ENVIRONMENTALLY FRIENDLY ALUMINUM COATINGS AS SACRIFICIAL COATINGS FOR HIGH STRENGTH STEEL ALLOYS

Abstract

Electroplating process is described for coating a ferrous alloy steel cathode substrate with an aluminum coating, the process comprises: a) immersing an aluminum anode substrate in a plating bath formulation comprising: a source of aluminum, an ionic liquid, a brightening agent, and a metal-salt compound; b) etching the cathode substrate by immersing it into the aluminum plating bath and conducting an anodic polarization step; c) electroplating the etched cathode substrate with the aluminum plating bath formulation; and d) rinsing with alcohol and water, and drying. Preferably, the process further comprises a heat treatment applied to the aluminum coated ferrous steel alloy obtained in step d).

Claims

1. An electroplating process for coating a ferrous alloy steel cathode substrate, comprising: providing an aluminum plating bath formulation comprising a source of aluminum, an ionic liquid, phenanthroline, and KCl, immersing an aluminum anode substrate in the aluminum plating bath formulation; immersing the ferrous steel alloy cathode substrate in the aluminum plating bath formulation; and electroplating an aluminum coating over the ferrous steel alloy cathode substrate.

2. The electroplating process of claim 1, further comprising pre-treating the aluminum anode substrate by: mechanical polishing the aluminum anode substrate to form a polished aluminum anode substrate; alkaline cleaning the polished aluminum anode substrate to form a cleaned aluminum anode substrate; and deoxidizing the cleaned aluminum anode substrate to form a deoxidized aluminum anode substrate.

3. The electroplating process of claim 1, further comprising pre-treating the strength ferrous steel alloy cathode substrate by: degreasing the ferrous steel alloy cathode substrate to obtain a degreased ferrous steel cathode substrate; and dry-blasting the degreased ferrous steel alloy cathode substrate to obtain a stripped ferrous steel alloy cathode substrate.

4. The electroplating process of claim 1, further comprising etching the ferrous steel alloy cathode substrate by performing an anodic polarization to form an etched ferrous steel alloy cathode substrate, wherein the aluminum coating is electroplated over the etched ferrous steel alloy cathode substrate.

5. The electroplating process of claim 1, heat treating the aluminum coating electroplated over the ferrous steel alloy cathode substrate.

6. An electroplating process for coating a ferrous alloy steel cathode substrate, comprising: providing an aluminum plating bath formulation, the aluminum plating bath formulation comprising: a source of aluminum and an ionic liquid; from 0.01 to 1.0 wt % of the brightening agent of 1,10-phenanthroline; and from 0.04 to 3.7 wt % of the metal salt of KCl; immersing an aluminum anode substrate in the aluminum plating bath formulation; immersing the ferrous steel alloy cathode substrate in the aluminum plating bath formulation; and electroplating an aluminum coating over the ferrous steel alloy cathode substrate.

7. The electroplating process of claim 6, wherein the source of aluminum is aluminum trichloride and the ionic liquid is 1-ethyl-3-methylimidazolium chloride, the aluminum plating bath comprising from 95.30 to 99.95 wt % a mixture of the aluminum trichloride and the 1-ethyl-3-methylimidazolium chloride in a molar ratio from 80:40 to 60:40.

8. The electroplating process of claim 6, wherein the electroplating is carried out with a current density from 1 mA/cm.sup.2 to 100 mA/cm.sup.2, at a temperature from 20 C. to 100 C. and under a dry inert gas.

9. The electroplating process of claim 6, wherein the electroplating is carried out with a current density from 5 mA/cm.sup.2 to 25 mA/cm.sup.2, a temperature from 40 C. to 75 C. and with stirring the aluminum plating bath formulation from 500 rpm to 1000 rpm.

10. The electroplating process of claim 6, wherein the ferrous alloy steel cathode substrate is a high strength ferrous steel alloy cathode substrate containing between 0.2 and 0.5 wt % of carbon and not more than 8 wt % of alloying elements.

11. The electroplating process of claim 6, wherein the source of aluminum is an aluminum halide.

12. The electroplating process of claim 6, wherein the ionic liquid is a nitrogen-containing compound selected from N-alkyl-pyridinium salts, N-alkyl-N-alkyl imidazolium salts, N-alkyl-N-alkylpyrrolidinium salts, N-alkyl-N-alkyl piperidinium salts, quaternary ammonium salts, and combinations thereof.

13. The electroplating process of claim 6, further comprising applying a conversion coating to the aluminum coating over the ferrous steel alloy cathode substrate.

14. The electroplating process of claim 6, further comprising pre-treating the aluminum anode substrate by: mechanical polishing the aluminum anode substrate to form a polished aluminum anode substrate; alkaline cleaning the polished aluminum anode substrate to form a cleaned aluminum anode substrate; and deoxidizing the cleaned aluminum anode substrate to form a deoxidized aluminum anode substrate.

15. The electroplating process of claim 6, further comprising pre-treating the strength ferrous steel alloy cathode substrate by: degreasing the ferrous steel alloy cathode substrate to obtain a degreased ferrous steel cathode substrate; and dry-blasting the degreased ferrous steel alloy cathode substrate to obtain a stripped ferrous steel alloy cathode substrate.

16. The electroplating process of claim 6, further comprising etching the ferrous steel alloy cathode substrate by performing an anodic polarization to form an etched ferrous steel alloy cathode substrate, wherein the aluminum coating is electroplated over the etched ferrous steel alloy cathode substrate.

17. The electroplating process of claim 6, heat treating the aluminum coating electroplated over the ferrous steel alloy cathode substrate.

18. An aluminum coating formed over a ferrous alloy steel cathode substrate by: providing an aluminum plating bath formulation, the aluminum plating bath formulation comprising: a source of aluminum and an ionic liquid; from 0.01 to 1.0 wt % of the brightening agent of 1,10-phenanthroline; and from 0.04 to 3.7 wt % of the metal salt of KCl; immersing an aluminum anode substrate in the aluminum plating bath formulation; immersing the ferrous steel alloy cathode substrate in the aluminum plating bath formulation; and electroplating an aluminum coating over the ferrous steel alloy cathode substrate.

19. The aluminum coating of claim 18, wherein the aluminum coating is uniform, adherent, and levelled.

20. The aluminum coating of claim 18, wherein the ferrous alloy steel cathode substrate is selected from a group consisting of an aeronautical cathode substrate, an automotive cathode substrate, a marine cathode substrate, a construction cathode substrate, an industrial cathode substrate, and a household cathode substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0130] FIG. 1: Aluminum electroplating process flow-diagram according to a particularly preferred embodiment.

[0131] FIGS. 2a and 2b: Cross section micrographs of each coating. (1) With Cr-VI post-treatment; (2) Bare aluminum without conversion coating post-treatment; (3) In-house formulated AlCl.sub.3-EMIC 60:40; (4) Basionics Al01 based; (5) Water rinsing during post-treatment; (6) Ethyl-alcohol rinsing during post-treatment; (8) F-220 alumina grit blasting during pre-treatment; (9) F-80 alumina grit blasting during pre-treatment; (10) F-36 alumina grit blasting during pre-treatment.

[0132] FIG. 3: Representative photographs of aluminum electroplated panels subjected to the scribe-grid +tape adhesion tests. (1) With Cr-VI post-treatment; (2) Bare aluminum without conversion coating post-treatment; (3) In-house formulated AlCl.sub.3-EMIC 60:40; (4) Basionics Al01 based; (5) Water rinsing during post-treatment; (6) Ethyl-alcohol rinsing during post-treatment; (8) F-220 alumina grit blasting during pre-treatment.

[0133] FIG. 4: Representative photographs of aluminum electroplated panels subjected to the bend adhesion tests. (1) With Cr-VI post-treatment; (2) Bare aluminum without conversion coating post-treatment; (3) In-house formulated AlCl.sub.3-EMIC 60:40; (4) Basionics Al01 based; (5) Water rinsing during post-treatment; (6) Ethyl-alcohol rinsing during post-treatment; (8) F-220 alumina grit blasting during pre-treatment; (9) F-80 alumina grit blasting during pre-treatment; (10) F-36 alumina grit blasting during pre-treatment.

[0134] FIG. 5: Representative panels of each coating after the corrosion tests, unscribed panels. (1) With Cr-VI post-treatment; (2) Bare aluminum without conversion coating post-treatment; (3) In-house formulated AlCl.sub.3-EMIC 60:40; (4) Basionics Al01 based; (5) Water rinsing during post-treatment; (6) Ethyl-alcohol rinsing during post-treatment; (8) F-220 alumina grit blasting during pre-treatment.

[0135] FIG. 6: Representative panels of each coating after the corrosion tests, scribed panels. (1) With Cr-VI post-treatment; (2) Bare aluminum without conversion coating post-treatment; (3) In-house formulated AlCl.sub.3-EMIC 60:40; (4) Basionics Al01 based; (5) Water rinsing during post-treatment; (6) Ethyl-alcohol rinsing during post-treatment; (8) F-220 alumina grit blasting during pre-treatment.

[0136] FIGS. 7a and 7b: Results of the throwing power assessment. (1) With Cr-VI post-treatment; (2) Bare aluminum without conversion coating post-treatment; (3) In-house formulated AlCl.sub.3-EMIC 60:40; (4) Basionics Al01 based; (5) Water rinsing during post-treatment; (6) Ethyl-alcohol rinsing during post-treatment; (8) F-220 alumina grit blasting during pre-treatment.

EXAMPLES

1. Ionic Liquid Electrolytes

[0137] The ionic liquid electrolytes used in these examples were synthesized as follows:

[0138] B01: Either the as-received Basionics Al01 ionic liquid electrolyte from BASF or the house-made AlCl.sub.3-EMIC 60:40 electrolyte (see below) were independently used as baseline electrolytes to be modified with the different additives.

[0139] AlCl.sub.3-EMIC 60:40 electrolyte was prepared by mixing the corresponding amounts of aluminum trichloride and 1-ethyl-3-methyl-imidazolium chloride, as follows: The 1-ethyl-3-methylimidazolium chloride [EMIC] (Fluka Ref. 30764, purity min 93%), was dried at 70 C. under vacuum for several hours. Then, it was placed into a glass vessel. The aluminum trichloride [AlCl.sub.3] (Across Organics Ref. 19578, anhydrous, 99%, granules) was weighted (as received) inside a glovebox filled with argon inside a glass dispenser; then, it was transferred to an addition funnel, taken out of the glovebox, and placed on top of the glass vessel already containing the EMIC. The ionic liquid electrolyte was synthesized by slowly adding the AlCl.sub.3 to the EMIC under an argon flow. Finally, the ionic liquid electrolyte was cooled down and stored in a humidity-free atmosphere.

[0140] B01-phen: The baseline electrolyte was heated up to 80 C. in a closed vessel under a dry inert gas stream while stirring. Then, a range from 0.1 to 1.0% wt of 1,10-phenanthroline was added. The Basionics Al01 ionic liquid modified with the 1,10-phenanthroline was stirred for 2 h at 80 C. in the closed vessel under a dry inert gas stream. Finally, the ionic liquid formulation obtained was cooled down and stored in a humidity-free atmosphere.

[0141] B01-phen-KCl: An ionic liquid formulation comprising 1,10-phenanthroline obtained as described above (B01-phen) was heated at 80 C. in a closed vessel under a dry inert atmosphere gas stream while stirring. Then, a range from 5 to 50 g/L of KCl was added and the formulation obtained was stirred for 2 h at 80 C. in the closed vessel under a dry inert gas stream. Finally, the aluminum plating formulation bath was cooled down and stored in a humidity-free atmosphere.

2. Electroplating Process:

2.1 Pre-Treatment of the Aluminum Anode Substrates

[0142] To plate onto flat rectangular panels, a rectangular slot in the center of the electrochemical cell's cover fixes the cathode. The cathode was a high strength steel rectangular sheet panel. In particular, the cathode was a rectangular flat panel machined from 4130 alloy steel conforming to AMS 6350 steel sheet. The anodes were 2 rectangular 99.999% purity aluminum sheets and were positioned at both sides of the cathode.

[0143] To plate onto specimens with cylindrical geometry, there was a cylindrical hole in the center of the electrochemical cell's cover to fix the cathode. The cathode was a high strength steel cylindrical specimen. In particular, the cathode was a cylindrical 1.a.1 geometry type AISI 4340/SAE AMS-S-5000 steel specimen with the size and geometry required by the ASTM F-519 standard. The material was certified by the supplier according to the requirements of the ASTM F-519 standard. The anode was an Al1050 aluminum cylindrical sheet, which was positioned around the cathode.

[0144] The aluminum anode substrates were all pre-treated following a same procedure, independently of the plating bath's formulation and the electroplating conditions. These pre-treatments involved: [0145] Mechanical polishing: The aluminum anode substrates were first manually polished with P-120 emery paper and the powder remaining on the surface was then removed with a white cloth. [0146] Alkaline cleaning: The polished aluminum anode substrates were immersed in a cleaning bath which contained a range from 45 to 60 g/L of Turco-4215 NC LT and a range from 1 to 3 g/L of T-4215 NC LT ADD (additive) during a period ranging from 5 to 30 min. Alkaline cleaning was carried out stirring at a range from 200 to 500 rpm, at a temperature ranging from 45 to 55 C. After that, the aluminum anode substrates were manually rinsed with tap water followed by deionized water rinsing. [0147] Deoxidizing: The cleaned aluminum anode substrates were immersed in an deoxidizing bath which contained a range from 60 to 120 g/L of Turco Smut Go NC and a range from 15 to 30 g/L of HNO.sub.3 (42 B) during a period ranging from 1 to 10 min. Deoxidizing was carried out at a temperature in the range from 20 to 50 C. After that, the aluminum anode substrates are manually rinsed with tap water followed by deionized water rinsing. [0148] Drying: The deoxidized aluminum anode substrates were manually rinsed with acetone and were dried using hot air. [0149] Racking: Finally, the aluminum anode substrates were placed in the holding rack.

2.2 Pre-Treatment of the High Strength Steel Alloy Cathode Substrates

[0150] The steel cathode substrates were all pre-treated following the same procedure, independently of the plating bath formulation and the electroplating conditions. These pre-treatments involved: [0151] Degreasing: The steel cathode substrates were first manually degreased with acetone and then they were immersed in acetone which was placed in an ultrasonic bath for 10 minutes, until neither oil nor grease remained on their surface. After that, the specimens were dried using hot air. [0152] Stripping: The degreased steel surface was then dry-blasted with F-220, F-80 or F-36 grit alumina to remove any possible oxide and impurities off the steel substrate. The powder remaining on the surface after blasting was removed with compressed air. [0153] Masking: The areas of a part which do not need to be plated were masked using conventional means which do not contaminate the plating bath formulation, such as masking tape. [0154] Racking: The pre-treated steel cathode substrates were placed in the holding rack.

2.3 Bath Conditioning and Etching

[0155] Prior to the anodic polarization step, the aluminum anode substrates were immersed in the plating bath and the electrolyte was conditioned by purging the plating bath formulation with a dry inert gas stream placed inside the plating bath during 30 minutes. Once the electrolyte had been conditioned, the dry inert gas purger was placed outside the electrolyte.

[0156] After that, the steel cathode substrates were immersed in the conditioned ionic liquid bath, which was to be used afterwards for aluminum plating, and an anodic polarization step of 0.6

[0157] V was applied for 30 seconds. Etching was performed at the same temperature as plating.

2.4 Electroplating

[0158] The experimental set-up for aluminum plating was the same independently of the plating bath's composition and the plating conditions. This set-up slightly changed depending on the geometry of the specimens (cathode substrates) to be electroplated.

[0159] The electrochemical cell consisted of a closed vessel containing a predetermined amount of the ionic liquid electrolyte. The electroplating was conducted under a dry inert gas stream in order to prevent contact of the electrolyte with the ambient's moisture. However, an accurate control of oxygen and moisture in the electrochemical cell was not needed. The cover of the vessel had different slots and holes where the cathode, the anodes, the temperature controller and the inert gas inlet and exhaust were assembled.

[0160] The electroplating process comprised the immersion of the pre-treated steel specimens in the bath formulation, closing the electric circuit with the adequate fixtures and applying a pre-determined cathodic direct current density to the cathode for a pre-determined amount of time and temperature while the electrolyte is kept at a pre-determined temperature.

[0161] The electroplating experiments were performed using a current rectifier to provide the power supply under dry inert gas stream. A hot plate with magnetic stirrer coupled to a temperature controller provided heat and stirred the electrolyte at different rpms.

[0162] The process conditions for aluminum coatings subjected to the preliminary qualification tests are summarized in the following table (Table I).

TABLE-US-00001 TABLE I Aluminum electroplating conditions Current density Temperature Bath Plating time Ref. (mA/cm.sup.2) ( C.) agitation (minutes) B01-1 2.5-7.5 50 No 60-180 B01-2 5 40 No 270 B01-phen 5-25 40-75 Yes 30-120 B01-phen-KCI 5-25 40-75 Yes 30-120

2.5 Post-Treatment

[0163] After the cathode substrates were electroplated, the aluminum coatings were all post-treated following the procedure described below, independently of the plating bath's composition and the plating conditions used.

[0164] The aluminum plated cathode substrates were manually rinsed with deionized water or, alternatively, with ethyl alcohol followed by deionized water until a clean surface free of any rest of ionic liquid were obtained.

[0165] If rinsed only with water, a corrosion of the aluminum coating was observed in the recessed areas of the cylindrical specimens because of the resulting hydrolysis products, mainly hydrochloric acid. Thus, rinsing with ethyl alcohol followed by water rinsing was the preferred option.

[0166] The aluminum plated cathode substrates were dried using hot air. Finally, some of the aluminum plated cathode substrates were baked at 19014 C. for 23 hours.

[0167] The aluminum plated cathode substrates were stored in a controlled atmosphere without humidity.

2.6 Conversion Coating

[0168] Some of the aluminum plated cathode substrates were conversion coated using the conventional Cr VI based conversion treatment Alodine 1200S.

3. Performance-Qualification Tests

[0169] The high strength steel specimens Al plated using the electrolyte compositions and process conditions described above were tested in terms of coating's appearance, thickness, composition, cross section morphology, adhesion, corrosion resistance, throwing power and hydrogen embrittlement susceptibility according to the test procedures described in Table II (see below).

[0170] LHE Cd plated specimens conforming to MIL-STD-870B specification Class 2 Type II were also tested for comparison. The different aluminum plated coatings as well as the LHE Cd controls were rated, at a minimum, providing pass/fail results according to the success criteria agreed in Table II for each test. A pass rating typically indicates a performance equivalent or better than that of Cd. The results were also compared to those found for AlumiPlate in the literature ([Final report WP-200022] and [Report number JF130828, Juergen Fischer et. al, Electrodeposition of aluminum with different ionic liquid based electrolytes and their comparison with the AlumiPlate layer, University of North Dakota, January 2014]). The corrosion results were also evaluated according to the MIL-DTL-83488D specification (Detail Specification, Coating, Aluminum, High purity) standard considered by the aerospace industry for the evaluation of Cd replacement candidates whose composition is pure Al (e.g. IVD Al, AlumiPlate, etc) (see Table II).

[0171] The types of substrates and test specimens that were used for evaluating coating appearance, thickness, composition, cross section morphology, adhesion and corrosion resistance were rectangular flat panels machined from 4130 alloy steel conforming to AMS 6350 steel sheet.

[0172] The test-specimens for thickness and composition determination, cross section morphology examination and adhesion tests were nominally 1 inch4 inch0.04 inches (25.4 mm101.6 mm0.10 mm). Unless otherwise specified, two specimens were used for each test.

[0173] The test-specimens for corrosion resistance tests were nominally 2 inch4 inch0.04 inches (50.8 mm101.6 mm0.10 mm). Unless otherwise specified, two specimens were used for each test (2 scribed and 2 unscribed).

[0174] The types of substrates and test-specimens that were used for hydrogen embrittlement were cylindrical 1.a.1 geometry type AISI 4340 / SAE AMS-S-5000 steel specimens with the size and geometry required by the ASTM F-519 standard. The material and the test-specimens were certified by the supplier according to the requirements of the ASTM F-519 standard. Unless otherwise specified, four specimens were used for hydrogen embrittlement testing.

[0175] The test-specimens for the throwing power assessment were cylindrical 1.a.1 geometry type AISI 4340/SAE AMS-S-5000 steel specimens conforming to ASTM F-519 standard. Unless otherwise specified, the coverage of the notch by the coating in all specimens to be subjected to hydrogen embrittlement tests was evaluated.

[0176] Tested samples are:

LHE Cd (1)

B01-1 (2)(3)(5)(8)

B01-2 (2)(3)(5)(8)

[0177] B01-phen (2)(4)(5)(8)
B01-phen-KCl (2)(4)(6)(8)
B01-phen-KCl (1)(4)(6)(8)
B01-phen-KCl (2)(4)(6)(7)(8)
B01-phen-KCl (2)(4)(6)(9)
B01-phen-KCl (2)(4)(6)(10)
wherein [0178] B01-phen: 0.1% wt 1,10-phenanthroline, [0179] B01-phen-KCl: 0.1% 1,10-phenanthroline and 5 g/L KCl

[0180] (1) with Cr-VI post-treatment

[0181] (2) bare Al without conversion coating post-treatment

[0182] (3) in-house formulated AlCl.sub.3-EMIC 60:40

[0183] (4) Basionics Al01 based

[0184] (5) water rinsing during post-treatment

[0185] (6) ethyl-alcohol rinsing during post-treatment

[0186] (7) baking post-treatment

[0187] (8) F-220 alumina grit blasting during pre-treatment

[0188] (9) F-80 alumina grit blasting during pre-treatment

[0189] (10) F-36 alumina grit blasting during pre-treatment

3.1 Appearance

[0190] In general, the appearance of all tested coatings was determined to be acceptable and all candidate coatings as well as the baseline LHE Cd coating were given a pass rating for appearance. The detailed results from the visual examination of the coatings are shown in Table III.

TABLE-US-00002 TABLE III Appearance Pass/ Coating Appearance results Fail AlumiPlate Coating is continuous, uniform, smooth, adherent, free from Pass blisters, pits, excessive powder and contamination. LHE Cd Coating is continuous, uniform, smooth, adherent, free from Pass (1)(8) blisters, pits, excessive powder and contamination. B01-1 White-grey colored and dull appearance. Pass (2)(3)(5)(8) Coating is continuous, uniform, smooth, adherent, free from blisters, pits, excessive powder and contamination. B01-2 White-grey colored and dull appearance. Pass (2)(3)(5)(8) Coating is continuous, uniform, smooth, adherent, free from blisters, pits, excessive powder and contamination. B01-phen White-grey colored and semi-bright reflective appearance. Pass (2)(4)(5)(8) Coating is continuous, uniform, smooth, adherent, free from blisters, pits, excessive powder and contamination. B01-phen- White-grey colored and semi-bright reflective appearance. Pass KCI Coating is continuous, uniform, smooth, adherent, free from (2)(4)(6)(8) blisters, pits, excessive powder and contamination. B01-phen- Yellowish colored and semi-bright appearance. Coating is Pass KCI continuous, uniform, smooth, adherent, free from blisters, (1)(4)(6)(8) pits, excessive powder and contamination. B01-phen- White-grey colored and semi-bright reflective appearance. Pass KCI Coating is continuous, uniform, smooth, adherent, free from (2)(4)(6)(9) blisters, pits, excessive powder and contamination. B01-phen- White-grey colored and semi-bright reflective appearance. Pass KCI Coating is continuous, uniform, smooth, adherent, free from (2)(4)(6)(10) blisters, pits, excessive powder and contamination.

3.2 Thickness

[0191] The thickness of B01-phen and B01-phen-KCl coatings was determined to be acceptable (between 12 and 20 m) as well as that of the baseline LHE Cd coating. Thus, these coatings were given a pass rating for thickness. The thickness of the B01-1 and B01-2 coatings was not fine-tuned to be within 12-20 m and, thus, they were given a fail rating. The detailed results of the cross section's inspection of the coatings (according to ASTM B-487) are shown in Table IV.

TABLE-US-00003 TABLE IV Thickness (cross-section examination ASTM B-487) Reading average (m) Specimen Specimen Pass/ Coating 1 2 Fail AlumiPlate 13 (targeted 23) Pass LHE Cd (1)(8) 12 12 Pass B01-1 (2)(3)(5)(8) 7.3 6.9 Fail B01-2 (2)(3)(5)(8) 23 25 Fail B01-phen (2)(4)(5)(8) 12 12 Pass B01-phen-KCI 14 14 Pass (2)(4)(6)(8) B01-phen-KCI 17 16 Pass (1)(4)(6)(8)

3.3 Composition

[0192] The composition of the tested coatings was determined to be acceptable (e.g., not less than 99% of Al). Thus, the coatings were given a pass rating for composition. The composition of B01-phen-KCl (1)(4)(6)(8) was less than 99% of Al due to the Cr-VI post-treatment on top of the aluminum coating. The detailed results of the surface SEM/EDS examination are shown in Table V.

TABLE-US-00004 TABLE V Composition (surface SEM/EDS examination) Reading Average Wt % Wt % Wt % Wt % Wt % Pass/ Coating Wt % O Wt % Al S Cl Cr Fe Cd Fail AlumiPlate 100 Pass LHE Cd 53.73 0 0.80 0 7.66 0 37.81 (1)(8) B01-1 0 100 0 0 0 0 0 Pass (2)(3)(5)(8) B01-2 (2)(3)(5)(8) B01-phen 0 100 0 0 0 0 0 Pass (2)(4)(5)(8) B01-phen- 0 99.14 0 0.0 0 0.86 0 Pass KCl (2)(4)(6)(8) B01-phen- 19.47 75.66 0.25 0 4.02 0.61 0 KCl (1)(4)(6)(8)

3.4 Cross Section Morphology

[0193] The cross section morphology of the coatings electroplated from the B01-phen and B01-phen-KCl electrolytes was determined to be acceptable (uniform, adherent, dense and levelled coatings) as well as that of the baseline LHE Cd coating. Thus, these coatings were given a pass rating for cross section morphology. The coatings electroplated from the B01-1 and B01-2 electrolytes failed since non-uniform, non-dense coatings tending to dendritic morphology were obtained.

[0194] The cross section morphology of the aluminum coatings was radically improved when the AlCl.sub.3-EMIC 60:40 (Basionics Al01) baseline electrolyte was modified with the 1,10-phenanthroline additive. The addition of KCl did not jeopardize the cross section morphology of the coatings while improving other properties.

[0195] The cross section morphology for B01-phen-KCl coatings was acceptable even if a bigger alumina particle size of F-80 grit was used during blasting in the pre-treatment.

[0196] The detailed results from the cross section inspection of the coatings are shown in Table VI. FIGS. 2a and 2b show representative cross section's micrographs of each coating.

TABLE-US-00005 TABLE VI Cross section morphology Pass/ Coating Cross section examination results Fail AlumiPlate Coating showing with complete Pass coverage of the substrate LHE Cd Uniform adherent and levelled coatings Pass (1)(8) that completely covered the substrate; Borders were uniformly and well covered. B01-1 Non-uniform coating, non-dense, non- Fail (2)(3)(5)(8) compact, dendritic, especially in the edges B01-2 Non-uniform coating, non-dense, non- Fail (2)(3)(5)(8) compact, dendritic, especially in the edges B01-phen Uniform adherent and levelled coatings Pass (2)(4)(5)(8) that completely covered the substrate; Borders were uniformly and well covered. B01-phen-KCI Uniform adherent and levelled coatings Pass (2)(4)(6)(8) that completely covered the substrate; Borders were uniformly and well covered. B01-phen-KCI Uniform adherent and levelled coatings Pass (1)(4)(6)(8) that completely covered the substrate; Borders were uniformly and well covered. B01-phen-KCI Uniform adherent and levelled coatings Pass (2)(4)(6)(9) that completely covered the substrate; Borders were uniformly and well covered. B01-phen-KCI Uniform adherent and levelled coatings Pass (2)(4)(6)(10) that completely covered the substrate; Borders were uniformly and well covered.

3.5 Scribe-Grid Tape Adhesion

[0197] In general, the scribe-grid tape adhesion of all tested coatings was determined to be acceptable (no coating detachment between the scribed lines) and all candidate coatings as well as the baseline LHE Cd coating were given a pass rating for scribe-grid tape adhesion. The detailed results of the visual examination conducted after subjecting the specimens to the adhesion test are shown in Table VII. FIG. 3 shows representative panels of each candidate coating after the adhesion testing.

TABLE-US-00006 TABLE VII Scribe-grid and tape adhesion (ASTM B571/s. 13 applying a pressure sensitive tape) Scribe grid + tape Pass/ Coating adhesion results Fail LHE No coating detachment Pass Cd (1)(8) between the scribed lines B01-1 No coating detachment Pass (2)(3)(5)(8) between the scribed lines B01-2 No coating detachment Pass (2)(3)(5)(8) between the scribed lines B01-phen No coating detachment Pass (2)(4)(5)(8) between the scribed lines B01-phen-KCI No coating detachment Pass (2)(4)(6)(8) between the scribed lines B01-phen-KCI No coating detachment Pass (1)(4)(6)(8) between the scribed lines

3.6 Bend Adhesion

[0198] When the substrates were pre-treated using F-220 alumina grit during pre-treatment, the bend adhesion of the coatings electroplated from the B01-1 electrolyte was determined to be acceptable, since little to no separation of the coating from the basis metal at the rupture edge occurred, as well as that of the baseline LHE Cd coating. These coatings were given a pass rating for bend adhesion. The rest of the coatings failed, even if the failure was only marginal for the coatings electroplated from the B01-phen-KCl electrolyte.

[0199] The coatings electroplated from the B01-2 electrolyte were considerably thicker than those plated from the B01-1 electrolyte, which hindered the adhesion.

[0200] The bend adhesion of the aluminum coatings seemed to decrease when using the 1,10-phenanthroline and KCl additives in the AlCl.sub.3-EMIC 60:40 (Basionics Al01) baseline electrolyte.

[0201] However, when increasing the particle size of the alumina grit used during blasting (i.e. when F-80 or F-36 alumina grit was used during pre-treatment instead of F-220 alumina grit), the coatings electroplated from the B01-phen-KCl electrolyte passed the adhesion test.

[0202] The detailed results of the visual examination conducted after subjecting the specimens to the adhesion test are shown in Table VIII. FIG. 4 shows representative panels of each candidate coating after the adhesion tests.

TABLE-US-00007 TABLE VIII Bend adhesion (ASTM B571/s. 3) Coating Bend adhesion results Pass/Fail AlumiPlate Cracking of coating up to 1/8 inch. Pass LHE Cd (1)(8) No separation of the coating from Pass the basis metal at the rupture edge. B01-1 No separation of the coating from Pass (2)(3)(5)(8) the basis metal at the rupture edge. B01-2 Significant coating detachment Fail (2)(3)(5)(8) in the rupture edge B01-phen Significant coating detachment Fail (2)(4)(5)(8) in the rupture edge B01-phen-KCI Slight coating detachment in the Fail but (2)(4)(6)(8) central area of the rupture edge and marginal especially at the side edges. B01-phen-KCI Coating detachment in the central area Fail (1)(4)(6)(8) and at the borders of the rupture edge. B01-phen-KCI No cracks or coating detachment in Pass (2)(4)(6)(9) the central area of the tested face. Some coating detachment at the borders of the ruptured edge. B01-phen-KCI No cracks or coating detachment Pass (2)(4)(6)(10) in the central area of the tested face. Some coating detachment at the borders of the ruptured edge.

3.7 Unscribed Salt Spray Corrosion Resistance

[0203] The corrosion resistance of unscribed panels of coatings electroplated from the B01-phen-KCl electrolyte was determined to be acceptable (more than 3,000 hours to red rust) as well as that of the baseline LHE Cd coating, both with CrVI post-treatment on top. These coatings were given a pass rating for unscribed salt spray corrosion resistance according to HSSJTP criteria. The B01-2 coatings were also given a pass since they were able to withstand more than 3,000 hours to red rust without any kind of conversion coating post-treatment on top.

[0204] On the other hand, the corrosion resistance of the coatings obtained with B01-1, B01-2 and B01-phen-KCl (without or with conversion coating post-treatment on top) was determined to be acceptable according to the criteria of the MIL-DTL-83488D standard (Class 3 coatingsminimum of 8 micron thick: more than 168 hours to red rust for unpassivated coatings; Class 2 coatingsminimum of 13 microns thick: more than 336 hours to red rust for unpassivated coatings; Class 3 coatingsminimum of 8 micron thick: more than 336 hours to red rust for coatings with supplementary CrVI treatment; Class 2 coatingsminimum of 13 microns thick: more than 504 hours to red rust for coatings with supplementary CrVI treatment).

[0205] The coatings electroplated from the B01-2 electrolyte were considerably thicker than those plated from the B01-1 electrolyte, which provided the corrosion resistance.

[0206] The corrosion resistance of the aluminum coatings decreased when using the 1,10-phenanthroline and KCl additives in the AlCl.sub.3-EMIC 60:40 (Basionics Al01) baseline electrolyte.

[0207] The detailed results of the visual examination conducted after subjecting the specimens to the corrosion test are shown in Table IX. FIG. 5 shows representative panels of each coating after the corrosion test.

TABLE-US-00008 TABLE IX NSSF Corrosion resistance-Unscribed panels (ASTM B-117 angle 6 off) Hours Pass/Fail Reading to red HSSJTP average rust (with MIL- thickness (2 CrVI post- DTL- Coating (m) speciments) treatment) 83488 AlumiPlate 13 >3,000 Pass Pass (targeted 23) LHE Cd (1)(8) 12 >3,000 Pass B01-1 10 216 Pass (2)(3)(5)(8) 216 Pass B01-2 ~30 3,864 Pass Pass (2)(3)(5)(8) 5,208 Pass Pass B01-phen (2)(4)(5)(8) B01-phen-KCI ~17 504 Pass (2)(4)(6)(8) 504 B01-phen-KCI ~17 >3,500 Pass Pass (1)(4)(6)(8) >3,500

3.8 Scribed Salt Spray Corrosion Resistance

[0208] The corrosion resistance of scribed panels of the B01-phen-KCl coatings and that of the baseline LHE Cd coating (both with Cr-VI post-treatment on top) was determined to be acceptable (requirement of more than 1,000 hours to red rust) and were given a pass rating for scribed salt spray corrosion resistance according to HSSJTP criteria.

[0209] The rest of the coatings tested, i.e. B01-1, B01-2 and B01-phen-KCl without Cr-VI post-treatment on top, were not evaluated with respect to the HSSJTP and the MIL-DTL-83488 criteria since they do not set-up specifications respectively for coatings without Cr-VI post-treatment and for scribed coatings.

[0210] The higher thickness of the coatings plated from the B01-2 electrolyte in comparison to those plated from the B01-1 electrolyte provided the coatings' corrosion resistance.

[0211] The corrosion resistance of the aluminum coatings seemed to decrease when using the 1,10-phenanthroline and KCl additives in the AlCl.sub.3-EMIC 60:40 (Basionics Al01) baseline electrolyte.

[0212] The detailed results of the visual examination conducted after subjecting the specimens to the corrosion test are shown in Table X. FIG. 6 shows representative panels of each coating after the corrosion tests.

TABLE-US-00009 TABLE X NSSF Corrosion resistance-Scribed panels (ASTM B-117 angle 6 off) Reading Pass/Fail average Hours (HSSJTP) thickness to red (with CrVI Coating (m) (3) rust post-treatment) AlumiPlate 13 (targeted 23) 1000 Pass LHE Cd (1)(8) 12 >1,000 Pass B01-1 9.5 192 (2)(3)(5)(8) 168 B01-2 ~30 1512 (2)(3)(5)(8) 336 B01-phen (2)(4)(5)(8) B01-phen-KCI ~19 336 (2)(4)(6)(8) 336 B01-phen-KCI 21 >3,500 Pass (1)(4)(6)(8) 17 3,168

3.9 Throwing Power

[0213] The throwing power of the coatings electroplated from the B01-2 and B01-phen-KCl electrolytes was determined to be acceptable, since achieved full coating coverage in the notch, as well as that of the baseline LHE Cd coating. Thus, these coatings were given a pass rating for throwing power. The coatings electroplated from the B01-1 and B01-phen electrolytes failed.

[0214] The throwing power of the aluminum coatings seemed to decrease when using the 1,10-phenanthroline additive in the AlCl.sub.3-EMIC 60:40 (Basionics Al01) baseline electrolyte. However, the addition of KCl to the B01-phen electrolyte considerably improved the throwing power without jeopardizing the rest of the properties.

[0215] Rinsing with ethyl alcohol rather than water during post-treatment helped to remove completely the remaining electrolyte from the notch avoiding stains and preventing possible corrosion due to the presence of electrolyte.

[0216] The detailed results of the visual examination of the coatings are shown in Table XI. FIGS. 7a and 7b show representative photographs of the notched areas of 1.a.1 geometry type specimens.

TABLE-US-00010 TABLE XI Throwing power (surface/cross section examination) Coverage of 1.a.1 Coating geometry type notch Pass/Fail AlumiPlate Full coating coverage in the notch Pass LHE Cd (1)(8) Full coating coverage in the notch Pass B01-1 (2)(3)(5)(8) Uncoated areas in the notch root Fail B01-2 (2)(3)(5)(8) Full coating coverage in the notch Pass B01-phen (2)(4)(5)(8) Uncoated areas in the notch root Fail B01-phen-KCI (2)(4)(6)(8) Full coating coverage in the notch Pass B01-phen-KCI (1)(4)(6)(8) Full coating coverage in the notch Pass B01-phen-KCI Full coating coverage in the notch Pass (2)(4)(6)(7)(8)

3.10 Hydrogen Embrittlement

[0217] The aluminum coatings electroplated from the B01-1 and B01-2 electrolytes, not subjected to any baking post-treatment, passed the hydrogen embrittlement test (e.g., minimum of 200 hours without fracturing). Also, both the B01-phen-KCl and the LHE Cd coatings, when subjected to a baking step after aluminum electroplating, passed the hydrogen embrittlement test. All these coatings were given a pass rating for hydrogen embrittlement.

[0218] The B01-phen-KCl specimens not subjected to a baking post-treatment failed the test. The embrittling properties of the aluminum electroplating process seemed to decrease when using the 1,10-phenanthroline and KCl additives in the AlCl.sub.3-EMIC 60:40 (Basionics Al01) baseline electrolyte. The detailed results of the hydrogen embrittlement tests are shown in Table XII.

TABLE-US-00011 TABLE XII Hydrogen embrittlement (ASTM F-519) Load/Loading Hours time required by without Coating ASTM F-519 fracturing Pass/Fail AlumiPlate 200 Pass 200 200 200 LHE Cd (1)(8) 75% NFS/200 h 200 Pass 200 200 200 B01-1 (2)(3)(5)(8) 75% NFS/200 h 200 Pass 200 200 200 B01-2 (2)(3)(5)(8) 75% NFS/200 h 200 Pass 200 200 200 B01-phen (2)(4)(5)(8) B01-phen-KCI (2)(4)(6)(8) B01-phen-KCI 75% NFS/200 h 216 Fail (1)(4)(6)(8) 123.3 215.4 177.6 B01-phen-KCI 75% NFS/200 h 200 Pass (2)(4)(6)(7)(8) 200 200 200

4. Summary of Results

[0219] The commercially available AlCl.sub.3-EMIC 60:40 ionic liquid without any additives (B01) led to about 30 micron thick coatings which complied with the requirements for appearance, thickness, composition, throwing power, corrosion resistance, hydrogen embrittlement and scribe-grid adhesion. However, they had a dendritic morphology and insufficient bend adhesion for the approximately 30 m thick coatings.

[0220] When plating from the AlCl.sub.3-EMIC 60:40 +1,10-phenanthroline ionic liquid (B01-phen) the morphology was improved, but jeopardizing the throwing power and the bend adhesion for approximately 12 m thick coatings. Nonetheless, achieving dense and levelled aluminum coatings over the grit blasted high strength steel surfaces was an important breakthrough. This electrolyte allowed an acceptable aluminum plating at higher current density and higher temperature than the AlCl.sub.3-EMIC 60:40 baseline electrolyte (without any additives), which results in higher electrodeposition rates.

[0221] Significant improved results were obtained with the AlCl.sub.3-EMIC 60:40+1,10-phenanthroline+KCl electrolyte (B01-phen-KCl) since the coatings plated were uniform, not powdery, and had a semi-bright metallic appearance. In terms of coating's appearance, the electroplating process was quite robust, since coatings with very similar appearance were produced within all the tested operating ranges, i.e., with a current density ranging from 5 to 25mA/cm.sup.2, at a temperature ranging from 40 to 75 C. and under a dry inert gas. The coatings had continuous, uniform, levelled and compact cross section morphology, comparable to that of the coatings electroplated from the B01-phen. The adhesion was similar to that of B01-phen coatings.

[0222] The throwing power of the electrolyte was considerably improved with respect to that of the B01-phen. This electrolyte also allowed an acceptable aluminum plating at higher current density and higher temperature than the B01 (without any additives), which results in higher electrodeposition rates.

[0223] The B01-phen-KCl electroplating bath achieves an improvement of the electrical conductivity of the bath and facilitates the deposition of aluminum because of the shift of the reduction potential of Al, so that an improvement of the throwing power can also be achieved.

[0224] The B01-phen-KCl electroplating process also achieved good adhesion properties of the resulting aluminum coating when F-80 to F-36 alumina grit blasting was used during pre-treatment.

[0225] The B01-phen-KCl electroplating process also achieved good hydrogen embrittlement resistance when a baking step at 19014 C. for at least 23 hours was used during post-treatment.

[0226] These coatings showed comparable or superior behavior to LHE Cd and Alumiplate reference coatings.

[0227] Moreover, the aluminum coating complying with all of the tests reported may be considered a more environmentally friendly coating than other sacrificial coatings for high strength ferrous steel parts such as Cd and Zn-Ni. The process to achieve such coating would be considered more environmentally friendly, more safe and easier to handle than Cd plating, Zn/Ni plating, Al plating from organic solvents or AlumiPlate plating process.

[0228] Besides, the aluminum coating complying with most of the tests reported (except bend adhesion and/or hydrogen embrittlement) may still be considered a more environmentally friendly coating than other sacrificial coatings for ferrous steel parts such as Cd and Zn-Ni providing similar or superior corrosion resistance performance than Cd or Zn/Ni. The process to achieve such coating would be still considered more environmentally friendly, more safe and easier to handle than Cd plating, Zn/Ni plating, Al plating from organic solvents or AlumiPlate plating process.