A pvd surface treatment method and coating structure for a screw and barrel for semi-solid magnesium alloy injection molding

Abstract

The application discloses a PVD surface treatment method and coating structure of a screw and a barrel for semi-solid magnesium alloy injection molding, and belongs to the field of metal material surface engineering. The method adopts high-power pulse magnetron sputtering or arc ion plating technology to deposit a gradient transition layer, a wear-resistant bearing layer and a functional barrier-anti-sticking surface layer on the inner wall surface of the screw and the barrel from inside to outside, so as to form a multilayer gradient composite coating. The gradient transition layer is a Cr or Ti layer, the wear-resistant bearing layer is a CrN, Cr2N or TiN layer, and the functional surface layer is a CrAlN or CrAlSiN bottom layer and a nano composite layer doped with diamond-like or MoS2. The coating has high density and strong bonding force, is not infiltrated by a magnesium alloy melt, has low friction coefficient, can effectively prevent mold sticking and barrier Fe element dissolution from polluting products, significantly prolongs the service life of the screw and the barrel, does not affect subsequent processing of magnesium alloy products, and is suitable for industrialized batch application.

Description

Technical Field

[0001] This invention relates to the fields of metal material surface engineering and polymer / metal molding machinery, specifically to a PVD surface treatment method and coating structure for screws and barrels used in semi-solid magnesium alloy injection molding. Background Technology

[0002] Semi-solid magnesium alloy injection molding technology combines the advantages of die casting and injection molding, offering near-net-shape forming and dense microstructure. However, this process suffers from the following technical challenges: Severe mold sticking: Magnesium alloy melt (especially semi-solid slurry) has high adhesion, easily adhering to the screw surface and barrel inner wall, leading to injection pressure fluctuations, product quality degradation, and even equipment jamming. Iron contamination: Under high temperature and pressure (580-630℃), iron (Fe) elements in the screw and barrel easily dissolve into the magnesium alloy melt, forming a harmful Fe-rich phase, drastically reducing the corrosion resistance of the magnesium alloy product. Low wear life: The magnesium alloy melt causes erosion corrosion to the metal matrix, and glass fiber reinforced magnesium alloy composites cause severe abrasive wear on the screw. This invention aims to solve these three problems simultaneously through a specific PVD coating technology. Summary of the Invention

[0003] The purpose of this invention is to provide a PVD surface treatment method and coating structure for screws and barrels used in semi-solid magnesium alloy injection molding, which solves the technical problems of severe mold sticking, severe iron contamination, and low wear life in the prior art.

[0004] To achieve the above objectives, the present invention provides a PVD surface treatment method for screws and barrels used in semi-solid magnesium alloy injection molding, characterized by comprising the following steps: Step 1: Substrate pretreatment - The screw and inner wall of the barrel are precision ground to make the surface roughness Ra ≤0.1 μm. After ultrasonic cleaning and drying, the surface oxide layer is removed by glow discharge sputtering in a vacuum furnace. Step 2: Deposit gradient transition layer – Using high-power pulsed magnetron sputtering or arc ion plating, deposit a pure metal Cr or Ti transition layer with a thickness of 0.5~1.5 μm on the pretreated substrate surface; Step 3: Deposit the wear-resistant bearing layer – Deposit a CrN, Cr2N, or TiN wear-resistant bearing layer with a thickness of 2~5 μm using high-power pulsed magnetron sputtering technology; Step 4: Deposition of functional barrier-anti-sticking surface layer - Deposit CrAlN or CrAlSiN bottom layer using high-power pulsed magnetron sputtering or arc ion plating, and dope diamond-like carbon or MoS2 on the surface layer to form a nanocomposite layer with a thickness of 1~2 μm.

[0005] Preferably, the gradient transition layer in step two forms a pseudo-diffusion layer on the steel substrate, and the adhesion between the coating and the substrate reaches the HF1 level.

[0006] Preferably, the wear-resistant bearing layer in step three has a dense columnar crystal or nanocrystalline structure with a hardness of HV 2000~2800.

[0007] Preferably, the functional barrier-anti-sticking surface layer in step four is a composite layer composed of a Cr0.5Al0.5N bottom layer and a (Cr,Al)N / DLC nanolayer top layer.

[0008] Preferably, the coefficient of friction of the functional barrier-anti-stick surface layer in step four is 0.15~0.25.

[0009] Preferably, the density of the functional barrier-anti-stick surface layer described in step four is greater than 99.9%, and it is free of pinholes.

[0010] This invention also provides a coating structure for a screw and barrel used in semi-solid magnesium alloy injection molding, comprising, from the inside out: A gradient transition layer is attached to the surface of a steel substrate, wherein the gradient transition layer is a pure metal Cr or Ti layer with a thickness of 0.5~1.5 μm; A wear-resistant bearing layer is attached to the surface of the gradient transition layer. The wear-resistant bearing layer is a CrN, Cr2N or TiN layer with a thickness of 2~5 μm. A functional barrier-anti-sticking surface layer is attached to the surface of the wear-resistant bearing layer. The functional barrier-anti-sticking surface layer is a nanocomposite layer of CrAlN or CrAlSiN bottom layer and doped diamond-like carbon or MoS2, with a thickness of 1~2 μm.

[0011] Preferably, the functional barrier-anti-stick surface layer is a composite layer consisting of a Cr0.5Al0.5N bottom layer and a (Cr,Al)N / DLC nanolayer top layer.

[0012] Preferably, the hardness of the wear-resistant bearing layer is HV 2000~2800, and the hardness of the functional barrier-anti-stick surface layer is HV 3000 or higher.

[0013] Preferably, the contact angle between the functional barrier-anti-stick surface layer and the magnesium alloy melt is greater than 120°, the coefficient of friction is 0.15~0.25, and the high-temperature oxidation resistance temperature is increased to above 900°C.

[0014] Compared with the prior art, the present invention has the following outstanding substantive features and significant progress: I. Significantly Reduced Friction Coefficient and Material Adhesion: Utilizing the low surface energy and high hardness of the CrAlSiN / DLC coating, the adhesion of magnesium alloy semi-solid slurry to the screw surface is reduced by more than 95%. After 1000 hours of continuous operation, there is no material accumulation on the screw surface, and the injection pressure fluctuation is less than ±1%. II. Significantly Improved Corrosion Resistance of Magnesium Alloy: Through the physical isolation effect of the PVD coating (density >99.9%), the diffusion channels of Fe elements from the matrix to the magnesium melt are blocked. ICP (Inductively Coupled Plasma) testing shows that the Fe content in magnesium alloy products produced using the coated screw is <0.002% (compared to >0.03% for traditional steel screws), and the salt spray test (ASTM B117) corrosion resistance life is increased by 3-5 times. III. Extended Screw / Barrel Service Life: The surface hardness of the coating can reach HV 3000 or higher, and the high-temperature oxidation resistance temperature is increased to over 900℃. Under semi-solid injection molding conditions using AZ91D magnesium alloy containing 30% glass fiber, the wear rate of the coated screw is only 1 / 10 that of the uncoated H13 steel. The average service life of the screw is extended from the conventional 3-6 months to more than 24 months.

[0015] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0016] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0017] Example 1 H13 hot-work die steel screws with a diameter of 50 mm were selected as the base material after quenching and tempering. The working surfaces of the screw (including the screw ridges and grooves) were precision ground to achieve a surface roughness Ra ≤ 0.1 μm. The screws were then ultrasonically cleaned sequentially with acetone, alcohol, and deionized water, each cleaning cycle lasting 15 minutes. After cleaning, the screws were dried at 120℃ for 30 minutes. The cleaned and dried screws were then placed in a vacuum coating apparatus and evacuated to a vacuum level of 5 × 10⁻⁶. - The pressure is increased to 3 Pa and heated to 400°C, then held for 30 minutes to thoroughly degas the surface. Argon ion glow discharge cleaning is then performed for 30 minutes to remove any remaining oxide layer.

[0018] The coating deposition was carried out using high-power pulsed magnetron sputtering (HiPIMS) technology. The specific parameters and steps are as follows: (1) Deposition of Cr gradient transition layer: using a pure Cr target as the target material, the target current is 80 A, the substrate bias is -800 V, and the deposition time is controlled to make the Cr layer thickness reach 0.8 μm. (2) Deposition of CrN wear-resistant bearing layer: nitrogen gas is introduced at a flow rate of 200 sccm, the substrate bias is adjusted to -120 V, and the CrN layer is deposited with a thickness controlled at 3 μm. (3) Deposition of CrAlN bottom layer: using a CrAl alloy target (Cr:Al atomic ratio 1:1), the nitrogen flow rate is 250 sccm, the substrate bias is -60 V, and the Cr0.5Al0.5N layer is deposited with a thickness of 1.5 μm. (4) Deposition of CrAlN / aC:H nanocomposite top layer: After the CrAlN deposition is completed, pulsed C2H2 gas is introduced to introduce carbon source while maintaining CrAl target sputtering, forming CrAlN / aC:H (hydrogen-doped diamond-like carbon) nanocomposite layer with a thickness of 0.5 μm.

[0019] Performance testing: The coated screw, after the above treatment, was installed in a 350-ton semi-solid magnesium alloy injection molding machine. The injection material was AZ91D magnesium alloy, and the barrel temperature was set to 610℃. After 2000 hours of continuous operation, an evaluation was conducted: macroscopic observation of the screw surface showed a uniform metallic luster, no yellow aluminum-magnesium adhesion, clear screw edge contours, and no obvious wear marks. Wear at key points of the screw edge was measured using a profilometer, and the results showed wear less than 0.01 mm. A neutral salt spray test (ASTM B117 standard) was performed on mobile phone mid-frame products manufactured using this coated screw. After 72 hours of testing, no corrosion spots appeared on the sample surface. ICP testing showed that the Fe content in the product was 0.0018% (mass percentage), far lower than the Fe content level of products manufactured using uncoated screws (typically >0.03%).

[0020] Example 2 A nickel-based alloy screw with a diameter of 70 mm was selected as the substrate and subjected to precision grinding, ultrasonic cleaning and vacuum glow cleaning in accordance with the same pretreatment process as in Example 1.

[0021] The coating deposition adopts arc ion plating technology, and the specific steps are as follows: (1) Deposit Ti gradient transition layer: using a pure Ti target as the target material, the arc current is 75 A, the substrate bias voltage is -750 V, and the Ti layer thickness is 1.0 μm. (2) Deposit TiN wear-resistant bearing layer: nitrogen gas is introduced at a flow rate of 180 sccm, the substrate bias voltage is -100 V, and the TiN layer is deposited with a thickness of 4 μm. (3) Deposit CrAlSiN bottom layer: using a CrAlSi alloy target, the nitrogen flow rate is 220 sccm, the substrate bias voltage is -50 V, and the CrAlSiN layer is deposited with a thickness of 1.2 μm. (4) Deposit CrAlSiN / MoS2 nanocomposite top layer: after the CrAlSiN deposition is completed, a MoS2 target is introduced for co-sputtering to form a CrAlSiN / MoS2 nanocomposite layer with a thickness of 0.6 μm.

[0022] Performance testing: The treated screw was installed in a 500-ton semi-solid magnesium alloy injection molding machine. The injection material was AZ91D magnesium alloy composite material reinforced with 20% glass fiber, and the barrel temperature was 620℃. After 1500 hours of continuous operation, the screw surface showed no material adhesion, and the screw edge wear was less than 0.015 mm. The product had an Fe content of 0.0015%, and its salt spray corrosion resistance life was more than 4 times that of the uncoated screw.

[0023] Example 3 H13 hot work die steel screw with a diameter of 35 mm was selected and processed according to the same pretreatment procedure as in Example 1.

[0024] The coating deposition was performed using high-power pulsed magnetron sputtering (HiPIMS) technology. The specific steps are as follows: (1) Deposit a Cr gradient transition layer: target current 70 A, substrate bias -850 V, Cr layer thickness 0.5 μm. (2) Deposit a Cr2N wear-resistant bearing layer: nitrogen flow rate 150 sccm, substrate bias -130 V, deposit a Cr2N layer with a thickness of 2.5 μm. (3) Deposit a CrAlN bottom layer: CrAl alloy target, nitrogen flow rate 200 sccm, substrate bias -70 V, deposit a Cr0.5Al0.5N layer with a thickness of 1.0 μm. (4) Deposit a CrAlN / DLC nanocomposite top layer: introduce pulsed C2H2 gas to form a CrAlN / DLC nanomultilayer structure with a thickness of 0.4 μm.

[0025] Performance testing: The treated screw was installed in a 180-ton semi-solid magnesium alloy injection molding machine, with AM60B magnesium alloy as the injection material and a barrel temperature of 600℃. After 2500 hours of continuous operation, the following tests were conducted: no material adhered to the screw surface, wear was less than 0.008 mm, and the injection pressure fluctuation was less than ±0.8%. The product had an Fe content of 0.0012%, and its salt spray corrosion resistance life was more than 5 times that of the uncoated screw.

[0026] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0027] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0028] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A PVD surface treatment method for screws and barrels used in semi-solid magnesium alloy injection molding, characterized in that, Includes the following steps: Step 1: Substrate pretreatment - The screw and inner wall of the barrel are precision ground to make the surface roughness Ra ≤ 0.1 μm. After ultrasonic cleaning and drying, the surface oxide layer is removed by glow discharge sputtering in a vacuum furnace. Step 2: Deposit gradient transition layer – Using high-power pulsed magnetron sputtering or arc ion plating, deposit a pure metal Cr or Ti transition layer with a thickness of 0.5~1.5 μm on the pretreated substrate surface; Step 3: Deposit wear-resistant bearing layer – Deposit CrN, Cr2N or TiN wear-resistant bearing layer with a thickness of 2~5 μm using high-power pulsed magnetron sputtering technology; Step 4: Deposition of functional barrier-anti-sticking surface layer - Deposit CrAlN or CrAlSiN bottom layer using high-power pulsed magnetron sputtering or arc ion plating, and dope diamond-like carbon or MoS2 on the surface layer to form a nanocomposite layer with a thickness of 1~2 μm.

2. The PVD surface treatment method for the screw and barrel used in semi-solid magnesium alloy injection molding according to claim 1, characterized in that, The gradient transition layer described in step two forms a pseudo-diffusion layer on the steel substrate, and the adhesion between the coating and the substrate reaches the HF1 level.

3. The PVD surface treatment method for the screw and barrel used in semi-solid magnesium alloy injection molding according to claim 1, characterized in that, The wear-resistant bearing layer described in step three has a dense columnar crystal or nanocrystalline structure with a hardness of HV 2000~2800.

4. The PVD surface treatment method for the screw and barrel used in semi-solid magnesium alloy injection molding according to claim 1, characterized in that, The functional barrier-anti-sticking surface layer mentioned in step four is a composite layer composed of a Cr0.5Al0.5N bottom layer and a (Cr,Al)N / DLC nano-multilayer top layer.

5. The PVD surface treatment method for the screw and barrel used in semi-solid magnesium alloy injection molding according to claim 1, characterized in that, The coefficient of friction of the functional barrier-anti-stick surface layer described in step four is 0.15~0.

25.

6. The PVD surface treatment method for the screw and barrel used in semi-solid magnesium alloy injection molding according to claim 1, characterized in that, The density of the functional barrier-anti-stick surface layer described in step four is greater than 99.9%, and it is free of pinholes.

7. A coating structure for a screw and barrel used in semi-solid magnesium alloy injection molding, characterized in that, From the inside out, the following are included: A gradient transition layer is attached to the surface of a steel substrate, wherein the gradient transition layer is a pure metal Cr or Ti layer with a thickness of 0.5~1.5 μm; A wear-resistant bearing layer is attached to the surface of the gradient transition layer. The wear-resistant bearing layer is a CrN, Cr2N or TiN layer with a thickness of 2~5 μm. A functional barrier-anti-sticking surface layer is attached to the surface of the wear-resistant bearing layer. The functional barrier-anti-sticking surface layer is a nanocomposite layer of CrAlN or CrAlSiN bottom layer and doped diamond-like carbon or MoS2, with a thickness of 1~2 μm.

8. The coating structure according to claim 7, characterized in that, The functional barrier-anti-stick surface layer is a composite layer consisting of a Cr0.5Al0.5N bottom layer and a (Cr,Al)N / DLC nano-multilayer top layer.

9. The coating structure according to claim 7, characterized in that, The hardness of the wear-resistant bearing layer is HV 2000~2800, and the hardness of the functional barrier-anti-stick surface layer is HV 3000 or higher.

10. The coating structure according to claim 7, characterized in that, The contact angle between the functional barrier-anti-stick surface layer and the magnesium alloy melt is greater than 120°, the coefficient of friction is 0.15~0.25, and the high-temperature oxidation resistance temperature is increased to over 900°C.