Formula of high-temperature phosphating solution for highly wear-resistant and high-temperature-resistant cylinder sleeve

Abstract

The invention provides a formula of a high-temperature phosphating solution for a high-wear-resistant and high-temperature-resistant cylinder sleeve, and belongs to the field of process manufacturing of automobile parts. Aiming at the problems of insufficient wear resistance, poor high-temperature resistance, weak oil storage capacity and the like of a film layer in the existing normal-temperature and medium-temperature phosphating process, the invention provides a high-temperature phosphating solution suitable for the cast iron cylinder sleeve by optimizing formula composition and process parameters. The formula comprises 20-35 g / L of acidic manganese phosphate, 15-50 g / L of zinc nitrate, 1-3 g / L of calcium chloride, 0.5-2 g / L of sodium nitrite, 13 ml / L of phosphoric acid and 2-3 g / L of pure scrap iron, and a phosphating film is formed under the condition of 88-99 DEG C. Through the synergistic effect of all the components, the thickness of a film layer reaches 2-8 microns, the hardness is larger than or equal to HV350, the wear resistance is improved by 140%, the film layer can tolerate the high temperature of 300 DEG C, the oil storage content is 0.1-1.2 cm, the technical requirements of cast iron cylinder sleeves such as HT250 / QT500-7 and the like are met, the service life of an engine is remarkably prolonged, the comprehensive cost is reduced, and the coating is suitable for the manufacturing field of high-end engines such as heavy-duty diesel engines and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of automobile parts process manufacturing, more particularly, relates to a high-temperature phosphating solution formula for a high-wear and high-temperature-resistant cylinder liner. BACKGROUND

[0002] In the field of automobile parts manufacturing, the engine cylinder liner is a core friction component directly contacting the piston, and the surface treatment quality of the inner wall directly affects the power performance, fuel economy and service life of the engine. Among them, phosphating treatment is the key process to improve the wear resistance, corrosion resistance and oil storage performance of the inner wall of the cylinder liner, but its technical effect is significantly affected by the phosphating method and solution formula.

[0003] In the prior art, cylinder liner phosphating mainly adopts normal temperature phosphating (15-30℃) and medium temperature phosphating (50-70℃) processes, which has the following outstanding problems:

[0004] 1. The film layer has insufficient wear resistance and cannot meet the demand of high-strength working conditions:

[0005] The film layer formed by the normal temperature phosphating process is mainly zinc phosphate salt, with loose crystallization (porosity > 8%) and hardness of only HV200-250. In the GB / T12444-2006 wear resistance test (abrasive wheel speed 200r / min, load 50N), the film layer life is generally <500 revolutions. After the normal temperature phosphating of a heavy-duty diesel engine cylinder liner, the inner wall wear amount reached 0.3mm at the rated speed of 1500r / min for 50,000km, far exceeding the design allowable limit of 0.1mm, and the engine needs to be overhauled in advance.

[0006] Although the medium temperature phosphating slightly improves the film layer density (porosity 6%-7%) by increasing the temperature, the film layer surface roughness Rz still reaches 6.3-8μm due to the lack of components to refine the crystal in the formula, resulting in a 15% increase in the friction coefficient between the piston ring and the cylinder liner, and an additional 3%-5% increase in fuel consumption.

[0007] 2. Poor high-temperature resistance, film layer easily fails under high-temperature working conditions:

[0008] The existing phosphating film layer mainly relies on the crystal structure of zinc phosphate and manganese phosphate to achieve protection, but at the normal working temperature of the engine (180-250℃), the crystal bonding force will decrease with the increase of temperature. The normal temperature phosphating film will appear local discoloration (gray scale card ΔE > 3) after 2h at 200℃, and the film layer bonding force with the substrate will decrease by 40% (cross-hatch test from 0 to 3) at 300℃; the medium temperature phosphating film will be oxidized at the grain boundary above 250℃, resulting in a 30% blockage rate of the oil storage hole, losing the oil storage and lubrication effect.

[0009] For turbocharged engines (in-cylinder maximum temperature up to 350℃), the existing phosphating film layer has more than 20% of the film layer falling off area ratio in 1000 hours durability test, directly causing dry friction of the piston ring and the cylinder liner, and even causing cylinder pulling failure.

[0010] III. Insufficient oil storage capacity affects the stability of the lubrication system:

[0011] The normal temperature phosphating film is easy to be blocked by loose crystals in the oil storage hole (diameter 0.5-1mm) due to the coarse crystallization, and the actual measured oil content Q is only 0.05-0.08cm³, which is lower than the design requirement of 0.1-1.2cm³. Although the medium temperature phosphating can improve the oil storage capacity by prolonging the treatment time (8-10min), the film layer is too thick (>10μm), which will cause the clearance between the cylinder liner and the piston to decrease by 0.02-0.03mm, increasing the cold start resistance.

[0012] In addition, the existing formula lacks buffering components, and the solution pH value fluctuates greatly (±0.5), resulting in a deviation of 40% in the oil storage capacity of the same batch of cylinder liners, which cannot guarantee the consistency of lubrication performance.

[0013] IV. Poor process stability and high maintenance cost:

[0014] The normal temperature phosphating solution has a short service life (only 5-7 days), and the bath solution needs to be replaced every 1000 cylinder liners produced, and the Fe² + concentration is easy to exceed the standard (>5g / L), resulting in red-brown spots on the film layer, and the rework rate reaches 15%. Although the medium temperature phosphating solution has a service life of 15 days, the ratio of free acid to total acid needs to be adjusted frequently (2-3 times a day), and each adjustment takes 1-2 hours, which seriously affects the production efficiency.

[0015] At the same time, the existing formula contains heavy metals or toxic components such as nickel nitrate and sodium fluoride, and the wastewater treatment cost is high (more than 50 yuan per ton of wastewater treatment), and the sediment (containing 0.5% of nickel) is a hazardous waste, and the disposal cost is 5 times that of ordinary solid waste.

[0016] V. Limited material compatibility, unable to meet the needs of cast iron cylinder liners:

[0017] The existing phosphating formula is mainly designed for steel parts, and has poor adaptability to HT250, QT500-7 and other cast iron materials. Due to the adsorption of graphite phase in cast iron, the local thickness deviation of the film layer can reach 5μm (for the same workpiece), and the probability of "no phosphating layer bright spot" reaches 8%, which requires additional coating process, increasing the cost of each batch by 2000-3000 yuan.

[0018] In summary, the existing normal temperature and medium temperature phosphating process cannot meet the technical requirements of engine cylinder liner on wear resistance, high temperature resistance, oil storage capacity and process stability, and a new type of high temperature phosphating solution formula and process method is urgently needed to solve the above technical bottlenecks. SUMMARY

[0019] In order to solve the above technical problems, the application provides a high wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formula to solve the above problems.

[0020] A high wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formula, which is composed of the following components: 20-35 g / L of acid manganese phosphate, 15-50 g / L of zinc nitrate, 0.5-2 g / L of sodium nitrite, 1-3 g / L of calcium chloride, 13 ml / L of phosphoric acid, 2-3 g / L of pure iron filings, and the rest is water; the working conditions of the formula are: 4-7 points of free acid, 40-60 points of total acidity, the ratio of total acidity to free acid is 8.5-10:1, the content of divalent iron (Fe² + ) is less than 4.5 g / L, and the temperature is 88-99°C; it is suitable for HT250, QT500-7 and other cast iron material cylinder liners, and can form a gray to black gray phosphating film on the inner surface of the cylinder liner, the thickness of the phosphating film is 2-8 μm, has high wear resistance (under the standard GB / T12444-2006, the service life is more than 1000 revolutions when the grinding wheel speed is 200 r / min and the load is 50N) and high temperature resistance (after 2 hours at 200°C, the film layer does not fall off and the color does not change).

[0021] Preferably, the concentration of the acid manganese phosphate is 25-30 g / L; the acid manganese phosphate provides PO4³ - ions for the phosphating film, and Fe² + , Zn² + reacts with PO4³ + ions to generate Mn3(PO4)2crystals, when the concentration is greater than 35 g / L, it will cause the film layer to be too thick (>8 μm) and block the oil storage holes on the surface of the cylinder liner, and when the concentration is less than 20 g / L, the film layer coverage rate will decrease to less than 90%.

[0022] Preferably, the concentration of the zinc nitrate is 25-40 g / L; the zinc nitrate provides Zn² + ions, which combine with PO4³ - ions to generate Zn3(PO4)2, which can improve the compactness of the phosphating film, when the concentration is less than 15 g / L, the hardness of the film layer will decrease by 15% (from 180HV to 153HV), and when the concentration is greater than 50 g / L, the crystalline particles will be coarsened (particle size >10 μm) to cause the wear resistance to decrease.

[0023] Preferably, the concentration of the calcium chloride is 1.5-2.5 g / L; the calcium chloride provides Ca² +ions, which can refine the crystalline particles of the phosphating film (particle size controlled at 3-5 μm) and reduce the porosity of the film layer (porosity < 3%), and when the concentration is > 3 g / L, Cl - An excess amount leads to a tendency of pitting corrosion of the film layer.

[0024] Preferably, the added amount of the phosphoric acid is 13 ml / L, which is used to stabilize the pH value of the solution at 2.5-3.5; the pH range can buffer the hydrolysis rate of the acidic manganese phosphate, avoid excessive corrosion of the substrate caused by excessive local acidity (pH < 2.5), or reduce the film forming rate ( < 1 μm / min) caused by weak acidity (pH > 3.5).

[0025] Preferably, the added amount of the pure iron filings is 2.2-2.8 g / L; the pure iron filings react with the phosphoric acid at high temperature to generate Fe² + (Fe + 2H + → Fe² + + H2↑), and Fe² + as a catalyst can accelerate the phosphating reaction, shorten the film forming time to 2-4 min, and when the added amount is < 2 g / L, the film forming rate is reduced by 30%.

[0026] Preferably, the concentration of the sodium nitrite is 1-1.5 g / L; the sodium nitrite is an inhibitor, which can slow down the corrosion of the cylinder liner substrate before phosphating by inhibiting the cathode reaction (O2+ 2H2O + 4e - → 4OH - ), and when the concentration is < 0.5 g / L, the substrate corrosion rate is increased to 0.02 mm / h, and when the concentration is > 2 g / L, the reaction with Fe² + will generate N2O gas to cause bubbles in the film layer.

[0027] Preferably, the total acidity of the solution is 45-55 points, the free acid is 5-6 points, and the ratio of the total acidity to the free acid is 9-9.5:1; the ratio range can ensure uniform crystallization of the phosphating film, and when the ratio is < 8.5:1, the free acid is too high to cause loose film layer, and when the ratio is > 10:1, the total acidity is too high to cause easy brittleness of the film layer.

[0028] Preferably, the working temperature is 90-95℃; the temperature range can balance the film forming rate and energy consumption, the film forming efficiency is increased by 15% compared with 88℃, the solution evaporation amount is reduced by 20% (evaporation amount < 5 L / m² per hour) compared with 99℃, and the decomposition of zinc nitrate at high temperature can be avoided (the decomposition temperature of zinc nitrate is 105℃).

[0029] Preferably, the oil content of the phosphating film is 0.1-1.2 cm³ (measured on the straight side of the heat sink 30-40 mm below the lower edge of the cylinder liner), the waviness (Wt) is ≤4.5 μm, and the profile depth (pt) is 10-50 μm (pt=wt+Rz). The oil content matches the pore structure of the film, which can ensure the oil storage capacity of the cylinder liner, while the waviness and profile depth meet the sealing requirements of the engine assembly.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. Significantly improves the core performance of cylinder liners: The phosphated film layer formed is stable in thickness at 2-8μm, with a hardness of HV350 or higher. The wear resistance is improved by 140% compared to room temperature phosphated (wear resistance test increased from 500 rpm to 1200 rpm), the high temperature resistance is improved to 300℃ (no peeling or discoloration above 200℃), and the oil storage capacity reaches 0.1-1.2cm³, fully meeting the technical requirements of engines for cylinder liner wear resistance, corrosion prevention, and lubrication reserves.

[0032] 2. Optimized formulation achieves synergistic performance enhancement: The synergistic effect of acid manganese phosphate and zinc nitrate increases the film density (porosity decreases from 8% to 3%), and calcium chloride refines the crystals (particle size shrinks from 5μm to 2μm). Combined with the phosphate buffer system (pH stabilized at 2.5-3.5), it solves the contradiction of traditional formulations where the film is too thick and blocks the oil storage pores or too thin and leads to insufficient performance. It is also suitable for the surface characteristics of cast iron materials such as HT250 / QT500-7.

[0033] 3. Outstanding process stability and economy: The high-temperature phosphating process parameters (88-99℃, free acid 4-7 points) are highly controllable. The component decay rate of the solution is less than 5% after 72 hours of continuous operation. Only a small amount of raw materials needs to be replenished for every 2000 cylinder liners produced, and the scrap rate is reduced from 8% in room temperature phosphating to 2%. Compared with medium-temperature phosphating, energy consumption per unit mileage is reduced by 25%, and the overall production cost is reduced by 30%.

[0034] 4. Excellent environmental protection and safety performance: The formula does not contain heavy metals such as nickel and chromium. After neutralization treatment, the phosphate concentration of the wastewater is <0.5mg / L (compliant with GB21900-2008 standard). The sludge can be recycled as a building additive (containing 15% phosphorus), reducing solid waste pollution. There are no toxic gas emissions during the process, improving the safety of the operating environment.

[0035] 5. High adaptability and industrialization value: It is compatible with pretreatment processes such as ZL-601B degreasing powder and 10% sulfuric acid corrosion, and can be directly integrated into existing production lines; it is suitable for various cylinder liner models such as heavy-duty diesel engines and construction machinery engines, and its mass production stability has been verified by 8,000 pieces, making it suitable for large-scale promotion and application. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the formulation components of the present invention. Detailed Implementation

[0037] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0038] Please see Figure 1 This invention provides a high-wear and high-temperature phosphating solution formula for cylinder liners. By optimizing the high-temperature phosphating solution formula and process parameters, this invention improves the wear resistance and high-temperature resistance of the phosphating film for cast iron cylinder liners, while also meeting the special requirement of preventing the oil reservoir from clogging.

[0039] Formulation composition and synergistic mechanism:

[0040] Basic formulation composition (weight / volume concentration):

[0041]

[0042] Core component functions and synergistic mechanisms:

[0043] Manganese acid phosphate (20-35 g / L):

[0044] Manganese phosphate is the main film-forming substance in the membrane layer, and it ionizes into PO4³ under high temperature (88-99℃) conditions. - Ions, Fe² dissolved on the cylinder liner surface + Mn² + A chemical reaction occurs:

[0045] 3Mn² + +2PO4³ - →Mn3(PO4)2↓;

[0046] Manganese phosphate crystals with a layered structure are formed. When the concentration is 25-30 g / L, the crystal growth rate is stable (1-2 μm / min), and the film is uniformly gray to dark gray. If the concentration is >35 g / L, the film will be too thick (>10 μm), which will block the oil reservoir holes on the inner wall of the cylinder liner (designed oil reservoir diameter 0.5-1 mm), causing the oil content Q to drop below 0.1 cm³. When the concentration is <20 g / L, the film formation is discontinuous, and bright spots without phosphate layer appear, resulting in a 40% decrease in wear resistance.

[0047] Zinc nitrate (15-50g / L):

[0048] Zinc nitrate provides Zn² + Ions, on the one hand, through interaction with PO4³ -The combination of Zn3(PO4)2 and Mn3(PO4)2 fills the interstitial spaces of the Mn3(PO4)2 crystals, improving the film density (porosity decreases from 8% to 3%); on the other hand, Zn2 + As a cathode inhibitor, it can accelerate the cathodic process of film formation, shortening the film growth time by 20%. Experimental data show that when the zinc nitrate concentration is 30-40 g / L, the film hardness reaches its maximum value (HV350); if the concentration is <15 g / L, the film hardness drops to HV297 (a decrease of 15%), and the salt spray resistance decreases from 500h to 300h; when the concentration is >50 g / L, it leads to increased film brittleness, and cracks appear during the bending test (30 mm diameter mandrel).

[0049] Calcium chloride (1-3g / L):

[0050] Ca² + Ions adsorb onto the crystalline surface of the phosphating film, hindering the preferential growth of crystals and thus refining the crystal structure. When the calcium chloride concentration is 2 g / L, the crystal particle size is refined from 5 μm to 2 μm, and the surface roughness Rz of the film layer decreases from 6.3 μm to 3.2 μm. When the concentration is <1 g / L, the refining effect is not obvious. When the concentration is >3 g / L, a Ca3(PO4)2 impurity phase is generated, leading to a decrease in the adhesion between the film layer and the substrate (the cross-cut test grade drops from 0 to 2).

[0051] Synergistic effect of additives:

[0052] Phosphoric acid (13 ml / L): Maintains the solution pH between 2.5 and 3.5 through ionization equilibrium. When pH < 2.5, the substrate corrodes too quickly, resulting in a loose film; when pH > 3.5, the film-forming reaction stagnates. An addition of 13 ml / L of phosphoric acid ensures that the pH fluctuation of the solution does not exceed ±0.3 after 72 hours of continuous use.

[0053] Pure iron filings (2-3 g / L): undergo a micro-cell reaction with zinc nitrate at high temperature to produce Fe²⁺. + Ions (Fe+Zn²) + →Fe² + +Zn), Fe² + As a catalyst, it can accelerate the reaction of PO4³ - The binding with metal ions shortens the film formation time from 4 minutes to 2 minutes. If the amount of iron filings added is <2 g / L, the catalytic effect is insufficient; when >3 g / L, Fe²⁺… + Concentrations exceeding 4.5 g / L resulted in reddish-brown spots appearing on the membrane.

[0054] Sodium nitrite (0.5-2 g / L): As an oxidant, it can inhibit excessive corrosion during the phosphating process (2Fe + O2 + 2H2O → 2Fe(OH)2). When the concentration is 1 g / L, the corrosion rate is controlled at 0.5 g / (m²·h); when the concentration is <0.5 g / L, the corrosion rate increases to 1.2 g / (m²·h), and pinholes appear in the film; when the concentration is >2 g / L, NaFePO4 precipitate will be generated, contaminating the solution.

[0055] Application scope and boundary conditions of the formulation:

[0056] Material compatibility:

[0057] This formula is specifically designed for cast iron cylinder liners and is suitable for materials such as HT250 (pearlitic gray cast iron) and QT500-7 (ductile iron). For HT250, the adhesion between the phosphate coating and the graphite phase is superior to other materials, and no peeling occurs in the cross-cut test (1mm grid). For QT500-7, the zinc nitrate concentration needs to be increased to 40-50 g / L to compensate for the effect of ductile iron on Zn²⁺. + Adsorption consumption. Not suitable for aluminum alloy cylinder liners (displacement reaction will occur, leading to film peeling).

[0058] High temperature stability parameters:

[0059] Boiling point of the solution: 102℃ under standard atmospheric pressure. The process setting temperature is 88-99℃, with a safety margin of 3℃ to avoid the volatilization of components due to boiling.

[0060] Long-term stability: After 72 hours of continuous high-temperature operation, the concentration decay rate of manganese phosphate was 4.8% (from 30 g / L to 28.56 g / L), and the decay rate of zinc nitrate was 2.7% (from 30 g / L to 29.19 g / L), both within acceptable ranges (decay rate < 5%).

[0061] Low-temperature storage stability: After the solution is frozen at -5℃ for 24 hours, no crystals are precipitated upon thawing, and the performance retention rate is 98%.

[0062] Example 1 (Basic Formula):

[0063] Formula composition:

[0064] Manganese phosphate 30g / L, zinc nitrate 30g / L, calcium chloride 2g / L, sodium nitrite 1g / L, phosphoric acid 13ml / L, pure iron filings 2.5g / L, water balance.

[0065] Process parameters:

[0066] Free acid 5 points, total acidity 50 points, total acidity: free acid = 10:1, Fe² + Concentration 3g / L, temperature 95℃, time 3min.

[0067] Performance metrics:

[0068]

[0069] Example 2 (High Wear-Resistant Optimized Formula):

[0070] Formula adjustments:

[0071] Manganese phosphate 35 g / L, zinc nitrate 40 g / L, calcium chloride 3 g / L (the remaining components are the same as in Example 1).

[0072] Performance changes:

[0073] The film thickness was increased to 7μm, and the hardness was improved to HV380;

[0074] Abrasion resistance test reaches 1500 revolutions (25% improvement);

[0075] The oil content has decreased to 0.6 cm³ (still within the acceptable range).

[0076] Example 3 (High-Temperature Stability Optimized Formulation):

[0077] Formula adjustments:

[0078] Zinc nitrate 50g / L, sodium nitrite 2g / L (the remaining components are the same as in Example 1).

[0079] Performance changes:

[0080] After a high-temperature test at 300℃ (2 hours), the film layer did not peel off (in Example 1, local discoloration occurred at 300℃).

[0081] Salt spray resistance improved to 600h;

[0082] The membrane layer is slightly more brittle, and a slight crack appeared during the bending test (30mm diameter mandrel) (which does not affect its use).

[0083] Comparative Example 1 (room temperature phosphating formulation):

[0084] Formula composition:

[0085] Zinc dihydrogen phosphate 80g / L, nickel nitrate 10g / L, citric acid 5g / L, temperature 25℃.

[0086] Performance comparison:

[0087]

[0088] Comparative Example 2 (Medium-temperature phosphating formulation):

[0089] Formula composition:

[0090] 60 g / L of manganese iron phosphate, 20 g / L of zinc nitrate, and a temperature of 60℃.

[0091] Performance comparison:

[0092]

[0093] Process and solution maintenance:

[0094] (a) Solution preparation steps:

[0095] Add 80% of the volume of tap water to the phosphating tank and heat it to 50°C;

[0096] Add manganese acid phosphate, zinc nitrate, and calcium chloride in sequence, and stir until completely dissolved;

[0097] Slowly add phosphoric acid (13 ml / L) and stir for 10 minutes (to prevent local overheating);

[0098] Add pure iron filings and stir until partially dissolved (the remaining iron filings can be recycled).

[0099] Add sodium nitrite, add water to the specified volume, and heat to 95°C;

[0100] Adjust the free acid to 5 points and the total acidity to 50 points (total acidity: free acid = 10:1).

[0101] (II) Process parameter control:

[0102] Determination of free acid and total acidity:

[0103] Determination of free acid: Take 10 ml of solution, add 3 drops of phenolphthalein indicator, and titrate with 0.1 mol / L NaOH until pink (the color does not fade in 30 s). The volume consumed is A (free acid = A × 10 points).

[0104] Total acidity determination: Take 10 ml of solution, add 3 drops of bromophenol blue indicator, and titrate with 0.1 mol / L NaOH until blue-violet color appears. The volume consumed is B (total acidity = B × 10 points).

[0105] Control frequency: Measured once every 200 cylinder liners produced, and adjusted by adding phosphoric acid (to reduce total acidity) or zinc nitrate (to increase total acidity).

[0106] Fe² + Concentration control:

[0107] Determination method: Take 10 ml of solution, add 5 ml of H2SO4 (1:1), and titrate with 0.1 mol / L K2Cr2O7 until orange (endpoint). Fe² + Concentration (g / L) = titration volume × 0.56;

[0108] When Fe²+ When the concentration is >4.5 g / L, add sodium nitrite (1 g / L can reduce Fe²). + 0.5g / L).

[0109] Temperature control:

[0110] It adopts a PID temperature control system with an accuracy of ±1℃, and the heating method is steam heating in the bottom coil of the tank (to avoid local overheating that could lead to solution decomposition).

[0111] (III) Solution Maintenance Procedures:

[0112] Regular cleaning: Remove the sediment (mainly FePO4 and Zn3(PO4)2) from the bottom of the tank weekly, and keep the sediment thickness at <50mm (too thick will affect heat conduction).

[0113] Concentration replenishment: For every 1000 cylinder liners produced, add 3kg of manganese phosphate and 2kg of zinc nitrate (calculated based on a 2000L tank).

[0114] Replacement cycle: When the solution is used for 1 month (approximately 8000 units produced) or the total acidity is <40 points, the entire tank solution should be replaced (the tank should be cleaned with 10% H2SO4 before replacement).

[0115] Collaborative control of the process:

[0116] (a) Matching of pretreatment processes:

[0117] Degreasing process: Use ZL-601B degreasing powder (50-70g / L) at a temperature of 70-80℃ to ensure continuous water film testing (no breakage). If degreasing is incomplete, pinholes will appear in the phosphating film (area percentage > 5%).

[0118] Corrosion process: 10% sulfuric acid solution (35-45℃), corrosion time 5 min, to increase the surface roughness Rz of the cylinder liner from 6.3μm to 12.5μm (increasing the film bonding area). Excessive corrosion (>7 min) will result in an excessively thin substrate (reduced by 0.2 mm), while insufficient corrosion (<2 min) will reduce the film bonding strength (cross-cut test grade 3).

[0119] (ii) Post-phosphating treatment:

[0120] Cleaning and drying: After phosphating, rinse three times with running cold water (total time 8 min) and once with hot water (70℃, 2 min) to ensure that the pH of the residual solution is >6.5 (tested with pH test paper); blow dry with compressed air (pressure 0.4-0.6MPa) to avoid moisture residue causing rust to return to the film.

[0121] Rust-preventive oil coating: Mix 50% No. 24 dehydrated rust-preventive oil with 50% kerosene, immerse at room temperature for 2 minutes to ensure a uniform oil film (thickness 5-10μm).

[0122] Performance testing methods and standards:

[0123] (a) Visual inspection:

[0124] 100% visual inspection (light intensity 500 lux) meets the following requirements:

[0125] Color: Gray to dark gray (a small amount of light yellowish ash is permissible and can be wiped off);

[0126] Defect: No bright spots without phosphate coating (single bright spot area < 0.5 mm² and total number < 3 are acceptable);

[0127] Uniformity: The crystalline structure allows for local color variations due to differences in machining, but the area percentage should be less than 10%.

[0128] (II) Measurement of film thickness:

[0129] Using a ComBiD3 coating thickness gauge (accuracy ±0.1μm), measure 4 points (90° distribution) at 30-40mm from the upper and lower edges of the cylinder liner, and take the arithmetic mean (zero point is calibrated with a cylinder liner without phosphate coating before measurement).

[0130] (III) Abrasion resistance test:

[0131] According to GB / T12444-2006, the MM-200 wear tester was used, with the grinding wheel material GCr15 (hardness HRC60), load 50N, and rotation speed 200r / min. The number of revolutions when the film layer was worn through was recorded (≥1000 revolutions is considered qualified).

[0132] (iv) High temperature resistance test:

[0133] Place the sample in an oven (300℃) and keep it warm for 2 hours. Then remove it, cool it to room temperature, and check whether the film layer peels off or changes color (compare with the grayscale card; ΔE < 2 is acceptable).

[0134] (v) Determination of oil content:

[0135] The weight method is used: the cylinder liner after being coated with oil is immersed in kerosene for 2 minutes, and then the weight gain of the kerosene is measured (converted to volume). The calculation formula is: Q=(m2-m1) / ρ (ρ is the density of kerosene, 0.8g / cm³).

[0136] This invention solves the problem of insufficient wear resistance and high-temperature resistance of room-temperature / medium-temperature phosphating films by optimizing the high-temperature phosphating solution formulation (manganese phosphate 20-35 g / L, zinc nitrate 15-50 g / L, calcium chloride 1-3 g / L, etc.) and combining it with precise process control (temperature 88-99℃, free acid 4-7 points, etc.). Example data shows that the phosphating film formed by this formulation has a thickness of 2-8 μm, a hardness of HV350 or higher, a 140% improvement in wear resistance, and a high-temperature resistance of 300℃, fully meeting the technical requirements of engine cylinder liners and possessing significant industrialization value.

[0137] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation, characterized in that, It is composed of the following components: 20-35 g / L of manganese phosphate, 15-50 g / L of zinc nitrate, 0.5-2 g / L of sodium nitrite, 1-3 g / L of calcium chloride, 13 ml / L of phosphoric acid, 2-3 g / L of pure iron filings, and the remainder is water; The operating conditions of the formulation are: free acid 4-7 points, total acidity 40-60 points, total acidity to free acid ratio of 8.5-10:1, and divalent iron (Fe²⁺). + Content < 4.5 g / L, temperature 88℃~99℃; The phosphating film has a thickness of 2-8 μm and exhibits high wear resistance and high temperature resistance.

2. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The concentration of the acidic manganese phosphate is 25–30 g / L; the acidic manganese phosphate provides PO4³ for the phosphating film. - Ions, with Fe² + Zn² + The reaction produces Mn3(PO4)2 crystals. When the concentration is >35g / L, it will cause the film to be too thick (>8μm) and block the oil reservoir on the cylinder liner surface. When the concentration is <20g / L, the film coverage drops to <90%.

3. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The concentration of zinc nitrate is 25–40 g / L; The zinc nitrate provides Zn². + Ions, with PO4³ - The combination of Zn3(PO4)2 can improve the density of the phosphating film. When the concentration is <15g / L, the hardness of the film decreases. When the concentration is >50g / L, the coarsening of the crystal particles leads to a decrease in wear resistance.

4. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The concentration of calcium chloride is 1.5–2.5 g / L; The calcium chloride provides Ca²⁺. + Ions can refine the crystalline particles of phosphating films and reduce film porosity. However, when the concentration is >3 g / L, Cl- will be introduced. - Excessive application can lead to pitting corrosion in the film.

5. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The amount of phosphoric acid added is 13 ml / L, used to stabilize the pH of the solution at 2.5–3.5; The specified pH range can buffer the hydrolysis rate of manganese phosphate, avoiding excessive corrosion of the substrate due to excessive local acidity, or a decrease in film formation rate due to insufficient acidity.

6. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The amount of pure iron filings added is 2.2–2.8 g / L; The pure iron filings react with phosphoric acid at high temperature to generate Fe²⁺. + (Fe+2H) + →Fe² + +H2↑); Fe² + As a catalyst, it can accelerate the phosphating reaction and shorten the film formation time to 2-4 minutes. When the addition amount is <2g / L, the film formation rate decreases by 30%.

7. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The concentration of sodium nitrite is 1–1.5 g / L. Sodium nitrite acts as a corrosion inhibitor, suppressing the cathodic reaction (O₂ + 2H₂O + 4e⁻). - →4OH - It slows down the corrosion of the cylinder liner substrate before phosphating. When the concentration is <0.5 g / L, the substrate corrosion rate increases to 0.02 mm / h. When the concentration is >2 g / L, it will react with Fe²⁺. + The reaction generates N2O gas, which causes bubbles to appear in the membrane.

8. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The total acidity of the solution is 45-55 points, the free acid is 5-6 points, and the ratio of total acidity to free acid is 9-9.5:

1. This ratio range can ensure uniform crystallization of the phosphating film. When the ratio is <8.5:1, the free acid is too high, resulting in a loose film layer. When the ratio is >10:1, the total acidity is too high, resulting in an embrittled film layer.

9. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The operating temperature is 90℃~95℃; this temperature range can balance the film formation rate and energy consumption, improve the film formation efficiency compared to 88℃, reduce the solution evaporation compared to 99℃, and avoid the decomposition of zinc nitrate at high temperatures.

10. The high-wear-resistant and high-temperature-resistant cylinder liner high-temperature phosphating solution formulation as described in claim 1, characterized in that, The phosphating film has an oil content of 0.1–1.2 cm³, a waviness (Wt) ≤ 4.5 μm, and a profile depth (pt) of 10–50 μm (pt = wt + Rz). The oil content is matched with the pore structure of the film to ensure the oil storage capacity of the cylinder liner, while the waviness and contour depth meet the sealing requirements of the engine assembly.

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