Effect of intermetallic phases on the anodic oxidation and corrosion of 5A06 aluminum alloy

Structure of D.C Machine 压铸机结构accumulator group 蓄能器central lubrication 中央润滑系统closing cylinder 油箱connection block 端子板cooling of die and injection unit 冷却系统core pull system 抽芯系统core spraying program 抽芯喷涂程序die closing unit 压铸合模系统die height adjustment 型厚调整ejector 顶出装置（顶针）extracting delay time 抽出延时fixed platen 定型板hydraulic connections 液压连结器hydraulic tank 液压油箱injection unit 压射中心lifting cylinder 起落液压油箱limit switch ejector back 顶回开关limit switch ejector forward 凑近开关locking device of tie bar nut 拉杠螺栓销紧装置machine base 机座main valve 主阀门manual central pressurecontrol 手动中央压力控制moving platen 动型板multiplication 增压Nitrogen bottles 氮气瓶pilot valve 控制阀门piston-type distributor 活塞式分配器plunger 压射冲头pressurecontrol valve 压力控制阀pressureintensifier 增压器rearplaten 后座板set collar 调整圈sliding bands 滑板（座）solenoid valve 电磁阀spindle螺柱split nut对开螺母squeezepin挤压销tank aerator油箱吸气口tie bar pulling抽杠tie bars拉杠toggle head曲肘头toggle system曲肘系统Melting熔炼aluminum alloy铝合金crane吊车dross浮渣flux溶剂forklift叉车furnace liner炉衬holding furnace保温炉melting熔炼melting furnace (pot)熔炼炉melting temperature溶化温度D.C (die-casting) related 压铸相关air blow 喷涂冷却backpressure 背压casting weight 铸件重量cavity 型腔cavity filling 型腔填补cavity filling time/injection time 填补时间cavity insert 型腔抽芯die area 模具面积die lubricant; 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plane figure平面图polish agent磨光剂polyester聚酯纤维proof stress允许应力prototype/casting原型、毛坯quality assurance质量保证R state R 面radiator散热器residual stress残留应力resistance to abrasion耐麿性rib肋；筋条roll thread thru滚丝攻通roughness/cleanness洁净度roughness/flatness平面度salt residure盐渍section剖面图service life of dies模具寿命shadedarea cast暗影毛坯地域shrink缩短shrinkage porosity缩孔sliver碎片soldering mark烧伤standard/std标准strengh division强度范围stripped mark; peeling分层；剥落surface finish清理表面tensile strengh抗拉强度uncored hole不通孔unless otherwise specified未注unspecified/unmarked未注vein grain凸纹/直纹wall thickness壁厚yield point折服点Other 其余adhesive 胶合剂align v. 对准校准detail 角落处deviations 变差diesel oil 柴油dirt 污物engage v. 连接，啮合flush with v. 与齐平grease 油脂insulating paint 绝缘油漆pallet 托盘recess 壁凹riser 冒口viscose sponge 粘胶海绵报价 Quotationacceptable inspection standard合用检测标准additional casting cost 压铸附带费casting cost 锻造费depreciation expenses 折扣费estimated price 估定价钱finishing cost 后加工费fixed rate method 定率法go-ahead of product 先行生产ingot price 铝锭价钱insert cost 插件费inspection cost 检测费lot, batch 批melting cost 熔炼费overhead manufacturing expense 制造间接费profit added 附带利益rejection percentage 废品比率residual value/scrap value 报废市价值running cost of machine 机器运行费selling expense 卖价selling overhead 销售间接费service life 寿命standard alloying ratio 掺合比率standard price 标准价钱standard rejection rate 废品率time of trial shot 试铸时间total cost 总价钱trial casting cost 试铸费trimming cost 除浇口费yield 生产yield rate 生产率yield rate of finishing 后加工合格率yield rate of melting 熔炼生产率工具量具类 (Tools and Gauges)plug gauge 塞规screw tap 丝攻taper gauge 锥度规thread plug gauge 螺纹塞规vernier caliper 游标卡尺Defects/flaws/blemishes/imperfections缺点blisters 气泡（金属表面）bubble 气泡chill zone 激冷区cold shortness 冷脆性cold shut; cold filling 冷隔crack 裂纹dot 铸点flower mark;stripping for shot blast 花纹foreign material: 外面资料galling 扣伤hair crack 发裂handling mark 搬运碰伤印痕hard spot 硬点heat checking 热裂纹hot cracking 热裂纹hot shortness 热脆性inside cut 崩入inverse swell 夹层（鸿图说法）pore 孔隙porosity 孔隙度 /气孔sand , slag, oxide, dross, metallic inclusion 沙粒、熔渣、氧化物、浮渣、金属杂质。

Ferroelectric and piezoelectric properties of tungsten substituted SrBi 2Ta 2O 9ferroelectric ceramicsIndrani Coondoo *,S.K.Agarwal a ,A.K.Jha ba Superconductivity and Cryogenics Division,National Physical Laboratory,Dr K.S.Krishnan Road,New Delhi 110012,India bDepartment of Applied Physics,Delhi College of Engineering,Bawana Road,Delhi 110042,India1.IntroductionDefects in crystals significantly influence physical and various other properties of materials [1].For instance,as it is well known,doping by other elements leads to significant changes in the electrical properties of silicon.Historically,‘‘defect engineering’’has been developed in the field of semiconducting materials such as compound semiconductors as well as in diamond,Si and Ge [2–4].Subsequently,the concept of defect engineering has been applied to other functional materials,and the significant improve-ment in material properties have been achieved in high transition-temperature superconductors [5],amorphous SiO 2[6],photonic crystals [7]and also in the field of ferroelectrics,such as BaTiO 3,Pb(Ti,Zr)O 3(PZT),etc.[8,9].Various structural and electrical properties of bismuth layer-structured ferroelectrics (BLSF)are also strongly affected on deviation from stoichiometric composi-tions and defects have been recognized as a crucially important factor [10–13].It has been found that in BLSF small changes in chemical composition result in significantly altered dielectric and ferroelectric properties including dielectric constant and remanent polarization.In SrBi 2Ta 2O 9(SBT)and SrBi 2Nb 2O 9(SBN),orthor-hombic structural distortions with non-centrosymmetric spacegroup A 21am cause spontaneous ferroelectric polarization (P s )along a axis [14,15].SBT,a member of the BLSF family,has occupied an important position among the Pb-free ferroelectric memory materials [16–18].Tungsten (W 6+)has recently been investigated as a dopant for bismuth titanates and lanthanum doped bismuth titanates,in which the remanent polarization was observed to enhance when a small amount of Ti 4+was substituted by W 6+[19,20].With the objective to improve structural,dielectric and ferroelectric proper-ties,the hexavalent tungsten (W 6+)was chosen as a donor cation for partial replacement of the pentavalent tantalum (Ta 5+)SBT.In this report,the effect of tungsten substitution in SBT (SBTW),on the microstructural,ferroelectric and piezoelectric properties is reported.The results including the improvement in polarization properties have been discussed.2.ExperimentalSamples of compositions SrBi 2(W x Ta 1Àx )2O 9(SBWT),with x =0.0,0.025,0.050,0.075,0.10and 0.20were synthesized by solid-state reaction method taking SrCO 3,Bi 2O 3,Ta 2O 5and WO 3(all from Aldrich)in their stoichiometric proportions.The powder mixtures were thoroughly ground and passed through sieve of appropriate size and then calcined at 9008C in air for 2h.The calcined mixtures were ground and admixed with about 1–1.5wt%polyvinyl alcohol (Aldrich)as a binder and then pressed at $300MPa into disk shaped pellets.The pellets were sintered at 12008C for 2h in air.Materials Research Bulletin 44(2009)1288–1292A R T I C L E I N F O Article history:Received 3October 2008Received in revised form 5December 2008Accepted 6January 2009Available online 15January 2009Keywords:A.CeramicsC.X-ray diffractionD.FerroelectricityA B S T R A C TTungsten substituted samples of compositions SrBi 2(W x Ta 1Àx )2O 9(x =0.0,0.025,0.050,0.075,0.10and 0.20)were synthesized by solid-state reaction method and studied for their microstructural,electrical conductivity,ferroelectric and piezoelectric properties.The X-ray diffractograms confirm the formation of single phase layered perovskite structure in the samples with x up to 0.05.The temperaturedependence of dc conductivity vis-a`-vis tungsten content shows a decrease in conductivity,which is attributed to the suppression of oxygen vacancies.The ferroelectric and piezoelectric studies of the W-substituted SBT ceramics show that the remanent polarization and d 33values increases with increasing concentration of tungsten up to x 0.05.Such compositions with low conductivity and high P r values should be excellent materials for highly stable ferroelectric memory devices.ß2009Elsevier Ltd.All rights reserved.*Corresponding author.Present address:Liquid Crystal Group,National Physical Laboratory,Dr K.S.Krishnan Road,New Delhi 110012,India.Tel.:+919810361727;fax:+911125170387.E-mail address:indrani_coondoo@ (I.Coondoo).Contents lists available at ScienceDirectMaterials Research Bulletinj o ur n a l h o m e p a g e :w w w.e l se v i e r.c om /l oc a t e /m a t r e sb u0025-5408/$–see front matter ß2009Elsevier Ltd.All rights reserved.doi:10.1016/j.materresbull.2009.01.001X-ray diffractograms of the sintered samples were recorded using a Bruker diffractometer in the range 108 2u 708with CuK a radiation.The sintered pellets were polished to a thickness of 1mm and coated with silver paste on both sides for use as electrodes and cured at 5508C for half an hour.Electrical conductivity was performed using Keithley’s 6517A Electrometer.The polarization–electric field (P –E )hysteresis measurements were done at room temperature using an automatic P –E loop tracer based on Sawyer–Tower circuit.Piezoelectric charge co-efficient d 33was measured using a Berlincourt d 33meter after poling the samples in silicone–oil bath at 2008C for half an hour under a dc electric field of 60–70kV/cm.3.Results and discussion3.1.Structural and micro-structural studiesThe phase formation and crystal structure of the ceramics were examined by X-ray diffraction (XRD),which is shown in Fig.1.The XRD patterns of the samples show the characteristic peaks of SBT.The peaks have been indexed with the help of a computer program–POWDIN [21]and the refined lattice parameters are given in Table 1.It is observed that a single phase layered perovskite structure is maintained in the range 0.0 x 0.05.Owing to the same co-ordination number i.e.6and the smallerionic radius of W (0.60A˚)in comparison to Ta (0.64A ˚),there is a high possibility of tungsten occupying the tantalum site.The observance of unidentified peak of very low intensity in the compositions with x >0.05indicates the solubility limit of W concentration in SBT.The unidentified peak is possibly due to tungsten not occupying the Ta sites in the structure as the intensity of this peak is observed to increase with tungsten content.Composition and sintering temperature influences the micro-structure such as grain growth and densification of the specimen,which in turn control other properties of the material [11,13].The effects of W substitution on the microstructure have been examined by SEM and the obtained micrographs are shown in Fig.2.It shows the microstructure of the fractured surface of the studied samples.It is clearly observed that W substitution has pronounced effect on the average grain size and homogeneity of the grains.Randomly oriented and anisotropic plate-like grains are observed in all the samples.It is also observed that the average grain size increases gradually with increasing W content.The average grain size in the sample with x =0.0is $2–3m m while that in the sample with x =0.20the size increases to $5–7m m.3.2.Electrical studiesThe electrical conductivity of ceramic materials encompasses a wide range of values.In insulators,the defects w.r.t.the perfect crystalline structure act as charge carriers and the consideration of charge transport leads necessarily to the consideration of point defects and their migration [22].Many mechanisms were put forward to explain the conductivity mechanism in ceramics.Most of them are approximately divided into three groups:electronic conduction,oxygen vacancies ionic conduction,and ionic and p-type mixed conduction [22].Intrinsic conductivity results from the movement of the component ions,whereas conduction resulting from the impurity ions present in the lattice is known as extrinsic conductivity.At low temperature region (ferroelectric phase),the conduction is dominated by the extrinsic conduction,whereas the conduction at the high-temperature paraelectric phase ($300–7008C)is dominated by the intrinsic ionic conduction [23,25].Fig.3shows the temperature dependence of dc conductivity (s dc )for the undoped and doped SBT samples.The curves show that the conductivity increases with temperature.This is indicative of negative temperature coefficient of resistance (NTCR)behavior,a characteristic of dielectrics [22].It is observed in Fig.3that throughout the temperature range,the dc conductivity of the doped samples are nearly two to three orders lower than that of the undoped sample.Two predominant conduction mechanisms indicated by slope changes in the two different temperature regions are observed in Fig.3.Such changes in the slope in the vicinity of the ferro-paraelectric transition region have been observed in other ferroelectric materials as well [23,24].In addition,it is also observed (Table 2)that the activation energy calculated using the Arrhenius equation [22]in the paraelectric phase increase from $0.80eV for the undoped sample to $2eV for the doped samples.The X-ray photoemission spectroscopic study has confirmed that when Bi 2O 3evaporates during high-temperature processing,vacancy complexes are formed in the (Bi 2O 2)2+layers [26].As a result,defective (Bi 2O 2)2+layers are inherently present in SBT.The undoped SBT shows n-type conductivity,since when oxygen vacancies are created,it leaves behind two trapped electrons [27]:O o !12O 2"þV o þ2e 0(1)where O o is an oxygen ion on an oxygen site,V o is a oxygen vacant site and e 0represents electron.The conductivity in the perovskites can be described as an ordered diffusion of oxygen vacancies [28].Their motion is manifested by enhanced ionic conductivity associated with an activation energy value of $1eV [26].These oxygen vacancies can be suppressed by addition of donors,since the donor oxide contains more oxygen per cation than the host oxide it replaces [29].It has been reported that conductivity in Bi 4Ti 3O 12(BIT)can be significantly decreased,up to three orders of magnitude with the addition of donors,such as Nb 5+and Ta 5+at the Ti 4+sites [23,30].A few other studies on layered perovskites have also reported a decrease inconductivityFig.1.XRD patterns of SrBi 2(W x Ta 1Àx )2O 9samples sintered at 12008C.Table 1Lattice parameters of SrBi 2(W x Ta 1Àx )2O 9samples.Concentration of W a (A ˚)b (A ˚)c (A ˚)0.0 5.5212 5.513924.92230.025 5.5214 5.520225.10790.05 5.5217 5.519925.05850.075 5.5191 5.504525.05670.10 5.5142 5.506125.0850.205.51335.493925.0861I.Coondoo et al./Materials Research Bulletin 44(2009)1288–12921289with addition of donors [23,24,31].In the present study,the Ta 5+-site substitution by W 6+in SBT can be formulated using a defect chemistry expression as WO 3þV o!Ta 2O 512W Ta þ3O o (2)It shows that the oxygen vacancies are reduced upon the substitution of donor W 6+ions for Ta 5+ions.Hence,it is reasonable to believe that the conductivity in SBT is suppressed by donor addition.As per the above discussion,the high s dc observed in the undoped SBT (Fig.3)can be attributed to the motion of oxygen vacancies.As already discussed,the doped samples show reduced conductivity because the transport phenomena involving oxygen vacancies are greatly reduced.The high E a value of $1.75–2eVcorresponding to the high-temperature region in the doped ceramics is consistent with the fact that in the donor-doped materials,the ionic conduction reduces [32].The activation energy E a in the low temperature ferroelectric region (Table 2)corre-sponds to extrinsic conduction.At lower temperatures the extrinsic conductivity results from the migration of impurity ions in the lattice.Some of these impurities may also be associated with lattice defects.Pure SBT has large number of Schottky defects (oxygen vacancies)in addition to impurity ions whereas in the doped samples,due to charge neutrality,there is relatively less content of oxygen vacancies.Thus,in the doped samples the conductivity in the low temperature region is largely due to the impurity ions only.This explains the high activation energy in pure SBT in the low temperature region compared to doped samples (Table 2).In the high-temperature region,the value of E a in the doped samples is observed to increase with W concentration up to x =0.05but beyond that,it decreases (Table 2).The decrease in the activation energy for samples with x >0.05suggests an increase in the concentration of mobile charge carriers [33].This observation can be ascribed to the existence of multiple valence states of tungsten.Since tungsten is a transitional metal element,the valence state of W ions in a solid solution most likely varies from W 6+to W 4+depending on the surrounding chemical environment [34].When W 4+are substituted for the Ta 5+sites,oxygen vacancies would be created,i.e.one oxygen vacancy would be created for every two tetravalent W ions entering the crystal structure,whichFig.3.Variation of dc conductivity with temperature in SrBi 2(W x Ta 1Àx )2O 9samples.Fig.2.SEM micrographs of fractured surfaces of SrBi 2(W x Ta 1Àx )2O 9samples with (a)x =0.0,(b)x =0.025,(c)x =0.050,(d)x =0.075,(e)x =0.10and (f)x =0.20Table 2Activation energy (E a )in the high-temperature paraelectric region and low temperature ferroelectric region;Curie temperature (T c )in SrBi 2(W x Ta 1Àx )2O 9samples.Concentration of W E a (high temp.)(eV)E a (low temp.)(eV)T c (8C)0.00.790.893110.025 1.920.593080.05 1.960.543250.075 1.940.543380.10 1.860.573680.201.740.54390I.Coondoo et al./Materials Research Bulletin 44(2009)1288–12921290explains the increase in the concentration of mobile charge carriers which ultimately results in an decrease in the E a beyond x>0.05. Hence it is reasonable to conclude that W ions in the SBWT exists as a varying valency state,i.e.at lower doping concentration they exist in hexavalent state(W6+)and at a higher doping concentra-tion,they tend to exist in lower valency states[8].The P–E loops of SrBi2(Ta1Àx W x)2O9are shown in Fig.4.It is observed that W-doping results in formation of well-defined hysteresis loops.Fig.5shows the compositional dependence of remanent polarization(2P r)and the coercivefield(2E c)of SrBi2(Ta1Àx W x)2O9samples.Both the parameters depend on W content of the samples.It is observed that2P rfirst increases with x and then decreases while2E cfirst decreases with x and then increases(Fig.5).The optimum tungsten content for maximum2P r ($25m C/cm2)is observed to be x=0.075.It is known that ferroelectric properties are affected by compositional modification,microstructural variation and lattice defects like oxygen vacancies[10,35,36].In hard ferroelectrics, with lower valent substituents,the associated oxide vacancies are likely to assemble in the vicinity of domain walls[37,38].These domains are locked by the defects and their polarization switching is difficult,leading to an increase in E c and decrease in P r[38]. On the other hand,in soft ferroelectrics,with higher valent substituents,the defects are cation vacancies whose generation in the structure generally increases P r.Similar observations have been made in many reports[38–41].Watanabe et al.[42]reported a remarkable improvement in ferroelectric properties in the Bi4Ti3O12ceramic by adding higher valent cation,V5+at the Ti4+ site.It has also been reported that cation vacancies generated by donor doping make domain motion easier and enhance the ferroelectric properties[43].Further,it is known that domain walls are relatively free in large grains and are inhibited in their movement as the grain size decreases[44].In the larger grains, domain motion is easier which results in larger P r.Also for the SBT-based system,it is known that with increase in the grain size the remanent polarization also increases[45,46].Based on the obtained results and above discussion,it can be understood that in the undoped SBT,the oxygen vacancies assemble at sites near domain boundaries leading to a strong domain pinning.Hence,as observed,well-saturated P–E loop for pure SBT is not obtained.But in the doped samples,the suppression of the oxygen vacancies reduces the pinning effect on the domain walls,leading to enhanced remanent polarization and lower coercivefield.Also,the increase in grain size in tungsten added SBT,as observed in SEM micrographs(Fig.2)contribute to the increase in polarization values.In the present study,the grain size is observed to increase with increasing W concentration.However, the2P r values do not monotonously increase and neither the E c decreases continuously with increasing W concentration(Fig.5). The variation of P r and E c beyond x>0.05,seems possibly affected by the presence of secondary phases(observed in XRD diffracto-grams),which hampers the switching process of polarization [47–50].Also,beyond x>0.05the increase in the number of charge carriers in the form of oxygen vacancies leads to pinning of domain walls and thus a reduction in the values of P r and increase in E c is observed.Fig.6shows the variation of piezoelectric charge coefficient d33 with x in the SrBi2(Ta1Àx W x)2O9.The d33values increases with increase in W content up to x=0.05.A decrease in d33values is observed in the samples with x!0.075.The piezoelectric coefficient,d33,increases from13pC/N in the sample with x=0.0to23pC/N in the sample with x=0.05.It is known that the major drawback of SBT is its relatively higher conductivity,which hinders proper poling[51].High resistivity is therefore important for maintenance of poling efficiency at high-temperature[52,53].The W-doped SBT samples show an electrical conductivity value up to three orders of magnitude lower than that of undoped sample(Fig.3).The positional variation of2P r and2E c in SrBi2(W x Ta1Àx)2O9samples.Fig.6.Variation of d33in SrBi2(W x Ta1Àx)2O9samples.Fig. 4.P–E hysteresis loops in SrBi2(W x Ta1Àx)2O9samples recorded at roomtemperature.I.Coondoo et al./Materials Research Bulletin44(2009)1288–12921291decrease in conductivity upon donor doping improve the poling efficiency resulting in the observed higher d33values.Moreover, since the grain size increases with W content in SBT,it is reasonable to believe that the increase in grain size will also contribute to the increase in d33values[54].The decrease in the value of d33for samples with x!0.075is possibly due to the presence of secondary phases as observed in diffractograms[1,51,55]and the increase in oxygen vacancies for samples with x>0.05.4.ConclusionsX-ray diffractograms of the samples reveal that the single phase layered perovskite structure is maintained in the samples with tungsten content x0.05.SEM micrographs reveal that the average grain size increases with increase in W concentration. The temperature dependence of the electrical conductivity shows that tungsten doping results in the decrease of conductivity by up to three order of magnitude compared to W free SBT.All the tungsten-doped ceramics have higher2P r than that of the undoped sample.The maximum2P r($25m C/cm2)is obtained in the composition with x=0.075.The reduced conductivity allows high-temperature poling of the doped samples.Such compositions with low loss and high P r values should be excellent materials for highly stable ferroelectric memory devices.The d33value is observed to increase with increasing W content up to x0.05.The value of d33 in the composition with x=0.05is$23pC/N as compared to$13 pC/N in the undoped sample.AcknowledgmentsThe authors sincerely thank Prof.P.B.Sharma,Dean,Delhi College of Engineering,India for his generous support and providing ample research infrastructure to carry out the research work.The authors are thankful to Dr.S.K.Singhal,Scientist, National Physical 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间隙腐蚀间隙腐蚀是发生于间隙及有停滞溶液之遮蔽表面处的局部电化学腐蚀。

若要产生间隙腐蚀，必须有一个间隙其宽度足够让液体进入，但却也可使液体停滞不流出。

因此，间隙腐蚀通常发生于开口处有百万分之几公尺或更小宽度的间隙。

粒间腐蚀粒间腐蚀是发生在合金晶界及晶界附近的局部腐蚀现象。

在正常情况下，若金属均匀腐蚀时，晶界的反应只会稍快于基质的反应。

但在某些情况下，晶界区域会变得很容易起反应而导致粒间腐蚀，如此会使合金的强度下降，甚至导致晶界分裂。

应力腐蚀金属的应力腐蚀破裂(SCC)是指由拉伸应力及腐蚀环境结合效应所导致的破裂。

在SCC期间，金属表面通常只受到很轻微的侵蚀，但局部裂缝却很快沿着金属横断面传播。

产生SCC所需的应力可以是残留应力或施加应力。

裂缝会开始于金属表面上的蚀孔或其他不连续处。

在裂缝开始成长时，其尖端会开始向前，此时作用在金属上的拉伸应力会在裂缝尖端处形成高应力，当裂缝尖端向前传播时，在裂缝尖端处也会产生电化学腐蚀而使阳极金属溶解。

裂缝会沿着垂直于拉伸应力的方向成长，直到金属破坏为止。

若应力或腐蚀其中任一停止，则裂缝将停止成长。

冲蚀腐蚀冲蚀腐蚀可被定义为由于腐蚀性流体与金属表面相对运动而导致金属腐蚀速率加速的现象。

当腐蚀性流体的相对运动速率相当快时，机械磨擦效应将会相当严重。

冲蚀腐蚀的特征为金属表面具有与腐蚀性流体流动方向相同的凹槽、蚀孔与圆孔等。

涡穴损伤此类型的冲蚀腐蚀是由接近金属表面之液体中的气泡及充气孔穴破灭所造成的。

涡穴损伤通常发生在具有高速液体流动及压力改变的金属表面。

移擦腐蚀移擦腐蚀发生在材料承受振动及滑动负荷的界面处，它会形成具有腐蚀生成物的凹槽或蚀孔。

当金属发生移擦腐蚀时，磨擦表面间的金属碎片会被氧化且某些氧化膜会因磨擦动作而剥落，因此摩擦表面间会累积可当研磨剂用的氧化物颗粒。

选择性腐蚀选择性腐蚀是指固体合金内某一特定金属被优先去除的腐蚀过程。

此类型腐蚀最常见的例子是黄铜内之脱锌作用。

第29卷　第4期2008年8月大连交通大学学报JOURNAL　OF　DAL I A N　J I A OT ONG　UN I V ERSI TYVol.29　No.4　Aug.2008　　文章编号:167329590(2008)04200682045083铝合金搅拌摩擦焊焊缝的电化学腐蚀行为赵亚东1,沈长斌1,刘书华1,葛继平1,黄振晖2,董春林3(1.大连交通大学材料科学与工程学院,辽宁大连116028; 2.中国北车集团唐山轨道客车有限责任公司产品研发中心,河北唐山063035; 3.中国搅拌摩擦焊中心,北京100024)摘　要:通过室温静态挂片实验以及动电位极化曲线测试,在0.2mol/L NaHS O3+0.6mol/L NaCl溶液中,对5083铝合金搅拌摩擦焊(FS W)焊缝以及5083铝合金母材的电化学腐蚀行为进行了研究.结果表明:主轴转速为300r/m in,焊接速度为160mm/m in,搅拌头倾角为3°时的焊缝与母材相比,平均腐蚀速率较小,腐蚀电位Ecorr 正向移动,腐蚀电流Icorr变小.同时使用扫描电子显微镜(SE M)对室温静态挂片实验试样的表面形貌进行了观察,发现焊缝表面上局部只出现少量较浅的点蚀坑,而母材表面的点蚀现象较为严重.关键词:铝合金;搅拌摩擦焊;焊缝;电化学腐蚀中图分类号:TG172.9文献标识码:AElectrochem i ca l Corrosi on Behav i or of Fr i cti on Sti rW eld i n g W eld of5083A lu m i n u m A lloyZHAO Ya2dong1,SHEN Chang2bin1,L I U Shu2hua1,GE J i2p ing1,HUAN Zhen2hui2,DONG Chun2lin3(1.School of M aterials Science and Engineering,Dalian J iaot ong University,Dalian116028,China;2.R&DCenter,CNR Tangshan Rail w ay Vehicle Co.,L td,Tangshan063035,China;3.China FS W Center,Beijing100024,China)Abstract:Electr oche m ical corr osi on behavi or of fricti on stir welding weld of5083alu m inum al2l oy and parent material were comparatively investigated in the s oluti ons of0.2M NaHS O3and0.6M NaCl at r oom te mperature by static weight l oss experi m ent(gravi m etric test)and poten2ti odyna m ic polarizati on technique.The corr osi on rate of the weld at the t ool r otati on rate of300r/m in,and the traverse s peed of160mm/m in with3°t ool tilt was less than that of the parent ma2terial.The corr osi on potential of the weld was more positive than that of the parent material,andthe corr osi on current density was less than that of the parent material.SE M observati on showedthat a fe w shall ow p its p resented on the surface of the weld,however,a large number of deeperp its e merged on the surface of the parent material.Key words:alu m inu m all oy;fricti on stir welding;weld;electr oche m ical corr osi on铝合金搅拌摩擦焊焊缝的腐蚀性能研究具有一定的理论意义和工程应用价值.作者对5083铝合金搅拌摩擦焊焊缝在室温0.2mol/L NaHS O3+0.6mol/L NaCl溶液中的电化学腐蚀行为进行了较为详尽的研究.3收稿日期:2007211223基金项目:大连市经委资助项目作者简介:赵亚东(1983-),男,硕士研究生E2ma il:shencb@.　第4期赵亚东,等:5083铝合金搅拌摩擦焊焊缝的电化学腐蚀行为691　试验材料及方法试验材料采用厚度为8mm的5083铝合金,其化学成分见表1所示.试验所采用的搅拌摩擦焊试件是在北京赛福斯特技术有限公司提供的搅拌摩擦焊设备上进行,其工艺参数为:主轴转速为300r/m in,焊接速度为160mm/m in,搅拌头倾角为3°.表1　5083铝合金的化学成分%材料Si Fe Cu Mg Mn Cr Zn Ti其它A l50830.400.400.10.40 4.40.090.250.150.15余量静态失重试验(质量法)中的样品处理方法是先用水磨碳化硅砂纸打磨至1000#,然后用去离子水冲洗,酒精除油脂,吹风机吹干,置于干燥器中备用.腐蚀介质采用0.2mol/L NaHS O3+0.6mol/L NaCl混合溶液,所用NaHS O3、NaCl为分析纯试剂,用去离子水进行配制.样品悬挂于盛有2000mL室温0.2mol/L NaHS O3+0.6mol/L NaCl溶液的长方体状电解池底部,平行样品数为3个.挂片一定时间后,取出样品,先用50mL H3P O4+20g Cr O3+1L蒸馏水配成溶液去除腐蚀产物后,再浸入浓硝酸5m in除去残余的腐蚀产物[1].使用的电子天平由上海民桥精密科学仪器有限公司生产的,型号为F A1104A,精度达到0.1mg.动电位极化曲线是在上海辰华仪器公司生产的CH I600B型电化学工作站上进行的.电解池为全玻璃电解池,三电极系统,极化范围为-1.5～1.5V,扫描速度为0.01V/s,参比电极为饱和甘汞电极(SCE),辅助电极为光亮箔片(面积为3c m2),工作电极通过线切割从大块样品取得,工作面积为1c m2 (注:焊缝的取样原则是尽量取焊缝中间区域),其余非工作表面镶嵌在单组分室温硫化硅橡胶中.工作电极的工作表面的处理方法与静态失重实验中样品的处理方法一样,腐蚀介质亦一样.扫描电子显微镜(SE M)观察采用日本JEOL公司生产的JS M-6360LV型扫描电子显微镜.2　结果与讨论2.1　静态失重试验(质量法)静态失重法(质量法)是最简单和可靠的确定腐蚀速率的方法,它用于测量整个腐蚀期间的平均腐蚀速率.失重试验的结果列入表2(表2中的样品1号为5083铝合金搅拌摩擦焊焊缝,样品2号为5083铝合金母材).使用了三个平行试样,腐蚀速率ν通过下式计算:ν=m0-m1s×t(1)式中,m0为腐蚀试验前的试样质量;m1为腐蚀试验后的试样质量;s为暴露于腐蚀介质的试样总面积;t为腐蚀试验时间.根据式(1),主轴转速为300r/m in,焊接速度为160mm/m in,搅拌头倾角为3°时焊缝的平均腐蚀速率小于5083母材的平均腐蚀速率.表25083铝合金搅拌摩擦焊焊缝和母材在室温0.2m ol/LNaHS O3+0.6m ol/L NaC l溶液中静态失重测试结果试样编号s×10-6m2m1gm2gthv×10-1g・m-2・h-1v×10-1g・m-2・h-1 1146 6.0276 6.020124 2.7311139 6.0062 5.9980243 2.88 1146 6.0323 6.024324 2.911160 6.2421 6.231624 3.7721160 6.2787 6.267724 3.95 3.89 1160 6.2425 6.231524 3.9570　大连交通大学学报第29卷2.2　5083铝合金搅拌摩擦焊焊缝的动电位极化曲线图15083铝合金搅拌摩擦焊焊缝和母材在室温0.2m ol/L NaHS O 3+0.6m ol/L NaC l 溶液中的动电位极化曲线表35083铝合金搅拌摩擦焊焊缝和母材在室温0.2m ol/L NaHS O 3+0.6m ol/LNaC l 溶液中的电化学参数试样Ecorr/mV SCE I corr /(μA ・c m -2)1-709.310.032-717.520.15083铝合金搅拌摩擦焊焊缝的动电位极化曲线如图1所示.对焊缝和母材在室温0.2mol/L NaHS O 3+0.6mol/L NaCl 溶液中的动电位极化曲线进行分析,得出它们的腐蚀电位E corr 和腐蚀电流I corr ,其结果见表3.从结果中可以看出,5083铝合金搅拌摩擦焊焊缝的腐蚀电位E corr 大于母材的腐蚀电位E corr ,其腐蚀电流I corr 值约为母材的1/3.焊缝的动电位极化曲线位于母材的动电位极化曲线的左上侧.图1和表3表明主轴转速为300r/m in,焊接速度为160mm /m in,搅拌头倾角为3°时焊缝的耐腐蚀能力与母材相比较好.2.3　5083铝合金搅拌摩擦焊焊缝腐蚀形貌对失重后的样品用肉眼观察发现,5083铝合金搅拌摩擦焊焊缝的腐蚀形貌均一,相对比较平坦,5083母材的腐蚀形貌比较粗糙,点蚀现象比较严重.图2是1号试样和2号试样的扫描电子显微镜(SE M )的失重试验后的表面形貌图.图2　铝合金搅拌摩擦焊焊缝和母材的腐蚀形貌图(×50)2.4　讨　论在搅拌摩擦焊过程中,焊缝区要经受严重塑性变形,导致晶粒尺寸减小,单位面积内晶粒数目增加,位错密度增加,残余应力也增大(归结为因素1),同时,也使得焊缝区的化学成分均质化(归结为因素2)[2].根据经典理论,材料经过严重塑性变形后单位面积内的晶粒的数目增加,单位面积内的晶界数目亦增加,位错密度增大,这些晶体缺陷的大量增加导致了晶粒和晶界在电化学性能上的不均匀性增大[3],残余应力也增大,从而使材料的耐腐蚀能力降低,即因素1会导致材料耐腐蚀性能的恶化.从腐蚀学的角度,化学成分均质化,降低了材料形成局部腐蚀原电池的倾向,从而提高了材料的耐腐蚀性能[4],即因素2会提高材料耐腐蚀性能.因此,材料经过搅拌摩擦焊后,与母材相比,其电化学腐蚀性能的变化,取决于以上两种因素综合作用的结果,即谁占主导地位.假如,前者占主导地位,材料的电化学腐蚀性能降低[5];假如,后者占主导地位,材料的电化学腐蚀性能得到提高[629].根据实验结果,5083铝合金搅拌摩擦焊焊缝的平均腐蚀速率比5083母材的平均腐蚀速率小,其腐　第4期赵亚东,等:5083铝合金搅拌摩擦焊焊缝的电化学腐蚀行为71　蚀电流也比母材的腐蚀电流小,焊缝的腐蚀电位E corr 与母材的腐蚀电位E corr 相比,向正向移动.焊缝的腐蚀形貌均一,相对比较平坦,但是母材的腐蚀形貌比较粗糙,点蚀现象比较严重.焊缝的电化学腐蚀性能与母材相比,得到提高,是由于焊缝的化学成分均质化占主导地位.3　结　语(1)在室温0.2mol/L NaHS O 3+0.6mol/L NaCl 溶液中,主轴转速为300r/min,焊接速度为160mm /m 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