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AD-A267 205ARmyW RESEARCH LABORATORYAssessment of Chromate andNon-Chromate Conversion Coatingsfor Al Alloys Using ElectrochemicalImpedance SpectroscopyF. Chang, M. Levy, andR. HuieARL-TR-1 42Jue13DTIC.S JL21199 3Approved .for public release; distribution unlimited.I-D1II63I 76l'IfCioI*3
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includingeni met for revwevtg Intructionls. searchingexistingd a souces,Pubi creporting burden for t11. collecUtioof Information isestimatedto average1 hour Per responsie.regardingMaiburdmnestixme ora"amter aspectof Itutsof Informtiaon.Send conwtientsold rev wwg the collectiongflt rng amt mtaWttaiinthedael needed.arlt COMPiebingfor Infome b"ionpereiltso and! Reports. 1215 Jeffersoncollection,of Infrtefo.inudg ugeb"f fOrreducing "SthiX w. to washigon IHeadilu llers SeN.,.,. Directoratesant B get. Psotoi Reductio Prqect (0190.188). Wasigot CC 2053.22202-4302. and 10the Offie of MagDavis Hihway. Suie 0.Ato.V2. REPORT DATEblank)1. AGENCY USE ONLY 'LleaveJune 19933. REPR TYPAND DATES COVEREDReprint-Final4. TITLE AND SUBTITLEReportS&FUNDING NUMBERSAssessment of Chromate and Non-Chromate ConversionCoatings for Al Alloys Using ElectrochemicalImDedance Spectroscopy6. AUTHOR(S)F. Chang, M. Levy, and R. Huie11.PERFORMING ORGANIZATION7.PERFORMING ORGANIZATION NAME(S) AND ADORESS(ES)U.S. Army Research LaboratoryREOTNMRWatertown, MassachusettsATTN: AMSRL-MA-MA02172-0001ARL-TR- 142S.SPONSORING/MONITORING AGENCY NAMAE(S)AND ADORESS(ES)10. SPONSORINIGMONITOICI NGAGENCY REPORT NUMBERU.S. Army Research Laboratory2800 Powder Mill RoadAdeiphi, Maryland 20783-119711.SUPPLEMENTARY NOTESPublished in Proceedings of the Tni-Service Conf. on Corrosion, May 12-14,1992, Plymouth, MA12b. DISTRIBUTION CODE12e. DISTRIBUTIONIAVAILASIlI1Y STATEMENTApproved for public release; distribution unlimited.j200 etordti;13.ABSTRACT (AftornmwnA study was conducted to evaluate whether a nun-chzr.mate conversioncoating (Sanchem) for Al alloys (Al 2024 and 7075) could be a suitablereplacement for the currently used chromate conversion coating (Alodine)without compromising corrosion resistance.Electrochemical impedancespectroscopy (EIS) and, salt spray testing were employed to compare thecorrosion behavior of coatings consisting of a) pretreatment only (Sanchemor Alodine), b) pretreatment (Sanchem or Alodine) plus primer (epoxypolyamide or waterborne epoxy), and c) pretreatment (Sanchem or Alodine)plus epoxy polyamide primer plus polyurethane topcoat.Results indicatedthat the experimental impedance values provided a reliable estimate of thefilm integrity and corrosion protective capability, that the Sanchem conversion coating generally compared favorably with the Alodine coating, andthat higher impedance values attributed to the application of topcoat ofboth alloys which were treated with either Sanchem or Alodine and epoxypolyamide are characteristic of low conductivity, good barrier type coatings. However, additional tests are required before the Sanchem can berecommnended as a reliable alternative to the Alodine coating.Is. SUBJECT TERMS15.NUMBER OF PAGESAluminum alloys, Chromate coatings, Non-chromate coatingsCorrosion resistance, and EISI17.SECURITY CLASSIFICATIONOF REPORTUnclassifiedNSN 754001.280.5501S.SECURITY CLASSIFICATIONOF THIS PAGE19.SECURITY CLASSIFICATIONOF ABSTRACTUnclassifiedUnclassified21IS.PRICE CODE20.LIMITATION OF ABSTRACTULStmndardl Form 2969(Ron, 2 89)1Pr.scnbeitbypANSI Std Z-31%
&lcedAssessment of Chromate and Non-Chromate Conversion Coatings for AlAlloys Using Electrochemical Impedance Spectroscopy By.El--------.Distribution IF. Chang, M. Levy, R. Huie,Army Materials Technology Laboratory,Watertown, MA 02172-0001IntroductionAvailability CodesAvail and (orSpecialDist/Environmental restrictions are demanding changes in common coatings such as chromium (Cr') and cadmium as well as processing technologiesincluding electroplating and immersion treatments that produce high levels ofhazardous materials at Army Depots. Concomitantly there is a dramaticincrease in cost and logistical problems associated with safe waste disposal.As a consequence new alternative environmentally acceptable solutions mustbe found.Chromium and its salts that are used in the processing of conversioncoatings for Al alloys are on the Environmental Protection Agency's list of 17materials that the Government and industry are trying to reduce by 50% by1995. This paper evaluates whether a non-chromate conversion coating for Alalloys could be a suitable replacement for the currently used Alodine chromate conversion coating without compromising corrosion resistance. Specifically, Electrochemical Impedance Spectroscopy (AC Impedance) and saltspray testing have been employed to compare the corrosion behavior of thenon-chromate conversion coating against the Alodine treatment in combination with selected primers and a topcoat.ExperimentalCoated test panels, 7.62 cm x 12.7 cm x 0.1 cm, were supplied by theNaval Air Warfare Center (NAWC), Warminster, PA, as shown in Table 1.Before AC Impedance testing each treated panel was removed from adesiccator and examined visually for the presence of defects. Each panel waspositioned in the test cell shown in Figure 1 without any water rinsing orsolvent cleaning. AC impedance was performed with a PAR 378 Electrochemical Impedance System consisting of a 5208 two-phase lock-in analyzer,a model 273 potentiostat/galvanostat, and a IBM PC XT computer and printer.Periodic measurements were made from the sample exposed to 0.5N NaCIsolution at the corrosion potential (stabilized within 1 hour) over the frequency (f) range 5 mHz to 100 KHz during a 300 day period at room tempera181
ture. The single sine technique with an input sinusoidal voltage of 5 mV wasused in the frequency range 100 KHz - 5 Hz. In the frequency range 10-0.005Hz, the multisine technique was used with an input sinusoidal voltage of 10mV. The data collected were plotted and evaluated in both Bode and Nyquistformats. Impedance values were extrapolated from the linear region of theBode plot at low frequency to 1 mHz at the log IzI axis and plotted as a function of exposure time. Mansfeld and Kendig (1) have used similar experimental data for determining corrosion resistance of anodized Al alloys. Leidheiser(2) has reported that coating system impedance measured by AC impedancetechniques degraded with time: at a lower limit of about 106 ohms cm2 corrosion was found to occur underneath the coating. Salt spray testing by theNAWC was performed in accordance with ASTM B 117, using a 5% NaCIsolution at 950F.ResultsPre-Treatment Only TestsFigure 2 contains plots of impedance (derived from Bode plots, log Izivs. log f) as a function of exposure time for Al 2024-T3 samples treated withan aqueous solution of chemicals conforming to MIL-C-81706 (standardAlodine chromate conversion coating) and with the Sanchem Boehmiteprocess (non-chromate conversion coating, processing steps shown in Figure3). The Sanchem treated sample characteristically exhibits an order of magnitude higher impedance than the standard Alkdine treated alloy (10' vs. I0Yohms cm 2 ). Also, the Sanchem treated material showed no evidence of degradation (decrease in impedance) over a 200 day period of exposure to the 0.5NNaCl solution. After 75 days of exposure the Alodine treated alloy showed adecreasing trend in impedance, thus increasing the difference in impedancebetween the two conversion coatings, indicating a reduction in its corrosionresistance. Figure 4 contains SEM photomacrographs showing the Sanchemand Alodine treated Al 2024 alloys before and after completion of the impedance test. The Sanchem treated alloy remained unaffected after the 200 hourexposure to 0.5N NaCI solution while the Alodine treated alloy(1) F. Mansfeld and M.W. Kendig, Impedance Spectroscopy as QualityControl and Corrosion Test for Anodized Al Alloys, CORROSION, 41, (8),490 (1985).(2) H. Leidheiser, Jr., Review of Electrochemical and Electrical MeasurementMethods for Predicting Corrosion at the Metal-Organic Coating Interface,CORROSION, 38, (7), 374 (1982).182
showed the presence of pits and corrosion products. These observations are inaccord with the impedance data. Nevertheless both treatments passed the 336hour salt spray test (Table 1).Plots of impedance as a function of exposure time for both treatmentson the Al 7075-T6 alloy are shown in Figure 5. Impedance values for theintervals up to 40 hours of exposure time are fairly constant for both meatments, although the Alodine treatment exhibits somewhat higher values. Forboth treatments, as exposure time increased to 200 hours impedance valuesgenerally decreased but the Sanchem processed alloy displayed the lowerimpedance. The impedance data are in good agreement with thephotomacrographs shown in Figure 6; the Alodine treatment provided bettercorrosion reb-istance than the Sanchem treated alloy. But both treatmentsprovided the Al 7075-T6 alloy with 336 hours of acceptable salt spray resistance (Table 1).The Alodine and Sanchem conversion coatings were analyzed by anESCA/Auger and Scanning Auger Microprobe (SAM) before and after theimpedance tests. The results of Auger analyses are contained in Figures 7 and8. The Auger spectra for the Alodine treated Al 2024-T3 and Al 7075-T6alloys (Figure 7 a -d) show that the conversion coating (thickness - 2000A*)contains chromate as the major constituent both before and after the test.Aluminum is neither present as a constituent of the coating nor exposed as thesubstrate. These data are in good agreement with the other reported test data.Comparable spectra for the Sanchem treated alloys (Figure 8 a - d) indicatesthe conversion coating (4000A" thick) contains an oxide of aluminum as themajor constituent. This coating remains essentially intact after 200 hours ofexposure to the 0.5N NaCI solution. These data also appear to be in accordwith the other test data.Pre-Treatment plus MIL-P-23377 Epoxy Polyamide Primer TestsThe effect of the epoxy polyamide primer (MIL-P-23377) on theimpedance of Al 2024-T3 which was pretreated with either the Alodine orSanchem process is shown in Figure 9. The impedance values are in therange 106 to 107 ohms cm 2 . This primer significantly improves the performance of the Alodine treated alloy; impedance increased from 105 to 107 forthe first 65 days of exposure. Beyond 65 days the impedance drops to 106ohms which is comparable to the impedance of the Sanchem plus primersystem. The epoxy primer had little effect on the performance of the Sanchemtreated alloy; the impedance which was constant throughout the 200 days ofthe test remained at 106 ohms cm 2 , which was surprisingly equivalent to the183
bare pretreatment values after exposure. Post test visual examination showedno evidence of corrosion for either protective scheme. However microscopicexamination of the Alodine plus primer system revealed a small blister whichappeared unbroken (Figure 10a). This defect however did not appear to affectthe impedance. At times, impedance plots may be insensitive to certain paintcoating failures such as the formation of non-perforated blisters. If the blisterhad been perforated the impedance would fall (3). Microscopic examinationof the Sanchem plus primer system showed no evidence of corrosion (Figure10b).Impedance vs. time plots for the Al 7075-T6 alloy treated with eitherthe Alodine or Sanchem process in combination with the MIL-P-23377 primerare contained in Figure 11. Impedance values for both systems were higherthan the bare pretreated samples and remained quite stable during the entiretest; the Alodine treated scheme impedance was 107 ohms cm 2, the Sanchemprocessed scheme was 106 ohms cm 2 . Post-test microscopic examination(Figures 12a b) showed the presence of small unperforated blisters in bothprotective schemes but they were undetected by the impedance plot.Both alloys treated with Alodine-P-23377 primer scheme passed the336 hour salt spray test and the Sanchem/MIL-P-23377 primer processedalloys completed 1000 hours of salt spray without failure.Pre-Treatments Plus MIL-P-85582 Waterborne Epoxy Primer TestsFigure 13 compares impedance vs. time plots for Al 2024-T3 given theAlodine and Sanchem pretreatments plus an overcoat of the waterborne epoxyprimer. Impedance values are in the same range (106-107 ohms cm 2 ) asreported above for the MIL-P-23377 epoxy polyamide primer. The plot forthe Alodine treated systems shows that impedance fluctuated with time butremained above 106 ohms cm 2. The Sanchem pretreatment exhibited relatively stable behavior during the course of the exposure (106 ohms cm 2 ). Posttest microscopic examination showed the presence of several non-perforatedblisters on the Alodine/primer scheme and a single non-perforated blister wasobserved on the Sanchem/primer scheme (Figure 14 a b). Again, theseblisters passed unnoticed in the impedance plot.(3) S. Feliu, J.C. Galvan and M. Marcillo, "The Charge Transfers Reaction inNyquist Diagrams of Painted Steel", Proceedings of the Symposium onAdvances in Corrosion Protection by Organic Coatings, Volume 89-13,p. 281, Electrochemical Society, 1989.184
Impedance vs. time plots for these protective schemes applied to theAl 7075-T6 alloy are contained in Figure 15. The very erratic impedancebehavior of the Sanchen/MIL-C-85582 primer treated alloy (impedancebelow 105 ohms cm 2 after 200 hours of exposure) is reflected in thephotomacrograph of Figure 16a which shows the presence of numerousblisters, both perforated and unperforated. The Alodine/primer treated alloydisplays some fluctuation in impedance but generally remains in the range of106 to 107 ohms cm 2 . A single unperforated blister is revealed in the post testmicroscopic examination (Figure 16b). Nevertheless these protective schemespassed the 336 hour salt spray test.Pre-Treatments Plus Primer Plus Topcoat TestsImpedance values for this series of protective schemes (Figure 17)were higher than our other samples (107 - 109 ohms cm 2 ). These higherimpedance values are characteristic of low conductivity, good barrier typecoatings. Differences between the Alodine and-Sanchem pretreatments areminimal, particularly in the case of the Al 7075-T6 alloy where the impedance is 109 ohms cm 2 in the time intervals between 200 and 320 days. Microscopic examination supports the impedance data although some staining wasobserved only on the Sanchem treated alloys (Figure 18 a b).Conclusions1.The good agreement between the impedance data, microscopic observations, and salt spray results suggests that the experimental impedance valuesprovide a reliable estimate of the film integrity and corrosion protectivecapability of the coatings/substrates studied. However, at times, impedancevalues appeared to be insensitive to the formation of non-perforated paintblisters; in the case where the ionic resistance of the paint film is much greaterthan the metal transfer resistance.2.The non-chromate conversion coating generally compared favorablywith the standard chromate conversion coating; used singly'or in combinationwith a primer and topcoat. Additional testing is required before we canrecommend this environmentally acceptable conversion coating as a reliablealterna:ive to the currently used chromate conversion coating.3.The higher impedance values attributed to the application of thetopcoat to both alloys which were treated with either the non-chromate or185
chromate conversion coating and the MIL-P-23377 epoxy polyamide primerare characteristic of low conductivity, good barrier type coatings.AcknowledgementThe authors gratefully acknowledge the assistance of Steve Spadafora,NAWC, in providing the coated test panels and salt spray data.186
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COATEDWO-- ING ELECTrROoCZNNECTIOfiMEOTr. IPE-MENFig. I Test Cell for Electrochemical Impedance MeasurementsFig. 2 Al 2024, Sanchem vs. Alodine.7S-Sanchern--3001209060I80150210Time (Days)Fig. 3 Non Chromated Conversion CoatingsSANCHEM Boehmile Coating ProcessSolvent Cleanv a ll-set109.-AlkalineEtch Clean--mW.ptwq.SoEr.1.a015t74. Deoxiclize,D'.SEAL #1SEAL #2Nitrate --PermanganateAlr0N.S%WO.,188SForm Coatingl Water-).9S. A 0.'59Seal #3---*Silicateee*-Alodine
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Fig. 5 Al 7075, Sanchem vs. AlodineoO Sanchen'SAlodirtc0306012090limeISOI80210(Days)Fig. 6 Saiichern vs. Alodine on 70 75 AlA. Sanchem Before Testing at lOOXC. Alodine Before Testing at lOOXB. Sanchem After Testing at lOOXD. Alodine After Testing at lOOX190
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Fig. 9 Al 2024 P23377, Alodine vs. Sanchern8700 SarichcmrSAlodine6 -103060X Macro of Al 20246090120Time(Days)15018021060X Macro of Al 2024 P23377with Sarichemn After 200 Days P237with Alodine After 200 DaysFig. 10193
Fig. II Al 7075P23377, Sanchem vs. Alodine s)(a(b).460X Macro of Al 7075 P23377with Alodine After 200 Days60X Macro of A] 7075 P23377with Sanchem After 200 DaysFig. 12194
Fig. 13 Al 2024 P85582, Sanchem vs. Alodine7SS -030 6090Time'201500Sa.ncha'n'.OtDay )(a)(b)40X Macro of Al 2024 P85582with Alodine After 200 Days-- 40X Macro of Al 2024 P85582with Sanchemn After 200 DaysFig. 14195
Fig. 15 Al 7075N P85582, Sanchem vs. Alodine7-C30 3a)090Timei20(Days)iS0180M--.C.2iG (lox Macro of Al 7075 P85582with Sanchemn After 200 Days60X Macro of Al 7075 P85582with Alodine After 200 DaysFig. 16196
(a) C83286 P23377Al 2024Sanchemnvs. 00360Time (Days)Fig. 17 C83286 P23377(b) Al 7075Sanchemvs. Alodine10-Cý8Sanchem,Alodinc 7.060120180240300360Time (Days)(a)-(b)" ".60X Macro of Al 7075 P23377 C83286 with Alodint After 200 Days-'"60X Macro of Al 7075 P23377 C83286 with Sanchemn After 200 DaysFig. 18197
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Pre-Treatment plus MIL-P-23377 Epoxy Polyamide Primer Tests The effect of the epoxy polyamide primer (MIL-P-23377) on the impedance of Al 2024-T3 which was pretreated with either the Alodine or Sanchem process is shown in Figure 9. The impedance values are in the range 106 to 107
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ARL established the Center for UAS Propulsion with four academic institutions: University of Illinois at Urbana—Champaign, . ARL is engaging with joint faculty appointments and senior leadership (Vice Chancellor of Research, Vice President of Research, Federal Liaisons) to . Pascal and the Hochschule Mannheim. Mr. Austen Motily is a PhD .
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5 HIGHLIGHTS ARL ACADEMIC LAW LIBRARY STATISTICS, 2002-03 Out of 113 ARL university libraries, 75 responded to this survey.1 Law libraries reported median values of 304,887 volumes held and 8,248 volumes added. Also, these libraries employed the full-time equivalent of 2,243 staff members in the fiscal year 2002-03. Responding libraries
Edward .M. J Colbert (Editor, Chaps. 1 , 2 , 11 , and 16 ) currently performs com-puter security research for the Army Research Laboratory (ARL) in Adelphi, Maryland. At ARL, Dr. Colbert leads research on methods for defending Army SCADA and ICS systems. Before working at ARL, Dr. Colbert performed telecom-
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3 CLEFS The clef, a symbol that sits at the leftmost side of the staff, specifies which lines and spaces belong to which notes. In a sense, the clef calibrates or orients the staff to specific notes. The three most common clefs are: The Treble clef for high range notes The Bass clef for low range notes The Alto clef for middle range notes The Treble clef (also called the G Clef because it .
