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Zagnelis® Protect - Double-sided ZnMgAl galvanized steels

Description

Zagnelis® coatings have been specially designed to add a stage in vehicle corrosion protection, while meeting automotive manufacturers' statements of requirements: drawing, welding etc. More specifically, they offer corrosion resistance far superior to that of provided by 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 dynamics and enhancing edge protection. 

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

 

Applications

Thanks to an aluminium and magnesium content (3.7% Al – 3% Mg) above the European market average, Zagnelis®Protect offers greater protection against corrosion and is therefore ideally suited to numerous automotive applications. On interior body parts, it allows a reduction in the thickness of the coating used or, for the same thickness as a zinc-based coating, it can protect parts or modules requiring enhanced corrosion protection: confined areas, voids, seams, etc.

For certain applications,such as chassis parts, Zagnelis®Protect can advantageously replace traditional high-thickness zinc coatings (e.g. 20 µm and thicker), delivering 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 exhibitslow powdering properties and a lower coefficient of friction than traditional zinc coatings, resulting in less pollution and greater productivity for the tools on the drawing line.

Mechanical properties

Surface appearance

The crystalline structure of Zagnelis® Protect is not visible to the naked eye. Its high surface quality delivers a finished paint appearance which meets the requirements of the automotive industry for non-exposed or semi-exposed 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 Zagnelis® Protect coating thicknesses offered (per side, measured at three points) are as follows:

Similar standard Minimum
(both sides)
Minimum
(per side)
Maximum
(per side)
(g/m²) µm g/m² µm g/m²
ZM70 70 5.6 35 8.1 50
ZM90 90 7.3 45 10.5 65
ZM120 120 9.7 60 12.9 80

Greater thicknesses are available upon 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

Typical layout of a galvanizing line

Recommendations

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 in particular to the formation of highly stable corrosion products. These products not only act as a barrier, but also substantially reduce the coating consumption dynamics. Edge protection is also significantly enhanced. It therefore allows a reduction in the thickness of the coating used or enhanced corrosion protection for 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 adhesive tape) 
Stone-chipping resistance (twelve cycles of VDA 233-102 - after adhesive tape)

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 exhibits a very low level of abrasion in the drawing dies, thereby increasing their life cycle and thus productivity in production.

Weldability

Zagnelis® Protect coated steels are well-suited to spot welding, with a welding range compatible with industrial requirements. The welding process and electrode life in particular 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 customers 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 exhibits good adhesive bonding behaviour 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 behaviour is poorer than with traditional zinc coatings. For these applications, ArcelorMittal suggests that alkali activation is applied to the coating surface which will deliver excellent bonding behaviour, 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 (including stone-chipping resistance) and resistance to corrosion under paint.

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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