ch.In order to improve electroless nickel plating technology of aluminum 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