镁合金微弧氧化膜结构及耐蚀性的初步研究_百度文库

1、镁合金微弧氧化膜结构及耐蚀性的初步研究刘元刚,张巍,李久青,申磊(北京科技大学材料科学与工程学院,北京100083摘要空气中由于AZ 91D 镁合金耐腐蚀性差,影响实际应用。为了弄清腐蚀原因,增加应用效果,作者利用扫描电镜和X 射线衍射分析了AZ 91D 镁合金表面微弧氧化膜的形貌、结构和相组成,并对氧化膜的耐蚀性作了初步试验分析。研究表明,AZ 91D 微弧氧化膜呈3层结构,外层氧化膜存在一些孔洞;中间层氧化膜疏松、具有较大厚度;内层氧化膜与基体金属结合紧密。氧化膜主要由MgO ,MgS iO 3,MgAl 2O 4,Mg 3(PO 42组成。经1周3%NaCl 溶液浸泡试验,结果表明微弧氧

2、化膜可以较大程度地提高AZ 91D 镁合金的耐蚀性,但氧化膜表面富含S i ,P 的颗粒是易发生腐蚀的电化学活性点,导致氧化膜发生局部腐蚀。关键词AZ 91D 镁合金;微弧氧化膜;耐蚀性中图分类号TG 174.451文献标识码A 文章编号10011560(200401001702收稿日期200308230前言镁合金具有高的比强度和比刚度、良好的可铸性、可锻性和延展性,具有能量衰减系数大以及优良的电磁屏蔽性等特点,被誉为21世纪理想的电子产品壳体和汽车构件的替用材料1。但镁的化学性质活泼,在空气中镁合金表面往往形成一层很薄的氧化膜,膜层多孔且比较脆,对基体金属没有保护作用。因此,耐蚀性差成为制约

3、镁合金发挥优势的一个主要因素,必须对其表面进行防腐蚀处理。随着双阶段氧化、脉冲阳极氧化的发展和应用,阳极氧化技术日趋多样化,近年来兴起了微弧氧化技术2,3。微弧氧化是在有色金属表面原位生长陶瓷层的新技术,又称微等离子体氧化或阳极火花沉积。它是将Al ,T i ,Mg 等金属及合金置于电解质溶液中,在热化学、等离子化学和电化学的共同作用下,使材料表面产生火花放电生成陶瓷层。微弧氧化因可显著提高上述材料的耐蚀性、耐磨性和硬度而广泛应用于航空、航天、机械、电子、纺织、装饰等领域。AZ 91D 镁合金具有均衡的力学性能、铸造性能和耐蚀性能,是用于汽车工业的重要镁合金之一。作者研究了微弧氧化条件下AZ

4、91D 镁合金表面形成的氧化膜的形貌、结构、相组成及耐蚀性。1材料及试验方法试验材料为AZ 91D 镁合金,化学成分是:Al 9.0%,Mn 0.13%,Zn 0.7%,余量Mg 。圆盘状试样的尺寸是40mm ×3mm 。微弧氧化使用大功率直流电源,电解液是钠盐体系的溶液,采用循环水冷却并用气泵搅拌。不同微弧氧化处理时间分别为30min ,60min ,90min ,120min 。利用扫描电镜(Cambridge S360观察微弧氧化膜的表面及截面形貌、结构和盐水浸泡后的氧化膜形貌,用M21X 超大功率X 射线衍射仪(铜靶,K射线研究相组成。2试验结果与分析2.1处理时间对微弧氧化

5、膜形貌的影响经不同时间微弧氧化处理的氧化膜表面都分布着几微米到几十微米的孔洞(见图1,其成因可以由如下的过程来解释。随处理时间的延长,初期生成的氧化膜不断被击穿;击穿导致的瞬间高温使膜层/溶液界面产生大量的水蒸气,同时高温熔融物的表层与溶液直接接触而先于内层凝固,致使内部气体的逸出通道被封闭,来不及逸出的气体在氧化膜下次被击穿时逸出,形成孔洞4,5。随着氧化膜厚度的增加,击穿氧化膜将消耗更多的能量,膜层每次被击穿释放的气体也越来越多,造成孔洞尺寸逐步增大。此外,氧化膜表面有许多微米级颗粒。随时间延长,颗粒的数量和尺寸都明显增加。分别对颗粒及整个表面进行E DS 成分分析,结果见表1和表2。比较

6、表1和表2认为 ,图1不同微弧氧化时间AZ 91D 微弧氧化膜表面形貌材料保护2004年1月第37卷第1期表面颗粒相对富含S i ,而整个膜层相对富含P 。表1氧化膜表面小颗粒的成分与处理时间的关系40.4214.0511.8530.94表2氧化膜表面的成分与处理时间的关系时间/min 306090120M g 摩尔分数/%54.9245.0843.3340.5133.202.2微弧氧化膜结构分析图2为AZ 91D 微弧氧化膜截面形貌 。图2AZ 91D 微弧氧化膜截面形貌膜层基体对氧化膜(60min 试样沿垂直于表面方向切割,其截面形貌见图2a 。由此可见,氧化膜为3层的分层结构,外层存在很

7、多孔洞,是气体的逸出通道;中间层比较疏松,厚度约占整个氧化膜厚度的60%;内层与基体结合紧密。这与蒋百灵6和薛文斌7等的研究结果相似。此外,在内层氧化膜与基体的结合区域中有大量微裂纹。E DS 分析发现,裂纹内含有大量P ,越接近裂纹尖端的P 含量越低。沿垂直于氧化膜(60min 表面方向切割,超过试样一半厚度时将其敲断。氧化膜自然断口部位的截面形貌见图2b 。整个氧化膜仍分为内层氧化膜、中间疏松层和外层氧化膜3部分。在表面形貌中所看到的孔洞并不贯穿整个氧化膜,一般始于外层氧化膜,止于中间疏松层。比较图2a 和图2b 认为,裂纹可能是试样在打磨、抛光过程中受机械力和化学作用造成的。此外,内层氧

8、化膜含有P 元素也可能是产生裂纹的原因。2.3微弧氧化膜相成分分析图3是微弧氧化处理(60min 的AZ 91D 镁合金的X 射线衍射图。由图可知,膜层主要由MgO ,MgAl 2O 4,MgS iO 3和Mg 3(PO 42构成。MgAl 2O 4,MgS iO 3和Mg 3(PO 42的生成是由于电解液成分在镁合金表面的电化学沉积8。生成MgO 原因为,对试样进行微弧氧化时发生微区弧光放电并释放出巨大的能量,使镁合金中的Mg 原子在高于自身熔点的温度下发生微区熔融,同时在电解液的冷却作用下与吸附在合金表面的氧原子迅速结合,生成MgO 并沉积。2.4微弧氧化膜耐蚀性的初步分析将未处理过的AZ

9、 91D 放入3%NaC l 溶液中,几秒钟后即产生大量气泡,表面发生腐蚀溶解。有微弧氧化膜(90min 图3AZ 91D 微弧氧化膜相成分的X 射线衍射图的AZ 91D 浸泡5h 后,白色氧化膜表面才开始出现黑色腐蚀斑点。微弧氧化处理(90min 的AZ 91D 浸泡1周后,部分表面仅有腐蚀斑点(见图4a ,部分表面腐蚀严重并产生局部脱落(见图4b 。表3的能谱分析表明,斑点主要含有Mg ,P 以及少量的S i 和Cl ,氧化膜剥落后基体部分主要由Mg 和P 组成。而P 是氧化膜的重要组成元素。这说明这些部位可能仍残留内层氧化膜,对基体仍有一定的保护作用。盐水浸泡试验表明,微弧氧化处理可显著

10、提高AZ 91D 镁合金的耐蚀性 。图4AZ 91D 微弧氧化膜浸泡1周后的腐蚀形貌表3微弧氧化膜浸泡后腐蚀斑点和氧化膜的能谱分析摩尔分数%M g56.0340.54- 3.43氧化膜表面富含S i ,P 的颗粒可能是发生腐蚀的敏感部位,它们先被溶解掉,进而是氧化膜中的电化学活性点。膜剥落后基体中存在少量的Cl 是溶液中的Cl -在氧化膜表面吸附造成的。3结论(1AZ 91D 微弧氧化膜表面多孔,分为外层、中间疏松层和内层致密层。随微弧氧化时间的延长,氧化膜表面富含S i ,P 的颗粒的数量和尺寸都增大。(2AZ 91D 微弧氧化膜由MgO ,MgAl 2O 4,MgS iO 3,Mg 3(P

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26、威,来永春,等.镁合金微等离子体氧化膜的特性J.材料科学与工艺,1997,5(2:8992.编辑:段金弟Jan.2004V ol.37N o.1Materials Protection纳米结构镀层的制备及其应用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