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Zagnelis® Surface - 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 properties 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

Because Zagnelis® Surface contains between 1 and 2% aluminum and magnesium, it is compliant with standard VDA239-100 and offers greater protection against corrosion than traditional zinc-based coatings. You can therefore reduce the thickness of the coating used on coated parts or enhance the corrosion protection obtained at the same thickness. The product is available for visible and non-visible parts and can therefore be used on any type of coated part.

The Zagnelis® Surface 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

Zagnelis® Surface is available for non-visible and visible parts.

Zagnelis® Surface Ultra is a Zagnelis® Surface product with a visual appearance which also delivers guarantees on post-drawing waviness and roughness levels.

 

Hardness

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

 

Morphology

Scanning electron micrograph of Zagnelis® Surface appearance after skin pass

Cross-cut appearance of Zagnelis® Surface

Coating thickness

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

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® Surface coating offers a greater 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 the same coating thickness.

 

Extragal® 7 µm

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

 

Bonding

The Zagnelis® Surface 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® Surface can be phosphated and painted using current trication phosphatation processes (Zn, Ni, Mn). 

This type of coating is also particularly well-suited to certain 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.

Thanks to a controlled post-drawing waviness level, Zagnelis® Surface Ultra is the perfect coating for future applications with increasingly compact surface treatment and paint processes.

 

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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