With its ability to limit repeated waviness during deformation, combined with the proven qualities of Extragal® (surface quality, corrosion protection), Ultragal® is a coating specifically recommended for visible part applications in the automotive sector.
With the Ultragal® production process, waviness in steel products can be controlled both before and after forming. In an optimized painting process configuration, Ultragal® lends the painted part very high-quality paint appearance (even better than a standard galvanized substrate). With waviness reduced to a very low value, Ultragal® also contributes to enhanced reproducibility of paint appearance quality. It is recommended for parts requiring a premium aspect level or when a compact paint process system is used.
The crystal structure of Ultragal® is not visible to the naked eye and the product offers optimum surface quality before and after painting. Control of the operating drive factors amplifying waviness at the secondary processing stage, in particular during drawing, further enhances paint appearance.
We offer a waviness guarantee expressed as Wa 0.8 mm after drawing, which ensures product quality. Guarantee offered on Ultragal is Wa 0,8 ≤ 0.40 µm ±0.02 µm after equiaxial 3.5% stamping. This demanding criterion enables Ultragal to meet other types of specifications such as Wa 0,8 ≤ 0.50 µm ±0.02 µm after equiaxial 5% stamping or Wsa ≤ 0.50µm after equiaxial 5% stamping.
Ultragal® coating is relatively ductile, which reduces the risk of coating damage in the drawing tool.
Surface appearance of Ultragal® coating (scanning electron micrograph)
Cross-section of Ultragal® coating
Unless otherwise specified, the standard coating thicknesses offered for Ultragal® (per side, measured at 3 points) are as follows:
Other coating thicknesses may be considered. Please contact us for more information.
Ultragal® coating is obtained by hot dip galvanizing (the steel sheet is fed through a bath of molten zinc) of a steel substrate which can be selected from most of our cold rolled steels.
The Ultragal® manufacturing process includes adjustments at all process stages, from steel mill to skin pass. It is subject to rigorous control and inspection. These measures produce an exceptional galvanized coating with surface optimized for top-quality paint appearance in automotive body parts.
Ultragal® coating provides excellent corrosion protection, even in the event of damage (impact, scratches, stone chipping), due to the electro-chemical behaviour of the Fe-Zn galvanic couple, in which the zinc acts as a sacrificial anode.
Ultragal® offers drawing quality equivalent to that of Extragal®, the galvanized steel product with pure zinc coating on both sides. Ultragal® has a friction coefficient of approximately 0.10 to 0.20 (depending on oiling), which lends it excellent drawability. The type and quantity of lubricant and the surface texture are obviously of prime importance during sheet-tool contact; any comparison of coatings must be carried out under identical conditions. Furthermore, the ductility of pure zinc limits the risk of powdering in the drawing tools.
For complicated parts, the use of NIT surface treatment is recommended.
Ultragal® coated products offer a welding range suited to industrial requirements. The welding process, and in particular electrode life (typically 400 spot welds without current adjustment per ISO standard 18278-2 on a 0.8 mm substrate), can be optimized by fine-tuning electrode composition, geometry and current adjustment frequency as well as welding parameters (current type and intensity, current incrementation, joining pressure, cycle time).
ArcelorMittal specialist teams are available to assist customers in optimizing the welding process.
Ultragal® coating has good adhesive bonding behaviour, good adhesion to the coating, good adhesion of the coating to the metal and good cohesion of the coating.
The most significant parameters determining bond quality remain the type of adhesive, the joining conditions, the nature of the protective oil, and any chemical treatments that may have been performed.
Ultragal® can be phosphated and painted at the user's premises using current trication processes (Zn, Ni, Mn). Alternative "environmentally-friendly" (particularly nickel-free) treatment processes being developed make prior validation necessary for any change in the bodywork surface treatment process.
ArcelorMittal can provide specialized technical assistance regarding these issues.