New Qualicoat additional label for best aluminum corrosion protection

Highest corrosion protection is offered by pre-anodized and coated aluminum products according to the international Qualicoat quality label. New additions include the new "PreOx" label and the inclusion of external pre-anodization in the Qualicoat specifications.

The corrosion resistance of aluminum is a concern for designers and materials engineers, the surface finishing sector, industry and end customers. Highest corrosion protection is offered by pre-anodized and coated aluminum products according to the international quality mark Qualicoat, which is constantly being further developed. The Verband für die Oberflächenveredelung von Aluminium e. V. (VOA), general licensee in Germany, provides information on the latest developments: the new "PreOx" label and the inclusion of external pre-anodization, which is frequently practiced in Germany, in the globally valid Qualicoat specifications from January 1, 2024.

Pre-anodization represents an alternative to the common chemical pre-treatment methods, chromating or chromium-free and chromium-VI-free processes. It can be used as a pretreatment for powder coating to significantly reduce the risk of filiform corrosion on aluminum, for example in application areas with high salt concentration - such as coastal regions, swimming pools or places where road salt is used - but also in industrial zones with high emission levels with altered air parameters. The general licensor Qualicoat already takes these conditions, which can be described as "extreme," into account with its "Seaside" suffix, which has higher requirements in the specifications. The "Qualicoat Seaside" label stands for powder-coated aluminum products, suitable for long-term use under difficult environmental conditions, and offers customers both outstanding quality and safety for professional use. According to Qualicoat specifications, as of 01.07.2023, there are currently two pretreatment methods available for "Seaside": chemical treatment with increased pickling removal of at least 2 gr/m² and pre-anodization. From next year, the general licensor will go one step further.

Research results of the general licensor Qualicoat

The development was complex, but the result is convincing: The research layout was carried out in the Qualicoat "Pre-Anodizing" Working Group, in which the VOA is also represented by excellent experts. This group examined a total of 2,622 pre-anodized and chemically treated samples from all over the world between 2018 and 2020 in order to gain further insights into the corrosion resistance of surface-finished aluminum and thus generate a meaningful basis for the planned changes to the specifications. In evaluating the representative data sets, the experts found that pre-anodizing, which is more complex and therefore more energy- and cost-intensive, delivers better results in terms of corrosion protection compared with chemical pretreatment: In the acetic acid salt spray test, 86% of the pre-anodized samples had an infiltration length of less than/equal to 1 mm, while the figure for the chemically treated samples was only 76%. In terms of corroded area, 89% of the pre-eroded test specimens showed a corroded surface area of 5 mm² or less, while 81% of the chemically treated specimens showed a corroded surface area of 5 mm² or less. In the filiform corrosion test, pre-anodization even performed significantly better. In the pre-anodized samples, 84% had an underwall of less than/equal to 1 mm, in the chemically pre-treated 55%. Even 91 % of the pre-anodized test pieces showed an average filament length of less than/equal to 1 mm, in the chemically treated ones the value was 74 %.

The figures impressively illustrate that the combination of pre-anodizing and painting can produce extremely corrosion-resistant end products. The general licensor Qualicoat is taking the evaluation as an opportunity to introduce the new additional label "PreOx" for the international Qualicoat quality mark via the specifications and is thus setting the standard for durable surface-finished aluminum products with maximum corrosion protection.

External pre-anodization according to Qualicoat

At the start of the new year 2023, the general licensor, on the initiative of the VOA, will also lay down detailed rules for external pre-anodization in its specifications. The reason for this move was that, for structural reasons in Germany, as in some other countries, many coating companies concentrate on their core business and outsource anodizing to external partner companies if required. In these cases, the quality result depends on at least two players, the anodizer and the coater. Due to this interface, unintentional errors can creep in, caused, for example, by communication between the two parties or by different or uncoordinated process steps, incompatibilities of the materials during further processing, or varying qualities, since not all powders react in the same way to pre-anodization. The special requirement of the general licensor Qualicoat is the same for all components: the finished coated component must withstand a wet adhesion test, the so-called boil test. Here, the special focus is on the complete removal of sulfuric acid from the pores of the pre-anodization layer.

To ensure uniform, professional and lasting quality, the general licensor Qualicoat will standardize the procedure in the specifications in the future. The focus is clearly on the interface between the anodizer and the coater. Despite a great deal of freedom in terms of responsibilities, emphasis is placed on processes that always run in the same way, which are to be defined in the process description to be agreed in detail between the anodizer and coater, as well as the special rules on documentation and the exchange of information in order processing. In addition, the general licensor establishes rules both for the coater for coating pre-anodized material and for the external anodizer, who receives the PreOx license once a year after passing an external examination by a testing institute. In addition, there are technical specifications such as the prescribed coating thickness of 4 to 10 µm and for the post-treatment, which is now specified in much greater detail. In the case of the latter, it has been shown that the application of a suitable passivation to the pre-anodization layer can significantly improve quality. For this reason, the new specifications provide for the suitability of passivation systems for this application, which are provided with their own approvals.

Top prepared for the updated specifications thanks to the new VOA tools

At the meeting of the Technical Circle, i.e. the technically interested members of the VOA, on June 22, 2022, the association already presented the corresponding update sheet "Introduction of off -site anodic pretreatment" of the general licensor. The VOA took the reactions and in particular the many questions as an opportunity to support the member companies with the newly founded project group "External pre-anodization according to Qualicoat" from July 2022. The experts from the ranks of the VOA members then developed useful tools for daily practice in German and English: the process description for the detailed definition of the interface between anodizer and coater as well as the order checklist for the exchange of information. The tools enable both parties to fully cover Qualicoat's requirements regarding the organization of cooperation. The association's practical work aids are available free of charge to VOA members, either after logging in via the download area at www.voa.de or directly from the office. This will enable Qualicoat licensees to easily implement the future specifications and impress their international customers with their quality.

The now modified specifications at the beginning of the coming year represent a further milestone on the way to even greater quality and reliability worldwide in the field of coating aluminum surfaces with the Qualicoat quality mark. (OM-09/23)

Pre-anodized and subsequently powder-coated aluminum workpieces offer the highest corrosion protection of all processes commonly used in the architectural sector and are particularly suitable for highly stressed areas. Pre-anodizing is mainly carried out in horizontal lines. The employees of the anodizing plant fix the parts to be anodized, after which they are generally degreased and pickled in tubs by means of immersion treatment, mainly alkaline. After rinsing and neutralization, anodic oxidation takes place in the actual anodizing bath. In dilute sulfuric acid, a layer of aluminum oxide with a honeycomb structure and a thickness of 4 to 10 µm is formed by applying a DC voltage to the workpiece connected as an anode. The layer grows both into and out of the workpiece surface. It is intimately bonded to the base material. In the further course, the anodizing operation rinses the anodized workpieces for as long and at such a temperature as is necessary to eliminate the acid from the pores so that the requirements of the wet adhesion test can be met after the subsequent powder coating. During transport and further handling of the workpieces, it is important to reliably prevent contamination of the surface or to ensure that this is removed before application of the powder coating. The anodization layer provides a reliable adhesion primer and, above all, excellent corrosion protection in combination with the powder coating.

Contact

Verband für die Oberflächenveredelung von Aluminium e. V. (VOA)
Haus der Bayerischen Wirtschaft
Max-Joseph-Str. 5
80333 Munich (Germany)
Phone: +49 89 / 5517 8670
Email: info@voa.de
www.voa.de

About the VOA

As a trade association, the Verband für die Oberflächenveredelung von Aluminium e. V. (VOA) forms the industry network of companies in the surface finishing of aluminum and other materials and promotes the economic, political and technical interests of its members at national and international level.

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