CN114686949A - Surface treatment method for magnesium-aluminum alloy formed casting - Google Patents

Abstract

The invention discloses a surface treatment method for magnesium-aluminum alloy molded castings, and particularly relates to the technical field of magnesium-aluminum alloy casting processing, which comprises the following steps: s1, polishing to remove the naturally formed oxide layer; s2, carrying out micro-arc oxidation treatment; s3, acid leaching to form compact pores; s4, soaking the surface treatment agent to form a protective layer; and S5, drying and polishing the magnesium-aluminum alloy casting soaked by the surface treating agent to obtain a finished magnesium-aluminum alloy casting. According to the surface treatment method for the magnesium-aluminum alloy formed casting, an oxide film layer is formed on the surface of the magnesium-aluminum alloy casting by adopting a micro-arc oxidation method, a certain number of small holes are formed by soaking the magnesium-aluminum alloy casting in a sodium phosphate solution, and the nano acid-calcium resistant nano magnesium-aluminum alloy casting is matched with a silane coupling agent, epoxy resin and polyvinyl alcohol, so that the bonding property of the magnesium-aluminum alloy casting soaked by the surface treatment agent is improved, a protective layer is not easy to fall off, and the corrosion resistance of the magnesium-aluminum alloy casting is improved.

Description

Surface treatment method for magnesium-aluminum alloy formed casting

Technical Field

The invention relates to the technical field of magnesium-aluminum alloy casting processing, in particular to a surface treatment method for magnesium-aluminum alloy formed castings.

Background

Magnesium aluminum and its alloys are mainly classified into Mg-Al-Mn series, Mg-Al-Zn-Mn series, Mg-Al-Si-Mn series, and Mg-Al-RE series according to their compositions. The magnesium-aluminum alloy has small density which is about 2/3 of aluminum density, high specific strength and specific stiffness, strong shock absorption, strong electromagnetic wave interference resistance, good dimensional stability, machinability, electric and thermal conductivity and the like, and is widely concerned in a plurality of fields of automobiles, electronic appliances, aviation and the like.

Due to the high strength/weight ratio, easy forming and processing and excellent physical and chemical properties, the magnesium-aluminum alloy material becomes a metal material which is more used than aluminum alloy in the industry at present. However, the magnesium-aluminum alloy material has low hardness and poor wear resistance, and is often worn and damaged, and when the magnesium-aluminum alloy is used in environments such as moist, industrial gas, fuel gas, salt, dust atmosphere and the like, pitting corrosion, crevice corrosion, stress corrosion, corrosion fatigue and the like are very easy to occur, so that the application range of the magnesium-aluminum alloy is limited, and the service life of the magnesium-aluminum alloy is shortened. Therefore, in order to meet various industrial requirements and to prolong the service life of the metal, it is necessary to perform decoration and protective treatment on the metal surface.

In view of the above, the invention provides a surface treatment method for magnesium-aluminum alloy molded castings.

Disclosure of Invention

The invention mainly aims to provide a surface treatment method for magnesium-aluminum alloy formed castings, which can effectively solve the problems of easy corrosion and short service life of the magnesium-aluminum alloy castings.

In order to realize the purpose, the invention adopts the technical scheme that:

a surface treatment method for a magnesium-aluminum alloy forming casting comprises the following specific steps:

s1, polishing the surface of the magnesium-aluminum alloy casting after die-casting forming, and removing an oxide layer formed on the surface of the magnesium-aluminum alloy casting due to natural oxidation;

s2, carrying out micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting to form an oxide film on the surface of the magnesium-aluminum alloy casting;

s3, soaking the magnesium-aluminum alloy casting subjected to micro-arc oxidation in an acid solution to activate the surface of the magnesium-aluminum alloy casting, so that an oxide film layer formed by micro-arc oxidation on the surface of the magnesium-aluminum alloy casting is partially dissolved to form compact pores;

s4, soaking the magnesium-aluminum alloy casting processed by the acid solution into a surface treating agent, and combining the surface treating agent and the compact pores formed in the S3 on the surface of the magnesium-aluminum alloy casting to form a protective layer;

and S5, drying and polishing the magnesium-aluminum alloy casting soaked by the surface treating agent to obtain a finished magnesium-aluminum alloy casting.

Preferably, the specific process of grinding the surface of the magnesium-aluminum alloy casting in S1 is as follows:

utilize abrasive paper at first to polish for the first time along same direction to magnadure foundry goods surface, then adopt the abrasive paper of same mesh number to polish once more along the direction that perpendicular to was polished for the first time, until the magnadure mar disappears, repeat above-mentioned step 3 and accomplish the operation of polishing promptly to 3 times the abrasive paper mesh number that the in-process of polishing adopted do in proper order: 800 meshes, 1000 meshes and 1200 meshes.

Preferably, the specific method for performing micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting in S2 comprises the following steps: and (3) taking the polished magnesium-aluminum alloy casting as an anode of the electrolytic cell, taking another stainless steel container as a cathode of the electrolytic cell, and performing micro-arc oxidation treatment on the magnesium alloy by adopting pulse current with constant current density.

Preferably, the micro-arc oxidation process parameters are as follows: the current density is 35-40mA/cm²The duty ratio of the positive and negative pulses is 5-20% respectively, the frequency is 500-900HZ, the power-on time is 45-55s, the temperature of the electrolyte is 25-40 ℃, and the voltage is 300-500V.

Preferably, the acidic solution adopted in S3 is a sodium phosphate solution with the concentration of 8-10g/L, and the soaking time is 8-10 minutes.

Preferably, the surface treating agent used in S4 comprises the following components in parts by weight: 4-10 parts of polyvinyl alcohol, 5-12 parts of silane coupling agent, 3-5 parts of sodium tartrate, 2-6 parts of epoxy resin, 3-10 parts of nano calcium carbonate and 45-52 parts of distilled water.

Preferably, the magnesium-aluminum alloy casting treated by the acid solution is placed into the surface treating agent for soaking for 6-8 hours.

Preferably, in the step S5, the temperature for drying the magnesium aluminum alloy casting soaked by the surface treatment agent is 60 ℃, and the thickness of the protective layer after polishing is 0.5-1 mm.

Compared with the prior art, the invention has the following beneficial effects:

in the invention, the oxide layer naturally formed on the surface of the magnesium-aluminum alloy molded casting is firstly removed, then the micro-arc oxidation method is adopted to form the oxide film layer on the surface of the magnesium-aluminum alloy casting, and a certain number of small holes are formed by soaking the raw materials in a sodium phosphate solution, and by adding nano acid-calcium resistant, in combination with the silane coupling agent, the epoxy resin and the polyvinyl alcohol, the silane coupling agent can be partially crosslinked with the polyvinyl alcohol and the epoxy resin, and the hydrogen bond action between the polyvinyl alcohol and the silane coupling agent improves the bonding property of the magnesium-aluminum alloy casting soaked by the surface treating agent, meanwhile, the adhesive capacity and the bonding effect between the surface treating agent and the magnesium-aluminum alloy casting are improved by utilizing the small holes formed by acid leaching on the oxide film layer, thereby improving the stability and permeability of the surface treating agent, ensuring that the protective layer is not easy to fall off, and improving the corrosion resistance of the magnesium-aluminum alloy casting.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.

The applicant finds that the silane coupling agent can be matched with polyvinyl alcohol and epoxy resin for use, in practice, the silane coupling agent can be partially crosslinked with polyvinyl alcohol and epoxy resin, the bonding performance of the aluminum alloy casting soaked by the surface treatment agent is improved by the hydrogen bond action between the polyvinyl alcohol and the silane coupling agent, meanwhile, an oxide film layer is formed on the surface of the magnesium-aluminum alloy casting by a micro-arc oxidation method, a certain number of small holes can be formed by soaking the magnesium-aluminum alloy casting in a sodium phosphate solution, and the magnesium-aluminum alloy casting is matched with the silane coupling agent, the epoxy resin and the polyvinyl alcohol by adding nano acid-calcium resistant, so that the adhesive capacity and the bonding effect between the surface treatment agent and the magnesium-aluminum alloy casting are improved by the small holes, thereby improving the stability and permeability of the surface treating agent, ensuring that the protective layer is not easy to fall off, and improving the corrosion resistance of the magnesium-aluminum alloy casting.

Specifically, the surface treatment method for the magnesium-aluminum alloy formed casting disclosed by the invention is specifically described below with reference to specific examples:

example 1

The embodiment discloses a surface treatment method for a magnesium-aluminum alloy forming casting, which is realized by the following specific steps:

s1, polishing the surface of the magnesium-aluminum alloy casting after die-casting forming, and removing an oxide layer formed on the surface of the magnesium-aluminum alloy casting due to natural oxidation, specifically: utilize abrasive paper at first to polish for the first time along same direction to magnadure foundry goods surface, then adopt the same mesh number abrasive paper to polish once more along the direction that perpendicular to was polished for the first time again, until the magnadure mar disappears, repeat above-mentioned step 3 and accomplish the operation of polishing promptly to the abrasive paper mesh number that 3 times of polishing in-process adopted is in proper order: 800 mesh, 1000 mesh and 1200 mesh;

s2, carrying out micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting to form an oxide film on the surface of the magnesium-aluminum alloy casting, wherein the method specifically comprises the following steps: taking the polished magnesium-aluminum alloy casting as an anode of an electrolytic cell, taking another stainless steel container as a cathode of the electrolytic cell, and carrying out micro-arc oxidation treatment on the magnesium alloy by adopting pulse current with constant current density;

wherein, the micro-arc oxidation process parameters are as follows: current density 35mA/cm²The duty ratio of the positive pulse and the negative pulse is respectively 5%, the frequency is 500HZ, the electrifying time is 45s, the temperature of the electrolyte is 25 ℃, and the voltage is 300V;

s3, soaking the magnesium-aluminum alloy casting subjected to micro-arc oxidation in an acid solution to activate the surface of the magnesium-aluminum alloy casting, so that an oxide film layer formed by micro-arc oxidation on the surface of the magnesium-aluminum alloy casting is partially dissolved to form compact pores; specifically, the adopted acid solution is a sodium phosphate solution with the concentration of 8g/L, and the specific soaking time is 8 minutes;

s4, soaking the magnesium-aluminum alloy casting treated by the acid solution into a surface treating agent to enable the surface treating agent and the compact pores formed in the S3 to be combined with the surface of the magnesium-aluminum alloy casting to form a protective layer, wherein the surface treating agent comprises the following components in parts by weight: 4 parts of polyvinyl alcohol, 5 parts of silane coupling agent, 3 parts of sodium tartrate, 2 parts of epoxy resin, 3 parts of nano calcium carbonate and 45 parts of distilled water, wherein the magnesium-aluminum alloy casting is placed into the surface treating agent for soaking for 6 times;

s5, drying and polishing the magnesium-aluminum alloy casting soaked by the surface treatment agent, wherein the drying temperature is 60 ℃, and the thickness of the protective layer is 0.5-1mm after polishing and polishing are completed, so that the finished magnesium-aluminum alloy casting is obtained.

Example 2

The embodiment discloses a surface treatment method for a magnesium-aluminum alloy forming casting, which is realized by the following specific steps:

s1, polishing the surface of the magnesium-aluminum alloy casting after die-casting forming, and removing an oxide layer formed on the surface of the magnesium-aluminum alloy casting due to natural oxidation, specifically: utilize abrasive paper at first to polish for the first time along same direction to magnadure foundry goods surface, then adopt the same mesh number abrasive paper to polish once more along the direction that perpendicular to was polished for the first time again, until the magnadure mar disappears, repeat above-mentioned step 3 and accomplish the operation of polishing promptly to the abrasive paper mesh number that 3 times of polishing in-process adopted is in proper order: 800 mesh, 1000 mesh and 1200 mesh;

s2, carrying out micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting to form an oxide film on the surface of the magnesium-aluminum alloy casting, wherein the method specifically comprises the following steps: taking the polished magnesium-aluminum alloy casting as an anode of an electrolytic cell, taking another stainless steel container as a cathode of the electrolytic cell, and carrying out micro-arc oxidation treatment on the magnesium alloy by adopting pulse current with constant current density;

wherein, the micro-arc oxidation process parameters are as follows: current density 36mA/cm²The duty ratio of the positive pulse and the negative pulse is respectively 10%, the frequency is 600HZ, the electrifying time is 47s, the temperature of the electrolyte is 30 ℃, and the voltage is 320V;

s3, soaking the magnesium-aluminum alloy casting subjected to micro-arc oxidation in an acid solution to activate the surface of the magnesium-aluminum alloy casting, so that an oxide film layer formed by micro-arc oxidation on the surface of the magnesium-aluminum alloy casting is partially dissolved to form compact pores; specifically, the adopted acid solution is a sodium phosphate solution with the concentration of 8g/L, and the specific soaking time is 8 minutes;

s4, soaking the magnesium-aluminum alloy casting treated by the acid solution into a surface treating agent to enable the surface treating agent and the compact pores formed in the S3 to be combined with the surface of the magnesium-aluminum alloy casting to form a protective layer, wherein the adopted surface treating agent comprises the following components in parts by weight: 5 parts of polyvinyl alcohol, 7 parts of silane coupling agent, 3 parts of sodium tartrate, 4 parts of epoxy resin, 5 parts of nano calcium carbonate and 46 parts of distilled water, wherein the magnesium-aluminum alloy casting is put into the surface treating agent for soaking for 6 hours;

s5, drying and polishing the magnesium-aluminum alloy casting soaked by the surface treatment agent, wherein the drying temperature is 60 ℃, and the thickness of the protective layer is 0.5-1mm after polishing and polishing are finished, so that the finished magnesium-aluminum alloy casting is obtained.

Example 3

The embodiment discloses a magnesium-aluminum alloy molding casting surface treatment method, which is realized by adopting the following specific steps:

s1, polishing the surface of the magnesium-aluminum alloy casting after die-casting forming, and removing an oxide layer formed on the surface of the magnesium-aluminum alloy casting due to natural oxidation, specifically: utilize abrasive paper at first to polish for the first time along same direction to magnadure foundry goods surface, then adopt the same mesh number abrasive paper to polish once more along the direction that perpendicular to was polished for the first time again, until the magnadure mar disappears, repeat above-mentioned step 3 and accomplish the operation of polishing promptly to the abrasive paper mesh number that 3 times of polishing in-process adopted is in proper order: 800 mesh, 1000 mesh and 1200 mesh;

s2, performing micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting to form an oxide film on the surface of the magnesium-aluminum alloy casting, wherein the method specifically comprises the following steps: taking the polished magnesium-aluminum alloy casting as an anode of an electrolytic cell, taking another stainless steel container as a cathode of the electrolytic cell, and carrying out micro-arc oxidation treatment on the magnesium alloy by adopting pulse current with constant current density;

wherein, the micro-arc oxidation process parameters are as follows: current density 38mA/cm²The duty ratio of the positive pulse and the negative pulse is respectively 13%, the frequency is 700HZ, the electrifying time is 42s, the temperature of the electrolyte is 30 ℃, and the voltage is 400V;

s3, soaking the magnesium-aluminum alloy casting subjected to micro-arc oxidation in an acid solution to activate the surface of the magnesium-aluminum alloy casting, so that an oxide film layer formed by micro-arc oxidation on the surface of the magnesium-aluminum alloy casting is partially dissolved to form compact pores; specifically, the adopted acid solution is a sodium phosphate solution with the concentration of 9g/L, and the specific soaking time is 9 minutes;

s4, soaking the magnesium-aluminum alloy casting treated by the acid solution into a surface treating agent to enable the surface treating agent and the compact pores formed in the S3 to be combined with the surface of the magnesium-aluminum alloy casting to form a protective layer, wherein the adopted surface treating agent comprises the following components in parts by weight: 7 parts of polyvinyl alcohol, 8 parts of silane coupling agent, 4 parts of sodium tartrate, 5 parts of epoxy resin, 8 parts of nano calcium carbonate and 50 parts of distilled water, wherein the magnesium-aluminum alloy casting is placed into the surface treating agent to be soaked for 7 hours;

s5, drying and polishing the magnesium-aluminum alloy casting soaked by the surface treatment agent, wherein the drying temperature is 60 ℃, and the thickness of the protective layer is 0.5-1mm after polishing and polishing are completed, so that the finished magnesium-aluminum alloy casting is obtained.

Example 4

The embodiment discloses a magnesium-aluminum alloy molding casting surface treatment method, which is realized by adopting the following specific steps:

s1, polishing the surface of the magnesium-aluminum alloy casting after die-casting forming, and removing an oxide layer formed on the surface of the magnesium-aluminum alloy casting due to natural oxidation, specifically: utilize abrasive paper at first to polish for the first time along same direction to magnadure foundry goods surface, then adopt the same mesh number abrasive paper to polish once more along the direction that perpendicular to was polished for the first time again, until the magnadure mar disappears, repeat above-mentioned step 3 and accomplish the operation of polishing promptly to the abrasive paper mesh number that 3 times of polishing in-process adopted is in proper order: 800 mesh, 1000 mesh and 1200 mesh;

s2, performing micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting to form an oxide film on the surface of the magnesium-aluminum alloy casting, wherein the method specifically comprises the following steps: taking the polished magnesium-aluminum alloy casting as an anode of an electrolytic cell, taking another stainless steel container as a cathode of the electrolytic cell, and carrying out micro-arc oxidation treatment on the magnesium alloy by adopting pulse current with constant current density;

wherein, the micro-arc oxidation process parameters are as follows: current density 38mA/cm²The duty ratio of the positive pulse and the negative pulse is respectively 18 percent, the frequency is 800HZ, the electrifying time is 50s, the temperature of the electrolyte is 35 ℃, and the voltage is 450V;

s3, soaking the magnesium-aluminum alloy casting subjected to micro-arc oxidation in an acid solution to activate the surface of the magnesium-aluminum alloy casting, so that an oxide film layer formed by micro-arc oxidation on the surface of the magnesium-aluminum alloy casting is partially dissolved to form compact pores; specifically, the adopted acid solution is a sodium phosphate solution with the concentration of 10g/L, and the specific soaking time is 10 minutes;

s4, soaking the magnesium-aluminum alloy casting treated by the acid solution into a surface treating agent to enable the surface treating agent and the compact pores formed in the S3 to be combined with the surface of the magnesium-aluminum alloy casting to form a protective layer, wherein the adopted surface treating agent comprises the following components in parts by weight: 9 parts of polyvinyl alcohol, 10 parts of silane coupling agent, 5 parts of sodium tartrate, 5 parts of epoxy resin, 8 parts of nano calcium carbonate and 50 parts of distilled water, wherein the magnesium-aluminum alloy casting is placed into the surface treating agent to be soaked for 9 hours;

s5, drying and polishing the magnesium-aluminum alloy casting soaked by the surface treatment agent, wherein the drying temperature is 60 ℃, and the thickness of the protective layer is 0.5-1mm after polishing and polishing are completed, so that the finished magnesium-aluminum alloy casting is obtained.

Example 5.

The embodiment discloses a magnesium-aluminum alloy molding casting surface treatment method, which is realized by adopting the following specific steps:

s1, polishing the surface of the magnesium-aluminum alloy casting after die-casting forming, and removing an oxide layer formed on the surface of the magnesium-aluminum alloy casting due to natural oxidation, specifically: utilize abrasive paper at first to polish for the first time along same direction to magnadure foundry goods surface, then adopt the same mesh number abrasive paper to polish once more along the direction that perpendicular to was polished for the first time again, until the magnadure mar disappears, repeat above-mentioned step 3 and accomplish the operation of polishing promptly to the abrasive paper mesh number that 3 times of polishing in-process adopted is in proper order: 800 mesh, 1000 mesh and 1200 mesh;

s2, carrying out micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting to form an oxide film on the surface of the magnesium-aluminum alloy casting, wherein the method specifically comprises the following steps: taking the polished magnesium-aluminum alloy casting as an anode of an electrolytic cell, taking another stainless steel container as a cathode of the electrolytic cell, and carrying out micro-arc oxidation treatment on the magnesium alloy by adopting pulse current with constant current density;

wherein, the micro-arc oxidation process parameters are as follows: current density 40mA/cm²The duty ratio of the positive pulse and the negative pulse is respectively 20%, the frequency is 900HZ, the electrifying time is 55s, the temperature of the electrolyte is 40 ℃, and the voltage is 500V;

s3, soaking the magnesium-aluminum alloy casting subjected to micro-arc oxidation in an acid solution to activate the surface of the magnesium-aluminum alloy casting, so that an oxide film layer formed by micro-arc oxidation on the surface of the magnesium-aluminum alloy casting is partially dissolved to form compact pores; specifically, the adopted acid solution is a sodium phosphate solution with the concentration of 10g/L, and the specific soaking time is 10 minutes;

s4, soaking the magnesium-aluminum alloy casting treated by the acid solution into a surface treating agent to enable the surface treating agent and the compact pores formed in the S3 to be combined with the surface of the magnesium-aluminum alloy casting to form a protective layer, wherein the adopted surface treating agent comprises the following components in parts by weight: 10 parts of polyvinyl alcohol, 12 parts of silane coupling agent, 5 parts of sodium tartrate, 6 parts of epoxy resin, 10 parts of nano calcium carbonate and 52 parts of distilled water, wherein the magnesium-aluminum alloy casting is put into the surface treating agent for soaking for 6-8 hours;

s5, drying and polishing the magnesium-aluminum alloy casting soaked by the surface treatment agent, wherein the drying temperature is 60 ℃, and the thickness of the protective layer is 0.5-1mm after polishing and polishing are completed, so that the finished magnesium-aluminum alloy casting is obtained.

The following tests were performed on the shaped castings (size: 15cm by 10cm by 1.3 cm) of the magnesium-aluminum alloys of examples 1-5 above, and the results are shown in table 1, in the following manner:

1. and (3) testing acid resistance: the magnesium-aluminum alloy formed casting is placed in 15% concentrated sulfuric acid to be soaked for 1000 hours, the soaking area is 50% of the total area of the magnesium-aluminum alloy formed casting, and the test results are shown in table 1.

2. Alkali resistance test: and (3) soaking the magnesium-aluminum alloy molded casting in 20% sodium hydroxide solution for 1000h, wherein the soaking area is 50% of the total area of the magnesium-aluminum alloy molded casting, and the test results are shown in table 1.

3. Testing neutral smoke resistance: according to the neutral salt spray resistance of GB/T1771-2007, the corrosion area proportion of a specific test sample after a 2000h salt spray test is shown in Table 1.

	Acid resistance test corrosion area ratio (%)	Corrosion area ratio (%) in alkali resistance test	Corrosion area ratio (%) in neutral salt spray resistance test
				Example 1	10.9	13.2	3.4
Example 2	10.3	12.3	2.7
				Example 3	9.2	11.9	2.1
Example 4	8.9	11.4	1.8
				Example 5	9,8	12.7	2.5

Table 1: performance test results of surface-treated magnesium-aluminum alloy molded castings of examples 1 to 5

As can be known from the above table, after the surface treatment is performed on the magnesium-aluminum alloy molded casting by the surface treatment method for the magnesium-aluminum alloy molded casting disclosed by the invention, the corrosion resistance of the magnesium-aluminum alloy molded casting is remarkably improved, and particularly in example 3, the treated magnesium-aluminum alloy molded casting has the best acid resistance, alkali resistance and central smoke resistance.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (8)

1. A surface treatment method for a magnesium-aluminum alloy molding casting is characterized by comprising the following specific steps:

s1, polishing the surface of the magnesium-aluminum alloy casting after die-casting forming, and removing an oxide layer formed on the surface of the magnesium-aluminum alloy casting due to natural oxidation;

s2, carrying out micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting to form an oxide film on the surface of the magnesium-aluminum alloy casting;

s3, soaking the magnesium-aluminum alloy casting subjected to micro-arc oxidation in an acid solution to activate the surface of the magnesium-aluminum alloy casting, so that an oxide film layer formed by micro-arc oxidation on the surface of the magnesium-aluminum alloy casting is partially dissolved to form compact pores;

s4, soaking the magnesium-aluminum alloy casting processed by the acid solution into a surface treating agent, and combining the surface treating agent and the compact pores formed in the S3 on the surface of the magnesium-aluminum alloy casting to form a protective layer;

and S5, drying and polishing the magnesium-aluminum alloy casting soaked by the surface treating agent to obtain a finished magnesium-aluminum alloy casting.

2. The surface treatment method for the magnesium-aluminum alloy formed casting according to claim 1, wherein the specific process of grinding the surface of the magnesium-aluminum alloy casting in S1 is as follows:

utilize abrasive paper at first to polish for the first time along same direction to magnadure foundry goods surface, then adopt the same mesh number abrasive paper to polish once more along the direction that perpendicular to was polished for the first time again, until the magnadure mar disappears, repeat above-mentioned step 3 and accomplish the operation of polishing promptly to the abrasive paper mesh number that 3 times of polishing in-process adopted is in proper order: 800 meshes, 1000 meshes and 1200 meshes.

3. The surface treatment method for the magnesium-aluminum alloy molded casting according to claim 1, wherein the specific method for performing micro-arc oxidation treatment on the polished magnesium-aluminum alloy casting in S2 comprises the following steps: and (3) taking the polished magnesium-aluminum alloy casting as an anode of the electrolytic cell, taking another stainless steel container as a cathode of the electrolytic cell, and carrying out micro-arc oxidation treatment on the magnesium alloy by adopting pulse current with constant current density.

4. The surface treatment method for the magnesium-aluminum alloy formed casting according to claim 3, characterized by comprising the following steps: the micro-arc oxidation process parameters are as follows: the current density is 35-40mA/cm²The duty ratio of the positive and negative pulses is 5-20% respectively, the frequency is 500-900HZ, the power-on time is 45-55s, the temperature of the electrolyte is 25-40 ℃, and the voltage is 300-500V.

5. The surface treatment method of the magnesium-aluminum alloy formed casting according to claim 1, wherein the acidic solution adopted in the step S3 is a sodium phosphate solution with the concentration of 8-10g/L, and the soaking time is 8-10 minutes.

6. The surface treatment method for the magnesium-aluminum alloy formed casting according to claim 1, wherein the surface treatment agent adopted in the step S4 comprises the following components in parts by weight: 4-10 parts of polyvinyl alcohol, 5-12 parts of silane coupling agent, 3-5 parts of sodium tartrate, 2-6 parts of epoxy resin, 3-10 parts of nano calcium carbonate and 45-52 parts of distilled water.

7. The surface treatment method for the magnesium-aluminum alloy formed castings according to claim 6, characterized in that the magnesium-aluminum alloy castings subjected to the treatment with the acid solution are placed into the surface treatment agent for soaking for 6-8 hours.

8. The surface treatment method for the magnesium-aluminum alloy formed casting according to claim 1, wherein the temperature for drying the magnesium-aluminum alloy casting soaked by the surface treatment agent in S5 is 60 ℃, and the thickness of the protective layer after grinding and polishing is 0.5-1 mm.

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