Aluminum alloy section pickling process

Abstract

The invention relates to the technical field of acid pickling processing, and discloses an aluminum alloy profile acid pickling process. Through an activating treatment process, the activating effect of the surface of aluminum alloy is remarkably improved through the synergistic effect of nano cerium dioxide and potassium fluotitanate; the gradient pickling process design realizes efficient removal of an oxide layer and precise protection of a matrix; a passivation film with excellent corrosion resistance is constructed by adopting a nano material modified composite passivation technology; waste liquid recycling realizes efficient recycling of the pickling waste liquid; and the process water consumption is greatly reduced through water circulation. According to the aluminum alloy pickling process, the pollution emission problem existing in a traditional pickling process is reduced, and meanwhile the aluminum alloy pickling process has the advantages of being high in treatment efficiency, easy and convenient to operate, low in pickling cost and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of pickling processing, and specifically relates to an aluminum alloy profile pickling process. Background Art

[0002] Aluminum alloy profiles are widely used in the fields of aerospace, architectural decoration, automobile manufacturing, etc. The surface of aluminum alloy profiles needs to be pickled to remove the oxide layer and processing residues to obtain a clean and active surface, which lays a foundation for subsequent anodic oxidation, spraying and other treatments.

[0003] Traditional pickling processes mostly use a nitric acid-hydrofluoric acid mixed system. Although it can effectively remove aluminum oxide, it has the following defects: (1) A large amount of toxic NOx gas is released during the pickling process, and a complex tail gas purification system is required; (2) Chromate passivation results in wastewater containing hexavalent chromium pollutants, with high treatment costs and prominent environmental risks; (3) Single-tank pickling has insufficient control over substrate corrosion and is prone to over-etching patterns; (4) The waste acid regeneration technology is not mature, and the resource utilization rate is less than 30%. In recent years, although improved processes such as organic acid substitution and ultrasonic assistance have been developed, there are still bottlenecks such as low treatment efficiency (≥20 minutes), poor corrosion resistance of the passivation film (salt spray life <500 hours), and high energy consumption for waste liquid regeneration, which seriously restricts the green transformation of the industry; Therefore, an aluminum alloy profile pickling process is proposed. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides an aluminum alloy profile pickling process to solve the problems in the background art.

[0005] To achieve the above object, the present invention provides the following technical solution: An aluminum alloy profile pickling process, including the following steps: Step 1: Activation treatment: Immerse the profile in a pretreatment solution containing 1.2 - 1.8% tartaric acid, 0.4 - 0.7% potassium fluotitanate, 0.07 - 0.1% nano-cerium dioxide, and the balance being water, and treat it for 3 - 5 minutes under the conditions of an ultrasonic frequency of 40 - 60 kHz and a power density of 0.3 - 0.8 W / cm²; Step 2: Gradient pickling: Primary pickling: Immerse the profile after activation treatment in a primary pickling solution containing 14 - 21% phosphoric acid, 1.4 - 2.1% gluconic acid, 0.04 - 0.09% sodium thiosulfate, and the balance being water, control the temperature at 40 - 50°C, and treat it for 3 - 8 minutes.

[0006] Secondary pickling: Immerse the profiles after primary pickling into the secondary pickling solution containing 5%-10% malic acid, 0.8%-2.5% ammonium fluoride, 0.025-0.05% polydopamine-modified carbon nanotubes, and the balance being water. Control the temperature at 25-30°C and process for 2-3 minutes.

[0007] Rinsing: Immerse the profiles after secondary pickling into clean water for rinsing.

[0008] Step 3: Composite passivation: Immerse the profiles after secondary pickling into the passivation solution containing 1.5-2.3% 3-aminopropyltriethoxysilane, 0.06-0.12% graphene oxide quantum dots, 0.25-0.38% lithium molybdate nanosheets, and the rest being water, and alternately apply forward / reverse current to deposit a three-dimensional network passivation film.

[0009] Step 4: Water recycling: The rinsing water is recycled after multi-stage membrane treatment; Step 5: Waste liquid resource utilization: The waste liquid from primary pickling is regenerated by pulsed electrochemical oxidation, and the waste liquid from secondary pickling is used to recover calcium malate by the method of bio-mineralization with engineering bacteria.

[0010] Preferably, in the activation treatment, the ultrasonic power density is 0.5 W / cm², and nano-cerium dioxide forms a Ti-O-Ce bonding structure with potassium fluotitanate, and the bonding energy ≥ 2.3 eV.

[0011] Preferably, the thickness of the polydopamine coating layer of the polydopamine-modified carbon nanotubes is 5-8 nm, and the Zeta potential of the polydopamine-modified carbon nanotubes ≥ +35 mV (at pH = 3), forming a three-dimensional conductive network in the pickling solution, and the interfacial electron transfer resistance is 80-100 Ω·cm².

[0012] Preferably, the multi-stage membrane treatment sequentially includes ultrafiltration, reverse osmosis, and electrodialysis treatment.

[0013] Preferably, the volume ratio of the primary pickling solution to the secondary pickling solution is 1.5:1 - 2:1, and gas-liquid isolation is used to isolate between the two pickling tanks.

[0014] Preferably, the mass ratio of silane / graphene oxide / lithium molybdate is (60-65):(15-18):(20-22), and the thickness of the passivation film is 80-120 nm.

[0015] Preferably, in the pulsed electrochemical oxidation regeneration in Step 5, a titanium-based anode, a frequency of 80-120 Hz, and a duty cycle of 60-80% are used for regeneration.

[0016] Preferably, the engineering bacteria is Escherichia coli BL21 / pET28a-MsfA, which expresses the MsfA protein to regulate the crystallization process.

[0017] Preferably, in step three, the specific parameters of the forward / reverse current are as follows: The forward current density is 2 - 3 A / dm², and the duration is 30 - 40 seconds; The reverse current density is 0.5 - 1 A / dm², and the duration is 10 - 15 seconds; The number of alternating cycles is 8 - 12 times.

[0018] Compared with the prior art, the present invention has the following beneficial effects: Through the activation treatment process, the present invention utilizes the synergistic effect of nano - cerium dioxide and potassium fluotitanate to significantly improve the activation effect on the surface of aluminum alloy; the gradient pickling process design realizes the efficient removal of the oxide layer and the precise protection of the substrate; the composite passivation technology modified with nanomaterials constructs a passivation film with excellent corrosion resistance; the resource utilization of waste liquid realizes the efficient recycling of pickling waste liquid; the water circulation greatly reduces the process water consumption. This aluminum alloy pickling process reduces the pollution emission problems existing in the traditional pickling process, and at the same time has the advantages of high processing efficiency, simple operation, and low pickling cost.

[0019] Other features and advantages of the present invention will be described in the subsequent description, and, in part, will be obvious from the description or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures pointed out in the description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the process flow chart of the aluminum alloy profile pickling process of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0022] Please refer to Figure 1 , a kind of aluminum alloy profile pickling process in the present invention includes the following content: Example 1:

[0023] Step 1: Activation treatment 1. Preparation of activation solution Raw materials: Tartaric acid Potassium fluotitanate Nano - cerium dioxide (particle size 20 - 50 nm, octahedral morphology accounting for 75%) Formulation method: Add 15 kg of tartaric acid, 5.5 kg of potassium fluotitanate, and 0.9 kg of nano-cerium dioxide to 1 ton of deionized water in sequence; Stir mechanically (rotation speed 300 rpm) for 30 minutes, and use after standing to defoam.

[0024] 2. Ultrasonic activation operation Equipment: Kunshan Shumei KQ-500DE ultrasonic cleaner (frequency 40 kHz, adjustable power); Parameters: frequency 50 kHz, power density 0.5 W / cm², treatment time 4 minutes; Process: Vertically suspend the aluminum alloy profile in the activation solution; Turn on the ultrasonic wave, take out the profile after the treatment, and rinse it with a high-pressure water gun (pressure 0.3 MPa) for 10 seconds.

[0025] 3. Detection of activation effect Surface morphology: SEM shows that microcracks are generated in the oxide layer (density 210 pieces / mm²); Contact angle: Drop from 82° before treatment to 9° (Krüss DSA100 water contact angle meter); Bonding structure: XPS analysis confirms the appearance of Ti-O-Ce characteristic peaks in the Ce 3d spectrum.

[0026] Step two: Gradient pickling 1. Primary pickling Preparation of pickling solution: 160 kg of phosphoric acid (85%, industrial grade); 18 kg of gluconic acid (food grade); 0.6 kg of sodium thiosulfate (analytical pure); Make up to 1 ton with deionized water.

[0027] Process parameters: Temperature 45°C (±1°C), treatment time 5 minutes; Material of pickling tank: PPH acid-resistant plastic, equipped with titanium alloy heating coils.

[0028] Effect: Etching rate of aluminum oxide 5.8 μm / min (measured by metallographic microscope); Substrate corrosion rate 0.12 mm / a (calculated by weight loss method).

[0029] 2. Secondary pickling Preparation of pickling solution: 80 kg of malic acid (food grade); 12 kg of ammonium fluoride (analytical pure); 0.35 kg of polydopamine-modified carbon nanotubes (coating thickness 6 nm, self-made); Make up to 1 ton with deionized water.

[0030] Dispersion system: Ultrasonic disperser (Branson 450 by Branson, power 70 W / L); Mechanical stirring paddle (diameter 200 mm, linear velocity 4 m / s).

[0031] Process parameters: Temperature 28 °C (±1 °C), treatment time 2.5 minutes; Monitor the nanotube concentration in real time (UV-Vis method, λ = 260 nm), with fluctuation < 3%.

[0032] Effect: Surface roughness Ra = 0.48 μm (Mitutoyo SJ-410 profilometer); Grain boundary corrosion depth ≤ 1.2 μm (SEM cross-section analysis).

[0033] Step 3: Composite passivation Preparation of passivation solution 3-aminopropyltriethoxysilane (KH550, 20 kg); 0.9 kg of graphene oxide quantum dots (particle size 5 nm, Nanjing Xianfeng Nano); 3.2 kg of lithium molybdate nanosheets (thickness ≤ 2 nm, Zhongke Shidai Nano); Make up to 1 ton with deionized water.

[0034] pH adjustment: Citric acid / sodium citrate buffer system, naturally stabilized to pH 4.2.

[0035] Electrodeposition process Equipment: Princeton VersaSTAT 4 electrochemical workstation; Parameters: Positive current density 2.5 A / dm², duration 35 seconds; Negative current density 0.8 A / dm², duration 12 seconds; Alternation period 10 times, total treatment time 8 minutes.

[0036] Deposition process: Initial stage (cycles 1-2): Hydrolysis and polycondensation of silane to form a substrate film (thickness about 20 nm); Middle stage (cycles 3-7): Embedding of graphene oxide quantum dots, significant increase in film impedance; Final stage (cycles 8-10): Filling of pores with lithium molybdate nanosheets to form a dense outer layer.

[0037] Passivation film performance Film layer structure: Outer layer: Silane-graphene oxide composite layer (thickness 65 nm, contact angle 112°); Inner layer: Lithium molybdate nanosheet layer (thickness 25 nm).

[0038] Corrosion resistance: No white rust after 1320 h of neutral salt spray test; Electrochemical impedance (1 kHz).

[0039] Step 4: Water circulation Rinsing water treatment process Ultrafiltration unit: Molecular weight cut-off 10 kDa (Hydranautics HYDRAcap 60 membrane); Reverse osmosis unit: Desalination rate 98.5% (Dow SW30HRLE-4040 membrane); Electrodialysis unit: Desalinated to conductivity 42 μS / cm (Asahi Kasei ACS-20C membrane stack).

[0040] Operating data Raw water quality: COD 850 mg / L, conductivity 3200 μS / cm; Recycled water quality: COD < 5 mg / L, 2.8 ppm; Water consumption: 1.0 m³ / ton of profiles, water saving rate 87.5%.

[0041] Step 5: Waste liquid resource utilization Regeneration of primary pickling waste liquid Electrochemical oxidation device: Anode: Titanium substrate Coated electrode (Baoji Titanium Industry); Cathode: 316L stainless steel plate; Power supply: Pulse mode (frequency 100 Hz, duty cycle 70%).

[0042] Regeneration effect: Phosphoric acid recovery rate 89%, purity 85.3%; Residual metal ions: Al³⁺ 3.2 ppm, Fe²⁺ 0.8 ppm.

[0043] Treatment of secondary pickling waste liquid Biomineralization reactor: Engineering bacteria: E.coli BL21 / pET28a-MsfA (OD600 = 6.0); Reaction conditions: pH 6.8, 30 °C, stirring rate 150 rpm; Product characteristics: The calcium malate purity is 96.2%, and the specific surface area is 34 m² / g (BET method); The activity remains >90% after the cells are reused 8 times.

[0044] Example 2:

[0045] Step 1: Activation treatment 1. Preparation of the activation solution Step 1: Activation treatment The activation solution uses 1.5% tartaric acid, 0.55% potassium fluotitanate, and the rest is water. The ultrasonic activation operation is cancelled. The aluminum alloy profile is vertically suspended in the activation solution and activated for 4 minutes. After the treatment, the profile is taken out and rinsed with a high-pressure water gun (pressure 0.3 MPa) for 10 seconds.

[0046] Steps 2 - 5 are the same as in Example 1.

[0047] Example 3:

[0048] Step 1 is the same as in Example 1.

[0049] Step 2: Pickling The pickling solution uses 10% citric acid, 3% ammonium fluoride, 0.02% polydopamine-CNTs, and the rest is water. The temperature is 30°C (±1°C), and the treatment time is 15 minutes.

[0050] Steps 3 - 5 are the same as in Example 1.

[0051] Comparative Example 1: Comparative Example 1: Traditional nitric acid pickling process Pickling steps: 1. Pretreatment: Alkaline degreasing: Immerse the profile in a degreasing solution containing 5% sodium hydroxide and 2% trisodium phosphate (temperature 60°C), and mechanically stir (200 rpm) for 5 minutes to remove the surface oil.

[0052] Water washing: Spray and rinse with 40°C clean water for 2 minutes.

[0053] 2. Nitric acid pickling: Pickling solution formula: 20% nitric acid (industrial grade, concentration 68%) + 5% hydrofluoric acid (40% concentration) Process parameters: Pickling tank material: PPH plastic lining, titanium alloy heating coil Temperature: 50 ± 2°C Treatment time: 15 minutes (the profile is completely immersed) Reaction mechanism:

[0054] Waste gas treatment: The acid mist is collected through a PP material air duct and enters an alkali liquor spray tower (5% NaOH solution). Concentration of tail gas NOx: 85 mg / m³ (3 times higher than the GB 16297-1996 standard). 3. Chromate passivation: Passivation solution: 3% sodium chromate ( ) + 0.5% sodium fluoride (pH = 3.5, adjusted with sulfuric acid). Process parameters: Current density: 2 A / dm² (DC power supply). Treatment time: 10 minutes Waste liquid treatment: In the passivation waste water Concentration: 7.8 mg / L (limit value of GB 8978-1996 is 0.5 mg / L). Treatment method: Lime neutralization (CaO dosage 15 kg / m³) → Filter press sludge (moisture content 60%, HW17 hazardous waste number).

[0055] Comparative example 2: Commercially available environmentally friendly acid pickling agent 1. Acid pickling steps: Pretreatment: Alkaline degreasing: 5% NaOH solution (spray at 60 °C for 3 minutes). Water washing: Countercurrent rinsing in 3 stages (conductivity ≤ 200 μS / cm). 2. Citric acid-hydrogen peroxide acid pickling: Acid pickling solution formula: 8% citric acid (food grade). 5% hydrogen peroxide (30% concentration). 0.1% corrosion inhibitor (sodium dodecylbenzenesulfonate). Process parameters: Treatment method: Circulating spray (pressure 0.4 MPa). Temperature: 40 ± 2 °C Time: 25 minutes Reaction characteristics:

[0056] 3. Molybdate passivation: Passivation solution: Commercially available chromium-free passivating agent (containing ammonium molybdate, silica sol). Process parameters: Immersion time: 10 minutes Drying conditions: Hot air circulation at 80 °C for 20 minutes 4. Waste liquid treatment: Hydrogen peroxide decomposition: Add Catalyst (dosage: 0.5 kg / m³), reaction for 2 hours Evaporation and concentration: Triple-effect evaporator (steam consumption: 1.2 tons per ton of wastewater).

[0057] Comparative Example 3: Biological pickling process 1. Pickling step: Strain cultivation: Strain: Acidithiobacillus ferrooxidans (ATCC 23270) Culture medium: 9K culture medium (pH = 2.0, containing 44.7 g / L) Cultivation conditions: Shake cultivation at 30°C (120 rpm) for 72 hours, OD600 = 0.8 2. Biological pickling: Reaction system: Inoculation amount of bacterial solution: 15% (v / v) Substrate addition: 5% ferrous sulfate Reaction temperature: 30°C Treatment time: 50 minutes (terminate when pH drops to 1.8) Reaction monitoring: Real-time detection of Fe²⁺ oxidation rate (o-phenanthroline spectrophotometry) Endpoint determination: Fe²⁺ concentration < 0.1 g / L 3. Phytic acid passivation: Passivation solution: 5% phytic acid solution (pH = 3.0, adjusted with NaOH) Process parameters: Impregnation time: 15 minutes Drying method: Natural drying at room temperature for 24 hours 4. Bacterial cell recovery: Ceramic membrane filtration: Pore size 0.2 μm, transmembrane pressure difference 0.15 MPa Detection of bacterial cell activity: INT dehydrogenase activity method (activity of the 5th generation: 42%).

[0058]

[0059] In Example 1 of the present invention, through a gradient pickling system (synergy of a dual-tank of phosphoric acid / malic acid) and a nano-composite passivation technology (a three-dimensional network of silane-graphene oxide-lithium molybdate), efficient stripping of the oxide layer on the surface of aluminum alloy profiles is achieved, forming a corrosion-resistant gradient passivation film. At the same time, through a waste liquid resource utilization system, the pickling cost of the profiles is comprehensively reduced, and the pollution emission is reduced by 95%. In Examples 2-3, the necessity of the process synergy effect is verified by canceling the nano-activation or gradient pickling design, while the existing pickling technologies in Comparative Examples 1-3 expose industrialization bottlenecks such as high pollution, high energy consumption, and low quality, highlighting the technological breakthrough of the present invention in the fields of green manufacturing and precision surface treatment.

Claims

1. A pickling process for aluminum alloy profiles, characterized in that: The following steps are involved: Step 1: Activation treatment: immerse the profile in a pretreatment solution containing 1.2-1.8% tartaric acid, 0.4-0.7% potassium fluorotitanate, 0.07-0.1% nano-cerium dioxide, and the balance is water, and treat for 3-5 minutes under the conditions of ultrasonic frequency 40-60kHz and power density 0.3-0.8W / cm²; Step 2: Gradient acid washing: Primary pickling: immerse the activated profiles in a primary pickling solution containing 14-21% phosphoric acid, 1.4-2.1% gluconic acid, 0.04-0.09% sodium thiosulfate, and the balance water, control the temperature at 40-50°C, and the treatment time is 3-8 minutes; Secondary pickling: Immerse the profile after primary pickling in a secondary pickling solution containing 5%-10% malic acid, 0.8%-2.5% ammonium fluoride, 0.025-0.05% polydopamine-modified carbon nanotubes, and the balance water, control the temperature at 25-30°C, and treat for 2-3 minutes; Rinsing: After the secondary pickling, immerse the profile in clean water for rinsing; Step 3: Composite passivation: Immerse the profile after secondary pickling in a passivation solution containing 1.5-2.3% 3-aminopropyltriethoxysilane, 0.06-0.12% graphene oxide quantum dots, 0.25-0.38% lithium molybdate nanosheets, and the rest water, and alternately apply forward / reverse current to deposit a three-dimensional network passivation film; Step 4: Water circulation: Rinse water is treated by multi-stage membranes and then reused; Step 5: Waste liquid resource utilization: The primary pickling waste liquid is regenerated by pulse electrochemical oxidation, and the secondary pickling waste liquid is recovered by engineering bacteria biomineralization method for calcium malate.

2. The pickling process for aluminum alloy profiles according to claim 1, characterized in that: In the activation treatment, the ultrasonic power density is 0.5W / cm², and the nano-cerium dioxide and potassium fluorotitanate form a Ti-O-Ce bonding structure with a bonding energy of ≥2.3eV.

3. The pickling process for aluminum alloy profiles according to claim 1, characterized in that: The polydopamine coating layer of the polydopamine modified carbon nanotube has a thickness of 5-8 nm, wherein the Zeta potential of the polydopamine modified carbon nanotube is ≥+35 mV (at pH=3), a three-dimensional conductive network is formed in an acid wash solution, and the interface electron transfer resistance is 80-100 Ω·cm².

4. The pickling process for aluminum alloy profiles according to claim 1, characterized in that: Multi-stage membrane treatment includes ultrafiltration, reverse osmosis and electrodialysis treatment in sequence.

5. The pickling process for aluminum alloy profiles according to claim 1, characterized in that: The volume ratio of the primary pickling solution to the secondary pickling solution is 1.5:1-2:1, and the two-stage pickling tanks are isolated by gas-liquid isolation.

6. The pickling process for aluminum alloy profiles according to claim 1, characterized in that: The mass ratio of silane / graphene oxide / lithium molybdate is (60-65):(15-18):(20-22), and the thickness of the passivation film is 80-120 nm.

7. The aluminum alloy profile pickling process according to claim 1, characterized in that: In the pulse electrochemical oxidation regeneration of step 5, titanium-based Anode, frequency 80-120Hz, duty cycle 60-80% for regeneration.

8. The pickling process for aluminum alloy profiles according to claim 1, characterized in that: The engineering bacteria is Escherichia coli BL21 / pET28a-MsfA, which expresses MsfA protein to regulate the crystallization process.

9. The pickling process for aluminum alloy profiles according to claim 1, characterized in that: In step 3, the specific parameters of the forward / reverse current are: Forward current density 2-3A / dm², duration 30-40 seconds; Reverse current density 0.5-1A / dm², duration 10-15 seconds; Alternate cycles 8-12 times.

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