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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