Method for selectively phosphating a composite metal construction

Patent metadata

Field	Value
Publication number	US-9550208-B2
Application number	US-201213718342-A
Country	US
Kind code	B2
Filing date	Dec 18, 2012
Priority date	Jun 30, 2010
Publication date	Jan 24, 2017
Grant date	Jan 24, 2017

Abstract

A multistage method for treatment of composite metal structures containing metallic surfaces of aluminum, zinc and optionally iron, is provide wherein in a first step, selective zinc phosphating of zinc and ferrous surfaces proceeds using a phosphating solution containing a quantity of water-soluble inorganic silicon compounds sufficient to suppress white spot formation on zinc, but less than the quantity where zinc phosphating loses selectivity. In a following second step, aluminum surfaces are passivated with an acidic treatment solution. Also provided is a zinc phosphating solution suitable for said method containing at least 0.025 g/l, but less than 1 g/l of silicon as water-soluble inorganic compounds calculated as SiF 6 , wherein the product (Si/mM)·(F/mM) of the concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and the concentration of free fluoride [F in mM] divided by the free acid point number is no greater than 5.

First claim

The invention claimed is:

1. A zinc phosphating solution comprising:
(a) 5-50 g/l of phosphate ions,
(b) 0.3-3 g/l of zinc(II) ions,
(c) a concentration of free fluoride, in g/l which is at least 0.005 g/l, and no greater than 8/T g/l wherein T is the temperature at which the solution is used for coating,
(d) at least 0.025 g/l, but less than 1.0 g/l of silicon in the form of water-soluble inorganic compounds calculated as SiF 6 ,
said zinc phosphating solution having a free acid point number of at least 0.4 points, but of no more than 3 points and a pH value in the range from 2.2 to 3.6; wherein a product “(Si/mM)·(F/mM)” of concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and concentration of free fluoride [F in mM] divided by the free acid point number is no greater than 5, wherein the zinc phosphating solution is effective for coating zinc or iron surfaces to form a continuous coating, but forms no continuous coating on aluminum surfaces at under the same coating conditions used for coating zinc or iron surfaces to form a continuous coating.

2. The zinc phosphating solution according to claim 1 , comprising in total no more than 5 ppm of water-soluble compounds of zirconium, measured as zirconium, and/or titanium, measured as titanium.

3. The zinc phosphating solution according to claim 1 , comprising a free acid content of at least 0.6 points, but of no more than 2.5 points.

4. The zinc phosphating solution according to claim 1 , comprising a total acid content of at least 10 points, but no more than 50 points.

5. The zinc phosphating solution according to claim 1 , comprising in total no more than 1 ppm of water-soluble compounds of zirconium and/or titanium measured as zirconium and/or titanium, and having a free acid content of at least 1.0 point, but no more than 2.0 points, and a total acid content of at least 15 points, but no more than 25 points.

6. The zinc phosphating solution of claim 1 , wherein from 0.025 g/l to less than 0.9 g/l of silicon is contained in the solution.

7. The zinc phosphating solution of claim 1 , wherein the (Si/mM)·(F/mM) of concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and concentration of free fluoride [F in mM] divided by the free acid point number is no greater than 4.5.

8. The zinc phosphating solution of claim 1 , wherein the (Si/mM)·(F/mM) of concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and concentration of free fluoride [F in mM] divided by the free acid point number is no greater than 4.0.

9. The zinc phosphating solution of claim 1 , wherein the free acid point number is from 1.0 to 2.0.

10. The zinc phosphating solution of claim 1 , which provides a continuous coating on iron and/or zinc surfaces in an areal weight of >0.5 g/m 2 , while under the same conditions forms no continuous coating on aluminum surfaces under the same conditions, any discontinuous deposition on aluminum surfaces having an areal weight of <0.5 g/m 2 .

11. The zinc phosphating solution of claim 10 , which is effective to deposit a zinc phosphate layer having a areal weight of 1.0 g/m 2 to 4.0 g/m 2 on zinc and iron surfaces but which, under the same conditions, deposits no more than a discontinuous layer with an areal weight of <0.5 g/m 2 on aluminum surfaces.

12. The zinc phosphating solution of claim 10 , which is effective to deposit a zinc phosphate layer having a areal weight of 1.0 g/m 2 to 2.0 g/m 2 on zinc and iron surfaces but which, under the same conditions, deposits no more than a discontinuous layer with an areal weight of <0.5 g/m 2 on aluminum surfaces.

13. The zinc phosphating solution of claim 1 , which contains ≦5 ppm total of water soluble compounds of zirconium and titanium, calculated on the basis of the elements zirconium and titanium.

14. The zinc phosphating solution of claim 1 , which contains ≦1 ppm total of water soluble compounds of zirconium and titanium, calculated on the basis of the elements zirconium and titanium.

15. A zinc phosphating solution consisting essentially of:
(a) 5-50 g/l of phosphate ions,
(b) 0.3-3 g/l of zinc(II) ions,
(c) at least 10 ppm, but no more than 100 ppm of free fluoride ions,
(d) at least 0.025 g/l, but less than 1.0 g/l of silicon in the form of water-soluble inorganic compounds calculated as SiF 6 ,
(e) optionally, one or more accelerants, and
(f) optionally, one or more metal cations other than zinc cations, said zinc phosphating solution having a free acid point number of at least 0.4 points, but of no more than 3 points and a pH value in the range from 2.2 to 3.6; wherein a product “(Si/mM)·(F/mM)” of concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and concentration of free fluoride [F in mM] divided by the free acid point number is no greater than 5, wherein the zinc phosphating solution is effective for forming a continuous coating on zinc and/or iron surfaces but forms no continuous coating on aluminum surfaces under the same coating conditions.

16. A zinc phosphating solution consisting essentially of:
(a) 5-50 g/l of phosphate ions,
(b) 0.3-3 g/l of zinc(II) ions,
(c) at least 10 ppm, but no more than 100 ppm of free fluoride ions,
(d) at least 0.025 g/l, but less than 1.0 g/l of silicon in the form of water-soluble inorganic compounds calculated as SiF 6 ,
(e) optionally, one or more accelerants selected from the group consisting of chlorate ions, nitrite ions, nitroguanidine, N-methylmorpholine-N-oxide, m-nitrobenzene sulfonate ions, m-nitrobenzoate ions, p-nitrophenol, hydrogen peroxide, hydroxylamine, and reducing sugar, and
(d) optionally, one or more metal cations selected from the group consisting of nickel (II), cobalt (II), magnesium, calcium, iron (II), lithium, and tungsten,
said zinc phosphating solution having a free acid point number of at least 0.4 points, but of no more than 3 points and a pH value in the range from 2.2 to 3.6; wherein a product “(Si/mM)·(F/mM)” of concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and concentration of free fluoride [F in mM] divided by the free acid point number is no greater than 5, wherein the zinc phosphating solution is effective for forming a continuous coating on zinc and/or iron surfaces but forms no continuous coating on aluminum surfaces under the same coating conditions.

17. A zinc phosphating solution for use in the simultaneous coating of a composite article comprising at least one surface of iron or zinc, and at least one surface of aluminum, comprising:
(a) 5-50 g/l of phosphate ions,
(b) 0.3-3 g/l of zinc(II) ions,
(c) a concentration of free fluoride, in g/l which is at least 0.005 g/l,
(d) at least 0.025 g/l, but less than 1.0 g/l of silicon in the form of water-soluble inorganic compounds calculated as SiF 6 ,
said zinc phosphating solution having a free acid point number of at least 0.4 points, but of no more than 3 points and a pH value in the range from 2.2 to 3.6; wherein a product “(Si/mM)·(F/mM)” of concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and concentration of free fluoride [F in mM] divided by the free acid point number is no greater than 5, wherein the zinc phosphating solution does not deposit a complete-coverage zinc phosphate layer onto aluminum surfaces of said composite article, but does deposit a continuous coating of zinc phosphate onto surfaces of iron or zinc of said composite article.

18. The zinc phosphating solution of claim 17 whi

Assignees

• Henkel Ag & Co Kgaa

Inventors

• Brouwer Jan-Willem
• Pilarek Frank-Oliver
• Hamacher Matthias
• Balzer Marc
• Popp Roland

Classifications

• C23C22/73

  characterised by the process · CPC title

• B05D3/107 Primary

  Post-treatment of applied coatings · CPC title

• C23C22/365

  containing also zinc and nickel cations · CPC title

• C23C22/83

  Chemical after-treatment · CPC title

• C23C22/362 Primary

  containing also zinc cations · CPC title