TWI606143B - Chemical conversion coating and method of fabricating the same - Google Patents

Description

Chemical film and method of manufacturing same

The present invention relates to a surface treatment of a magnesium alloy, and more particularly to a chemical conversion film and a method of manufacturing the same.

Magnesium alloys have many advantages, such as light weight, ease of processing, high strength, protection against electromagnetic interference, and recycling. In recent years, in industrial designs such as 3C products, magnesium alloys have been widely used as outer casings of electronic products such as notebook computers and mobile phones due to demands for light weight and texture design.

However, since magnesium alloys have poor corrosion resistance to corrosive agents from the outside, they are considerably limited in development and application. Therefore, how to improve the corrosion resistance of a magnesium alloy substrate is an important issue in the current technology.

The present invention provides a chemical conversion film having good corrosion resistance and a method for producing the same.

An embodiment of the present invention provides a chemical conversion film disposed on a surface of a magnesium alloy substrate. The chemical conversion film contains manganese, magnesium, oxygen and strontium, wherein the content of manganese in the chemical conversion film is between 10 atom% and 20 atom%, and the content of bismuth in the chemical conversion film is between 5 atom% and 10 atom%. .

In an embodiment of the invention, the thickness of the chemical conversion film is between 600 nm and 800 nm.

In an embodiment of the invention, the content of magnesium in the chemical conversion film is between 15 atomic % and 25 atomic %.

In an embodiment of the invention, the oxygen content of the chemical conversion film is between 50 atomic % and 70 atomic %.

In an embodiment of the invention, the material for forming the film comprises MnO ₂ , MgO and cerium oxide.

In an embodiment of the invention, the material of the magnesium alloy substrate comprises a magnesium lithium zinc alloy, a magnesium aluminum manganese alloy or a magnesium aluminum zinc alloy.

Another embodiment of the present invention provides a method of manufacturing a chemical film comprising the following steps. The inorganic acidification liquid is provided, and the inorganic acidification liquid comprises a permanganate, a pH adjusting agent and a cerium salt, wherein the pH of the inorganic acidifying liquid is between 1 and 2.5. Forming a magnesium alloy substrate by inorganic acidification to form a film on the surface of the magnesium alloy substrate, wherein the concentration of permanganate in the inorganic acidification liquid is between 0.05 M and 0.15 M, And the concentration of the cerium salt in the inorganic acidification liquid is between 0.005 M and 0.05 M.

In an embodiment of the invention, the permanganate comprises KMnO ₄ .

In an embodiment of the invention, the cerium-containing nitrate comprises Ce(NO ₃ ) ₃ .

In an embodiment of the invention, the pH adjusting agent comprises H ₂ SO ₄ and the concentration of H ₂ SO ₄ in the inorganic acidifying solution ranges from 0.005 M to 0.1 M.

In an embodiment of the invention, the pH of the inorganic acidification liquid is between 1 and 2.

In an embodiment of the invention, the processing time of the chemical conversion process is between 10 seconds and 90 seconds.

In an embodiment of the invention, the processing temperature of the chemical conversion process is between 20 ° C and 40 ° C.

In an embodiment of the invention, the thickness of the chemical conversion film is between 600 nm and 800 nm.

In an embodiment of the invention, the material of the magnesium alloy substrate comprises a magnesium lithium zinc alloy, a magnesium aluminum manganese alloy or a magnesium aluminum zinc alloy.

In an embodiment of the invention, the inorganic acidifying liquid further comprises a stabilizer.

In an embodiment of the invention, the concentration of the stabilizer in the inorganic acidifying liquid ranges from 0.01 M to 0.05 M.

In an embodiment of the invention, the stabilizer comprises potassium pyrophosphate (K ₄ P ₂ O ₇ ).

Based on the above, in the method for producing a chemical film according to an embodiment of the present invention, since the inorganic acidification liquid having a pH between 1 and 2.5 includes permanganate and strontium salt, and inorganic acidification into a liquid The permanganate concentration is between 0.05 M and 0.15 M, and the concentration of the cerium salt in the inorganic acidification liquid is between 0.005 M and 0.05 M. Therefore, when the magnesium alloy substrate is chemically processed, it can be quickly A chemical film having good corrosion resistance, self-repairing ability, and light weight demand is formed on the surface of the magnesium alloy substrate.

The above described features and advantages of the invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing a method of manufacturing a film into a film according to an embodiment of the present invention. 2 is a schematic cross-sectional view of a chemical conversion film in accordance with an embodiment of the present invention.

Referring to FIG. 1 and FIG. 2 simultaneously, the manufacturing method of the chemical conversion film 110 includes a pre-processing step 200, a chemical conversion processing step 210, and a post-processing step 220 which are sequentially performed.

First, in the pre-treatment step 200, the dirt and native oxide on the surface of the magnesium alloy substrate 100 are removed. The above method of removing the dirt and the native oxide on the surface of the magnesium alloy substrate 100 is, for example, an alkali washing treatment, a pickling treatment, a deionized water cleaning treatment, a grinding treatment, or a combination thereof. In some embodiments, the magnesium alloy substrate 100 can be a magnesium lithium zinc alloy, a magnesium aluminum manganese alloy, or a magnesium aluminum zinc alloy. For example, a magnesium lithium zinc alloy is LZ91 having a duplex alloy structure, which may be composed of 89% magnesium, 9% lithium, 1% Zn, and 1% other metal additives. The magnesium aluminum manganese alloy may be AM30 having a single phase alloy structure. The magnesium aluminum zinc alloy may be AZ31 having a single phase alloy structure. In particular, the LZ91 described above can be widely used in industrial design products requiring high texture, such as a mobile phone casing, because of its good formability.

In some embodiments, since the pH of the inorganic acidification liquid used in the subsequent chemical conversion treatment step 210 is between 1 and 2.5, the native oxide or dirt on the surface of the magnesium alloy substrate 100 can be The inorganic acidification liquid is removed, so that the above pretreatment step 200 can be selectively omitted. In other embodiments, since the pH of the inorganic acidification liquid used in the subsequent chemical conversion treatment step 210 is between 1 and 2.5, the pickling in the pretreatment step 200 described above may also be selectively omitted. The process, for example, the magnesium alloy substrate 100 is subjected to a grinding treatment (grinding with a sandpaper of 400 to 1200), and then rinsed with deionized water to complete the pretreatment step 200.

Next, in the chemical conversion processing step 210, the magnesium alloy substrate 100 is subjected to a chemical conversion treatment with an inorganic acidification liquid to form a chemical conversion film 110 on the surface of the magnesium alloy substrate 100. The operation time of the formation processing step 210 is between 10 seconds and 90 seconds. In some embodiments, the operational time of the chemical processing step 210 is between 40 seconds and 60 seconds. The operating temperature of the chemical conversion process step 210 is between 20 ° C and 40 ° C. In some embodiments, the processing temperature of the chemical processing step 210 is 25 °C. It is worth mentioning that there is an unavoidable surface film 102 between the chemical conversion film 110 and the magnesium alloy substrate 100, which is a film layer having a large content of magnesium hydroxide (Mg(OH) ₂ ). If the rate at which the chemical conversion film 110 is formed on the surface of the magnesium alloy substrate 100 is too slow, the thickness of the surface film 102 is too thick, resulting in a decrease in adhesion between the chemical conversion film 110 and the magnesium alloy substrate 100.

The inorganic acidification liquid includes permanganate, a pH adjuster, and a phosphonium salt. In some embodiments, the permanganate is, for example, KMnO ₄ . The onium salt is, for example, Ce(NO ₃ ) ₃ . In the present embodiment, the pH adjusting agent is, for example, H ₂ SO _{4 having} a concentration of between 0.005 M and 0.1 M, but the invention is not limited thereto. The pH of the inorganic acidification solution is between 1 and 2.5. The concentration of permanganate in the inorganic acidification liquid is between 0.05 M and 0.15 M, and the concentration of the bismuth salt selected from the inorganic acidification liquid is between 0.005 M and 0.05 M. In this way, the chemical conversion film 110 formed by the above inorganic acidification liquid formation not only has sufficient density and thickness (for example, between 600 nm and 800 nm) to protect the surface of the magnesium alloy substrate 100 from the outside. The corrosive agent (for example, various acid liquids or air) is corroded, and the overall chemical reaction rate can be promoted by the action of the Guyard reaction to accelerate the rate at which the film 110 is formed on the surface of the magnesium alloy substrate 100. Not only the operation time of the chemical conversion processing step 210 is shortened (for example, from 10 minutes to 20 minutes to less than 2 minutes), but the thickness of the surface film 102 is lowered, thereby improving the adhesion between the chemical conversion film 110 and the magnesium alloy substrate 100. force. In addition, since the rate at which the chemical conversion film 110 is formed on the surface of the magnesium alloy substrate 100 is extremely fast (the operation time is, for example, between 40 seconds and 60 seconds), the reduction of the magnesium alloy substrate 100 (for example, LZ91 magnesium lithium alloy) can be reduced. The low potential is affected by the two-phase effect, and the problem of uniformity of thickness of the film 110 and poor integrity of the coating is avoided. In addition, since the chemical conversion film 110 contains bismuth, when it is damaged by external force damage, the damaged portion can be self-repaired to prevent the external etchant from corroding the magnesium alloy substrate 100 from the damaged portion. More specifically, when the corrosion factor (corrosive agent) corrodes the bare magnesium alloy substrate 100 from the damaged portion thereof, the tetravalent cerium ion (Ce ⁴⁺ ) in the chemical conversion film 110 is reduced to the cerium oxide to form a new one. The passivation film is removed to prevent the external etchant from corroding the magnesium alloy substrate 100 from the breakage. That is to say, the chemical conversion film 110 containing ruthenium has the ability to repair itself.

In some embodiments, the pH of the inorganic acidified liquid can also be adjusted to a pH between 1 and 2 to further enhance the thickness uniformity and coating integrity of the chemical film 110.

In addition, in some embodiments, in order to enhance the stability of the inorganic acidification liquid, a stabilizer may be added to the inorganic acidification liquid to prolong the shelf life of the inorganic acidification liquid. The stabilizer is, for example, potassium pyrophosphate (K ₄ P ₂ O ₇ ). The concentration of the stabilizer in the inorganic acidification liquid is, for example, between 0.01 M and 0.05 M. In some embodiments, potassium pyrophosphate is added to the inorganic acidification liquid, and the magnesium alloy substrate 100 is chemically treated in the same operation time, and the thickness of the chemical conversion film 110 formed on the magnesium alloy substrate 100 is 300 nm to 500 nm.

Thereafter, in a post-treatment step 220, the surface of the magnesium alloy substrate can be washed with deionized water and subjected to a drying treatment.

Referring to FIG. 1 again, the chemical conversion film 110 is disposed on the surface of the magnesium alloy substrate 100 as a protective layer of the magnesium alloy substrate 100. In the present embodiment, the chemical conversion film 110 has a single layer structure, but the invention is not limited thereto. In some embodiments, the chemical conversion film 110 contains manganese, magnesium, oxygen, and antimony, wherein the content of manganese in the film 110 is between 10 atom% and 20 atom%. The content of ruthenium in the chemical conversion film 110 is between 5 atom% and 10 atom%. The content of magnesium in the chemical conversion film 110 is, for example, between 15 atom% and 25 atom%. The content of oxygen in the chemical conversion film 110 is, for example, between 50 atom% and 70 atom%. For example, the material of the formation film 110 may be MnO ₂ , MgO, and cerium oxide, and the thickness thereof is between 600 nm and 800 nm. In this way, the chemical conversion film 110 not only has sufficient density and thickness to protect the surface of the magnesium alloy substrate 100 from corrosion by external corrosive agents (for example, various acid liquids or air), but also has good electrical conductivity and adhesion. It is placed on the magnesium alloy substrate 100 to meet the demand for weight reduction.

Hereinafter, the production method of the chemical conversion film of the present invention and the evaluation of the properties of the chemical conversion film will be further explained by the respective experimental examples and comparative examples. Although the following experimental examples are described, the materials used, the amounts and ratios thereof, the processing details, the processing flow, and the like can be appropriately changed without departing from the scope of the invention. Therefore, the invention should not be construed restrictively by the examples described below.

Experiment 1

The magnesium alloy substrate used in Experimental Example A1 to Experimental Example A5 and Comparative Example B1, the chemical conversion treatment operation temperature, the operation time of the chemical conversion treatment, the formulation of the inorganic acidification liquid, and the pH of the inorganic acidification liquid were as follows.

Magnesium alloy substrate: LZ91

Processing temperature for chemical processing: 25 °C

The processing time of the chemical processing: as shown in Table 1.

Formulation of inorganic acidification liquid: as shown in Table 1.

pH value of inorganic acidification liquid: as shown in Table 1.

Chemical solution of Comparative Example B1: commercial hexavalent chromium forming solution (K ₂ Cr ₂ O ₇ ) of model DOW 1 <Adhesion evaluation>

Each of the chemical conversion films (Experimental Examples A1 to A5 and Comparative Example B1) in Table 1 was subjected to a hundred-square test according to the item specified in ASTM D3359-02. After the test, the adhesion grade of the film was evaluated in accordance with the specifications of ASTM D3359-02, and the results are shown in Table 1 below. According to the specification of ASTM D3359-02, the adhesion grade is divided into 0B to 5B, and the higher the number, the better the adhesion, and the highest level is 5B. In detail, level 0B indicates that the shedding area is greater than 65%. Level 1B indicates that the shedding area is 35% to 65%. Level 2B indicates a shedding area of 15% to 35%. Grade 3B indicates a shedding area of 5% to 15%. Grade 4B indicates that the shedding area is less than 5%. Level 5B means that there is no shedding at all. <Anti-corrosion evaluation>

Each of the chemical conversion films (Experimental Examples A1 to A5 and Comparative Example B1) in Table 1 was subjected to a salt spray test for 72 hours using an aqueous solution of sodium chloride having a concentration of 5% by weight according to the item specified in ASTM B117. After the salt spray test, each of the chemical conversion films was evaluated for corrosion resistance of the film according to the specifications of ASTM D610-08, and the experimental results are shown in Table 1 below. According to the specification of ASTM D610-08, the corrosion resistance grade is divided into 0 to 10, and the higher the number, the better the corrosion resistance.

Table 1  <TABLE border="1" borderColor="#000000" width="85%"><TBODY><tr><td> No.</td><td> Composition of inorganic acidification liquid</td><td> Magnesium alloy substrate </td><td> pH value </td><td> operation time </td><td> operation temperature </td><td> thickness (nm) </td><td> adhesion Sex level </td><td> salt spray time </td><td> corrosion resistance grade </td></tr><tr><td> experimental example </td><td> A1 </td ><td> 1. KMnO₄:0.05 M 2. Ce(NO₃)₃:0.005 M 3. H₂SO₄(96%): 0.75 ml/L </td><td> LZ91 </td><td> 1.43 </td><td> 30 seconds</td ><td> 25°C </td><td> 700 </td><td> 5B </td><td> 72 hours</td><td> 3 </td></tr><tr> <td> A2 </td><td> 1. KMnO₄:0.075 M 2. Ce(NO₃)₃:0.01 M 3. H₂SO_{4</96> (96%): 0.25 ml/L </td><td> 1.25 </td><td> 45 seconds</td> <td> 700 </td><td> 5B </td><td> 4 </td></tr><tr><td> A3 </td><td> 1. KMnO_{4< /sub>:0.15 M 2. Ce(NO₃)₃:0.03 M 3. H₂SO₄ >(96%): 0.5 ml/L </td><td> 1.02 </td><td> 3 0 seconds</td><td> 600 </td><td> 5B </td><td> 4 </td></tr><tr><td> A4 </td><td> 1. KMnO₄: 0.01 M 2. Ce(NO₃)₃: 0.02 M 3. H₂SO< Sub>4}(96%):0.5 ml/L </td><td> 1.60 </td><td> 60 seconds</td><td> 650 </td><td> 5B < /td><td> 4 </td></tr><tr><td> A5 </td><td> 1. KMnO₄: 0.125 M 2. Ce(NO<sub >3})₃: 0.02 M 3. H₂SO₄(96%): 1.0 ml/L 4. K ₄P₂O₇: 0.02 M </td><td> 1.4 </td><td> 30 seconds</td> <td> 400 </td><td> 5B </td><td> 3 </td></tr><tr><td> Comparative Example </td><td> B1 </td><td > 1. K₂Cr₂O₇:0.687 M 2. HNO₃: 5.88 M </td ><td> -0.48 </td><td> 60 </td><td> 120 </td><td> 5B </td><td> 1 </td></tr></TBODY> </TABLE>

As can be seen from Table 1, the chemical conversion film of the experimental examples A1 and A5 had a corrosion resistance rating of 3 (i.e., the corrosion area was more than 10% and less than 16%). The chemical conversion films of Experimental Examples A2 to A4 all had a corrosion resistance level of 4 or more (that is, a corrosion area of more than 3% and less than 10%). Comparative Example B1 had a corrosion resistance rating of 1 (i.e., the corrosion area was greater than 33% and to less than 50%). This result shows that the corrosion resistance of Experimental Examples A1 to A5 is superior to that of Comparative Example B1, and is in line with the demand for general industrial use.

Further, as is clear from Table 1, the adhesion levels of the chemical conversion films of Experimental Examples A1 to A5 and Comparative Example B1 were 5B (that is, the case where no peeling occurred at all), which was in line with the demand for general industrial use.

Experiment 2 <Anti-corrosion evaluation>

3A to 3C are surface appearance views of a magnesium alloy substrate after a salt spray test at different times.

According to the project specified in ASTM B117, the magnesium alloy substrate was subjected to a salt spray test at different times using a sodium chloride aqueous solution having a concentration of 5% by weight, wherein the duration of the salt spray test was exemplified by 0 hours, 2 hours, and 12 hours. The description is made, but the invention is not limited thereto. 3A, 3B, and 3C are surface appearance views of the magnesium alloy substrate after a salt spray test for 0 hours, 2 hours, and 12 hours, respectively. It can be seen from Fig. 3A to Fig. 3C that after 2 hours of salt spray test, some magnesium alloy substrate surface has obvious corrosion phenomenon, and the corrosion phenomenon is further increased after the duration of the salt spray test is increased to 12 hours. Obviously, the surface of almost all magnesium alloy substrates is covered with corrosion products, and it is apparent that the magnesium alloy substrate 100 (for example, LZ91) has poor corrosion resistance. From this, it can be seen that in the case where no protective film is formed on the surface of the magnesium alloy substrate, the surface thereof is easily corroded by the external corrosive agent.

4A to 4D are surface appearance views of a chemical film formed by a salt spray test at different times according to an embodiment of the present invention.

According to the item specified in ASTM B117, the salt spray test of Experimental Example A4 was carried out at different times using a 5 wt% aqueous solution of sodium chloride, wherein the duration of the salt spray test was 0 hours, 24 hours, 48 hours, and 72 hours. The description is made by way of example, but the invention is not limited thereto. 4A, 4B, 4C, and 4D are surface appearance views of Experimental Example A4 after a salt spray test at 0 hours, 24 hours, 48 hours, and 72 hours. 4A to 4D, after the 72 hour salt spray test of Experimental Example A4 (as shown in FIG. 4D), the surface appearance of the magnesium alloy substrate was substantially the same as that before the salt spray test (as shown in FIG. 4A). )the same. From this, it is understood that the chemical conversion film of Experimental Example A4 can effectively protect the magnesium alloy substrate located thereunder, so that the surface of the magnesium alloy substrate is less susceptible to corrosion by external corrosive agents.

5A to 5D are surface appearance views of the chemical conversion film of Comparative Example B1 formed on the surface of the magnesium alloy substrate after salt spray test at different times.

According to the item specified in ASTM B117, Comparative Example B1 was subjected to a salt spray test at different times using a 5% strength by weight aqueous solution of sodium chloride, wherein the duration of the salt spray test was 0 hours, 24 hours, 48 hours, and 72 hours. The description is made by way of example, but the invention is not limited thereto. 5A, 5B, 5C, and 5D are surface appearance views of Comparative Example B1 after a salt spray test of 0 hours, 24 hours, 48 hours, and 72 hours, respectively. 5A to 5D, after 24 hours of salt spray test (as shown in Fig. 5B), some magnesium alloy substrate surface showed obvious corrosion phenomenon, and increased to 48 hours with the duration of the salt spray test. (as shown in Fig. 5C) or 72 hours (as shown in Fig. 5D), the corrosion phenomenon is more pronounced, and the surface of almost all the magnesium alloy substrates is covered with corrosion products, and it is apparent that the corrosion resistance of Comparative Example B1 is poor, so that magnesium The surface of the alloy substrate is susceptible to corrosion by external corrosive agents.

experiment 3

<thickness analysis>

Figure 6 is a cross-sectional view of a chemical conversion film under a transmission electron microscope (TEM) according to an embodiment of the present invention. The thickness analysis of Experimental Example A4 was carried out by TEM. As is apparent from Fig. 6, the chemical conversion film 110 has a single layer structure and its thickness is about 650 nm.

experiment 4

<Evaluation of surface cross-section corrosion resistance>

7A to 7D are surface appearance views of a film obtained by transversely cutting a surface of a film after performing a salt spray test at different times according to an embodiment of the present invention.

First, the surface of Experimental Example A4 was cross-cut with a sharp instrument, thereby destroying the chemical conversion film of Experimental Example A4, so that a significant cross cut was observed on the surface of Experimental Example A4 (as shown in Figs. 5A to 5D). Next, according to the item specified in ASTM B117, the cross-cut Experimental Example A4 was subjected to a salt spray test at different times using a sodium chloride aqueous solution having a concentration of 5% by weight, wherein the duration of the salt spray test was 0 hours, 24 hours. Hour, 48 hours, and 72 hours are described as examples, but the invention is not limited thereto. 7A, 7B, 7C, and 7D are surface appearance views of the experimental example A4 after a salt spray test at 0 hours, 24 hours, 48 hours, and 72 hours. 7A to 7D, after the 72 hour salt spray test of Experimental Example A4 (as shown in FIG. 7D), the surface appearance of the magnesium alloy substrate was substantially the same as that before the salt spray test (as shown in FIG. 7A). )the same. From this, it is understood that the chemical conversion film of Experimental Example A4 can not only protect the surface of the magnesium alloy substrate located thereunder from the corrosion of the external corrosive agent, and the chemical conversion film of Experimental Example A4 also has the ability to self-repair, and therefore, when it is subjected to When the damage of external force is damaged, the external corrosive agent can be prevented from corroding the magnesium alloy substrate from the damaged portion (such as the cross cut).

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

100‧‧‧Magnesium alloy substrate 102‧‧‧Surface film 110‧‧‧Chemical film 200‧‧‧Pre-processing steps 210‧‧‧Chemical processing steps 220‧‧‧post processing steps

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing a method of manufacturing a film into a film according to an embodiment of the present invention. 2 is a schematic cross-sectional view of a chemical conversion film in accordance with an embodiment of the present invention. 3A to 3C are surface appearance views of a magnesium alloy substrate after a salt spray test at different times. 4A to 4D are surface appearance views of a chemical conversion film formed on the surface of a magnesium alloy substrate after a salt spray test at different times according to an embodiment of the present invention. 5A to 5D are surface appearance views of the chemical conversion film of the comparative example formed on the surface of the magnesium alloy substrate after salt spray test at different times. Figure 6 is a cross-sectional view of a chemical conversion film under a transmission electron microscope (TEM) according to an embodiment of the present invention. 7A to 7D are surface appearance views of a chemical film formed by cross-cutting a surface after performing a salt spray test at different times according to an embodiment of the present invention.

100‧‧‧Magnesium alloy substrate

102‧‧‧Surface film

110‧‧‧Chemical film

Claims (18)

a chemical conversion film disposed on a surface of a magnesium alloy substrate, wherein the chemical conversion film contains manganese, magnesium, oxygen, and cerium, wherein a content of manganese in the chemical conversion film is between 10 atom% and 20 atom%, and The content of ruthenium in the chemical conversion film is between 5 atom% and 10 atom%. The chemical conversion film according to claim 1, wherein the chemical conversion film has a thickness of between 600 nm and 800 nm. The chemical conversion film according to claim 1, wherein the content of magnesium in the chemical conversion film is between 15 atom% and 25 atom%. The chemical conversion film according to claim 1, wherein the content of oxygen in the chemical conversion film is between 50 atom% and 70 atom%. The chemical conversion film according to claim 1, wherein the material for forming the film includes MnO ₂ , MgO, and cerium oxide. The chemical conversion film according to claim 1, wherein the material of the magnesium alloy substrate comprises a magnesium lithium zinc alloy, a magnesium aluminum manganese alloy or a magnesium aluminum zinc alloy. A method for producing a chemical film comprising: providing an inorganic acidifying liquid comprising a permanganate, a pH adjusting agent, and a phosphonium salt, wherein the inorganic acidifying liquid has a pH of from 1 to 2.5 And a chemical conversion treatment of the magnesium alloy substrate with the inorganic acidification liquid to form a chemical conversion film on the surface of the magnesium alloy substrate, wherein the permanganate concentration in the inorganic acidification liquid It is between 0.05 M and 0.15 M, and the concentration of the onium salt in the inorganic acidification liquid is between 0.005 M and 0.05 M. The method for producing a chemical conversion film according to claim 7, wherein the permanganate comprises KMnO ₄ . The method for producing a chemical conversion film according to claim 7, wherein the onium salt comprises Ce(NO ₃ ) ₃ . The method for producing a chemical film according to claim 7, wherein the pH adjusting agent comprises H ₂ SO ₄ , and the concentration of H ₂ SO ₄ in the inorganic acidifying liquid is in the range of 0.005 M to Between 0.1 M. The method for producing a chemical conversion film according to claim 7, wherein the inorganic acidification liquid has a pH of between 1 and 2. The method for producing a chemical conversion film according to claim 7, wherein the chemical conversion treatment has an operation time of between 10 seconds and 90 seconds. The method for producing a chemical conversion film according to claim 7, wherein the chemical conversion treatment has an operation temperature of between 20 ° C and 40 ° C. The method for producing a chemical conversion film according to claim 7, wherein the chemical conversion film has a thickness of between 600 nm and 800 nm. The method for producing a chemical conversion film according to claim 7, wherein the material of the magnesium alloy substrate comprises a magnesium lithium zinc alloy, a magnesium aluminum manganese alloy or a magnesium aluminum zinc alloy. The method for producing a chemical conversion film according to claim 7, wherein the inorganic acidifying liquid further comprises a stabilizer. The method for producing a chemical film according to claim 16, wherein the concentration of the stabilizer in the inorganic acidifying solution ranges from 0.01 M to 0.05 M. The method for producing a chemical conversion film according to claim 16, wherein the stabilizer comprises potassium pyrophosphate.