阅读说明：本技术 用于高硅压铸铝合金三价铬钝化的钝化液及钝化方法 (Passivation solution and passivation method for passivation of trivalent chromium of high-silicon die-casting aluminum alloy ) 是由 刘伦昌 张光波 于 2021-07-30 设计创作，主要内容包括：本发明属于金属表面处理技术领域,具体涉及用于高硅压铸铝合金三价铬钝化的钝化液,包括：硝酸铬3～10g/L、有机酸络合剂2～8g/L、多羟基醇络合剂1～6g/L、耐蚀剂1～3g/L、成膜促进剂1～3g/L。其钝化工艺是除油脱脂-热水洗-活化-水洗-钝化-水洗-热水洗-干燥。本方案加入耐蚀剂改善钝化膜耐蚀性能,提高高硅压铸铝合金的耐蚀性能。本方案的钝化液对压铸铝合金钝化后形成稍显淡兰色的薄膜,不改变压铸铝合金零件外观颜色；可以保证汽车轻量化零部件的防腐效果。(The invention belongs to the technical field of metal surface treatment, and particularly relates to a passivation solution for passivation of trivalent chromium in high-silicon die-casting aluminum alloy, which comprises the following components in percentage by weight: 3-10 g/L of chromium nitrate, 2-8 g/L of organic acid complexing agent, 1-6 g/L of polyhydroxy alcohol complexing agent, 1-3 g/L of corrosion inhibitor and 1-3 g/L of film forming promoter. The passivation process comprises degreasing, hot water washing, activation, water washing, passivation, water washing, hot water washing and drying. The corrosion resistance of the passive film is improved by adding the corrosion inhibitor, and the corrosion resistance of the high-silicon die-casting aluminum alloy is improved. The die-casting aluminum alloy passivation solution can form a slightly light blue film after the die-casting aluminum alloy is passivated, and the appearance color of a die-casting aluminum alloy part is not changed; the anti-corrosion effect of the light-weight parts of the automobile can be ensured.)

1. A passivation solution for passivation of trivalent chromium in high-silicon die-casting aluminum alloy comprises: 3-10 g/L of chromium nitrate, 2-8 g/L of organic acid complexing agent, 1-6 g/L of polyhydroxy alcohol complexing agent, 1-3 g/L of corrosion inhibitor and 1-3 g/L of film forming promoter.

2. The passivation solution for passivation of trivalent chromium in high-silicon die-cast aluminum alloy according to claim 1, characterized in that: the corrosion inhibitor is lanthanum nitrate, cerium nitrate or zirconium nitrate, and the content of the corrosion inhibitor is 1-3 g/L.

3. The passivation solution for passivation of trivalent chromium in high-silicon die-cast aluminum alloy according to claim 1, characterized in that: the organic acid complexing agent is malic acid, citric acid, malonic acid, oxalic acid or tartaric acid, and the content of the organic acid complexing agent is 2-8 g/L.

4. The passivation solution for passivation of trivalent chromium in high-silicon die-cast aluminum alloy according to claim 1, characterized in that: the polyhydric alcohol complexing agent is glycerol, ethylene glycol or butanediol, and the content of the polyhydric alcohol complexing agent is 1-6 g/L.

5. The passivation solution for passivation of trivalent chromium in high-silicon die-cast aluminum alloy according to claim 1, characterized in that: the film forming accelerant comprises an oxidation film forming accelerant and a corrosion-resistant film forming accelerant; the oxidation film-forming accelerant comprises nitrate, permanganate or molybdate; the corrosion-resistant film forming accelerant is nickel salt.

6. The preparation method of the passivation solution for passivation of trivalent chromium of the high-silicon die-casting aluminum alloy according to claim 1, comprising the following steps of: dissolving chromium nitrate in a proper amount of water according to a proportion, adding a corrosion inhibitor, adding an organic acid complexing agent, stirring and dissolving, adding polyhydroxy alcohol, stirring and dissolving, adding water to a constant volume, adding a film forming agent, stirring and dissolving, and standing to obtain a passivation solution.

7. The passivation solution passivation method for passivation of trivalent chromium in high-silicon die-cast aluminum alloy according to claim 1, comprising the following steps: the method comprises the following steps: degreasing, namely degreasing for 15-25 minutes at 50-70 ℃ by adopting 20-40 g/L of sodium silicate, 20-40 g/L of sodium phosphate and 3-5 ml/L of OP-10 emulsifier;

step two: washing with hot water at 50-70 deg.c;

step three: activating, namely reacting for 5-30 seconds at room temperature by adopting 5-10 ml/L of hydrofluoric acid;

step four: washing with water and deionized water for 20-30 s;

step five: passivating, namely passivating for 1-4 minutes at room temperature by adopting an organic acid complexing agent and a polyhydroxy alcohol complexing agent;

step six: washing with water and deionized water for 20-30 s;

step seven: washing with hot water at 50-70 deg.c;

step eight: and (3) drying, namely placing the passivated aluminum or aluminum alloy in a blast drying oven at the temperature of 70-90 ℃ for 5-10 min.

Technical Field

The invention belongs to the technical field of metal surface treatment, and particularly relates to a passivation solution and a passivation method for passivation of trivalent chromium of a high-silicon die-casting aluminum alloy.

Background

Cast aluminum alloy used on an automobile is not subjected to surface treatment and is extremely easy to corrode, and white corrosion points appear 2-4 hours after water is seen, so that anticorrosion treatment is needed. The hexavalent chromium passivation can better meet the requirement of corrosion resistance of the aluminum alloy. However, the european union and the united states have strictly limited the chemical substances for automobiles, and no matter the Rohs instruction of the european union or the law of the united states, the content of harmful substances in the finished automobiles and parts has been strictly limited, so that the application of hexavalent chromium in the surface treatment of the automobile parts has been prohibited, and the use of hexavalent chromium is prohibited in 2011 domestically.

Some foreign automobile companies establish good user public praise for improving the quality of products, and provide a public account with 'no wrench for automobiles within 5 years and no loss of functions of parts within 8 years'. Correspondingly, the standard of corrosion resistance of the aluminum alloy to parts is gradually improved, and the aluminum alloy is required to pass a neutral salt spray test for 240-480 hours without corrosion. On the other hand, in compliance with the requirements of continuous development, increasingly strict restrictions are imposed on some substances which are toxic, harmful and environmentally unfriendly. Such as hexavalent chromium, lead, mercury, etc., are banned or limited.

At present, when passivation treatment is carried out in the domestic metal surface treatment industry, high-concentration or medium-concentration chromate solution is generally adopted to carry out passivation on a plating layer so as to improve the corrosion resistance of the plating layer. But hexavalent chromium pollution generated by chromate causes serious harm to the environment and human health. The trivalent chromium has low toxicity and the characteristic similar to hexavalent chromium in many aspects, becomes a substitute of the hexavalent chromium, and along with the improvement of environmental protection requirements and the corrosion resistance requirements of automobiles on parts, the passivation of the trivalent chromium of the aluminum alloy becomes a better solution which can meet two conditions of the environmental protection requirements and the corrosion resistance.

The application number 201010533461.7 discloses a trivalent chromium natural color passivation solution for treating aluminum alloy, which comprises the following components in percentage by weight: 1-2 g/L of trivalent chromium salt, 0.05-0.1 g/L of zirconium salt, 0.01-0.03 g/L of NiSO 4.6H 2O 0.01, 0.4-0.8 g/L of film-forming agent, 0.3-0.6 g/L of trisodium citrate Na3C6H5O 7.2 2 H2O0.4-0.6 g/L and the balance of water; the passivation solution does not contain harmful substances such as hexavalent chromium, lead, mercury, cadmium, polybrominated diphenyl ether, polybrominated biphenyl and the like, can be recycled, and realizes clean production; can be passivated at normal temperature, and saves energy; the surface of the aluminum alloy treated by the trivalent chromium passivation solution is white and bright, the color is close to the natural color of the aluminum alloy, and the neutral salt spray corrosion performance of the film layer meets the national standard.

The application number 201010231687.1 discloses a trivalent chromium passivation concentrated solution, which comprises the following components in percentage by weight: 4-6% of chromium chloride, 8-12% of nitrate, 8-12% of cobalt salt or nickel salt, 3-5% of tartaric acid, 1-2% of gamma-aminopropyltriethoxysilane and the balance of water; the pH value of the concentrated solution is 2-3. The concentrated solution is prepared into working solution with the weight percentage concentration of 10 percent, and then the galvanized or galvanized alloy workpiece can be passivated. After the galvanized or zinc alloy workpiece is passivated by the concentrated solution, a uniform sky-blue protective film can be obtained on the surface of the galvanized layer or the zinc alloy layer, and the corrosion resistance can reach 120 hours without white rust in a salt spray test.

The silicon content has an influence on the wear resistance, corrosion resistance, linear expansion coefficient, density, conductivity and the like of the Al-Si binary alloy. The abrasion loss, the corrosion loss, the linear expansion coefficient, the density and the conductivity are all linearly reduced along with the increase of the silicon amount, and although the scheme has certain effect, the corrosion resistance can not be met under the condition of high corrosion resistance requirement of high-silicon die-cast aluminum, particularly aluminum alloy with silicon content of more than 10%.

Disclosure of Invention

The scheme provides the passivation solution and the passivation method for the passivation of the trivalent chromium of the high-silicon die-casting aluminum alloy, which have better corrosion resistance and lower cost.

In order to achieve the aim, the scheme provides a passivation solution for passivating trivalent chromium of a high-silicon die-casting aluminum alloy, which comprises the following components: 3-10 g/L of chromium nitrate, 2-8 g/L of organic acid complexing agent, 1-6 g/L of polyhydroxy alcohol complexing agent, 1-3 g/L of corrosion inhibitor and 1-3 g/L of film forming promoter.

The principle of the scheme is as follows: the technical scheme adopts the nitrate ions in the chromium nitrate as an oxidant to generate the oxidation effect and promote film formation, namely the film forming main salt and the oxidant are combined into a whole; the organic acid and the polyhydroxy alcohol are used in combination to achieve the purpose of being capable of being matched with Cr³⁺Complexing, and well adjusting the pH value to ensure that the pH value is stabilized in the working range of the passivation solution, and simultaneously forming a uniform passivation film; adding corrosion inhibitor to improve the corrosion resistance of the passive film and the corrosion resistance of the high-silicon die-casting aluminum alloy.

Further, the corrosion inhibitor is lanthanum nitrate, cerium nitrate or zirconium nitrate, and the content of the corrosion inhibitor is 1-3 g/L.

Further, the organic acid complexing agent is malic acid, citric acid, malonic acid, oxalic acid or tartaric acid, and the content of the organic acid complexing agent is 2-8 g/L.

Further, the polyhydric alcohol complexing agent is glycerol, ethylene glycol or butanediol, and the content of the polyhydric alcohol complexing agent is 1-6 g/L.

Further, the film forming accelerant comprises an oxidation film forming accelerant and a corrosion-resistant film forming accelerant; the oxidation film-forming accelerant comprises nitrate, permanganate or molybdate; the corrosion-resistant film forming accelerant is nickel salt. The oxidation film forming accelerant has certain oxidability, can activate the surface of the aluminum alloy substrate, and the corrosion-resistant film forming accelerant can be mixed in the passive film, so that the corrosion resistance of the film is improved, and the color and the appearance of the film are adjusted.

In order to achieve the aim, the invention also provides a preparation method of the passivation solution for passivating the trivalent chromium of the high-silicon die-casting aluminum alloy, which comprises the following steps: dissolving chromium nitrate in a proper amount of water according to a proportion, adding a corrosion inhibitor, adding an organic acid complexing agent, stirring and dissolving, adding polyhydroxy alcohol, stirring and dissolving, adding water to a constant volume, adding a film forming agent, stirring and dissolving, and standing to obtain a passivation solution.

In order to achieve the aim, the invention also provides a passivation method for trivalent chromium passivation of the high-silicon die-cast aluminum alloy, which comprises the following steps:

the method comprises the following steps: degreasing, namely degreasing for 15-25 minutes at 50-70 ℃ by adopting 20-40 g/L of sodium silicate, 20-40 g/L of sodium phosphate and 3-5 ml/L of OP-10 emulsifier;

step two: washing with hot water at 50-70 deg.c;

step three: activating, namely reacting for 5-30 seconds at room temperature by adopting 5-10 ml/L of hydrofluoric acid;

step four: washing with water and deionized water for 20-30 s;

step five: passivating, namely passivating for 1-4 minutes at room temperature by adopting an organic acid complexing agent and a polyhydroxy alcohol complexing agent;

step six: washing with water and deionized water for 20-30 s;

step seven: washing with hot water at 50-70 deg.c;

step eight: and (3) drying, namely placing the passivated aluminum or aluminum alloy in a blast drying oven at the temperature of 70-90 ℃ for 5-10 min. The invention has the beneficial effects that: 1. a slightly light blue film is formed after passivation, and the appearance color of the die-casting aluminum alloy part is not changed;

2. two kinds of complexing agents are used in combination, and an organic acid complexing agent Cr³⁺Complexing, regulating pH value to make it stable in the working range of passivating liquor, and using polyhydroxy alcohol complexing agent and Cr³⁺The complexation is stable so that a uniform passivation film is formed. The corrosion resistance is good and can be equivalent to hexavalent chromium passivation. The neutral salt spray test can reach over 240 hours;

3. safe, no toxic and forbidden substances; does not contain toxic substances such as hexavalent chromium, lead, mercury and the like, and is convenient for wastewater treatment;

4. the nickel salt accelerator is preferable, and can improve the corrosion resistance of the passive film and promote film formation.

The method is applied to surface anticorrosion treatment of cast aluminum parts, and the corrosion resistance of the aluminum alloy is obviously improved. The corrosion resistance of the aluminum alloy is over 200 hours after the application on an export product and the neutral salt spray test after the content of copper in the aluminum alloy is reduced. Because the aluminum alloy has small density and light weight, the application of the technology can ensure the anti-corrosion effect of the light-weight parts of the automobile.

Drawings

Fig. 1 is a schematic structural diagram of a passivation solution spraying device in embodiment 6 of the present invention.

FIG. 2 shows the surface morphology of the passivation film of the high silicon die-cast aluminum alloy of example 6 of the present invention.

FIG. 3 is a cross-sectional view of the passivation film of FIG. 2 in accordance with example 6 of the present invention.

Detailed Description

The following is further detailed by the specific embodiments:

reference numerals in the drawings of the specification include: the device comprises a rack 1, a processing table 2, a workpiece 3, a passivation liquid tank 4, a water tank 5, a flow control pipe 6, a first electric needle valve 7, a mixing pipe 8, a spray head 9, a humidity sensor 10, a zinc solution tank 11 and an air cooler 12.

Example 1:

the passivation solution for the passivation of the trivalent chromium of the high-silicon die-casting aluminum alloy comprises the following components: 3-10 g/L of chromium nitrate (8 g/L of chromium nitrate in the embodiment), 2-8 g/L of organic acid complexing agent (6 g/L of organic acid complexing agent in the embodiment), 1-6 g/L of polyhydroxy alcohol complexing agent (3 g/L of polyhydroxy alcohol complexing agent in the embodiment), 1-3 g/L of corrosion inhibitor (1 g/L of corrosion inhibitor in the embodiment), and 1-3 g/L of film forming accelerant (2 g/L of film forming accelerant in the embodiment).

The technical scheme adopts the nitrate ions in the chromium nitrate as an oxidant to generate the oxidation effect and promote film formation, namely the film forming main salt and the oxidant are combined into a whole; the organic acid and the polyhydroxy alcohol are used in combination to achieve the purpose of being capable of being matched with Cr³⁺Complexing, and well adjusting the pH value to ensure that the pH value is stabilized in the working range of the passivation solution, and simultaneously forming a uniform passivation film; adding corrosion inhibitor to improve the corrosion resistance of the passive film and the corrosion resistance of the high-silicon die-casting aluminum alloy.

The corrosion inhibitor is lanthanum nitrate, cerium nitrate or zirconium nitrate, and in this embodiment, the corrosion inhibitor is lanthanum nitrate.

The organic acid complexing agent is malic acid, citric acid, malonic acid, oxalic acid or tartaric acid, and in this embodiment, the organic acid complexing agent is oxalic acid.

The polyhydric alcohol complexing agent is glycerol, ethylene glycol or butanediol, and in this embodiment the polyhydric alcohol complexing agent is glycerol.

The film forming accelerant comprises an oxidation film forming accelerant and a corrosion-resistant film forming accelerant, and the oxidation film forming accelerant comprises nitrate, permanganate, molybdate and the like; the film forming promoter is nickel salt. The oxidation film forming accelerant has certain oxidability, can activate the surface of the aluminum alloy substrate, and the corrosion-resistant film forming accelerant can be mixed in the passive film, so that the corrosion resistance of the film is improved, and the color and the appearance of the film are adjusted.

The preparation method of the passivation solution for the passivation of the trivalent chromium of the high-silicon die-casting aluminum alloy comprises the following steps: dissolving chromium nitrate in a proper amount of water according to a proportion, adding a corrosion inhibitor, adding an organic acid complexing agent, stirring and dissolving, adding polyhydroxy alcohol, stirring and dissolving, adding water to a constant volume, adding a film forming agent, stirring and dissolving, and standing to obtain a passivation solution.

The passivation method for the passivation of the trivalent chromium of the high-silicon die-casting aluminum alloy comprises the following steps:

the method comprises the following steps: degreasing, namely degreasing for 15-25 minutes at 50-70 ℃ by adopting 20-40 g/L of sodium silicate, 20-40 g/L of sodium phosphate and 3-5 ml/L of OP-10 emulsifier;

step two: washing with hot water at 50-70 deg.c;

step three: activating, namely reacting for 5-30 seconds at room temperature by adopting 5-10 ml/L of hydrofluoric acid;

step four: washing with water and deionized water for 20-30 s;

step five: passivating, namely passivating for 1-4 minutes at room temperature by adopting an organic acid complexing agent and a polyhydroxy alcohol complexing agent;

step six: washing with water and deionized water for 20-30 s;

step seven: washing with hot water at 50-70 deg.c;

step eight: and (3) drying, namely placing the passivated aluminum or aluminum alloy in a blast drying oven at the temperature of 70-90 ℃ for 5-10 min.

Example 2: the difference between the example and the example 1 is that the chromium nitrate content is 8g/L, the lanthanum nitrate content is 3g/L, the zirconium nitrate content is 0g/L, the cerium nitrate content is 0g/L, and the other conditions are the same.

Example 3: the difference between the example and the example 1 is that the chromium nitrate content is 8g/L, the lanthanum nitrate content is 2g/L, the zirconium nitrate content is 0g/L, the cerium nitrate content is 0g/L, and the other conditions are the same.

Example 4: the difference between the example and the example 1 is that the chromium nitrate content is 8g/L, the lanthanum nitrate content is 0g/L, the zirconium nitrate content is 0g/L, the cerium nitrate content is 3g/L, and the other conditions are the same.

Example 5: the difference between the example and the example 1 is that the chromium nitrate content is 8g/L, the lanthanum nitrate content is 0g/L, the zirconium nitrate content is 3g/L, the cerium nitrate content is 0g/L, and the other conditions are the same.

Example 6: the difference between the embodiment and embodiment 1 is that a passivation solution spraying device is provided, as shown in fig. 1, specifically including: the device comprises a frame 1, a passivation liquid tank 4 and a water tank 5; a processing table 2 is welded on the rack 1, and a workpiece 3 is placed on the processing table 2. The welding has the support in frame 1, and the support is located processing platform 2 directly over, is equipped with two standing grooves on the support, and the standing groove is used for placing passivation liquid case 4 and water tank 5, and passivation liquid case 4 is filled there is the passivation stoste, when using, needs dilute the use to the passivation liquid stoste. Be equipped with the recess on the support, install flow control pipe 6 and hybrid tube 8 in the recess, flow control pipe 6 both ends communicate with passivation liquid case 4 and water tank 5 respectively, and flow control pipe 6 all is equipped with first electronic needle valve 7 with passivation liquid case 4 and water tank 5 intercommunication department, and first electronic needle valve 7 is used for controlling the volume of passivation liquid or water. Flow control pipe 6 horizontal installation is in the recess, and flow control pipe 6 is the V-arrangement, and mixing tube 8 is vertical to be installed in the recess, can make things convenient for passivation liquid and water to carry out intensive mixing at mixing tube 8, does not need the (mixing) shaft etc. to stir. The mixing pipe 8 is communicated with a spray head 9, and the spray head 9 is used for spraying diluted passivation solution to the workpiece 3. Humidity transducer 10 is installed to the bolt on the frame 1, specifically adopts ancorui WHD48-11 temperature and humidity sensor, and the bolt is installed the PLC controller on the frame 1, and specific PLC controller adopts stm32f103c8t 6's singlechip, and PLC controller and humidity transducer 10 are all connected with first electronic needle valve 7 electricity. The humidity sensor 10 is used for detecting the environment humidity, the humidity sensor 10 enables the PLC to control the first electric needle valve 7, when the humidity sensor 10 detects that the environment humidity is smaller than a set value, the environment is dry at the moment, the PLC controls the first electric needle valve 7 to enlarge the cross section area, the passing water flow is enlarged, the dilution degree of passivation liquid is changed, the water content in mist liquid medicine is increased, and the liquid medicine is prevented from becoming a semi-solid effect when contacting the workpiece 3 by changing the water content in the water mist; when the humidity sensor 10 detects that the environmental humidity is greater than a set value, the environment is relatively wet at the moment, the PLC controller controls the first electric needle valve 7 to reduce the cross-sectional area, so that the passing water flow is reduced, the dilution degree of the passivation solution is changed, the water content in the vaporific liquid medicine is reduced, the waste liquid amount is reduced, and the work load of recycling the waste liquid is reduced.

The zinc solution tank 11 is arranged on the rack 1, the zinc solution tank 11 is communicated with the flow control pipe 6, a second electric needle valve is arranged at the communication position of the zinc solution tank 11 and the flow control pipe 6, and the second electric needle valve is electrically connected with the PLC. A timer is arranged on the rack 1, and the PLC is electrically connected with the timer. The device also comprises an image recognition module, wherein the image recognition module is used for acquiring and recognizing the high-silicon die-casting aluminum alloy information and sending an adding signal to the PLC; the PLC receives the adding information and is used for controlling the opening of the timer and adjusting the second electric needle valve to add the zinc solution into the flow control pipe 6 according to the data of the timer, and the PLC controls the timer to be reset after the second electric needle valve is opened for set time and opens the air cooler 12 to dry the passivated high-silicon die-cast aluminum alloy.

The zinc solution tank 11 is arranged in a groove on the support, and the groove is used for limiting the zinc solution tank 11. The zinc solution is zinc oxide solution, and zinc solution tank 11 bottom is equipped with the export, and the exit intercommunication has the interpolation pipeline, adds the other one end of pipeline and flow control pipe 6 intercommunication, and the electronic needle valve of second of control zinc solution tank 11 is located zinc solution tank 11's opening part, prevents when not needing the interpolation zinc solution, and zinc solution remains in adding the pipeline, influences the zinc solution effect. The timer is mounted on the frame 1 by bolts, and specifically adopts an HH series time controller, and the specification is HH4-4 RN. The air cooler 12 is of the specific type HAG-P30A-43. The image acquisition and identification module comprises a camera, adopts a HIKVISION network camera, the image acquisition and identification module acquires a picture of the high-silicon die-cast aluminum alloy, judges whether the high-silicon die-cast aluminum alloy exists on the processing table 2 according to the stored picture of the high-silicon die-cast aluminum alloy and then sends information whether the zinc solution is added to the PLC controller, the PLC controller controls the opening of the timer according to the information of the image acquisition and identification module, and adjusting the second electric needle valve according to the timer data to add zinc solution into the flow control pipe 6, the PLC controller closes the second electric needle valve after opening the second electric needle valve controlling the zinc solution tank 11 for a set time 50S, and controlling a timer to reset and opening an air cooler 12 to dry the passivated high-silicon die-cast aluminum alloy, wherein the distance between the air cooler 12 and the high-silicon die-cast aluminum alloy is 20cm-30cm, and the cold air of the air cooler 12 is controlled at 10-15 ℃.

After the zinc-containing solution is added into the high-silicon die-casting aluminum alloy passive film in the passivation stage, the surface of the passive film is shown in figure 2, and criss-cross micro cracks are randomly distributed on the surface of the film layer, the specific reason is that the passivation stage can be basically divided into four stages, the dissolution of the aluminum alloy surface layer, the rapid growth of the film layer, the slow growth of the film layer and the growth and dissolution balance of the film layer, after the zinc oxide is added, because the metal activity of the zinc and the aluminum is similar, and the hydroxide properties of the zinc and the aluminum are also similar, in the rapid growth stage of the film layer, zinc and aluminum and respective hydroxides/oxides can form (inner film of) a passive film on the surface of a workpiece, the stability of the passive film at the stage can be ensured, after the zinc is consumed, the surface of (the outer film of) the passivation film forms criss-cross micro-cracks due to the change of the composition of the passivation film and the accumulation of internal stress; if the zinc-containing solution is not added in the passivation stage, microcracks formed on the surface of the film layer of the passivation film are less, and the subsequent painting treatment is inconvenient (namely, the film layer of the passivation film and the film layer of the paint film are not compact, and serious quality problems such as delamination and separation are easy to occur under severe use environments, such as sudden temperature change and the like).

This embodiment is after the passive film passivation (50S), dry rapidly, because the internal stress of the rete of the passive film that just forms still exists, the rete can produce tiny deformation (small shrink promptly) after being heated, adopt cold wind to carry out the rete drying, cold wind can remove the rete surface moisture, the rete is by cold contraction simultaneously, this kind of deformation (or shrink) can make the preceding depth increase of the microcrack that produces at passive film rete surface (promote the bonding strength of follow-up paint film and passive film), form this kind of crackle surface morphology, as shown in figure 3. Fig. 3 is a cross section of the passivation film shown in fig. 2, and it can be seen from fig. 3 that the inner layer structure of the passivation film is dense and has no cracking phenomenon, which indicates that microcracks exist only on the surface of the film layer and do not penetrate through the whole passivation film (ensuring the functionality of the passivation film). Therefore, even if a large number of cracks are present on the surface of the passivation film, the passivation film is intact, and the corrosion resistance thereof is not deteriorated by the presence of cracks.

Adding zinc solution into the silicon die-casting aluminum alloy passivation film in the passivation stage to ensure that zinc promotes the film forming reaction of the passivation film, and H⁺Is greatly consumed, and makes OH on a reaction interface in the passivation process of the high-silicon die-casting aluminum alloy^-The concentration is increased, a plurality of hydroxides are deposited on the surface of the zinc layer to form a passive film, partial hydroxides are dehydrated to form oxides in the drying process of the film layer, so that the components in the outer passive film are distributed more uniformly, the hydroxide content is higher, the structure of the film layer is more compact, the film layer can play a good role of a barrier layer, the corrosion resistance of the high-silicon die-casting aluminum alloy is effectively improved, and meanwhile, an air cooler 12 20-30 cm away from a workpiece blows air at 10-15 ℃ to expand microcracks formed on the surface of the passive film, improve the binding force between the passive film and a paint film and improve the corrosion resistance of the high-silicon die-casting aluminum alloy.

Comparative example 1: the difference between the comparative example 1 and the example 1 is that the chromium nitrate content is 8g/L, the lanthanum nitrate content is 0g/L, the zirconium nitrate content is 0g/L, the cerium nitrate content is 0g/L, and the other conditions are the same.

For the purpose of visual comparison, the components and contents of the passivation solutions of examples 1-5 and comparative example 1 are tabulated and shown in Table 1:

serial number	Chromium nitrate (g/L)	Cerium nitrate (g/L)	Zirconium nitrate (g/L)	Lanthanum nitrate (g/L)	Nickel nitrate (g/L)	Oxalic acid (g/L)	Glycerol (g/L)
								Example 1	8	0	0	1	2	6	3
Example 2	8	0	0	3	2	6	3
								Example 3	8	0	0	2	2	6	3
Example 4	8	3	0	0	2	6	3
								Example 5	8	0	3	0	2	6	3
Comparative example 1	8	0	0	0	2	6	3

Workpieces with the same size are passivated by the passivation solution prepared in all the examples and the comparative examples through the same treatment method, and the time required for the workpieces to reach the same corrosion area is tested according to the method of standard GB/T10125-1997 artificial atmosphere corrosion test-salt spray test. The test results are shown in table 2:

according to comparative example 1, example 4 and example 5, the corrosion resistance of the workpiece treated by the passivation solution prepared by respectively adding lanthanum nitrate, zirconium nitrate and cerium nitrate is obviously improved, and the corrosion resistance of the workpiece treated by the passivation solution without adding the three substances is the lowest. Lanthanum nitrate, zirconium nitrate and cerium nitrate can promote the improvement of the corrosion resistance of the passive film, wherein the corrosion resistance effect of lanthanum nitrate is optimal.

According to the embodiment 1, the embodiment 2 and the embodiment 3, the prepared passivation solution can be used for treating workpieces with optimal corrosion resistance when the lanthanum nitrate content is 3 g/L.

The invention forms a slightly light blue film after passivation, and does not change the appearance color of the die-casting aluminum alloy part; two kinds of complexing agents are used in combination, and an organic acid complexing agent Cr³⁺Complexing, regulating pH value to make it stable in the working range of passivating liquor, and using polyhydroxy alcohol complexing agent and Cr³⁺The complexation is stable so that a uniform passivation film is formed. The corrosion resistance is good and can be equivalent to hexavalent chromium passivation. The neutral salt spray test can reach over 240 hours; safe, no toxic and forbidden substances; does not contain toxic substances such as hexavalent chromium, lead, mercury and the like, and is convenient for wastewater treatment; the nickel salt promoter is preferred, so that the corrosion resistance of the passive film can be improved, and the film formation can be promoted; the method is applied to surface anticorrosion treatment of cast aluminum parts, and the corrosion resistance of the aluminum alloy is obviously improved. The corrosion resistance of the aluminum alloy is over 200 hours after the application on an export product and the neutral salt spray test after the content of copper in the aluminum alloy is reduced. Due to the fact that the aluminum alloy is small in density and light in weight, the application of the technology can guarantee the anti-corrosion effect of the light-weight automobile parts; compared with foreign aluminum alloy trivalent chromium passivation solution under the same conditions, the price is reduced, and the production cost is greatly reduced.

The foregoing is merely an example of the present invention and common general knowledge of known specific structures and features of the embodiments is not described herein in any greater detail. It should be noted that, for those skilled in the art, without departing from the structure of the present invention, several changes and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent. The scope of the claims of the present application shall be determined by the contents of the claims, and the description of the embodiments and the like in the specification shall be used to explain the contents of the claims.