Testing SILSBOND on

Aluminum Alloys

By Trevor Yates

Aluminum Alloys Aluminum used widely in the aircraft industry due

to its wear resistance and tensile strength For over fifty years hexavalent chromium has

been used as a corrosion-inhibiting compound for the protection of metal surfaces

Hexavalent chromium currently is the best performing pretreatment solution available for aluminum

Cr (VI) Toxicity Hexavalent Chromium recognized as a human

carcinogen European Union restricts use in electronic

equipment by Restriction of Hazardous Substances Directive

OR-OSHA adopted regulations to protect workers exposed to Chromium (VI) in the workplace 52 ug/m^3

SILSBOND

• Nano-films

• Excellent adhesion and corrosion protection for aluminum and galvanized steel and cold rolled steel

• Reduces process steps

Objectives Test SILSBOND against Alodine 1200 and 4200 Optimize process parameters Test new formulas modified to compete against

SILSBOND 01 and 02 and 03 Provide results and conclusions to NSF in order to

contribute to their overall goal of limiting Cr 6 use on aircraft aluminum

Procedure Al 7075 and 2024 and 6061Military Paints: MIL-PRE-53022D and MIL-PRE-53022E and MIL-PRE-23377J

1st Round: SILS01 3%+1.5% vs. 4200 3% pH 4.5 and Alodine 1200 and Untreated

2nd Round: SILS01 vs. SILS02 vs. SILS03

3rd Round: SILS02 vs. A21 and A22

Immersion Apply paint via pressurized air until desired

thickness achieved Cure 80 degrees Celsius for 30 minutes CASST chamber 240 hours and SST 500 hours

Testing Parameters Concentration (1.5 % and 3 % and 5%) Immersion time (60 seconds and 90 seconds and

120 seconds) Immersion temperature (RT and 105-110 F and 115-120 F and 125-130 F) Baking (NONE and 80 C for 5 minutes and 20

minutes)

Copper-Accelerated Acetic Acid Salt Spray Test

Specific Testing Conditions Chamber interior 49 Celsius and DIW 63 Celsius 95 parts water and 5 parts sodium chloride 0.25 gram reagent grade copper chloride per liter

of solution pH adjusted between 3.1-3.3 with acetic acid Flow rate 1.0-2.0 mL/hr and pressure 16 psi DIW placed on bottom floor to prevent cracking of

material from thermal expansion

Salt Spray Test

Specific Testing Conditions

Chamber interior 35 Celsius and DIW 50 Celsius 95 parts DIW and 5 parts sodium chloride pH must be between 6.5-7.2 Specific gravity 1.02-1.04 Flow rate 1.0-2.0 mL/hr and pressure 17-18 psi

Average Delamintaion (mm) 1st Round Salt Spray Test Al 2024

MIL-PRE-53022D MIL-PRE-53022E0

0.51

1.52

2.53

3.54

4.55

SILS 01 1.5%

SILS 01 3%

Alodine 1200

Untreated

4200

Average Delamintation (mm) 1st Round CASS Chamber Test Al 2024

MIL-PRE-53022D MIL-PRE53022E0

1

2

3

4

5

6

7SILS 01 1.5%

SILS 01 3%

Alodine 1200

Untreated

4200

2nd Round CASS Test

SILS 01 3% 2 days SILS 02 3% 5 days SILS 03 3% 2 days

Best Performers

Alodine 1200 9 days SILS 02 3% 115-120 F 9 days

3rd Round CASS Test (9 days)

4200 3% RINSE 4200 3% NO RINSE

3rd Round CASS Test Continued

SILS 02 1.5% SILS 02 3% SILS 02 5%

WORSTBEST

3rd Round CASS Test Continued BEST

A22 1.5% A22 3% A22 5%

WORSTBEST

Overall 9 Days Comparisona b c

da.) A22 1.5%b.) 4200 RINSEc.) SILS 02 1.5%d.) Alodine 1200

Further Investigate Optimize A22 1.5 % concentration sweet spot 125-130 F Immersion temperature sweet spot Post baking helps 80 C for 20 minutes