HARD ANODIZING OF
2XXX SERIES OF ALUMINUM ALLOYS

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

Introduction

The 2xxx series aluminum alloys are solution heat-treatable alloys with copper as the principal alloying element. The most important representative is alloy 2024, which is among the stronger of the 2xxx aluminum alloys. It is generally understood that 2xxx series aluminum alloys do not accept anodic coating well. Indeed, some in government specifications state that the finishability of this alloy is generally poor; its anodic coating is said to be rather unattractive and it is difficult to produce consistently good hard coating due to rapid catastrophic dissolution or "burning" of the alloyed aluminum articles. In the Aluminum Anodizing Council Anodizing Reference Guide, it is specifically not recommended to hardcoat 2011 alloy. Further, it states that the maximum hard coating thickness achievable for alloy 2014 and alloy 2017 is .001. The maximum thickness listed for 2024 is .015. Additionally, the Mil Spec permits a weight loss of 35 mg in the Taber test, while permitting only 15 mg loss for other alloys. Interestingly, the Aluminum Anodizing Council Anodizing Reference Guide also states that the coating properties for 2xxx series alloys is not only poor but produces inferior weather-resistant coatings.

The purpose of our study was to identify different processes available on the market for successful hardcoating of 2xxx series aluminum alloys. In our studies we employed 2 different power supplies and 4 different processes. All samples were 4"x4" squares of 2024-T3 aluminum alloy, and the same amount of Ampere-Minutes was used in each run. Additionally, since energy consumption is a large cost component of the hard anodizing process, data was gathered on the power draw of all processes run. This was accomplished by the use of a metering system, which measured kilowatt-hours scaled to 1/64th.

Introduction
Background of Study
Results of Study
Conclusions

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