A method for manufacturing a steel sheet with a ZnAlMg coating, corresponding coated steel sheet, part and vehicle

13:

• A method for manufacturing a steel sheet provided with a coating including from 0.80 to 1.40 wt. % of Al, from 0.80 to 1.40 wt. % of Mg, unavoidable impurities and optionally one or more additional elements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr or Bi, the weight content of each additional element in the coating being less than 0.3%, a remainder being Zn, the method comprising the following successive steps:
• A. providing the steel sheet,
• B. cold rolling the steel sheet, at least a last rolling pass being achieved with rectified and non-etched work rolls for which the work surfaces have a roughness Ra2.5 of less than or equal to 0.5 μm,
• C. annealing of the steel sheet in a continuous annealing line,
• D. depositing the coating by dipping thesteel sheet in a molten bath,
• E. running the coated steel sheet through a confinement zone including wiping nozzles projecting a wiping gas, through at least one outlet, on each side of the sheet along a main ejection direction (E), so that a wiping satisfies at least one of the following equations:
• V
• P
• ×
• (
• Z
• d
• )
• 2
• ≤
• 0.6566
• (
• 1
• )
• p
• O
• 2
• ≤
• [
• 200
• ×
• V
• P
• ln
• [
• 1.523
• ×
• V
• P
• ×
• (
• Z
• d
• )
• 2
• ]
• ]
• 2
• (
• 2
• )
• wherein:
• V is the running speed of the steel sheet in front of the nozzle, V being expressed in m·s−1,
• P is the pressure of the wiping gas in the nozzle, P being expressed in Pa
• Z is the distance between the steel sheet and the nozzle along the main ejection direction (E), Z being expressed in mm,
• d is the average height of the outlet of the nozzle along the running direction
• (S) of the steel sheet in front of the nozzle, d being expressed in mm, pO2 is the partial pressure in oxygen in the confinement zone;
• F. solidifying the coating;
• and
• G. skin-passing the coated steel sheet with work rolls having a roughness Ra2.5 below 5 μm.

15:

• The method as recited in claim 13 wherein at least one of the following equations is further satisfied:
• V
• P
• ×
• (
• Z
• d
• )
• 2
• ≤
• 0.4887
• (
• 3
• )
• p
• O
• 2
• ≤
• [
• 200
• ×
• V
• P
• ln
• [
• 2.046
• ×
• V
• P
• ×
• (
• Z
• d
• )
• 2
• ]
• ]
• 2
• (
• 4
• )