Method for corrosion-protective serial surface treatment of metallic components

Patent metadata

Field	Value
Publication number	US-9932677-B2
Application number	US-201514636457-A
Country	US
Kind code	B2
Filing date	Mar 3, 2015
Priority date	Sep 4, 2012
Publication date	Apr 3, 2018
Grant date	Apr 3, 2018

Abstract

The present invention relates to a method for serial surface treatment of metallic components comprising aluminum surfaces, wherein an alkaline pretreatment is followed by a conversion treatment. According to the invention, the intention during the alkaline pretreatment is that a maximum value for the concentration of dissolved zinc is not exceeded, in order to ensure a sufficient quality of the corrosion-protective coating on the aluminum surface of the components following the surface treatment. In a preferred embodiment, the content of dissolved zinc is effectively held below the respective bath-typical maximum value of dissolved zinc by the addition of compounds constituting a source of sulfide ions. The functionality of the surface treatment can be additionally increased by likewise controlling the content of dissolved aluminum in the alkaline pretreatment such that, by adding compounds constituting a source for silicate anions, a threshold value for dissolved aluminum is not exceeded.

First claim

What is claimed is:

1. A method for serial wet chemical surface treatment of metallic components, in which method metallic components having surfaces of aluminum as well as components having surfaces of zinc are subjected to wet chemical pretreatment by bringing them into contact with an alkaline bath solution which is stored in a system tank, and a wet-on-wet conversion treatment of at least the surfaces of aluminum of the metallic components subsequently takes place, the pH of the alkaline bath solution in the wet chemical pretreatment being greater than 10, and the free alkalinity being at least 0.5 points but less than 50 points, wherein the following maximum value for the concentration of dissolved zinc in the alkaline bath solution of the system tank is not exceeded:
Zn max =0.0004×(pH−9)×[ FA]+ 0.6×[ Y]

pH: pH value
Zn max : maximum value of the concentration of dissolved zinc, in mmol/L
[FA]: free alkalinity in mmol/L
[Y]: concentration in mmol/L of complexing agents Y in the form of water-soluble condensed phosphates calculated as P 2 O 6 and/or in the form of water-soluble organic compounds which contain at least one functional group selected from —COOX 1/n , —OPO 3 X 2/n , and/or —PO 3 X 2/n , where X represents either a hydrogen atom or an alkali and/or alkaline earth metal atom having the respective valence n;

wherein the serial wet chemical surface treatment of the metallic components takes place at least for such a number of metallic components that a total surface area comprising solely zinc surfaces of the metallic components, in square meters, which is greater than the following term:

V
B

×

Zn

ma
⁢

⁢
x

×

M
Zn

Δ
⁢

⁢

m
Zn

V B : bath volume in m 3
Zn max : maximum concentration of dissolved zinc in mmol/L
M Zn : molar mass of zinc in g/mol
ΔM Zn : surface-normalized pickling removal, based on the zinc surfaces of the metallic components in g/m 2 ,
is subjected to wet chemical pretreatment with the alkaline bath solution of the system tank.

2. The method claim 1 , wherein an exceedance of the maximum value Zn max in the wet chemical pretreatment is prevented by continuously or discontinuously removing dissolved zinc from the alkaline bath solution of the system tank, wherein this does not take place solely by discarding at least a portion of the alkaline bath solution of the system tank containing dissolved zinc, and adding another portion of an alkaline solution, which contains only the active components of the alkaline bath solution essential to adjusting alkalinity, to the system tank.

3. The method according to claim 2 , wherein an exceedance of the maximum value Zn max in the wet chemical pretreatment is prevented by adding a water-soluble compound, which represents a source of sulfide ions, to at least a portion of the alkaline bath solution of the system tank, and optionally separating a solid portion, which forms in this portion of the alkaline bath solution, from the alkaline bath solution.

4. The method according to claim 3 , wherein the portion of the alkaline bath solution of the system tank to which the water-soluble compound, which represents a source of sulfide ions, is added has a temperature of at least 40° C., but less than 65° C.

5. The method according to claim 4 , wherein partial volumes are continuously withdrawn from the alkaline bath solution of the system tank, to which partial volumes of the alkaline bath solution containing the water-soluble compound, which represents a source of sulfide ions, is added, after which the solid portion, which is formed in these partial volumes of the alkaline bath solution is separated from the alkaline bath solution by filtration thereby forming a filtrate, and the filtrate is then recirculated into the alkaline bath solution of the system tank.

6. The method according to claim 5 , wherein prior to being recirculated into the alkaline bath solution of the system tank, in order to reduce excess water-soluble compounds which represent a source of sulfide ions, a water-soluble oxidizing agent is added to the filtrate, the standard reduction potential of which oxidizing agent is greater than +0.6 V (SHE).

7. The method according to claim 6 , wherein the alkaline bath solution of the wet chemical pretreatment contains aluminum dissolved in water, wherein a maximum value of 20 mmol/L, for the concentration of dissolved aluminum in the alkaline bath solution of the system tank is not exceeded due to the fact that a water-soluble compound which represents a source of silicate anions is added to at least a portion of the alkaline bath solution of the system tank, and a solid portion comprising aluminum silicate, which forms in this portion of the alkaline bath solution is optionally separated from the alkaline bath solution by filtration.

8. The method according to claim 7 , wherein partial volumes are continuously withdrawn from the alkaline bath solution of the system tank, to which partial volumes the water-soluble compound which represents a source of silicate anions is added, after which the solid portion comprising aluminum silicate, which is formed in these partial volumes of the alkaline bath solution is separated from the alkaline bath solution by filtration, thereby forming a filtrate, and the filtrate is then recirculated into the alkaline bath solution of the system tank.

9. The method according to claim 8 , wherein the conversion treatment following the wet chemical pretreatment using an acidic aqueous composition and the bringing into contact with same take place for a period of time in which the surfaces of aluminum of the metallic components undergo a pickling removal of less than 0.1 g/m 2 .

10. The method according to claim 9 , wherein the conversion treatment following the wet chemical pretreatment takes place using an acidic aqueous composition containing water-soluble compounds of Zr, Ti, and/or Si, and optionally compounds which represent a source of fluoride ions.

11. The method according to claim 10 , wherein metallic components having a composite design are pretreated, the metallic components having surfaces wherein at least 2% of the metallic components' surfaces are aluminum surfaces, and at least 5% of the metallic components' surfaces are zinc surfaces.

12. A method for serial wet chemical surface treatment of metallic components, comprising:
a) contacting metallic components having surfaces of aluminum and surfaces of zinc with a wet chemical pretreatment comprising an alkaline bath solution which is stored in a system tank, said alkaline bath solution having a pH greater than 10 and free alkalinity of at least 0.5 points but less than 50 points, and
b) after step a) performing a wet-on-wet conversion treatment of at least the surfaces of aluminum of the metallic components,

wherein content of dissolved zinc in the alkaline bath solution of the system tank is

Assignees

• Henkel Ag & Co Kgaa

Inventors

• Brouwer Jan-Willem
• Pilarek Frank-Oliver
• Lill Kirsten Agnes
• Resano Artalejo Fernando Jose
• Henze Natascha

Classifications

• G05D21/02

  characterised by the use of electric means · CPC title

• C23C22/86

  Regeneration of coating baths · CPC title

• C23C22/07

  containing phosphates · CPC title

• C23C22/60

  using alkaline aqueous solutions with pH greater than 8 · CPC title

• C23G1/22

  Light metals · CPC title