HARD ANODIZING OF
2XXX SERIES OF ALUMINUM ALLOYS

William W. Corcoran, Sanford Process Corporation
Leonid M. Lerner, Sanford Process Corporation

Conclusions

In order to avoid burning in High Voltage DC processes the temperature of electrolyte is dropped to 32ºF (0ºC) and lower, but for high copper alloys even at low temperatures, burning is likely to occur. However, our tests demonstrate that need not occur when hardcoating 2xxx series alloys.

Our study in Table # 1 shows:

1. The use of an appropriate organic additive with HV DC hardcoating process may prevent burning (see column 9, row 4).
2. The use of Low Voltage DC+AC hardcoating process without an additive will prevent burning (see column 9, row 5).
3. 3.The use of Low Voltage DC+AC hardcoating process with an appropriate organic additive will completely prevent burning (see column 9, row 6).
   

Regarding energy consumption:

Hardcoating in low temperatures consumes large amounts of electrical energy. During our tests, kWh consumption was measured with an E-Mon kWh Meter calibrated at one sixty-fourth scale. The use of different power supplies and additives can save significant energy. The Low Voltage DC + AC power supply was able to produce excellent results at 45º F while the straight DC power supply was required to process at 32º F. (The energy consumption data in column 10 has been prorated to 2 mils. and entered in parentheses next to the actual recorded results).

Our study in Table # 1, Column 10 shows:

1. The HV DC process with the organic additive used 155 and 177 kWhr/64 (prorated) to produce 2 mils of hardcoat. This consumption exceeded all of the other processes except HV DC without the organic additive, which was substantially unsuccessful.
2. The Low Voltage DC + AC process without organic additive consumed 100 and 151 kWhr/64 (prorated) at 45º F (7º C) and 32º F (0º C) respectively. This represents savings of 35% and 3% when compared to HV DC with additive.
3. The Low Voltage DC + AC process with organic additive produced significant energy savings when compared to HV DC process with organic additive. The power draw for Low Voltage DC + AC (prorated) was 57 and 137 kWhr/64 (prorated) respectively. This represents savings of 63% and 22% respectively when compared to HV DC with additive.

Note: Processing 2xxx series alloys at temperatures above 32ºF (0ºC) in HV DC was generally unsuccessful, leading to numerous catastrophic dissolution of test panels.

Regarding Taber Abrasion Tests:

• Mil-A-8625F specifies that anodic coatings shall have a maximum wear index of 3.5 mg/1000 cycles (or 35 milligrams of weight loss per 10 thousand cycles) on aluminum alloys having a copper content of 2 percent or higher.
• Mil-A-8625F specifies that unsealed Type III anodic coating shall have a minimum coating weight of 4320 milligrams per square foot for every .001 inch of coating.

Our study in Tables 2, 3 & 4 show:

1. The coatings produced in our tests using an organic additive surpassed the requirements of Mil-A-8625F for non-copper content alloys.
2. The coatings produced in the Low Voltage DC + AC processes surpassed the requirements of Mil-A-8625F for non-copper content alloys and were extremely consistent.
3. The coating weights for the Low Voltage DC + AC process comfortably exceeded Mil-A-8625F for unsealed Type III anodic coatings.

Introduction
Background of Study
Results of Study
Conclusions

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