Anti-aging periodic variable reaction black chromium coating film and forming method thereof

Abstract

The disclosure provides an anti-aging periodic variable reaction black chromium coating film, sequentially comprising: an aluminum alloy matrix, a silane conversion film, a high-gloss organic resin coating, a metal compound and metal element periodic variable content alloy coating film, and a transparent resin coating. The disclosure simultaneously provides a method for forming the anti-aging periodic variable reaction black chromium coating film.

Claims

1. A method for forming an anti-aging black chromium coating film, comprising: (1) silane pretreating a surface of an aluminum alloy wheel, comprising subjecting the surface of the aluminum alloy wheel to all of the following steps: hot water washing, de-greasing and alkaline washing, hot water washing, water washing, acid washing, pure water washing, pure water washing, silane passivating, pure water washing, sealing, pure water washing, and moisture drying, (2) forming a high-gloss powder coating on the silane pretreated surface of the aluminum alloy wheel, by electrostatically spraying an epoxy powder coating material or a polyester powder coating material onto the silane pretreated surface of the aluminum alloy wheel from (1) and then curing the epoxy powder coating material or the polyester powder coating material, (3) depositing a physical vapor deposition (PVD) coating on the high-gloss powder coating by a high-vacuum magnetron sputtering coating machine which is provided with a pure chromium target and a nickel-chromium alloy target, wherein a power of the pure chromium target and a power of the nickel-chromium alloy target are set with different power according to a color of the PVD coating, wherein the aluminum alloy wheel rotates and revolves in the high-vacuum magnetron sputtering coating machine, wherein the PVD coating has an adhesion to the high-gloss powder coating, wherein a thickness of the PVD coating is 120-250 nm, wherein the depositing the PVD coating on the high-gloss powder coating comprises: introducing a premixed gas of argon and acetylene into a chamber of the high-vacuum magnetron sputtering coating machine, wherein the argon is used as a working gas and the acetylene is used as a reactive gas, first only sputtering the pure chromium target, so as to form a first film of chromium and chromium carbide with a thickness of 5-10 nm, secondly sputtering the pure chromium target and the nickel-chromium alloy target simultaneously, so as to form a second film of chromium, nickel, nickel-chromium alloy, chromium carbide and nickel carbide with a thickness of 80-150 nm, and finally only sputtering the pure chromium target, so as to form a third film of chromium and chromium carbide with a thickness of 5-10 nm, and (4) spraying transparent powder on the PVD coating and curing the transparent powder, wherein the transparent powder is an acrylic resin or a polyester powder coating material.

2. The method for forming the anti-aging black chromium coating film according to claim 1, wherein in (1), a silane conversion film is formed on the surface of the aluminum alloy wheel during the silane passivating, and the moisture drying is performed in an oven at a temperature of 150 C. for 30 min.

3. The method for forming the anti-aging black chromium coating film according to claim 1, wherein in (2), the high-gloss powder coating is sprayed to have a thickness of 80 to 150 m, a curing temperature of the epoxy powder coating material or the polyester powder coating material is 220 C., a curing time of the epoxy powder coating material or the polyester powder coating material is 20 min, and a hardness of the high-gloss powder coating obtained in (2) is 2H-3H; and after curing, a surface of the high-gloss powder coating reaches a mirror finish, and a glass transition temperature of the high-gloss powder coating is 80-120 C.

4. The method for forming the anti-aging black chromium coating film according to claim 1, wherein in (3), a temperature of the aluminum alloy wheel is 80-150 C., a flow rate of the working gas in the premixed gas is 40-80 cc/min, electric currents for the pure chromium target and the nickel-chromium alloy target are 15-30 A, a vacuum degree in the high-vacuum magnetron sputtering coating machine is 210.sup.3-810.sup.3 Pa, the working gas is 99.999% argon, and the reactive gas is acetylene having a purity of 99.999%; an environment humidity for depositing is less than or equal to 50%; the depositing the PVD coating on the high-gloss powder coating comprises: after the premixed gas of argon and acetylene is introduced, first the pure chromium target is sputtered for 3-7 seconds, and then the pure chromium target and the nickel-chromium alloy target are sputtered simultaneously for 14-24 seconds, and finally the pure chromium target is sputtered for 3-7 seconds, such that the PVD coating is formed, the aluminum alloy wheel rotates while being sputtered, and the pure chromium target and the nickel-chromium alloy target are cooled at a temperature of 15-20 C.

5. The method for forming the anti-aging black chromium coating film according to claim 1, wherein in (3), the argon and the acetylene are premixed in advance, a percentage of the acetylene in the premixed gas is more than 0% and less than or equal to 90%, and a total gas flow is 120-400 cc/min; and a brightness color L value of the PVD coating is between 55 and 85.

6. The method for forming the anti-aging black chromium coating film according to claim 1, wherein in (4), the transparent powder is sprayed to have a thickness of 80-150 m, a curing temperature of the transparent powder is 177 C., a curing time of the transparent powder is 20 min, and a hardness of the transparent powder after curing is 1H.

Description

DETAILED DESCRIPTION

(1) Two kinds of targets are used in the embodiments of the coating method of the disclosure, one is a pure chromium target containing 99.95% of chromium by mass, and the other one is a nickel-chromium alloy having the purity of 99.95% and containing 18% of nickel. The working gas is argon having the purity of 99.999%; the reaction gas is acetylene having the purity of 99.999%; the equipment is a high-vacuum magnetron sputtering coating machine, and can be used for a reactive sputtering coating process. The aluminum wheel material is A356.2 aluminum alloy; the pretreatment adopts silane passivation treatment; the high-gloss medium coating is made of an epoxy powder coating; and the transparent coating is made of a pure acrylic transparent powder coating.

(2) The coating is inspected in accordance with the US general motor hub coating performance standards, and the inspection items include Adhesion Cross-Cut Test, CASS, FLIFORM, high humidity resistance test, coating ultraviolet aging resistance, etc.

(3) A method for forming an anti-aging periodic variable reaction black chromium coating film includes the process flow of: silane pretreatment, spraying of high-gloss medium powder, coating, and spraying of transparent powder.

(4) (1) The silane pretreatment includes the steps of hot water washing, de-greasing and alkaline washing, hot water washing, water washing, acid washing, pure water washing, pure water washing, silane passivation, pure water washing, sealing, pure water washing, and moisture drying.

(5) (2) The spraying of a high-gloss powder refers to electro-statically spraying an epoxy powder coating onto the metal surface of a hub and curing same, in which the base powder is epoxy resin powder or a polyester powder coating. After the coating is cured, the surface achieves mirror finish and has good adhesion to the aluminum matrix. The spraying thickness is 150 m.

(6) (3) High-vacuum magnetron sputtering is performed on the surface of the hub after curing the medium powder, the sputtering targets include a pure chromium target and a nickel-chromium metal target, the sprayed high-gloss medium powder is completely cured, the temperature of the hub is 100 C., argon is introduced with the flow rate of 80 cc/min, the flow rate of acetylene is 240 cc/min, and the coating current is 15 A for the pure chromium target and 18 A for the nickel-chromium alloy target; the vacuum degree is 510.sup.3 Pa, the mixed gas is introduced, the pure chromium alloy is opened at the first stage, the coating time is 6 s, and the auto-rotation and revolution time is 3 s/rev; the pure chromium target and the nickel-chromium alloy target are opened at the second stage, the coating time is 30 s, and the auto-rotation and revolution time is 3 s/rev; and the pure Cr target is opened at the third stage, the coating time is 6 s, and the auto-rotation and revolution time is 3 s/rev. The nickel-chromium alloy used is an alloy material having the nickel content of 80%.

(7) (4) The spraying of transparent powder refers to spraying transparent powder onto the surface of the hub after the PVD coating and curing same, the transparent powder is an acrylic resin powder coating, the transparent coating has good binding force with the coating film, and the resin itself also has aging resistance and other properties.

Comparative Example 1

(8) A PVD protective layer is prepared using a common method in the art. The target is a single pure Cr target, the base powder is black, and the PVD semi-permeable film reaches a black chromium coating film. The adopted process method and coating structure are the same as those of the preparation method of the disclosure.

Comparative Example 2

(9) A PVD protective layer is prepared using a common method in the art. The target is a single NiCr alloy target, the base powder is black, and the PVD semi-permeable film reaches a black chromium coating film. The adopted process method and coating structure are the same as those of the preparation method of the disclosure.

(10) The following tests and comparisons are carried out using the multi-layer sputtered coatings with metal surface ductility in example 1 and comparative examples 1 and 2, as shown in the following table:

(11) TABLE-US-00001 Comparative Comparative Group Example 1 Example 1 Example 2 Coating color L = 65.0, a = 0.1, L = 64.5, a = 0.1, L = 65.2, a = 0.1, b = 2.2 b = 2.2 b = 2.2 Surface No cracks Cracked No cracks cracking Coating film 130 nm 56 nm 58 nm thickness Adhesion 100% 100% 100% Cross-Cut Test shedding-free shedding-free shedding-free CASS 1.0 mm 1.6 mm 3.8 mm FLIFORM 2.3 mm 3.1 mm 5.8 mm Water No change, No change, No change, resistance test adhesion 100% adhesion 91% adhesion shedding-free shedding-free 77% shedding- free Anti-aging No change, No change, No change, adhesion 100% adhesion 65% adhesion coating film coating film 61% coating film shedding-free shedding-free shedding-free

(12) It can be seen that in the method of the disclosure, the coating temperature, the argon flow rate, the acetylene flow rate, the coating current, the vacuum degree, the NiCr alloy target and the pure Cr coating time are the key parameters, and the mixing proportion of acetylene and argon and the coating parameters are the key of obtaining the coating film color, thickness and aging resistance. A coating film with good properties is obtained by the above process. In the disclosure, the technical solution of the example obtains the optimal condition by exploring the above conditions. Coating test results are best under this optimal condition.