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. A method for forming a coating film resistant to change of properties over time for an aluminum alloy wheel hub, comprising: pretreating the aluminum alloy wheel hub, comprising forming a silane conversion film on a surface of the aluminum alloy wheel hub; forming a high-gloss medium powder coating on the silane conversion film by electrostatically spraying an epoxy powder coating material and curing the epoxy powder coating material, wherein a base powder of the high-gloss medium powder coating is epoxy resin powder or a polyester powder coating material; forming a physical vapor deposition (PVD) coating on the high-gloss medium powder coating by a high vacuum magnetron sputtering equipment which is provided with a pure C sputtering target and a pure Cr metal sputtering target, wherein a power of the pure C sputtering target and a power of the pure Cr metal sputtering target are set so as to adjust content of C and thus adjust degree of blackness of the PVD coating, wherein the pure C sputtering target and the pure Cr metal sputtering target are activated in a predetermined sequence, wherein rotation and revolution of the aluminum alloy wheel hub in the high vacuum magnetron sputtering equipment allow the PVD coating to be formed uniformly in thickness and color, and wherein the PVD coating has binding force with the high-gloss medium powder coating; and 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, and wherein the transparent coating has binding force with the PVD coating.

2. The method for forming a coating film resistant to change of properties over time for an aluminum alloy wheel hub according to claim 1, wherein the epoxy powder coating material is cured for 20 min at a temperature of 220 C., wherein a hardness of the high-gloss medium powder coating is 2-3 H, wherein a color of the base powder is black or gray, wherein a glass transition temperature of the base powder is 80-120 C., wherein a thickness of the high-gloss medium powder coating is 80-150 m, wherein a temperature of the aluminum alloy wheel hub is set as 80-150 C. for forming the PVD coating, wherein a flow rate of argon with a purity of 99.999% as a working gas in the high vacuum magnetron sputtering equipment is set as 40-80 cc/min, wherein electric currents of the pure C sputtering target and the pure Cr metal sputtering target for forming the PVD coating are set as 15-30 A, wherein voltages of the pure C sputtering target and the pure Cr metal sputtering target for forming the PVD coating are set as 550-800 V, wherein a vacuum degree in the high vacuum magnetron sputtering equipment for forming the PVD coating is set as 210.sup.3-810.sup.3 Pa, wherein an ambient humidity for forming the PVD coating is set as less than or equal to 50%, wherein the predetermined sequence of activating the pure C sputtering target and the pure Cr metal sputtering target is as follows: first activating the pure Cr metal sputtering target for 3-7 seconds; secondly activating the pure C sputtering target and the pure Cr metal sputtering target simultaneously for 14-24 seconds; and finally activating the pure Cr metal sputtering target for 3-7 seconds, wherein C content changes from 90% to 0%, and Cr content changes from 10% to 100% in the PVD coating, thereby obtaining an alloy black chromium coating film with C content and Cr content changing periodically, wherein the transparent powder is cured for 20 min at a temperature of 175 C., and wherein a thickness of a layer formed by spraying the transparent powder is 80-150 m.

Description

DETAILED DESCRIPTION

(1) 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.

(2) 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.

(3) 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;

(4) 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.

(5) 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%.

(6) 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.

(7) 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.

(8) 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.

(9) 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:

(10) 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

(11) 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.