Non-chrome pssivation process for zinc and zinc alloys

Abstract

A non-chrome containing composition and process are disclosed for enhancing the corrosion resistance of zinc or zinc alloy surfaces. The composition comprises a source of titanium ions or titanates, an oxidant and fluorides or complex fluorides. The composition also preferably comprises an organic acid and / or a group II metal compound, preferably a group II metal chloride.

Description

Background technique

[0001] The automotive industry has utilized galvanized parts for many years. Chromization of zinc deposits is a common method of delaying the appearance of white corrosion products over the life of such parts. The two most commonly used chrome treatments are clear "blue" and "iridescent yellow" films (although black and green variants are also known). More recently, zinc alloys have been cited which have improved resistance to the formation of white corrosion products when used in combination with chroming treatments. However, hexavalent chromium is a toxic and carcinogenic substance. The material is capable of leaching from chromed zinc deposits, causing damage to the environment and to those who routinely handle chromed parts. Therefore, appropriate alternatives need to be sought. Chromating is a very cost-effective and effective method of improving the corrosion resistance of galvanized or zinc-alloyed parts. Any suitable alternative should be cost...

Examples

Embodiment 1

[0025] A solution consisting of the following was stirred and the pH adjusted to 2.0 with 10% sodium hydroxide:

[0026] 10 wt% TiCl in 20-30 wt% HCl 3 Solution 2 g / L

[0027] 35%H 2 o 2 3 g / l

[0028] NaF 0.2 g / L

[0029] Deionized water up to 1 liter

[0030] A steel plate coated with 8 micron zinc was immersed in the solution for 1 minute at 25°C, rinsed and then dried. Forms a uniform clear to blue conversion coating.

[0031] The corrosion resistance of conversion coatings was evaluated by measuring the time required for the formation of white abrasive products in a neutral salt spray chamber (according to ASTM B-117). The first white corrosion appeared on the panel at 12 hours.

Embodiment 2

[0033] A solution consisting of the following was stirred and the pH adjusted to 2.0 with 10% sodium hydroxide:

[0034] 10 wt% TiCl in 20-30 wt% HCl 3 Solution 2 g / L

[0035] 35%H 2 o 2 3 g / L

[0036] NaBF 4 5 g / L

[0037] Deionized water up to 1 liter

[0038] A steel plate coated with 8 micron zinc was immersed in the solution for 1 minute at 25°C, rinsed and then dried. Forms an attractive blue conversion coating.

Embodiment 3

[0040] A solution consisting of the following was stirred and the pH adjusted to 2.0 with 10% sodium hydroxide:

[0041] 10 wt% TiCl in 20-30 wt% HCl 3 Solution 2 g / L

[0042] 35%H 2 o 23 g / L

[0043] NaBF 4 5 g / l

[0044] SrCl 2 6H 2 O 1 g / L

[0045] Deionized water up to 1 liter

[0046] A steel plate coated with 8 micron zinc was immersed in the solution for 1 minute at 25°C, rinsed and then dried. Forms an attractive blue conversion coating.

[0047] In the corrosion test, the panel first showed white corrosion at 24 hours. This result was found to be comparable to blue conversion coatings formed with chromium-based products.

Background technique

[0001] The automotive industry has utilized galvanized parts for many years. Chromization of zinc deposits is a common method of delaying the appearance of white corrosion products over the life of such parts. The two most commonly used chrome treatments are clear "blue" and "iridescent yellow" films (although black and green variants are also known). More recently, zinc alloys have been cited which have improved resistance to the formation of white corrosion products when used in combination with chroming treatments. However, hexavalent chromium is a toxic and carcinogenic substance. The material is capable of leaching from chromed zinc deposits, causing damage to the environment and to those who routinely handle chromed parts. Therefore, appropriate alternatives need to be sought. Chromating is a very cost-effective and effective method of improving the corrosion resistance of galvanized or zinc-alloyed parts. Any suitable alternative should be cost...

Examples

Embodiment 1

[0025] A solution consisting of the following was stirred and the pH adjusted to 2.0 with 10% sodium hydroxide:

[0026] 10 wt% TiCl in 20-30 wt% HCl 3 Solution 2 g / L

[0027] 35%H 2 o 2 3 g / l

[0028] NaF 0.2 g / L

[0029] Deionized water up to 1 liter

[0030] A steel plate coated with 8 micron zinc was immersed in the solution for 1 minute at 25°C, rinsed and then dried. Forms a uniform clear to blue conversion coating.

[0031] The corrosion resistance of conversion coatings was evaluated by measuring the time required for the formation of white abrasive products in a neutral salt spray chamber (according to ASTM B-117). The first white corrosion appeared on the panel at 12 hours.

Embodiment 2

[0033] A solution consisting of the following was stirred and the pH adjusted to 2.0 with 10% sodium hydroxide:

[0034] 10 wt% TiCl in 20-30 wt% HCl 3 Solution 2 g / L

[0035] 35%H 2 o 2 3 g / L

[0036] NaBF 4 5 g / L

[0037] Deionized water up to 1 liter

[0038] A steel plate coated with 8 micron zinc was immersed in the solution for 1 minute at 25°C, rinsed and then dried. Forms an attractive blue conversion coating.

Embodiment 3

[0040] A solution consisting of the following was stirred and the pH adjusted to 2.0 with 10% sodium hydroxide:

[0041] 10 wt% TiCl in 20-30 wt% HCl 3 Solution 2 g / L

[0042] 35%H 2 o 23 g / L

[0043] NaBF 4 5 g / l

[0044] SrCl 2 6H 2 O 1 g / L

[0045] Deionized water up to 1 liter

[0046] A steel plate coated with 8 micron zinc was immersed in the solution for 1 minute at 25°C, rinsed and then dried. Forms an attractive blue conversion coating.

[0047] In the corrosion test, the panel first showed white corrosion at 24 hours. This result was found to be comparable to blue conversion coatings formed with chromium-based products.