Metal sheet treatment method and metal sheet treated with this method
AssigneeArcelorMittal
InventorsFrida Gilbert, Lydia Rachiele, Delphine Thai, Christian Allely
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Abstract
The invention relates to a steel substrate coated on at least one of its faces with a metallic coating based on zinc or its alloys wherein the metallic coating is itself coated with a conversion layer comprising: zincsulphate hydrate, aluminium in an amount up to 14 mg·m−2, wherein the conversion layer comprises neither zinc hydroxysulphate, nor free water molecules nor any compounds having free hydroxyl groups, the surface density of sulphur in the conversion layer being greater than or equal to 5.0 mg/m2. The invention also relates to the corresponding treatment method.
Claims16
A coated steel comprising:
- a steel substrate;
- and
- a metallic coating, the steel substrate coated on at least one face with the metallic coating, the metallic coating based on zinc or a zinc alloy wherein the metallic coating is itself coated with a conversion layer comprising:
- zincsulphate hydrate,
- aluminium, wherein aluminum is present in an amount of no more than 14 mg·m−2,
- wherein the conversion layer comprises neither zinc hydroxysulphate, nor free water molecules nor any compounds having free hydroxyl groups, a surface density of sulphur in the conversion layer being greater than or equal to 5.0 mg/m2.
A treatment method for a moving metal strip comprising the following steps:
- i. coating a strip of steel on at least one face with a metallic coating based on zinc or a zinc alloy;
- ii. applying an aqueous treatment solution comprising at least 0.01 mol·L−1 of zinc sulphate and at least 0.01 mol·L−1 of aluminium sulphate to the metallic coating by simple contact so as to form a wet film,
- iii. subsequently drying the aqueous treatment solution with air to form, on the metallic coating, a conversion layer comprising:
- zincsulphate hydrate,
- aluminium, wherein aluminum is present in an amount of no more than 14 mg·m−2,
- wherein the conversion layer comprises neither zinc hydroxysulphate, nor free water molecules nor any compounds having free hydroxyl groups, the surface density of sulphur in the conversion layer being greater than or equal to 5.0 mg/m2.
Dependencies are inferred from the claim text.