Flux compositions for steel galvanization

Abstract

This invention relates to a flux composition for treating a metal surface, comprising (a) more than 40 and less than 70 wt. % zinc chloride, (b) 10 to 30 wt. % ammonium chloride, (c) more than 6 and less than 30 wt. % of a set of at least two alkali metal chlorides including sodium chloride and potassium chloride, (d) from 0 to 2 wt. % lead chloride, and (e) from 0 to 15 wt. % tin chloride, provided that the KCl/NaCl weight ratio of said set of at least two alkali metal chlorides ranges from 2.0 to 8.0. This invention also relates to a fluxing bath comprising this flux composition dissolved in water for use in galvanizing processes, by batch or continuously, of metal articles such as iron or steel long products and flat products including wires, plates, coils, rods, reinforcing bars, tubes, strips and sheets.

1 . A flux composition for treating a metal surface, comprising (a) more than 40 and less than 70 wt. % zinc chloride, (b) 10 to 30 wt. % ammonium chloride, (c) more than 6 and less than 30 wt. % of a set of at least two alkali metal chlorides including sodium chloride and potassium chloride, (d) from 0 to 2 wt. % lead chloride, and (e) from 0 to 15 wt. % tin chloride, provided that the KCl/NaCl weight ratio of said set of at least two alkali metal chlorides ranges from 2.0 to 8.0 
     
     
         2 . A flux composition according to  claim 1 , wherein said the combined amounts of lead chloride and tin chloride represent at least 2.5 wt. % of said composition. 
     
     
         3 . A flux composition according to  claim 1 , further comprising at least one metal chloride selected from the group consisting of nickel chloride, cobalt chloride, manganese chloride, cerium chloride, antimony chloride and lanthanum chloride. 
     
     
         4 . A flux composition according to  claim 1 , further comprising up to 1.5 wt. % nickel chloride. 
     
     
         5 . A flux composition according to  claim 1 , further comprising at least one nonionic surfactant. 
     
     
         6 . A flux composition according to  claim 1 , further comprising at least one corrosion inhibitor. 
     
     
         7 . A flux composition according to  claim 1 , being fluoride salts-free. 
     
     
         8 . A flux composition according to  claim 1 , being free from volatile organics. 
     
     
         9 . A fluxing bath for hot dip galvanization comprising a flux composition according to  claim 1  dissolved in water. 
     
     
         10 . A fluxing bath according to  claim 9 , wherein the total concentration of components of the flux composition in water ranges from 200 to 750 g/l. 
     
     
         11 . A process for the hot dip galvanization of a metal article, comprising a step of treating said article in a fluxing bath according to  claim 9 . 
     
     
         12 . A hot dip galvanization process according to  claim 11 , wherein said metal article is an iron or steel article. 
     
     
         13 . A hot dip galvanization process according to  claim 11 , wherein said treating step consists of immersing said article in said fluxing bath for a period of time from 0.01 to 30 minutes. 
     
     
         14 . A hot dip galvanization process according to  claim 11 , wherein said treating step is performed at a temperature ranging from 70° C. to 90° C. 
     
     
         15 . A hot dip galvanization process according to  claim 11 , wherein the treated article is further dried until its surface temperature ranges from 100° C. to 200° C. 
     
     
         16 . A hot dip galvanization process according to  claim 15 , wherein said drying step is performed under a poorly oxidative atmosphere. 
     
     
         17 . A hot dip galvanization process according to  claim 11 , further comprising a step of dipping the treated article in a molten zinc-based galvanizing bath. 
     
     
         18 . A hot dip galvanization process according to  claim 17 , wherein said molten zinc-based galvanizing bath comprising (a) from 4 to 24 wt. % aluminum, (b) from 0.5 to 6 wt. % magnesium, and (c) the rest being essentially zinc. 
     
     
         19 . A hot dip galvanization process according to  claim 17 , wherein dipping is performed at a temperature between 380 and 440° C. and wherein said molten zinc-based galvanizing bath comprising (a) from 4 to 7 wt. % aluminum, (b) from 0.5 to 3 wt. % magnesium, and (c) the rest being essentially zinc. 
     
     
         20 . A galvanized iron or steel product being pre-treated with a flux composition according to  claim 1 , having a protective coating layer with a thickness ranging from 5 to 30 μm.