Bipolar plate forming process

Abstract

The invention discloses a bipolar plate forming process, which belongs to the technical field of bipolar plate manufacturing, and comprises the following steps: preparing a Fe-O microalloyed titanium alloy raw material, preparing a bipolar plate blank by adopting a punch forming process, and cleaning the formed bipolar plate blank by utilizing UCM ultrasonic waves to remove oil stains. The thickness uniformity is visually detected by using a CCD (Charge Coupled Device), and a magnetron sputtering and ion source composite PVD (Physical Vapor Deposition) coating machine is adopted for coating deposition to obtain the bipolar plate. The trace Y element is selectively adsorbed on the grain boundary, so that the grain boundary energy is reduced, the segregation of harmful impurities is inhibited, and the grain boundary bonding strength of the material is improved. The grain boundary purification effect and the phase change plastification of the Fe-O alloy form a synergistic effect, so that the tensile strength is improved while the high toughness of the material is maintained, and the mechanical strength requirement of the bipolar plate is met.

Description

Technical Field

[0001] The present invention relates to the technical field of bipolar plate manufacturing, and in particular to a bipolar plate forming process. Background Art

[0002] In hydrogen fuel cell systems, bipolar plates, as a core component, must simultaneously meet stringent requirements for high conductivity, corrosion resistance, mechanical strength, and gas tightness. Titanium, due to its superior strength-to-weight ratio, corrosion resistance, and lightweight construction, is an ideal alternative to stainless steel and graphite bipolar plates. However, titanium alloys exhibit significantly weaker plastic deformation than stainless steel, making them susceptible to microcracks due to stress concentration during the stamping process.

[0003] Microcracks in titanium alloys after stamping can reduce coating adhesion and make them susceptible to spalling after thermal cycling. Furthermore, stress concentration at the crack tip accelerates electrochemical corrosion at the interface between the coating and the substrate, reducing the long-term corrosion resistance of the bipolar plate.

[0004] Based on this, the present invention designs a bipolar plate forming process to solve the above problems. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a bipolar plate forming process, comprising the following steps: S1: Preparation of Fe-O microalloyed titanium alloy raw materials: TC4 scraps are crushed, soaked in nitric acid solution, rinsed and dried, and Fe2O3 powder and Y powder are added and mixed uniformly to obtain Fe-O microalloyed titanium alloy powder. The powder is then smelted, forged, hot-rolled, cold-rolled and cut to obtain plates; S2: Prepare bipolar plate blanks using a stamping process; S3: The formed bipolar plate blank is cleaned with UCM ultrasonic cleaning to remove oil stains, and the thickness uniformity is inspected using CCD visual inspection; S4: A magnetron sputtering and ion source composite PVD coating machine is used to deposit the coating to obtain a bipolar plate.

[0006] Furthermore, S1 specifically comprises: crushing the TC4 scraps into 5-10 mm blocks, soaking them in 30-50% nitric acid solution at room temperature for 20-30 minutes to remove the surface oxide layer, rinsing them with deionized water until neutral, and drying them in a vacuum drying oven at 80-100°C for 2-3 hours; Fe2O3 powder and Y powder were weighed and mixed evenly with the crushed TC4 scraps to obtain Fe-O microalloyed titanium alloy powder, which was then smelted, forged, hot rolled, cold rolled and cut to obtain plates.

[0007] Furthermore, in S1, Fe accounts for 3.0-6.0 wt% of the titanium matrix, and Y accounts for 0.05-0.1 wt% of the titanium matrix.

[0008] Furthermore, in S3, the tolerance of the thickness uniformity detected by CCD vision is ±3 μm.

[0009] Furthermore, S4 is specifically as follows: using a pure Ti target as a source, controlling the flow ratio of Ar gas to N2 gas, sputtering for 10-15 minutes at a medium frequency pulse power of 200-300W and under vacuum, while turning on a radio frequency ion source to assist in bombardment, to form a bottom TiN transition layer; After the bottom TiN transition layer is deposited, switch to a pure Cr target, adjust the flow ratio of Ar gas and N2 gas, and deposit under vacuum for 12-15 minutes at a DC magnetron sputtering power of 300-400W. At the same time, increase the ion source power and bombardment energy to 80-100eV to form a CrN conductive and corrosion-resistant layer to obtain a bipolar plate.

[0010] Furthermore, the ion source power is increased from 60-100W to 120-150W.

[0011] Furthermore, the flow ratio of Ar gas to N2 gas was adjusted from 3-5:1 to 3:2-2:1.

[0012] Furthermore, the thickness of the CrN conductive corrosion-resistant layer is 1.2-1.5 μm; the thickness of the TiN transition layer is 0.3-0.5 μm.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses a magnetron sputtering and ion source composite PVD process to deposit non-precious metal TiN / CrN coatings, replacing traditional precious metal coatings and significantly reducing costs. This coating structure design not only reduces surface contact resistance, but also improves coating bonding strength, has excellent corrosion resistance, solves the problem of metal corrosion and increased contact resistance in oxygen-rich and acidic environments, and meets the long-term stable operation requirements of fuel cells. 2. The addition of trace Y in the present invention selectively adsorbs at grain boundaries, reducing grain boundary energy and inhibiting the segregation of harmful impurities, thereby improving the material's grain boundary bonding strength. This grain boundary purification effect synergizes with the phase transformation plasticization of the Fe-O alloy, allowing the material to maintain high toughness while improving tensile strength, meeting the mechanical strength requirements of bipolar plates. DETAILED DESCRIPTION

[0014] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0015] Example 1: This example provides a bipolar plate forming process, comprising the following steps: S1: Preparation of Fe-O microalloyed titanium alloy raw materials; 1. Pretreatment of scrap titanium; The TC4 scraps were crushed into 10 mm blocks, soaked in 50% nitric acid solution at room temperature for 30 min to remove the surface oxide layer, rinsed with deionized water until neutral, and dried in a vacuum drying oven at 100 °C for 3 h; 2. Ingredients; Fe2O3 powder and Y powder were weighed and mixed evenly with the crushed TC4 scraps to obtain Fe-O microalloyed titanium alloy powder. The alloy was melted in a vacuum induction melting furnace at a temperature of 1700°C for 50 minutes to ensure a thorough and uniform mixing of the alloy components. After melting, the alloy was poured into a preheated 200°C metal mold to form an ingot, which was then heated to 900°C and held for 50 minutes before being forged using a hydraulic press. Four forging passes were performed, with a single deformation of 20%. After each forging pass, intermediate annealing (annealing temperature 700°C, holding temperature 1 hour) was required to refine the grains and eliminate forging stress. The slab was finally obtained and heated to 820°C. A reversible hot rolling mill was used, with eight rolling passes, a single-pass reduction of 10%, and a total reduction of 50%. A high-pressure water descaling system was used to remove surface oxide scale during rolling, and online annealing (annealing temperature 630°C, holding temperature 40 minutes) was performed after each rolling pass. A 20-high rolling mill is used. After full annealing (temperature 720°C, holding temperature for 2 hours) and mechanical descaling, the billet is cold rolled. The rolling speed is controlled at 20m / min, the pass reduction is 5%, and the total reduction is 40%. Rolling oil is used during the cold rolling process to reduce surface roughness. According to the designed dimensions of the bipolar plates, a laser cutting machine is used for cutting; the laser cutting power is 1kW and the cutting speed is 0.5m / min, ensuring the sheet dimensional accuracy and meeting the subsequent stamping forming requirements to obtain the plate; S2: Prepare bipolar plate blanks using a stamping process; S3: After forming, the plate is ultrasonically cleaned by UCM to remove oil stains, and the thickness uniformity is inspected by CCD vision (tolerance ±3μm); S4: Coating deposition is performed using a magnetron sputtering and ion source composite PVD coating machine; Using a pure Ti target as the source, the Ar gas and N2 gas flow ratio was controlled at 5:1, and sputtering was carried out for 15 minutes at 300W medium frequency pulse power and 0.5Pa vacuum. At the same time, a 100W radio frequency ion source was turned on to assist the bombardment, forming a TiN transition layer with a thickness of 0.5μm at the bottom. After the bottom TiN transition layer is deposited, switch to a pure Cr target, adjust the Ar gas and N2 gas flow ratio to 3:2, and deposit for 15 minutes at a vacuum of 0.3 Pa with a DC magnetron sputtering power of 400W. At the same time, increase the ion source power to 150W and the bombardment energy to 100eV to form a 1.5μm thick CrN conductive and corrosion-resistant layer on the surface to obtain a bipolar plate.

[0016] Example 2: This example provides a bipolar plate forming process, comprising the following steps: S1: Preparation of Fe-O microalloyed titanium alloy raw materials; 1. Pretreatment of scrap titanium; The TC4 scraps were crushed into 5 mm blocks, soaked in 30% nitric acid solution at room temperature for 20 min to remove the surface oxide layer, rinsed with deionized water until neutral, and dried in a vacuum drying oven at 80 °C for 2 h; 2. Ingredients; Fe3.0wt% and Y0.05wt% are added to the titanium matrix (i.e., TC4), and Fe2O3 powder and Y powder are weighed and evenly mixed with the crushed TC4 scraps to obtain Fe-O microalloyed titanium alloy powder; The alloy was melted in a vacuum induction melting furnace at a temperature of 1700°C for 50 minutes to ensure a thorough and uniform mixing of the alloy components. After melting, the alloy was poured into a preheated 200°C metal mold to form an ingot, which was then heated to 900°C and held for 50 minutes before being forged using a hydraulic press. Four forging passes were performed, with a single deformation of 20%. After each forging pass, intermediate annealing (annealing temperature 700°C, holding temperature 1 hour) was required to refine the grains and eliminate forging stress. The slab was finally obtained and heated to 820°C. A reversible hot rolling mill was used, with eight rolling passes, a single-pass reduction of 10%, and a total reduction of 50%. A high-pressure water descaling system was used to remove surface oxide scale during rolling, and online annealing (annealing temperature 630°C, holding temperature 40 minutes) was performed after each rolling pass. A 20-high rolling mill is used. After full annealing (temperature 720°C, holding temperature for 2 hours) and mechanical descaling, the billet is cold rolled. The rolling speed is controlled at 20m / min, the pass reduction is 5%, and the total reduction is 40%. Rolling oil is used during the cold rolling process to reduce surface roughness. According to the designed dimensions of the bipolar plates, a laser cutting machine is used for cutting; the laser cutting power is 1kW and the cutting speed is 0.5m / min, ensuring the sheet dimensional accuracy and meeting the subsequent stamping forming requirements to obtain the plate; S2: Prepare bipolar plate blanks using a stamping process; S3: After forming, the plate is ultrasonically cleaned by UCM to remove oil stains, and the thickness uniformity is inspected by CCD vision (tolerance ±3μm); S4: Coating deposition is performed using a magnetron sputtering and ion source composite PVD coating machine; Using a pure Ti target as the source, the Ar gas and N2 gas flow ratio was controlled to 3:1, and sputtering was carried out for 10 minutes at 200W medium frequency pulse power and 0.5Pa vacuum. At the same time, a 60W radio frequency ion source was turned on to assist the bombardment, forming a TiN transition layer with a thickness of 0.3μm at the bottom. After the bottom TiN transition layer is deposited, switch to a pure Cr target, adjust the Ar gas and N2 gas flow ratio to 2:1, and deposit for 12 minutes at a vacuum of 0.2 Pa with a DC magnetron sputtering power of 300W. At the same time, increase the ion source power to 120W and the bombardment energy to 80eV to form a 1.2μm thick CrN conductive and corrosion-resistant layer on the surface to obtain a bipolar plate.

[0017] Example 3: This example provides a bipolar plate forming process, comprising the following steps: S1: Preparation of Fe-O microalloyed titanium alloy raw materials; 1. Pretreatment of scrap titanium; The TC4 scraps were crushed into 8 mm blocks, soaked in 45% nitric acid solution at room temperature for 26 min to remove the surface oxide layer, rinsed with deionized water until neutral, and dried in a vacuum drying oven at 92 °C for 2 h; 2. Ingredients; Fe4.2wt% and Y0.08wt% are added to the titanium matrix (i.e., TC4), and Fe2O3 powder and Y powder are weighed and evenly mixed with the crushed TC4 scraps to obtain Fe-O microalloyed titanium alloy powder; The alloy was melted in a vacuum induction melting furnace at a temperature of 1700°C for 50 minutes to ensure a thorough and uniform mixing of the alloy components. After melting, the alloy was poured into a preheated 200°C metal mold to form an ingot, which was then heated to 900°C and held for 50 minutes before being forged using a hydraulic press. Four forging passes were performed, with a single deformation of 20%. After each forging pass, intermediate annealing (annealing temperature 700°C, holding temperature 1 hour) was required to refine the grains and eliminate forging stress. The slab was finally obtained and heated to 820°C. A reversible hot rolling mill was used, with eight rolling passes, a single-pass reduction of 10%, and a total reduction of 50%. A high-pressure water descaling system was used to remove surface oxide scale during rolling, and online annealing (annealing temperature 630°C, holding temperature 40 minutes) was performed after each rolling pass. A 20-high rolling mill is used. After full annealing (temperature 720°C, holding temperature for 2 hours) and mechanical descaling, the billet is cold rolled. The rolling speed is controlled at 20m / min, the pass reduction is 5%, and the total reduction is 40%. Rolling oil is used during the cold rolling process to reduce surface roughness. According to the designed dimensions of the bipolar plates, a laser cutting machine is used for cutting; the laser cutting power is 1kW and the cutting speed is 0.5m / min, ensuring the sheet dimensional accuracy and meeting the subsequent stamping forming requirements to obtain the plate; S2: Prepare bipolar plate blanks using a stamping process; S3: After forming, the plate is ultrasonically cleaned by UCM to remove oil stains, and the thickness uniformity is inspected by CCD vision (tolerance ±3μm); S4: Coating deposition is performed using a magnetron sputtering and ion source composite PVD coating machine; Using a pure Ti target as the source, the Ar gas and N2 gas flow ratio was controlled at 4:1, and sputtering was carried out for 12 minutes at 260W medium frequency pulse power and 0.5Pa vacuum. At the same time, an 80W radio frequency ion source was turned on to assist the bombardment, forming a TiN transition layer with a thickness of 0.4μm. After the bottom TiN transition layer is deposited, switch to a pure Cr target, adjust the Ar gas and N2 gas flow ratio to 3:2, and deposit for 14 minutes at a vacuum of 0.3 Pa with a DC magnetron sputtering power of 360W. At the same time, increase the ion source power to 140W and the bombardment energy to 90eV to form a 1.4μm thick CrN conductive and corrosion-resistant layer on the surface to obtain a bipolar plate.

[0018] Comparative Example 1: This comparative example differs from Example 3 in that no Y powder is added.

[0019] Comparative Example 2: This comparative example differs from Example 3 in that the bottom TiN transition layer is not plated.

[0020] Experimental example: 1. According to GB / T13298-2015 "Methods for the examination of metal microstructures", the microcrack density (cracks / mm 2 ).

[0021] 2. Test the coating adhesion (MPa) according to GB / T5210-2006 "Paint and varnish adhesion test by pull-off method".

[0022] 3. According to GB / T20042.6-2024 "Proton Exchange Membrane Fuel Cells Part 6: Bipolar Plate Characteristics Test Method", the salt spray corrosion rate (mm / a) after 1000 cycles of low temperature: -40°C (maintained for 30 minutes) and high temperature: 80°C (maintained for 30 minutes).

[0023] The results are shown in the following table:

[0024] It can be seen from the above table that the addition of Y powder can improve the adhesion of the coating and the transition layer can improve the corrosion resistance.

[0025] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A bipolar plate forming process, characterized in that: The following steps are involved: S1: Preparation of Fe-O microalloyed titanium alloy raw materials: TC4 scraps are crushed, soaked in nitric acid solution, rinsed and dried, and Fe2O3 powder and Y powder are added and mixed uniformly to obtain Fe-O microalloyed titanium alloy powder. The powder is then smelted, forged, hot-rolled, cold-rolled and cut to obtain plates; S2: Prepare bipolar plate blanks using a stamping process; S3: The formed bipolar plate blank is cleaned with UCM ultrasonic cleaning to remove oil stains, and the thickness uniformity is inspected using CCD visual inspection; S4: A magnetron sputtering and ion source composite PVD coating machine is used to deposit the coating to obtain a bipolar plate.

2. The bipolar plate forming process according to claim 1, characterized in that: S1 specifically includes: crushing TC4 scraps into 5-10 mm blocks, soaking them in 30-50% nitric acid solution at room temperature for 20-30 minutes to remove the surface oxide layer, rinsing them with deionized water until neutral, and drying them in a vacuum drying oven at 80-100°C for 2-3 hours; Fe2O3 powder and Y powder were weighed and mixed evenly with the crushed TC4 scraps to obtain Fe-O microalloyed titanium alloy powder, which was then smelted, forged, hot rolled, cold rolled and cut to obtain plates.

3. The bipolar plate forming process according to claim 1, characterized in that: In S1, Fe accounts for 3.0-6.0 wt% of the titanium matrix, and Y accounts for 0.05-0.1 wt% of the titanium matrix.

4. The bipolar plate forming process according to claim 1, characterized in that: In S3, the tolerance of the thickness uniformity detected by CCD vision is ±3 μm.

5. The bipolar plate forming process according to claim 1, characterized in that: S4 specifically includes: using a pure Ti target as a source, controlling the flow ratio of Ar gas to N2 gas, sputtering for 10-15 minutes at a medium frequency pulse power of 200-300W and vacuum, and simultaneously turning on a radio frequency ion source to assist in bombardment, to form a bottom TiN transition layer; After the bottom TiN transition layer is deposited, switch to a pure Cr target, adjust the flow ratio of Ar gas and N2 gas, and deposit under vacuum for 12-15 minutes at a DC magnetron sputtering power of 300-400W. At the same time, increase the ion source power and bombardment energy to 80-100eV to form a CrN conductive and corrosion-resistant layer to obtain a bipolar plate.

6. The bipolar plate forming process according to claim 5, characterized in that: The ion source power is increased from 60-100W to 120-150W.

7. The bipolar plate forming process according to claim 5, characterized in that: The flow ratio of Ar gas to N2 gas was adjusted from 3-5:1 to 3:2-2:

1.

8. The bipolar plate forming process according to claim 5, characterized in that: The thickness of the CrN conductive corrosion-resistant layer is 1.2-1.5 μm; the thickness of the TiN transition layer is 0.3-0.5 μm.

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