Common Defects: Burning

Burning can take on different degrees of severity. It can be a softer coating near the contact point that may not even be noticeable or it can be a part that has completely disintegrated in the anodize tank. Burning is usually associated with one or more of: the alloy, the electrical contact, or the anodize process conditions. Alloy: High copper alloys are certainly the most likely to burn. It is counterintuitive that for a given ASF the voltage required for 2XXX alloys is far higher than others. More heat is generated at the base of the coating, and the likelihood is higher for small asperities to form in the barrier layer. These conditions favor a catastrophic highly localized chain of events – a burn. As a result, great care must be taken when processing these alloys.

Electrical Contact

To avoid burning you must avoid localized heating and this can occur where there is too much electrical current flowing through a point contact. The rule of thumb is for aluminum racks < 20A per contact and for titanium racks < 8A per contact.

Anodize Process

A number of variables need to be considered. The bath temperature needs to be controlled (lower is better), and the agitation needs to be adequate, if not vigorous. Conductivity of the bath plays a role, and it is better to use higher acid concentrations rather than lower. Higher aluminum contents have a negative impact on conductivity. Additives, such as the Reynolds MAE have been shown to reduce the potential for a burn to occur. Power to the part plays an important role. Higher current densities favor burning. The initial ramp rate or step-ramp program may require tuning. Pulse power systems are claimed to be the superior choice over standard DC.

To our best knowledge, the information and recommendations contained herein are accurate and reliable. However, this information and our recommendations are furnished without warranty, representation, inducement or license of any kind, including, but not limited to the implied warranties of merchantability and fitness for a particular use or purpose. Customers are encouraged to conduct their own tests and to read the product labels carefully before using them. Furthermore, the customer assumes sole liability for any patent infringement that occurs by reason of their following our recommendations or using the information given.

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