AGING RESISTANCE COATING FILM FOR HUB AND METHOD FOR FORMING PROTECTIVE FILM

Abstract

Disclosed herein is an aging resistance coating film for a hub, sequentially comprising an aluminum alloy matrix, a silane conversion film, a high-gloss organic resin coating, a periodic variable alloy black chromium coating film and a transparent resin coating. In the coating film, the thickness of the black chromium coating film is increased and the blackness thereof is adjusted according to different content of C. The residual stress of the deposited metal layer is reduced, the problem of cracking during heating and rapid cooling of the coating film is solved, and the binding force between the coating film and the underlying high-gloss resin material is improved. Also disclosed herein is a method for forming an aging resistance coating film for a hub, comprising: (1) silane pretreatment, (2) spraying of high-gloss medium powder, (3) PVD coating, and (4) spraying of transparent powder.

Claims

1. An aging resistance coating film for a hub, sequentially comprising: an aluminum alloy matrix, a silane conversion film, a high-gloss organic resin coating, a periodic variable alloy black chromium coating film and a transparent resin coating; the periodic variable alloy black chromium coating film is a CCr periodic variable alloy black chromium coating film, 90%-0 of C component changes periodically, 10-100% of Cr metal component changes periodically, Cr is primed first with a thickness of 5-10 nm, then the double targets are opened, C and Cr change periodically in accordance with the ratio of 10:90 to 90:10 for coating with a thickness of 80-150 nm, finally only the pure Cr target is opened to form a thickness of 5-10 nm, and the thickness of the entire film is 100-170 nm; the thickness of the high-gloss organic resin coating is 120-250 m, and the thickness of the transparent resin coating is 80-150 m.

2. A method for forming an aging resistance coating film for a hub, comprising: (1) silane pretreatment, (2) spraying of high-gloss medium powder, (3) PVD coating, and (4) spraying of transparent powder; the silane pretreatment comprises 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, closing, pure water washing and moisture drying; the spraying of a high-gloss powder coating means that an epoxy powder coating material is electrostatically sprayed onto a metal surface of the hub and cured, wherein the base powder is epoxy resin powder or a polyester powder coating material; the PVD coating refers to high vacuum magnetron sputtering on the surface of the hub after the medium powder is cured, the sputtering target comprises a pure C target and a pure Cr metal target, the two targets are set with different power according to the colors and opened for coating in accordance with the process one after another, the hub in the equipment can rotate and revolve, the two targets are sputtered onto the surface of the hub in certain sequence and proportion of C and Cr, the surface coating film is uniform in thickness and color by means of rotation and revolution of the hub, and the coating film has good binding force with the underlying high-gloss resin coating; the spraying of transparent powder means that the transparent powder is sprayed onto the surface of the hub after the PVD coating and cured, the transparent powder is an acrylic resin or polyester powder coating material, the transparent coating has good binding force with the coating film, and the resin itself also has aging resistance and other properties.

3. The method for forming an aging resistance coating film for a hub according to claim 2, wherein step (1) of pretreating the surface comprises water washing, alkaline washing, water washing, acid washing, pure water washing, passivation, pure water washing, closing, pure water washing, pure water washing and drying, wherein a silane conversion film is obtained by the passivation; in step (2), the high-gloss medium powder is with a thickness of 80 to 150 m, the spoke surface curing temperature is 220 C., the curing time is 20 min, epoxy resin is preferred, and the hardness of the resin is preferably 2-3 H; the base powder may be black or gray; the T-G point is at 80-120 C.; in step (3), the temperature of the coated workpiece is 80-150 C., the flow rate of argon as working gas is 40-80 cc/min, the coating current for the C target and the chromium target is 15-30 A, and the voltage is more than or equal to 550 v and less than or equal to 800 v; the vacuum degree is (2-8)10.sup.3 Pa, the double target coating time is 15-40 s, the working gas is 99.999% argon, and the coating ambient humidity is less than or equal to 50%; according to the coating sequence, pure chromium is opened first for 3-7 seconds, then the double targets are opened 14-24 seconds at the same time, finally, pure chromium is opened 3-7 seconds for separate coating, the C and Cr content changes periodically, and a periodic variable alloy black chromium coating film is generated; in step (4), the pure acrylic transparent powder is sprayed with a thickness of 80-150 m, the surface curing temperature of the hub is 175 C., the curing time is 20 min, and the thicknesses of the surfaces A, B and C of the hub are not less than 80 m.

Description

DETAILED DESCRIPTION

[0024] Unless otherwise specified, the embodiments of the disclosure adopt two targets, one is C target, the mass percentage of C is 99.95%, the other one is pure Cr, and the purity of Cr metal is 99.99%. The PVD equipment is a high vacuum magnetron sputtering coating machine. Sputtering base materials: aluminum alloy with a surface A356.2; high-gloss medium powder coating material: pure epoxy resin coating material; transparent coating: pure acrylic transparent powder coating material. Coating inspection standards: inspect in accordance with the US general motor hub coating performance standards, with items including Baige adhesion, CASS, FLIFORM, high humidity resistance test, gravel impact, thermal shock resistance test, aging resistance, etc.

[0025] A method for forming an aging resistance coating film for a hub includes: (1) silane pretreatment, (2) spraying of high-gloss medium powder, (3) PVD coating, and (4) spraying of transparent powder.

[0026] 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, closing, pure water washing and moisture drying;

[0027] The spraying of a high-gloss powder coating means that an epoxy powder coating material is electrostatically sprayed onto the metal surface of the hub and cured, in which the base powder is epoxy resin powder or a polyester powder coating material. After the coating is cured, the surface achieves mirror finish and has good adhesion to the aluminum matrix.

[0028] High vacuum magnetron sputtering is performed on the surface of the hub after the medium powder is cured, the sputtering target includes a pure C target and a pure Cr metal target, the two targets are set with different power according to the colors and opened for coating in accordance with the process one after another, the hub in the equipment can rotate and revolve, the two targets are sputtered onto the surface of the hub in certain sequence and proportion of C and Cr, the surface coating film is uniform in thickness and color by means of rotation and revolution of the hub, and the coating film has good binding force with the underlying high-gloss resin coating; the temperature of the coated workpiece is 100 C., the flow rate of the working gas is 80 cc/min, the coating current is 15 A for the C target and 30 A for the pure chromium target, and the voltage is 675 v; the vacuum degree is 510.sup.3 Pa; in the first phase, pure Cr is opened, the coating time is 6 s, and the revolution speed is 3 seconds per revolution; in the second phase, pure Cr and pure C targets are opened, the coating time is 30 s, and the revolution speed is 3 seconds per revolution; in the third phase, pure Cr is opened, the coating time is 6 s, and the revolution speed is 3 seconds per revolution; the working gas is 99.999% argon, and the coating ambient humidity is 38%.

[0029] The spraying of transparent powder in the process means that the transparent powder is sprayed onto the surface of the hub after the PVD coating and cured, the transparent powder is an acrylic resin or polyester powder coating material, the transparent coating has good binding force with the coating film, and the resin itself also has aging resistance and other properties.

[0030] Comparative Example 1: 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 achieves a black chromium coating film. The adopted process method and coating structure are the same as those of the preparation method of the disclosure.

[0031] Comparative Example 2: 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 achieves a black chromium coating film. The adopted process method and coating structure are the same as those of the preparation method of the disclosure.

[0032] The following tests and comparisons are carried out using the multi-layer sputtered coatings with metal surface ductility in embodiment 1 and comparative examples 1 and 2, as shown in the following table:

TABLE-US-00001 Comparative Comparative Group Embodiment 1 example 1 example 2 Coating L = 65.0, L = 64.5, L = 65.2, color a = 0.1, a = 0.1, a = 0.1, b = 2.2 b = 2.2 b = 2.2 Surface No cracks Cracked No cracks cracking Coating 120 nm 56 nm 58 nm thickness Baige 100% 100% 100% adhesion shedding-free shedding-free shedding-free CASS 1.0 mm 1.1 mm 4.2 mm FLIFORM 2.3 mm 3.1 mm 5.8 mm Water No change, No change, No change, resistance adhesion 100% adhesion 91% adhesion 77% test shedding-free shedding-free shedding-free Thermal Shedding-free 10% shedding 13% shedding impact Aging No change, No change, No change, resistance adhesion 100% adhesion 65% adhesion 61% coating film coating film coating film shedding-free shedding-free shedding-free

[0033] It can be seen that in the method of the disclosure, the coating temperature, the argon flow rate, the coating current, the vacuum degree, the NiCr alloy target and the pure Cr coating time are the key parameters, and the proportion of C and Cr and the coating parameters are the key of obtaining the thickness of the coating film and the aging resistance. By optimizing the above process, a PVD coating film with good properties is obtained. In the disclosure, the technical solution of the embodiment obtains the optimum condition by exploring the above conditions. Coating test results are best under this optimal condition.