ANODIZE AND PRIME YOUR ALUMINUM WITHOUT ENVIRONMENTAL HEADACHES Robert L. Floyd, Jr. Blair C. Maddock Lockheed Aeronautical Systems Company Marietta,

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1 ANODIZE AND PRIME YOUR ALUMINUM WITHOUT ENVIRONMENTAL HEADACHES Robert L. Floyd, Jr. Blair C. Maddock Lockheed Aeronautical Systems Company Marietta, Georgia

3. PERFORMANCE Fluid resistance, corrosion resistance, and topcoat adhesion are critical measures of a primer system's performance. Resin-seal does well in all three categories. 3.

2 3. PERFORMANCE Fluid resistance, corrosion resistance, and topcoat adhesion are critical measures of a primer system's performance. Resin-seal does well in all three categories. 3.1 Fluid and Corrosion Resistance Testing has, to date, focused on aircraft applications. Of primary interest is RSA's resistance to fluids and service environments. Performance of the system is excellent in this regard, as shown in Table 1. Even without a topcoat, resin-seal anodized aluminum resists standard oils, hydraulic fluids, and jet fuel. Similarly, humidity and filiform corrosion tests show resin-seal perforrnance acceptable for aircraft environments. However, the simulated fuel tank exposures indicate that RSA with no topcoat is unsuitable for such applications; iron chloride and microbial byproducts, common fuel contaninants, attack the resin at elevated temperatures. For aircraft fuel tanks, a fuel-resistant topcoat would be required. 3.2 Topcoat Adhesion Adhesion tests show that the resin-seal anodic film is suitable for topcoating withoi;: a primer. As summarized in Table 2, testing demonstrates that both typical aerospace primers and topcoats adhere well to the resin surface. This allows elimination of the primer application step for those components requiring a topcoat, saving labor, reducing aircraft weight, and avoiding VOC and chromate generation. 4. BENSFITS Resin-seal anodizing reduces both volatile and liquid waste emissions while offering reduced manufacturing a d in-service costs. 4.1 Environmental Benefits The Lockheed Aeronautical Systems Company (LASC) plant in Marietta, Georgia is scjject to the Georgia Air Pollution Control Regulations ( ). Rule (ii) - Miscellaneous Metal Parts Coating governs most of the operations affected by RSA. Current painting and coating operations are severely reszricted by Georgia air 338

3 regulations. "Non-compliant" pa-:.ts, which contain over 0.42 kg/l (3.5 lb/gal) VOC, may only be applied -n controlled paint booths or with control equipment. Although compliant paints are used for some finishes, most of the paint applied in 199: was non-compliant. On average in 1990, over 45% of 7r.e monthly VOC emissions in Mar etta were attributed to the application of primers on aircraft parts - fin sh codes 1, 17, 19, 54, and 119 in Figure 2, totalling over 30% of the vo me of paint used. These coatings contribute a greater share of emissions than other finishes due to the lower volume of solids they contain, and the transition from them to resin-seal anodizing could substantially reduce VOC emissions, as shown in Figure 2. Of course, by reducing the volume of paints and coatings sprayed, the switch to resin-seal also reduces the level of direct exposure that painters experience. Much aerospace hardware is coated by hand-applied, air-atomized spray painting, so chis is significant. Conventional coating systems atomize many harmful compounds, including organic solvents, chrome compounds, and metal oxides. T~LS RSA benefits not only the general environment, but also the specific workplace environment. Coupled with the reduction in air emissions is the reduction in the hazardous waste stream from the conventional coating operations. Over 113,500 kg (250,000 lb) of waste paints, paint sludge and used solvents were transferred to hazardous wasce disposal and recycling companies during the last six months of 1990 at a cost exceeding $200,000. Transition to RSA will not only reduce this waste stream overall, but will significantly reduce the volume of one of the most objectionable waste products: the chromates present in all primers used at LASC. 4.2 Cost Reduction Aside from direct environmental benefits, RSA offers the potential for significant cost reductions and avoidance. For LASC, savings of 10-37% in finishing costs have been projected due to replacing conventional finishes with the RSA process. The savings results from eliminating the labor used to apply primer coats. Actual savings for other users will vary depending on the process ng methods being replaced and the degree to which they must add faci ities. For example, current users of sulfuric acid anodizing will genera ly only 339

4 require a new stainless steel tank and lid with the associated controls, and, in some cases, an additional rinse tank. Some changes in processing parameters - time, temperature, or bath chemistry - may be required in the rest of their existing anodizing system, but the equipment should be adequate. For an all new facility, the choice of resin-seal anodizing for aluminum processing may reduce or eliminate the requirements for treatment of the process stream to remove VOCs. Not only will initial facilities costs be reduced, but recurring operational costs will be reduced as well; power, filters, carbon, and maintenance associated with VOC removal systems are continuing expenses for the life of the equipment. As with existing facilities converting to RSA, the actual savings depend on the user, but can be dramatic when compared with other alternatives. Since resin-seal is a lighter system than alternative aluminum finishes, if weight is a factor in the operating cost of the product, life cycle costs will be lower with the use of RSA. The actual weight difference depends on the finish system being replaced; for example, some aircraft applications traditionally employ two coats of primer over the anodic film while others require only one. In general, primers add hundreds of pounds which can be eliminated by using RSA. Weight is a critical determinant of fuel cost over the life of an airplane - a pound saved on a C-5 aircraft is worth almost $100 over 20 years at today's fuel costs. Thus, the weight reduction caused by switching to RSA, while modest in terms of total vehicle weight, is nevertheless significant to total vehicle cost. 5. APPLICATION Resin-seal anodize is in service on selected C-5 Galaxy aircraft and has recently been approved for use on the C-130 Hercules transport. Some of the C-5 components are shown in process in Figure 3. Resin-sealed parts have been in service for approximately four years. Initial applications included components in the latrine drain support structure and the nose landing gear actuation system, both corrosion-prone areas. Periodic inspections have shown no indication of corrosion in these or any other locations where RSA is used. 340

On the C-130, over 23,000 part numbers have been identified as candidates for conversion to RSA. Selection criteria for aluminum parts to be resin-sealed are straightforward.

5 On the C-130, over 23,000 part numbers have been identified as candidates for conversion to RSA. Selection criteria for aluminum parts to be resin-sealed are straightforward. In general, RSA is applicable unless the part is bonded or welded. The process is not presently used on exterior skins because of cosmetic considerations; slight flow lines evident in the cured resin can translate through the topcoat. RSA is not suitable for tubing nor for parts which can trap solution while in the processing tanks. Potential non-aerospace applications are varied, including marine, automotive, and architectural components. Planned continued development of the process at Lockheed, including the addition of color and evaluation for bonded assemblies, will further expand the window of usage. 6. SUMMARY AND CONCLUSIONS Resin-seal anodizing is an excellent alternative to traditional aluminum processing methods. Testing and field performance show it to be corrosion resistant and to provide a suitable surface for topcoating, if required. By eliminating primers from the total finish system, RSA eliminates VOC and chromate emissions from the waste stream while reducing the cost of tha product. It is suitable for a variety of applications in a variety of industries and can therefore be a valuable tool to many organizations struggling to provide products using environmentally sound manufacturing processes which do not compromise product quality. 7. ACKNOWLEDGEMENTS The authors extend their thanks to T.C. Simmons of the Lockheed Aeronautical Systems Company for his assistance in providing detailed information on the environmental benefits of resin-seal anodizing. 8. REFERENCES (1) U.S. Pat. 4,515,919 (May 7, 1985) Robert E. Bradley and William R. Keithler (to the Lockheed Corporation). (2) R. E. Bradley, Plating and Surface Finishing, 29 (June 1988).

6 9. BIOGRAPHIES Robert L. Floyd, Jr. is a Specialist Engineer in Producibility, Materials, and Processes, evaluating and approving materials used for cleaning and chemical finishing of aircraft components. He has spent twelve years with Lockheed. Previously, in Manufacturing Research, he was responsible for development of materials, processes, and controls for cleaning and chemical finishing. This work included the implementation of resin-seal anodizing as a production process. Earlier, Mr. Floyd worked as an Analytical Chemist. He also spend thirteen years as a technical sales representative for a variety of sealants, adhesives, and coatings. Mr. Floyd graduated from the Georgia Institute of Technology vith a Bachelor of Science degree in Chemistry. Blair Maddock is a Senior Business Development Specialis?, handling the licensing of Resin-Seal Anodizing. She joined Lockheed in Ms. Maddock spent eight years in Materials and Processes Engizeering, specializing in non-metallic systems. During this time, she represented LASC in both the SAE Aerospace Materials Division Non-Metzllic Materials Committee and in the Suppliers of Advanced Composite Materials Association. More recently, she has been responsible fcr development of commercial subcontract opportunities for LAX. Ms. Madaczk holds a Bachelor of Ceramic Engineering degree from the Georgia :?.stitute of Technology and Master's degrees from the University of Michigan and Georgia State University. 342

7 ~ DESMUT ALKALINE CLEAN 1 Spray Rinse 1 DEOXIDIZE /Spray Rinse] I Immersion Rinse 1! I ALKALINE ETCH ISDrav Rinse1 Ispray Rinse/ I Immersion Rinse I! ANODIZE ISorav Rinse1 pmmersion Rinse 1 I NEUTRALIZING RINSE 1 Ispray Rinse/ I Immersion Rinse I RESIN SEAL I FIGURE 1. Processing Sequence for Resin-Seal Anodizing 343

TABLE 1 FLUID AND CORROSION RESISTANCE OF RESIN SEAL ANODIZING TEST CONDITIONS ALUMINUM SUBSTRATE TOPCOAT RESULTS FLUID RESISTANCE - Lube Oil - MIL-H-5606 Hydrocarbon - MIL-H-83282 Synthetic

8 TABLE 1 FLUID AND CORROSION RESISTANCE OF RESIN SEAL ANODIZING TEST CONDITIONS ALUMINUM SUBSTRATE TOPCOAT RESULTS FLUID RESISTANCE - Lube Oil - MIL-H-5606 Hydrocarbon - MIL-H Synthetic Hydraulic Fluid - Skydrol Distilled Water - JP-4 Jet Fuel Per NAS C 7 room temp C 7 room temp 4 49 C 30 room temp T6 clad 7075-T6 clad 7075-T6 clad 7075-T6 clad 7075-T6 clad 7075-T6 clad 2024-T3 clad MIL-C gloss polyurethane _- -_- - -_ Per MIL-A-8625 on unscribed panels --_ _--_-_--_--_--_-_- FILIFORM RESISTANCE C, 85% R.H., per NAS T3 bare 2024-T3 bare 7075-T6 bare 7075-T6 clad 7075-T6 clad 7075-T6 bare 7075-T6 clad MIL-C gloss polyurethane MIL-C gloss polyurethane MIL-C gloss polyurethane MIL-C gloss polyurethane Over 9500 hr. - -_-- SIMULATED FUEL TANK -Water - Salt waterlfuel - Iron chloride - Microbial byproducts Per MIL-C C C C 5 60 C 7075-T6 clad 7075-T6 bare 7075-T6 bare 7075-T6 bare 7075-T6 bare 7075-T6 bare MIL-C gloss polyurethane MIL-C gloss polyurethane Fail Fail -

TABLE 2 TOPCOAT ADHESION TO RESIN-SEAL ANODIZE BY WET TAPE TEST TEST ALUM IN U M TOPCOATI CONDITIONS SUBSTRATE PRIMER RESULTS Per MIL-C-83286B, 2024-T3 bare MIL-C-83286 gloss 24 hr. @ room temp.

9 TABLE 2 TOPCOAT ADHESION TO RESIN-SEAL ANODIZE BY WET TAPE TEST TEST ALUM IN U M TOPCOATI CONDITIONS SUBSTRATE PRIMER RESULTS Per MIL-C-83286B, 2024-T3 bare MIL-C gloss 24 room temp. polyurethane in distilled water 2024-T3 clad MIL-C gloss polyurethane 7075-T6 bare Epoxy polyamide (semigloss) 7075-T6 bare MIL-P epoxy 7075-T6 bare Epoxy amine primer 7075-T6 bare MIL-C urethane fuel tank coating 7075-T6 bare TT-P-1757 zinc chromate primer 7075-T6 bare TT-L-32 lacquer

CUMULATIVE #'a VOC (Thousands) 5 3-5 3 I CURRENT PAINTS 0 USINGRSA.. I I " 1 17 19 24 29 36 46 54 103119666999 PAINT TYPES I. ZINC CnRObIAlE PRIMER 17-ACID ':ASH PRIMER I9.EPOXY =RIMER 24.

10 CUMULATIVE #'a VOC (Thousands) I CURRENT PAINTS 0 USINGRSA.. I I " PAINT TYPES I. ZINC CnRObIAlE PRIMER 17-ACID ':ASH PRIMER I9.EPOXY =RIMER 24.EPhY ENAMEL 29.CAMOL'LdGE ~B.POLY!,S~THANE 4B'URETr;NE LACQUER PROTECTIVE 54.EPOAb 'OLYAMIDE PRIMER IO3,WdTER SORNE PROTECTIVE CO;-i-,G II9.WATEa S3RNE EPOXY PRIMER BB'S-SPECiii PRIMER K TOPCOAT 999.ALL OTHER PAINTS FIGURE 2. Comparison of Monthly 1990 VOC Emissions for LASC in Georgia With and Without RSA FIGURE 3. C-5 Components in Process on Resin-Seal Line 346

11 chrome emissions to the atmosphere from anodizing and plating operations to be reduced by 99% or to 0.03mg/Amp-hr. In the production of certain aircraft structures, Rohr Industries adhesively bonds components fabricated from dissimilar metals. To help prevent galvanic corrosion, aluminum components have been chromic acid anodized (CAA) prior to bonding. The resulting thick, nonconductive oxide coating acted as an electrical insulator separating the dissimilar metals. Additionally, CAA provided a durable bond surface with good adhesion properties. Hence, the bond integrity and corrosion resistance of the assembly required the aluminum to be chromic acid anodized. To comply with SCAQMD Rule 1169, Rohr considered several options; relocation, emission control equipment, and process substitution. Relocation of the CAA operation may have been viewed as the most economically viable action. However, with consideration given to the proliferation of environmental regulations, labor pools, and Rohr internal corporate policies, this option was rejected. Emissions control equipment provided a means of normal operations with minimal impact on product, production, and work force. But an evaluation of costs associated with a commitment to the "best available control equipment'! showed this alternative to be economically prohibitive. The last option of process substitution required an investment in the development and implementation of a new, 372

12 373

pan,els were chromic acid anodized. These surface preparation procedures were conducted per Rohr Process I Specification RPS 17.

13 pan,els were chromic acid anodized. These surface preparation procedures were conducted per Rohr Process I Specification RPS as follows: Sulfuric/Boric Acid Anodizinq Vapor Degrease - 3 Cycles (1,1,1 trichloroethane) DM Water Spray Rinse - 4 min. Alkaline Clean minutes (Isoprep 44) DM Water Spray Rinse - 4 min. Chromic Acid Anodizinq Vapor Degrease - 3 Cycles (l,l,l trichloroethane) DM Water Spray Rinse - 4 min. Alkaline Clean minutes (Isoprep 44) DM Water Spray Rinse - 4 min. Deoxidize - 10'2 min., 7'1 volts Deoxidize minutes (Phosphoric Acid Deoxidizer)' (Leeder 294-G) DM Water Spray Rinse - 4 min. Sulfuric Acid Anodize minutes, 15'1 volts DM Water Spray Rinse - 4 min. Ambient Air Dry DM Water Spray Rinse - 4 min. Chromic Acid Anodize 40'5 minutes, 40'2 volts DM Water Spray Rinse - 4 min. Ambient Air Dry Processed test panels were fabricated using materials and cure parameters shown in Table 1. Pretest environmental conditioning of mechanical test specimens were either hot/wet exposure to % humidity at 140 F for 750 hours per ASTM D-2247 or 5% salt spray exposure at 95 F for 750 hours per ASTM D-117. Test assembly and specimen fabrication for the mechanical and physical tests were conducted as follows: 1. Lap Shear - Lap shear specimens were fabricated and tested per ASTM D Specimens were tested at - 67"F, R.T., 350 F and at R.T. after humidity and salt spray exposure

2. 3. 4. 5. 6. 7. 8. Flatwise Tension - Flatwise tension test specimens were fabricated and tested per ASTM C-297. Specimens were tested at -67 F, R.T., 350 F, and at R.T. after hotlwet and salt spray exposure.

14 Flatwise Tension - Flatwise tension test specimens were fabricated and tested per ASTM C-297. Specimens were tested at -67 F, R.T., 350 F, and at R.T. after hotlwet and salt spray exposure. Wedge Crack Extension - Wedge crack extension tests were conducted per ASTM D-3762 Environment #8. Wet Floating Roller Peel - Floating roller peel tests were conducted per ASTM D-3167 with water applied to the bond line during testing. Double Cantilever Beam - Double cantilever beam tests were conducted per BSS 7208 Type 1 and Type 2. Coating Weights - Anodic coating weights were determined per ASTM B-137. Salt Spray - Salt spray specimens were tested per ASTM B-117 and examined after 336 and 750 hours of exposure. Wet Paint Adhesion - 6" X 12" X 0.040" panels were processed, sealed, and primed with Desoto 515x391 Fluid Resistant Primer to a dry film thickness of " to After a 48 hour air dry, specimens were subjected to 24 hours water immersion, then scribed. 3M Scotch #250 tape was applied over the scribed lines then removed at a 45" angle from the surface. Test panel and tape were examined for evidence of primer, anodic coating, or interfacial failure. Salt Spray and Paint Adhesion tests were conducted with SBAA and CAA specimens processed per RPS followed by a dilute chromate seal of 45 ppm Cr+6 as specified by BAC RESULTS All SBAA and CAA double cantilever beam and wedge crack specimens failed cohesively within the adhesive. This cohesive failure mode indicates the primerloxide interface to have a durable bond. See Figure 1 for crack extension results and Table 2 for double cantilever beam results.

15 Specimens from SBAA and CAA lap shear and flatwise tension testing failed cohesively within the primer, and/or the adhesive. SBAA was determined to be equivalent to CAA in lap shear and flatwise tension, as shown by Tables 3 and 4 respectively. Wet floating roller peel tests demonstrated SBAA to be superior to CAA. Peel stress in combination with water at the propagating crack tip, caused CAA specimens to adhesively fail at the primer/oxide interface. In contrast, SBAA specimens failed cohesively within the adhesive. Figure 2 shows the cohesively failed SBAA specimens to yield at significantly higher peel loads than the adhesively failed CAA. Salt spray test results showed all sealed SBAA and CAA specimens to meet the test specification requirements after 336 hours of exposure. Examination after 750 hours of exposure showed C U specimens exhibiting incipient pitting. SBAA specimens showed no visible evidence of pitting. Wet adhesion tape tests indicated no loss of paint adhesion to the sealed SBAA and CAA samples. As shown below, anodic coating weight of SBAA was determined to be slightly greater than that of CAA. weights are reported in mg/ft2. Coating BARE ALLOY SBAA CAA 2024-T T T

17 TABLE 1. TEST PRIMERS, ADHESIVES, AND CURE PARAMETERS

18 TEST ALLOY CONFIGURATION SBAA 2024T3 Bare GIC (Ibs/inch) 19.9 CRACK INITIATION CAA 17.6 GIA (Ibs/inch) 12.8 CRACK ARREST 11.4 GlSCC (Ibs/inch) 6.58 CRACK ARREST AT HUMIDITY 8.93 TABLE 2. DOUBLE CANTILEVER BEAM RESULTS 379

380 TEST ALLOY TEMPERATURE/ PROCESS AVERAGE (psi) CONDITION N=10 2024T3 Bare 67 deg. F SBAA 2270 67 deg. F CAA 2860 R.T. SBAA 2460 R.T. CAA 2920 350 deg. F SBAA 1980 350 deg.

19 380 TEST ALLOY TEMPERATURE/ PROCESS AVERAGE (psi) CONDITION N= T3 Bare 67 deg. F SBAA deg. F CAA 2860 R.T. SBAA 2460 R.T. CAA deg. F SBAA deg. F CAA 1690 Humidity S BAA 2690 Humidity CAA Salt Spray 2590 Salt Spray CAA T6 Bare 67 deg. F 67 deg. F I I 1 t I R.T R.T. 350 deg. F S BAA deg. F CAA 1830 Humidity SBAA 2500 Humidity CAA 2450 Salt Spray SBAA 2880 Salt Spray CAA 2720 TABLE 3. LAP SHEAR TEST RESULTS

20 TABLE 4. FLATWISE TENSION RESULTS

21 WEDGE CRACK EXTENSION 2024-T3 ADHERENDS 0.1 Crack Ex? ens i o n inches O k I KO Exposure Time, t - hours WEDGE CRACK EXTENSION 6061-T6 ADHERENDS Crack Extension inches Evposure Time, t ~ hours FIGURE 1. WEDGE CRACK EXTENSION RESULTS 382

*O I! 70 60 50 floating Roller Peel Strength, Ibs/inch 40 30 20 10

22 *O I! floating Roller Peel Strength, Ibs/inch SBAA CPA FIGURE 2. WET FLOATING ROLLER PEEL TESTS ON 2024-T3 383

Refer to Substrates & Surface Preparation.

Refer to Substrates & Surface Preparation. SELECTION & SPECIFICATION DATA Generic Type Description Features Color Finish Primer Dry Film Thickness Aliphatic Acrylic Polyurethane Thin film, high gloss finish with exceptional weathering performance