A method for preparing an automobile aluminum alloy part with a composite coating having a multi-color effect

Abstract

The application relates to a preparation method of an automobile aluminum alloy part with a composite coating with a multicolor effect, and belongs to the technical field of automobile aluminum alloy parts. The application discloses a preparation method of an automobile aluminum alloy part with a composite coating with a multicolor effect, and the preparation method comprises the following steps: S1, pretreating an aluminum alloy part after pretreatment; the pretreatment comprises treating the surface of the aluminum alloy part by means of multistage spraying of heated pretreatment liquid; S2, rinsing and baking the aluminum alloy part in S1; S3, performing PVD treatment on the aluminum alloy part in S2 to plate a PVD layer on the surface of the aluminum alloy part; and S4, covering a transparent protective layer on the surface of the PVD layer. The automobile aluminum alloy part with the composite coating with the multicolor effect prepared by the application meets the requirement in adhesion, and the requirement is met after 240h of CASS test.

Description

Technical Field

[0001] This invention belongs to the technical field of automotive aluminum alloy parts, and relates to a method for preparing automotive aluminum alloy parts with a multi-colored composite coating. Background Technology

[0002] With the rapid development of the automotive industry, people have placed increasingly higher demands on the ability of automobiles to withstand external environmental impacts, as well as their long-term reliability, stability, corrosion resistance, and aesthetic appearance. Currently, in commonly used powder coatings, the fineness and luster of metallic powders are insufficient, and the metallic texture does not achieve the effect of PVD (Polydioxide). Therefore, PVD technology is now widely used. However, directly depositing a PVD layer on the surface of aluminum alloy parts results in low adhesion between the coating and the substrate. Existing processes involve adding a UV primer layer between the PVD coating and the substrate, but this adds complexity to the process. Therefore, a new solution is needed to address the issues of poor coating adhesion and corrosion resistance while satisfying the requirements for colorful automotive appearances. Summary of the Invention

[0003] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a method for preparing automotive aluminum alloy parts with a multi-colored composite coating. This method involves directly performing PVD treatment on the surface of a pretreated aluminum alloy substrate, and achieving a multi-colored coating while maintaining good corrosion resistance.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] A method for preparing automotive aluminum alloy parts with a multi-colored composite coating, the method comprising:

[0006] S1. Pre-treat the aluminum alloy parts after the pre-treatment.

[0007] The pretreatment includes treating the surface of aluminum alloy parts by spraying a heated pretreatment solution through multiple stages; the heating temperature of the pretreatment solution is 55-75℃, and the spraying pressure is 3-300 kg / cm². 2 The spray flow rate is 0.1–1000 L / min, and the total spraying time is 0.1–1 min.

[0008] S2. Rinse and bake the aluminum alloy parts from S1 at a temperature of 150-230°C for 10-60 minutes.

[0009] S3. Perform PVD treatment on the aluminum alloy parts in S2 to coat their surfaces with a PVD layer.

[0010] S4. A transparent protective layer is applied to the surface of the PVD layer, and after heating and curing, a composite coating with colorful effects is obtained for automotive aluminum alloy parts.

[0011] Preferably, the pretreatment in step S1 includes one or more of fine polishing, ultrasonic water washing, and hot water washing.

[0012] Further optimization involves fine polishing, including mirror polishing using 40-80 count cotton cloth.

[0013] Preferably, the multi-stage spraying in step S1 includes two-stage spraying, and / or three-stage spraying, and / or four-stage spraying, and / or five-stage spraying, and / or six-stage spraying.

[0014] Further optimization involves using a two-stage spray system where the pressure of the first spray is 5–50 kg / cm². 2 The pressure of the second spray is 10-100 kg / cm². 2 Each spraying session lasts 10–40 seconds.

[0015] For three-stage spraying, the pressure of the first spray is 5–50 kg / cm². 2 The pressure of the second spray is 10-80 kg / cm². 2 The pressure of the third spray is 25-150 kg / cm². 2 Each spraying session lasts 10–30 seconds.

[0016] For level four spraying, the pressure of the first spray is 3–30 kg / cm². 2 The pressure of the second spray is 10-50 kg / cm². 2 The pressure of the third spray is 20-60 kg / cm². 2 The pressure for the fourth spray is 30–180 kg / cm². 2 Each spraying session lasts 5–20 seconds.

[0017] For five-stage spraying, the pressure of the first spray is 3–30 kg / cm². 2 The pressure of the second spray is 10-50 kg / cm². 2 The pressure of the third spray is 20-90 kg / cm². 2 The pressure for the fourth spray is 30–120 kg / cm². 2 The pressure for the fifth spray is 40–220 kg / cm². 2 Each spraying session lasts 5–20 seconds.

[0018] For a level 6 spray system, the pressure of the first spray is 3–30 kg / cm². 2 The pressure of the second spray is 10-50 kg / cm². 2 The pressure of the third spray is 20-60 kg / cm².2 The pressure for the fourth spray is 30–80 kg / cm². 2 The pressure for the fifth spray is 50–150 kg / cm². 2 The pressure for the sixth spray is 100–300 kg / cm². 2 Each spraying session lasts 3 to 20 seconds.

[0019] Preferably, the pretreatment solution is German Henkel neutral degreasing agent P3-NEUTRAPON 5088, and the concentration of the pretreatment solution is 10-30 g / L.

[0020] The multi-stage spraying of the pretreatment liquid and pretreatment process described in this invention can remove impurities and grease from the aluminum alloy surface while generating a passivation film on the surface of aluminum alloy parts. This facilitates subsequent PVD treatment and ensures good adhesion of the PVD layer.

[0021] If only the pretreatment solution described in this invention is used, but conventional soaking treatment and / or single spraying are employed, the treatment time needs to be further extended, and the adhesion effect of the PVD layer decreases.

[0022] Preferably, the material of the PVD layer in step S3 includes metals, metal compounds, and non-metal compounds; specifically, it includes one or more of the following: chromium, titanium, tungsten, silicon, copper, iron, nickel, cobalt, zirconium, chromium, platinum, silicon nitride, titanium nitride, chromium nitride, zirconium nitride, titanium carbide, and titanium oxide.

[0023] Preferably, the PVD treatment method in step S3 includes one or more of the following: vacuum evaporation, magnetron sputtering, hollow cathode ion plating, hot cathode ion plating, arc ion plating, reactive ion plating, radio frequency ion plating, and DC discharge ion plating.

[0024] Further preferred, the oxygen content in the PVD layer in step S3 is less than 15%, and the carbon content is greater than 5%.

[0025] Different colors can be displayed by changing the metal composition in the PVD layer, but the oxygen and carbon content needs to be controlled in order to obtain a composite coating with high adhesion and corrosion resistance and a colorful effect for automotive aluminum alloy parts.

[0026] Carbon content is an important factor affecting the hardness of PVD layers. In order to obtain a certain hardness, the carbon content needs to be controlled to be higher than 5%. Excessive oxygen content in PVD layers will lead to damage to coating performance.

[0027] Preferably, the raw materials for the transparent protective layer in step S4 include high Tg value acrylic resin and epoxy resin in a mass ratio of (0.5-5):(0.5-5).

[0028] More preferably, the Tg value of the acrylic resin is 50-100℃.

[0029] Further preferably, the acrylic resin is MR7313, Tg value is 97℃.

[0030] High Tg acrylic resin has high hardness, high temperature resistance, and wear resistance; when combined with epoxy resin, it further improves corrosion resistance and adhesion; thus, the resulting composite coating of automotive aluminum alloy parts with colorful effects can still maintain good performance in high-temperature environments in summer.

[0031] Preferably, the heating and curing temperature in step S4 is 70–220°C, and the time is 20–90 min.

[0032] An automotive aluminum alloy part with a multi-colored composite coating, the surface of which includes a passivation layer, a PVD layer, and a transparent protective layer in sequence.

[0033] Preferably, the weight of the passivation layer is 1–10 mg / m². 2 The thickness of the PVD layer is 100–200 nm, and the thickness of the transparent protective layer is 0.5–10 μm.

[0034] The passivation layer has different properties depending on its weight. The preparation method of this invention can obtain a passivation layer with better anti-corrosion performance. Spraying time that is too long or too short, pretreatment solution temperature that is too high or too low, and pretreatment solution concentration that is too high or too low will all affect the weight of the passivation layer.

[0035] Preferably, the adhesion of the composite coating on the automotive aluminum alloy parts with multi-colored effects meets the requirements and meets the requirements after 240 hours of CASS testing.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. This invention removes impurities and grease from the surface of aluminum alloys through multi-stage spraying, while forming a passivation film layer. Then, PVD treatment can be performed directly, saving time and improving production efficiency. Furthermore, the final composite coating on the surface of automotive aluminum alloy parts with colorful effects has excellent adhesion and corrosion resistance.

[0038] 2. This invention allows for adjustment of the raw materials and proportions in the PVD process to match the color of the PVD layer with the color of the plastic PVD exterior parts, resulting in a unified overall color. However, it is necessary to control the oxygen and carbon content of the PVD layer to ensure the coating's color, gloss, and hardness.

[0039] 3. The present invention covers the PVD layer with a transparent nano-layer, which can increase the wear resistance, chemical resistance, corrosion resistance and maintain the gloss of the PVD layer. Detailed Implementation

[0040] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0041] Unless otherwise specified, the materials used in this invention are commercially available products, and the methods used are conventional technical means.

[0042] The present invention provides a method for preparing automotive aluminum alloy parts with multi-colored composite coatings, comprising:

[0043] (1) Pre-treatment: The aluminum alloy parts are mirror polished with 40-80 count cotton cloth in sequence, and then ultrasonically washed.

[0044] (2) Pre-treat the aluminum alloy parts after pretreatment;

[0045] The pretreatment involves applying a heated pretreatment solution to the surface of the aluminum alloy parts through multi-stage spraying; the heating temperature of the pretreatment solution is 55–75°C, and the spraying pressure is 3–300 kg / cm². 2 The spray flow rate is 0.1–1000 L / min, and the total spraying time is 0.5–5 min.

[0046] The pretreatment solution is German Henkel neutral degreasing agent P3-NEUTRAPON 5088, and the concentration of the pretreatment solution is 10-30 g / L;

[0047] The multi-stage spraying includes two-stage spraying, and / or three-stage spraying, and / or four-stage spraying, and / or five-stage spraying, and / or six-stage spraying;

[0048] For secondary spraying, the pressure of the first spray is 5–50 kg / cm². 2 The pressure of the second spray is 10-100 kg / cm². 2 Each spraying session lasts 10–40 seconds.

[0049] For three-stage spraying, the pressure of the first spray is 5–50 kg / cm². 2 The pressure of the second spray is 10-80 kg / cm². 2 The pressure of the third spray is 25-150 kg / cm². 2 Each spraying session lasts 10–30 seconds.

[0050] For level four spraying, the pressure of the first spray is 3–30 kg / cm². 2 The pressure of the second spray is 10-50 kg / cm². 2 The pressure of the third spray is 20-60 kg / cm². 2 The pressure for the fourth spray is 30–180 kg / cm².2 Each spraying session lasts 5–20 seconds.

[0051] For five-stage spraying, the pressure of the first spray is 3–30 kg / cm². 2 The pressure of the second spray is 10-50 kg / cm². 2 The pressure of the third spray is 20-90 kg / cm². 2 The pressure for the fourth spray is 30–120 kg / cm². 2 The pressure for the fifth spray is 40–220 kg / cm². 2 Each spraying session lasts 5–20 seconds.

[0052] For a level 6 spray system, the pressure of the first spray is 3–30 kg / cm². 2 The pressure of the second spray is 10-50 kg / cm². 2 The pressure of the third spray is 20-60 kg / cm². 2 The pressure for the fourth spray is 30–80 kg / cm². 2 The pressure for the fifth spray is 50–150 kg / cm². 2 The pressure for the sixth spray is 100–300 kg / cm². 2 Each spraying session lasts 3–20 seconds.

[0053] (3) Rinse the above aluminum alloy parts and then bake them at a temperature of 150-230°C for 10-60 minutes.

[0054] The weight of the passivation layer is 1–10 mg / m² 2 ;

[0055] (4) The above aluminum alloy parts are subjected to PVD treatment to coat their surfaces with a PVD layer;

[0056] The material of the PVD layer includes metals, metal compounds, and non-metal compounds; specifically, it includes one or more of the following: chromium, titanium, tungsten, silicon, copper, iron, nickel, cobalt, zirconium, silicon nitride, titanium nitride, chromium nitride, zirconium nitride, titanium carbide, and titanium oxide.

[0057] PVD treatment methods include one or more of the following: vacuum evaporation, magnetron sputtering, hollow cathode ion plating, hot cathode ion plating, arc ion plating, reactive ion plating, radio frequency ion plating, and DC discharge ion plating.

[0058] The oxygen content in the PVD layer is less than 15%, and the carbon content is more than 5%.

[0059] The thickness of the PVD layer is 100–200 nm;

[0060] (5) A transparent protective layer is covered on the surface of the PVD layer, and after heating and curing, a composite coating with colorful effects is obtained for automotive aluminum alloy parts.

[0061] The heating and curing temperature is 70–220°C, and the time is 20–90 min;

[0062] The raw materials for the transparent protective layer include acrylic resin and epoxy resin in a mass ratio of (0.5-5):(0.5-5);

[0063] The Tg value of the acrylic resin is 50-100℃;

[0064] The acrylic resin is MR7313, Tg value is 97℃;

[0065] The surface of the automotive aluminum alloy parts with a multi-colored composite coating of the present invention comprises, in sequence, a passivation layer, a PVD layer, and a transparent protective layer;

[0066] The automotive aluminum alloy parts with the multi-colored composite coating met the requirements of CASS test (GB / T 12967.3-2008) after 240 hours; the adhesion (GB / T 9286-1998) also met the requirements (smooth cut edges, no coating peeling).

[0067] Example 1

[0068] The surface of the automotive aluminum alloy parts with multi-color composite coating in this embodiment includes, in sequence, a passivation layer, a PVD layer, and a transparent protective layer.

[0069] Preparation methods include:

[0070] (1) The aluminum alloy parts were mirror polished and ultrasonically washed in sequence using 60-count cotton cloth.

[0071] (2) Pretreatment was performed using a neutral degreasing agent (Henkel P3-NEUTRAPON 5088, Germany);

[0072] The pretreatment process involves spraying a pretreatment solution heated to 60°C onto the surface of the aluminum alloy parts through a multi-stage spraying process. The multi-stage spraying consists of three stages, with the first spraying pressure being 10 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the second spray is 20 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the third spray is 50 kg / cm². 2 The spraying time is 15 seconds;

[0073] (3) Rinse the pretreated aluminum alloy parts and then dry them at 180°C for 20 minutes.

[0074] (4) Next, PVD treatment is carried out: a PVD layer is deposited on the surface of the aluminum alloy parts by magnetron sputtering. The PVD layer has an oxygen content of 12%, a carbon content of 4%, a nitrogen content of 9%, a silicon content of 21%, a chromium content of 24%, an iron content of 20%, and the balance is platinum.

[0075] (5) Then, a transparent protective layer is applied to the surface of the PVD layer. The material of the transparent protective layer comprises acrylic resin in a mass ratio of 8:1. The mixture of MR7313, epoxy resin (Nanya 901), and 1 wt.% leveling agent (BYK306) was diluted with alcohol solvent and coated onto the PVD layer. Then, it was baked and cured at 80°C for 40 min. The thickness of the transparent protective layer was 1.5 μm, thus obtaining a composite coating for automotive aluminum alloy parts with a multi-colored effect.

[0076] The automotive aluminum alloy parts with multi-colored composite coatings prepared in this embodiment were subjected to performance tests. The adhesion met the requirements, and the adhesion also met the requirements after 240 hours of CASS testing.

[0077] Example 2

[0078] Compared with Example 1, the difference lies in that the pretreatment process involves five stages of spraying instead of multi-stage spraying, with the first spraying pressure being 5 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the second spray is 10 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the third spray is 22 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the fourth spray is 45 kg / cm². 2 The spraying time is 5 seconds, and the pressure of the fifth spray is 70 kg / cm². 2 The spraying time is 5 seconds;

[0079] The automotive aluminum alloy parts with multi-colored composite coatings prepared in this embodiment were subjected to performance tests. The adhesion met the requirements, and the adhesion also met the requirements after 240 hours of CASS testing.

[0080] Example 3

[0081] Compared to Example 1, the difference lies in that the multi-stage spraying is a two-stage spraying system, with the first spraying pressure being 8 kg / cm². 2 The spraying time is 20 seconds, and the pressure of the second spray is 30 kg / cm². 2 The spraying time is 20 seconds.

[0082] The automotive aluminum alloy parts with multi-colored composite coatings prepared in this embodiment were subjected to performance tests. The adhesion met the requirements, and the adhesion also met the requirements after 240 hours of CASS testing.

[0083] Example 4

[0084] Compared with Example 3, the difference lies in the fact that the pressure of the first spray in the secondary spraying is 5 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the second spray is 15 kg / cm². 2 The spraying time is 10 seconds.

[0085] The automotive aluminum alloy parts with multi-colored composite coatings prepared in this embodiment were subjected to performance testing. During the adhesion test, a small amount of coating peeled off at the intersection of the cuts.

[0086] In this embodiment, the spraying time is relatively short and the spraying pressure is relatively low, resulting in a decrease in adhesion and corrosion resistance.

[0087] Example 5

[0088] The difference from Example 1 is that no pretreatment is performed.

[0089] The composite coating with multi-colored effect obtained in this embodiment was subjected to performance testing on the surface of the automotive aluminum alloy parts. During the adhesion test, a small amount of coating peeled off at the intersection of the cuts, and local cracks appeared after 200 hours of CASS testing.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that a common neutral degreasing agent (Tomamine AO-455) was used.

[0092] The performance of the automotive aluminum alloy parts with multi-colored composite coating prepared in this comparative example was tested. In the adhesion test, the coating peeled off at the intersection of the cut and the edges. After 140 hours of CASS testing, cracks, blistering, etch spots and discoloration appeared.

[0093] Comparative Example 2

[0094] Compared with Example 1, the difference is that the pretreatment process involves immersing the aluminum alloy parts in a pretreatment solution of the same concentration at room temperature for 1 minute.

[0095] The automotive aluminum alloy parts with multi-colored composite coatings prepared in this comparative example were subjected to performance tests. During the adhesion test, a small amount of coating peeled off, and local cracks and blistering appeared after 200 hours of CASS testing.

[0096] Comparative Example 3

[0097] Compared to Example 1, the difference is that no baking is performed, only drying is carried out.

[0098] The automotive aluminum alloy parts with multi-colored composite coatings prepared in this comparative example were subjected to performance tests. During the adhesion test, some coatings peeled off at the cut edges, and cracks and blistering appeared after 120 hours of CASS testing.

[0099] Failure to bake and / or baking at too low a temperature and / or baking for too short a time will affect the passivation film, resulting in a decrease in the adhesion of the PVD coating on the material surface.

[0100] Comparative Example 4

[0101] The difference from Example 1 is that there is no transparent protective layer.

[0102] The color durability and corrosion resistance of the automotive aluminum alloy parts with multi-colored composite coatings prepared in this embodiment are reduced.

[0103] In summary, this invention achieves excellent adhesion and corrosion resistance on the surface of automotive aluminum alloy parts with a multicolored composite coating by applying a rare-earth-containing cathodic electrophoretic layer to the passivated / silanized coating surface via cathodic electrophoresis.

[0104] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing automotive aluminum alloy parts with a multi-colored composite coating, characterized in that, The preparation method includes: S1. Pre-treat the aluminum alloy parts after the pre-treatment. The pretreatment includes treating the surface of aluminum alloy parts by spraying a heated pretreatment liquid through multiple stages. The pretreatment solution is German Henkel neutral degreasing agent P3-NEUTRAPON 5088, and the concentration of the pretreatment solution is 10~30g / L; The heating temperature of the pretreatment liquid is 55-75℃, the spraying pressure is 3-300 kg / cm 2 , the spraying flow is 0.1-1000 L / min, and the total spraying time is 0.1-1 min. The multi-stage spraying includes two-stage spraying, or three-stage spraying, or four-stage spraying, or five-stage spraying, or six-stage spraying; S2. Rinse and bake the aluminum alloy parts from S1 at a temperature of 150~230℃ for 10~60 minutes to generate a passivation layer. S3. Perform PVD treatment on the aluminum alloy parts in S2 to coat their surfaces with a PVD layer. S4. A transparent protective layer is applied to the surface of the PVD layer, and after heating and curing, a composite coating with colorful effects is obtained for automotive aluminum alloy parts.

2. The preparation method according to claim 1, characterized in that, When the multi-stage spraying in step S1 is a two-stage spraying, the pressure of the first spraying is 5~50 kg / cm². 2 The pressure of the second spray is 10~100 kg / cm². 2 Each spraying session lasts 10-40 seconds. When the multi-stage spraying is a three-stage spraying system, the pressure of the first spraying stage is 5~50 kg / cm². 2 The pressure of the second spray is 10~80 kg / cm². 2 The pressure of the third spray is 25~150 kg / cm². 2 Each spraying session lasts 10-30 seconds. When the multi-stage spraying is a four-stage spraying system, the pressure of the first spraying stage is 3~30 kg / cm². 2 The pressure of the second spray is 10~50 kg / cm². 2 The pressure of the third spray is 20~60 kg / cm². 2 The pressure for the fourth spray is 30~180 kg / cm². 2 Each spraying session lasts 5-20 seconds; When the multi-stage spraying is a five-stage spraying system, the pressure of the first spraying stage is 3~30 kg / cm². 2 The pressure of the second spray is 10~50 kg / cm². 2 The pressure of the third spray is 20~90 kg / cm². 2 The pressure for the fourth spray is 30~120 kg / cm². 2 The pressure for the fifth spray is 40~220 kg / cm². 2 Each spraying session lasts 5-20 seconds; When the multi-stage spraying is a six-stage spraying system, the pressure of the first spraying stage is 3~30 kg / cm². 2 The pressure of the second spray is 10~50 kg / cm². 2 The pressure of the third spray is 20~60 kg / cm². 2 The pressure for the fourth spray is 30~80 kg / cm². 2 The pressure for the fifth spray is 50~150 kg / cm². 2 The pressure for the sixth spray is 100~300 kg / cm². 2 Each spraying session lasts 3 to 20 seconds.

3. The preparation method according to claim 1, characterized in that, The heating temperature of the pretreatment liquid in step S1 is 60°C; When the multi-stage spraying is a two-stage spraying system, the pressure of the first spraying stage is 8 kg / cm². 2 The spraying time is 20 seconds, and the pressure of the second spray is 30 kg / cm². 2 The spraying time is 20 seconds; When the multi-stage spraying is a three-stage spraying system, the pressure of the first spraying stage is 10 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the second spray is 20 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the third spray is 50 kg / cm². 2 The spraying time is 15 seconds; When the multi-stage spraying is a five-stage spraying system, the pressure of the first spray is 5 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the second spray is 10 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the third spray is 22 kg / cm². 2 The spraying time is 10 seconds, and the pressure of the fourth spray is 45 kg / cm². 2 The spraying time is 5 seconds, and the pressure of the fifth spray is 70 kg / cm². 2 The spraying time is 5 seconds.

4. The preparation method according to claim 1, characterized in that, The material of the PVD layer in step S3 includes metals, metal compounds, and non-metal compounds; specifically, it includes one or more of the following: chromium, titanium, tungsten, silicon, copper, iron, nickel, cobalt, zirconium, platinum, silicon nitride, titanium nitride, chromium nitride, zirconium nitride, titanium carbide, and titanium oxide.

5. The preparation method according to claim 1, characterized in that, In step S3, the oxygen content in the PVD layer is less than 15%, and the carbon content is greater than 5%.

6. The preparation method according to claim 1, characterized in that, The PVD treatment method described in step S3 includes one or more of the following: vacuum evaporation, magnetron sputtering, hollow cathode ion plating, hot cathode ion plating, arc ion plating, reactive ion plating, radio frequency ion plating, and DC discharge ion plating.

7. The preparation method according to claim 1, characterized in that, The raw materials for the transparent protective layer in step S4 include high Tg value acrylic resin and epoxy resin in a mass ratio of (0.5~5):(0.5~5).

8. The preparation method according to claim 1, characterized in that, The heating and curing temperature in step S4 is 70~220℃, and the time is 20~90min.

9. An automotive aluminum alloy part with a multi-colored composite coating prepared by the method according to any one of claims 1 to 8, characterized in that, The surface of the automotive aluminum alloy parts with the multi-colored composite coating includes, in sequence, a passivation layer, a PVD layer, and a transparent protective layer.

10. The automotive aluminum alloy parts with a multi-colored composite coating according to claim 9, characterized in that, The weight of the passivation layer is 1~10 mg / m 2 The thickness of the PVD layer is 100~200nm, and the thickness of the transparent protective layer is 0.5~10μm.