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Zagnelis® - Double-sided ZnMgAl galvanized steels

Presentation

Zagnelis® coating has been specially designed to improve corrosion protection of vehicles, while satisfying OEMs' specifications regarding manufacturability: stamping, welding, adhesive bonding, painting process...

 

More specifically, it offers a corrosion resistance much superior to the one of traditional zinc-based coatings.

Presence of Magnesium in the coating leads to the formation of compact and very stable corrosion products during the early stages of corrosion and thus decreases coating consumption kinetics and reinforces cut edges protection.

 

Furthermore, Zagnelis® coating presents an excellent stamping ability due to outstanding tribological properties for a zinc-based coating.

Applications

Because of its high corrosion protection capacity, Zagnelis® coating is recommended for numerous automotive applications. It is specifically recommended for parts requiring strengthened corrosion protection: confined and hollow areas, hem flanges…

 

Zagnelis® coating can contribute to reduce needs for additional corrosion protections measures such as waxes and sealers. It aims at answering car makers needs in terms of anti-corrosion warranty cost reduction. It also opens real perspectives of synergy and robustness when associated to new surface treatments and painting processes.

 

For some applications, Zagnelis® coating can advantageously replace traditional high-thickness zinc coatings (thicker than 20µm), ensuring better performances in weldability, stampability and durability.

 

It can also be figured out as an alternative to post-galvanizing and post-painting processes.

Technical characteristics

Surface appearance
The crystalline structure of Zagnelis® coating is not visible with the naked eye. Its high surface quality leads to a finished paint appearance meeting the requirements of the automotive industry for non-visible or semi-visible bodywork parts. Developments are running for surface quality optimization in order to allow manufacturing of exposed parts.

 

Hardness
Because of its multiphased structure (Zn/Al/MgZn2 ternary eutectic associated to primary Zinc), Zagnelis® ranges among hard coatings.

 

Morphology

Scanning electron micrograph of Zagnelis® coating surface after skin passing

Scanning electron micrograph of Zagnelis® coating surface before skin passing

Scanning electron micrograph of a Zagnelis® cross-cut

Coating thickness
Unless otherwise specified, the standard Zagnelis® coating thicknesses offered (measured at three points) are the following:

Similar standard

Minimum
(double-sided)

(g/m²)

Minimum
(per side)
µm          g/m² 

ZM90

90

  7.0           45

ZM120

120

 10.0          60

Other coating thicknesses may be considered on demand.

Coating process

Zagnelis® coatings are produced by continuous hot dip galvanizing, in which the steel strip is fed through a molten bath of Zinc, Magnesium and Aluminum. The steel substrate consist in almost any of our cold rolled grades and some of our hot rolled grades.

 

The Zagnelis® coating manufacturing includes fine-tuning of all stages of the process, from the steelworks to the skin-pass mill. It undergoes rigorous control and inspection steps. As a result of these measures, an exceptional multiphased ZnMgAl galvanized coating with an optimized surface is obtained. This ensures a very high level of protection against corrosion and a surface quality compatible with automotive market requirements.

Typical layout of a galvanizing line

Recommendations for use and secondary processing

Corrosion
Zagnelis® coating provides excellent corrosion protection, even in case of damage (impact, scratches, stone shipping) or high deformation. Presence of magnesium in the coating allows very high performances as corrosion products which are formed at product surface during the early stages of corrosion are compact and very stable. These corrosion products act as a barrier against corrosive media and limit coating consumption. Cut edges protection is also significantly reinforced.

 

Drawing
Zagnelis® friction coefficient is low (around 0,10 with standard oiling): metal flow between matrix and punch is easier so that Zagnelis® presents an excellent drawing ability.

The type and quantity of lubricant as well as the surface texture are obviously of prime importance during sheet-tool contact; any comparison of coatings must be carried out under the same conditions.

 

Spot Welding
Zagnelis® coated products offer a welding range suited to industrial requirements. The welding process, and in particular electrode life, can be optimized by fine-tuning electrode composition, electrode geometry and dressing frequency as well as welding parameters (current type and intensity, current incrementation, welding effort, cycle time).

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

Furthermore Zagnelis® offers the best compromise between corrosion resistance and weldability, especially for applications where needed corrosion resistance usually requires high Zn coating thickness (for instance post-galavanizing).

 

Adhesive bonding
Zagnelis® coating shows good adhesive bonding behavior with most adhesives used in automotive: good adhesion to the coating, good adhesion of the coating to the metal substrate and the good mechanical resistance of the coating itselve.

The most significant parameters influencing adhesive bonding quality remain the type of adhesive, the joining conditions, the nature of the protective oil and any chemical treatments that may have been performed.

 

Surface treatment
Zagnelis® can be phosphated and painted using current trication phosphatation process (Zn, Ni, Mn). It is also well-suited for alternative "environment-friendly" (phosphate-free) surface treatment processes, with excellent performances in terms of paint adherence (among them resistance to stone shipping) and underpaint corrosion resistance. Zagnelis® appears as the ideal coating for future applications including compact surface treatment and painting processes.

 

Recommendations:

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

ArcelorMittal can provide specialized technical assistance regarding these issues.

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