Method of cleaning pretreatment of ferrous components that have been joined by welding

Abstract

The present invention relates to a method of cleaning pretreatment of ferrous components that have been joined by welding, in which residues from the welding operation are removed from the surface of the component and, in this way, subsequent wet-chemical conversion treatments are enabled so as to produce defect-free coatings. For cleaning pretreatment, the component is contacted with an aqueous sulfuric acid etchant which comprises amino alcohols, ethoxylates and/or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the alcohol and iron ions, and is effective without the presence of fluorides. In a further aspect, the present invention encompasses an aqueous acidic etchant for cleaning pretreatment of ferrous components that have been joined by welding.

Claims

1. A method for cleaning pretreatment of a component assembled at least in part by welding, comprising: contacting the component assembled at least in part by welding, wherein at least one portion of the component comprises a material consisting of iron or steel integrally bonded to another portion of the component by welding, with an aqueous fluoride-free sulfuric pickle liquor containing: a) a total of at least 1 g/kg of amino alcohols per the aqueous fluoride-free sulfuric pickle liquor; b) a total of at least 0.5 g/kg of ethoxylates and/or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the fatty alcohol and comprising at least 6 ethylene and/or propylene oxide units per the aqueous fluoride-free sulfuric pickle liquor; and c) iron ions wherein the sulfuric pickle liquor has a pH below 2.0 and includes at least 20 g/kg of sulfuric acid.

2. The method according to claim 1, wherein the amino alcohols according to component a) are selected from 1,3-amino alcohols and the ethylene or 1,2-propylene glycol monoethers thereof.

3. The method according to claim 1, wherein component a) is present in an amount of at least 2 g/kg, but not more than 20 g/kg of the aqueous fluoride-free sulfuric pickle liquor.

4. The method according to claim 1, wherein the ethoxylates and/or propoxylates of the fatty alcohols according to component b) have an HLB value of less than 16 and more than 10.

5. The method according to claim 1, wherein the ethoxylates and/or propoxylates of the fatty alcohols according to component b) are selected from ethoxylates.

6. The method according to claim 1, wherein the ethoxylates and/or propoxylates of the fatty alcohols according to component b) are selected from ethoxylates of fatty alcohols having 8 to 12 carbon atoms in the fatty alcohol and having 8 to 10 ethylene oxide units.

7. The method according to claim 1, wherein the proportion of ethoxylates and/or propoxylates of fatty alcohols according to component b) in the aqueous fluoride-free sulfuric pickle liquor is at least 1 g/kg and no more than 10 g/kg of the aqueous fluoride-free sulfuric pickle liquor.

8. The method according to claim 1, wherein the aqueous fluoride-free sulfuric pickle liquor further comprises ethoxylates and/or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the fatty alcohol having less than 6 ethylene and/or propylene oxide units.

9. The method according to claim 1, wherein component c) is present in an amount of at least 10 g/kg and no more than 70 g/kg of the aqueous fluoride-free sulfuric pickle liquor.

10. The method according to claim 1, wherein the aqueous fluoride-free sulfuric pickle liquor contains a total of less than 1 g/kg dissolved phosphates, calculated as PO4, per the aqueous fluoride-free sulfuric pickle liquor.

11. The method according to claim 1, wherein the contacting with the aqueous fluoride-free sulfuric pickling liquor is preceded by alkaline degreasing of the component, the alkaline degreasing being carried out at a pH of at least 10.

12. The method according to claim 1, wherein the contacting with the aqueous fluoride-free sulfuric pickling liquor is followed by a wet-chemical conversion treatment of the component.

13. The method according to claim 12, wherein the wet-chemical conversion treatment is carried out by means of acidic aqueous compositions having a pH of greater than 1, but below 5.

14. The method according to claim 1, wherein the amino alcohols according to component a) include a 1,3-amino alcohol selected from 2-(2-aminoethoxy)ethanol, 2-(2-aminoethoxy)propanol, dimethylaminoethanol, diethylaminoethanol, N-methyldiethanolamine, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine and combinations thereof.

15. The method according to claim 14, wherein at least 80 wt. % of the 1,3 amino alcohol is selected from monoethanolamine, diethanolamine, triethanolamine and combinations thereof.

16. The method according to claim 1, further comprising ethoxylates and/or propoxylates of fatty alcohols, having 6 to 12 carbon atoms in the fatty alcohol and less than 6 ethylene and/or propylene oxide units, present in an amount of 0.5 to 5 g/kg of the aqueous fluoride-free sulfuric pickle liquor.

17. The method according to claim 1, wherein the iron ions according to component c) are sourced from iron(II) sulfate.

18. The method of claim 1, wherein the sulfuric acid is present in an amount of at least 60 g/kg and less than 120 g/kg.

19. The method of claim 1, wherein the aqueous fluoride-free sulfuric pickle liquor has a pH below 1.0.

20. An acidic aqueous pickle liquor having a pH of below 2.0 and containing: i) 40 to 120 g/kg of sulfuric acid, calculated as SO4; ii) 2 to 20 g/kg of amino alcohols; iii) 0.5 to 5 g/kg of ethoxylates and/or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the fatty alcohol and at least 6 ethylene and/or propylene oxide units; iv) 10 to 50 g/kg iron ions; v) less than 50 mg/kg of fluoride ions; vi) less than 1 g/kg of dissolved phosphates, calculated as PO4.

Description

EMBODIMENTS

(1) Test pieces assembled from two cut-out steel sheets (200×200×2 mm) by means of metal active gas welding (mixture gas M20: 90% argon, 10% CO.sub.2) were treated according to the process steps defined below. The welding was carried out in accordance with the AWS A 5.28/A 5.28M:2007 standard using a slag-forming silicon-containing welding filler material. The welding bead had a length of approximately 100 mm and a width of approximately 2-3 mm. A. Alkaline degreasing: The test piece was immersed in a mixture of Bonderite® C-AD 1563 (3 wt. %) and Bonderite® C-AD 1400 (0.3 wt. %) at 65° C. for 10 minutes. B. Acidic pickle liquor: B.1 The test piece was immersed at 60° C. for 4 minutes in a sulfuric pickle liquor containing:

(2) TABLE-US-00001 a) 77.8 g/kg H.sub.2SO.sub.4 b)  1.5 g/kg ethoxylated (8EO) fatty alcohol (C10) c)   20 g/kg iron(II) sulfate d) 0.45 g/kg ethoxylated (4EO) fatty alcohol (C8) B.2 The test piece was immersed at 60° C. for 15 minutes in a mixed-acid pickle liquor containing:

(3) TABLE-US-00002 a) 150 g/kg  H.sub.2SO.sub.4 b) 70 g/kg H.sub.3PO.sub.4 c) 40 g/kg iron(II) sulfate d) 1.8 g/kg  ammonium bifluoride C. Zinc phosphating: The test piece was immersed in Bonderite® M-ZN 958 at 52° C. for 4 minutes, the test piece being activated, however, immediately before with Bonderite® M-AC 950 at 25° C. for 1 minute, with an intermediate step of rinsing with deionized water (κ<1 μScm.sup.−1).

(4) In a process sequence A-B.1-C according to the invention, a shiny metal surface was obtained in the region of the weld seam. A minimal amount of residue from the welding slag could only be seen in this region using an optical microscope. Scanning electron microscopy (SEM) confirmed the good overall optical result and proved by means of energy-dispersive X-ray spectroscopy (EDX) that small amounts of silicon could still only be detected in portions.

(5) By contrast, despite the tripled treatment time in a conventional process sequence A-B.2-C using a fluoride-containing mixed-acid pickle liquor, residues of the welding slag were perceptible even to the naked eye as matte points. Optical microscopy and REM confirmed this. Furthermore, a zinc phosphate layer was not formed on the regions on which residues of the welding slag were identified by the naked eye before and immediately after pickling.