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Zagnelis® Protect - Double-sided ZnMgAl galvanized steels

Presentation

Zagnelis® coatings have been specially designed to improve the corrosion protection of vehicles, while satisfying the specifications of vehicle manufacturers: drawing, welding etc.

More specifically, they offer a corrosion resistance far superior to that of traditional zinc-based coatings. The presence of magnesium in the coating promotes the formation of compact corrosion products highly stable over time, thereby substantially reducing coating consumption kinetics and enhancing the protection of edges.

Zagnelis® coatings also present an excellent drawability performance due to outstanding tribological properties for a zinc-based coating.

Applications

Thanks to an aluminum and magnesium content (3.7% Al – 3% Mg) above the European market average, Zagnelis® Protect offers greater protection against corrosion and is therefore optimally suited to numerous automotive applications. On the interior parts of the body, you can reduce the thickness of the coating used or, at the same thickness as a zinc-based coating, you can protect parts or modules demanding a higher corrosion protection: confined and hollow areas, hem flanges etc.

For certain applications like chassis parts, Zagnelis® Protect can advantageously replace traditional high-thickness zinc coatings (eg. 20µm and thicker), delivering a better weldability, drawability and durability performance.

It could also be considered as an alternative to post-galvanizing and post-painting processes.

The Zagnelis® Protect coating also presents low powdering properties and a lower friction coefficient than traditional zinc coatings, resulting in less pollution and greater productivity of the tools on the drawing line.

Technical characteristics

Surface appearance

The crystalline structure of Zagnelis® Protect is not visible to the naked eye. Its high surface quality delivers a finished paint appearance meeting the requirements of the automotive industry for non-visible or semi-visible parts in industrial conditions.

 

Hardness

Because of its multiphased structure (Zn/Al/MgZn2 ternary eutectic associated to primary Zinc), Zagnelis® Protect is classed as a hard coating.

 

Morphology

Scanning electron micrograph of Zagnelis® Protect surface appearance after skin pass

Scanning electron micrograph of Zagnelis® Protect surface appearance before skin pass

Scanning electron micrograph of a Zagnelis® cross-cut

Coating thickness

Unless otherwise specified, the standard coating thicknesses proposed are 5, 7 and 10 µm per side. Greater thicknesses are available on request.

Coating process

Zagnelis® coatings are produced by hot dip galvanizing (steel strip is drawn through a molten bath of zinc partly loaded with magnesium and aluminum) across a substrate which can be selected from amongst most of our cold or hot rolled steels.

Typical layout of a galvanizing line

Recommendations for use and application

Corrosion

The Zagnelis® Protect coating provides exceptional corrosion protection, even in cases of damage (impact, scratches, stone chipping) or high deformation. The presence of magnesium in the coating delivers a very high performance, thanks notably to the formation of highly stable corrosion products. These products not only act as a barrier, but also substantially reduce the coating consumption kinetics. The protection of edges is also significantly enhanced. It therefore allows you to reduce the thickness of the coating used or increase corrosion protection at an equivalent coating thickness.

 

Extragal® 7 µm

Zagnelis® Protect 7 µm

Resistance to pitting corrosion (six cycles of VDA 233-102 – Metal and glass assemblies)

Resistance to cosmetic corrosion (twelve cycles of VDA 233-102 - 1 mm scratch, Sikken tool after Scotch) 
Stone-chipping resistance (twelve cycles of VDA 233-102 - After Scotch)

Drawing
Zagnelis® Protect has a low friction coefficient (from 0.10 to 0.15 with standard oiling), which facilitates metal flow between matrix and punch, delivering an excellent drawing performance.

 

Furthermore, this coating presents a very low level of abrasion in the drawing dies, thereby increasing their life cycle and thus shop productivity.

Weldability

Zagnelis® Protect coated steels are well-suited to spot welding, with a welding range compatible with industrial requirements. The welding process, and in particular the electrode life, can be optimized by fine-tuning the composition, geometry and dressing frequency of the electrodes as well as the welding parameters (current type and intensity, current incrementation, welding pressure, cycle time).

ArcelorMittal specialist teams are available to assist clients in optimizing the welding process.

Furthermore, the Zagnelis® Protect coating offers the best compromise between corrosion resistance and spot weldability, for applications where the corrosion resistance sought requires a high Zn coating thickness, particularly in hot dip galvanizing.

 

Adhesive bonding

The Zagnelis® Protect coating presents a good adhesive bonding behavior with most adhesives used in the automotive industry: good adhesion to the coating, good adhesion of the coating to the metal, cohesion of the coating.

It is possible that with certain adhesives, the bonding behavior is poorer than with traditional zinc coatings. For these applications, ArcelorMittal proposes that an alkali-activation is applied to the coating surface which will deliver an excellent bonding behavior, whatever the adhesive used. This product is then washed off at the degreasing stage, before painting, and therefore has no effect on the other coating wear properties.

 

Surface treatment
Zagnelis® Protect can be phosphated and painted using current trication phosphatation processes (Zn, Ni, Mn). This type of coating is also particularly well-suited to alternative "environment-friendly" (phosphate-free solution) surface treatment processes, with excellent performances in terms of paint adherence (among which stone-chipping resistance) and underpaint corrosion resistance.

 

Recommendations:

  • Use alkaline degreasing to remove any organic residues and oxides present on the surface
  • F- ions should be present in the phosphating bath to neutralize any Al3+ ions that may reduce bath activity

ArcelorMittal can provide its clients with the relevant specialist assistance.

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