KR20200137284A - Method for improving corrosion resistance of aluminum alloy surface - Google Patents

Abstract

The present invention relates to a method for improving corrosion resistance of a 5000 series aluminum alloy surface. According to the present invention, an anodized film is formed on an aluminum alloy surface by controlling time and voltage of anodizing so as to significantly improve corrosion resistance of an aluminum alloy at a predetermined condition. Moreover, the 5000 series aluminum alloy with corrosion resistance manufactured by the method can be used for structures for a ship, an aircraft, a train, or a vehicle or used for various industrial fields such as an architectural material, a home appliance, and a gasket.

Description

Method for improving corrosion resistance of aluminum alloy surface

The present invention relates to a method of improving the corrosion resistance of the surface of a 5000 series aluminum alloy, and a 5000 series aluminum alloy having corrosion resistance manufactured using the same.

The electrochemical anodization process has a density of 2.7 g/cm ³ , which is the lowest after magnesium among industrial metals, and has high electrical conductivity, thermal conductivity, and corrosion resistance, so it is not only automobile, home appliance, airplane, but also the marine industry. Widely used in In general, in order to improve mechanical strength and workability, magnesium (Mg), silicon (Si), copper (Cu) and manganese (Mn) are added and used in the form of an alloy. Since aluminum alloys contain various alloying elements, they are various and are manufactured in various forms such as foils, wire rods, and extruded materials, and are used in fields requiring high mechanical properties and workability, and their uses and usage are increasing. Since aluminum has a standard reduction potential of -1.667V, it immediately combines with oxygen in the atmosphere to form a natural oxide film with a thickness of several nm, which serves to protect the base material, but it is too thin to have sufficient corrosion resistance when exposed to various environments. Does not represent

On the other hand, anodic oxidation is one of the surface treatment technologies for metals. When a metal to be treated is connected to the anode and a current is applied from a liquid electrolyte, an oxide film having considerable adhesion to the metal is formed on the surface due to oxygen generated from the anode. The formed oxide film has a difference in thickness, density, hardness, etc. of the film depending on variables such as the type of electrolyte, temperature of the electrolyte, voltage, treatment time, and stirring speed. In addition, in the aluminum alloy anodization process, alloying elements affect film formation, which is known to affect film thickness and production efficiency.

Among aluminum alloys, aluminum 5052 alloy containing a large amount of Al and Mg has relatively high hardness, excellent formability, and durability, and is widely used industrially, such as ship and vehicle structure parts and construction materials. However, due to the included alloying elements, corrosion resistance is very low compared to pure aluminum.

Accordingly, the present inventors observed the growth behavior and electrochemical properties of the oxide film of the aluminum 5052 alloy manufactured by performing anodization treatment by changing the anodization time and voltage, and as a result, the corrosion resistance of the aluminum alloy under specific pressure and time conditions. It was confirmed that the present invention can be improved.

Korean Patent Registration No. 10-1246106

An object of the present invention is to provide a method of improving the corrosion resistance of the surface of a 5000 series aluminum alloy.

Another object of the present invention is to provide an aluminum alloy having corrosion resistance manufactured by the above method.

Another object of the present invention is to provide a structure for ships, aviation, trains or vehicles, construction materials, structures and gaskets for home appliances, including the aluminum alloy.

To achieve the above object,

The present invention provides a method for improving the corrosion resistance of a surface of a 5000 series aluminum alloy, comprising the step of anodizing an aluminum 5000 series alloy at 30-50V for 1-18 hours.

In addition, the present invention provides a 5000 series aluminum alloy having corrosion resistance manufactured by the above method.

Furthermore, the present invention provides a structure for ships, aviation, trains, or vehicles including the 5000 series aluminum alloy.

Furthermore, the present invention provides a building material comprising the aluminum alloy of 5000 series.

Furthermore, the present invention provides a structure for home appliances including the aluminum alloy of 5000 series.

Furthermore, the present invention provides a gasket including the 5000 series aluminum alloy.

The method of improving the corrosion resistance of the surface of the 5000 series aluminum alloy according to the present invention can significantly improve the corrosion resistance under certain conditions by forming an anodized film on the surface of the aluminum alloy through control of the anodization voltage and time. The 5000 series aluminum alloy having excellent corrosion resistance can be used in various industrial fields such as ships, aviation, trains, or vehicle structures or construction materials, home appliances, and gaskets.

1 is a FE-SEM showing the surface and cross-sectional shape of the aluminum anodized film of Examples 7 (a, d), 9 (b, e) and 11 (c, f) according to anodization treatment time under a voltage condition of 40 V. It is an image showing the result of analysis.
2 is a spectrum showing the result of component analysis through EDS for the composition of an aluminum oxide film generated under a voltage condition of 40V.
3 is an image showing the dynamic potential polarization curves of the anodized films of Examples 7, 9 and 11 according to the anodization treatment time under a voltage condition of 40V.

Hereinafter, the present invention will be described in detail.

Method to improve corrosion resistance of 5000 series aluminum alloy surface

The present invention provides a method for improving the corrosion resistance of a surface of a 5000 series aluminum alloy, comprising the step of anodizing an aluminum 5000 series alloy at 30-50V for 1-18 hours.

In the method for improving the corrosion resistance of the surface of a 5000 series aluminum alloy according to the present invention, the anodizing treatment may be anodizing treatment at 35-45V for 4-18 hours, more preferably 37-43V. It may be anodizing treatment at 5-16 hours, more preferably anodizing treatment at 38-42V for 5-13 hours, and anodizing treatment at 39-41V for 5.5-12.5 hours It is particularly preferred.

In the method for improving the corrosion resistance of the surface of a 5000 series aluminum alloy according to the present invention, the electrolyte solution subjected to the anodization treatment is sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ), oxalic acid ( Oxalic acid, C ₂ H ₂ O ₄ ), chromic acid, hydrofluoric acid, potassium hydrogen phosphate (dipotassium phosphate, K ₂ HPO ₄ ) can be used, or any one of these mixtures can be used. In the oxidation treatment tank containing the electrolyte, the anode is attached using the material on which the metal to be anodized is formed as a working electrode, and then the cathode is attached using a platinum (Pt) or carbon electrode as a counter electrode. It may be made by giving and oxidizing. Preferably, 0.1-0.5M oxalic acid may be used as an electrolyte and may be made at a temperature of -5 to 5°C, more preferably 0.2-0.4M oxalic acid and may be made at a temperature of -2 to 2°C. .

In the method for improving the corrosion resistance of the surface of a 5000 series aluminum alloy according to the present invention, the 5000 series aluminum alloy is Al 5005, Al 5023, Al 5042, Al 5052, Al 5054, Al 5056, Al 5082, Al 5083, Al 5084 , Al 5086, Al 5154, Al 5182, Al 5252, Al 5352, Al 5383, Al 5454, Al 5456, Al 5457, Al 5657 and Al 5754 may be one or more selected from the group consisting of.

According to an embodiment of the present invention, anodization having a pore diameter of 10 to 17 nm and a pore distance of 65 to 105 nm on the aluminum alloy surface by the method of improving the corrosion resistance of the surface of the 5000 series aluminum alloy according to the present invention The film may be formed, but is not limited thereto.

In addition, the present invention provides a 5000 series aluminum alloy having corrosion resistance manufactured by a method of improving the corrosion resistance of the surface of the 5000 series aluminum alloy.

The 5000 series aluminum alloy having corrosion resistance according to the present invention may have an aluminum anodized film formed on the surface of the alloy.

Furthermore, the present invention provides a structure for ships, aviation, trains, or vehicles including the 5000 series aluminum alloy having the corrosion resistance.

In this case, the structure may be an aluminum alloy shell plate or component of any one of ships, aviation, trains, and vehicles (automobiles), but is not limited thereto.

Furthermore, the present invention provides a building material comprising a 5000 series aluminum alloy having the corrosion resistance.

Furthermore, the present invention provides a structure for a home appliance including a 5000 series aluminum alloy having the corrosion resistance.

At this time, the home appliances include telephones, notebook computers, desktops, monitors, TVs, speakers, rice cookers, gas ranges, microwave ovens, hoods, refrigerators, vacuum cleaners, air purifiers, humidifiers, air conditioners, electric fans, dehumidifiers, dryers, washing machines, It may be one or more selected from the group consisting of a dryer, a dehydrator, a clothes purifier, a mixer, a juicer, a coffee machine, a toaster, an electric kettle, a water purifier, a dishwasher, and a sterilization dryer, and the structure is a housing or a component of the electronic product. It may be, but is not limited thereto.

Furthermore, the present invention provides a gasket including a 5000 series aluminum alloy having the above corrosion resistance.

The gasket may be an exhaust pipe, a high pressure pipe, a fuel cell, a heat exchanger, an electromagnetic wave shield, a pipe for a semiconductor or display industry, etc., and may be used for a joint or a joint to prevent leakage of water or gas, but is not limited thereto.

Hereinafter, the present invention will be described in more detail by the following examples. However, the following examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

< Example 1-19> Preparation of aluminum anodized film

An anodization process was performed on the aluminum alloy to form an oxide film on the surface.

Prepare an aluminum 5052 alloy (20mm×30mm×1mm) to remove the oxide film that naturally exists on the surface, and add perchloric acid (HClO, 70%) and ethanol (Ethanol, 95%) 1:4 ( In Volumetric Ratio), a voltage of 20 V was applied and electropolishing was performed at room temperature for 1 minute.

The electrolytically polished aluminum 5052 alloy was used as an anode, and platinum (Pt) was used as a cathode, and the two electrodes were separated at intervals of 5 cm. 0.3M oxalic acid was used as the electrolyte, and the cooling water was circulated into the double beaker using a low-temperature circulating water bath, so that the temperature of the electrolyte was kept constant at 0°C. A constant voltage of 30V to 50V was applied as shown in Table 1 below using a DC power supply, and anodization was performed for 1 to 18 hours under each voltage condition. After the anodization was completed, the solution on the surface of the specimen was removed using ethanol and distilled water to obtain aluminum anodized films of Examples 1 to 19.

Anodization voltage Anodization time Example 1 30V 1 hours Example 2 30V 6 hours Example 3 30V 12 hours Example 4 35V 1 hours Example 5 35V 6 hours Example 6 35V 12 hours Example 7 40V 1 hours Example 8 40V 3 hours Example 9 40V 6 hours Example 10 40V 10 hours Example 11 40V 12 hours Example 12 40V 15 hours Example 13 40V 18 hours Example 14 45V 1 hours Example 15 45V 6 hours Example 16 45V 12 hours Example 17 50V 1 hours Example 18 50V 6 hours Example 19 50V 12 hours

< Experimental example 1> Analysis of surface shape and thickness of aluminum anodized film

As shown in Table 1 above, the pores and thicknesses formed in the aluminum 5052 alloy under different conditions were observed with a Field Emission Scanning Electron Microscope (FE-SEM), and the chemistry of the oxide film surface Composition analysis was observed through an Energy Dispersive Spectroscopy (EDS).

1 is an image showing the results of analyzing the surface and cross-sectional shapes of aluminum anodized films of Examples 7, 9 and 11 according to the anodization treatment time under a voltage condition of 40V by FE-SEM.

As a result of checking the change in pore diameter, spacing between pores and film thickness with increasing anodizing time, the average pore diameter, interpore distance, and film thickness ( It was confirmed that both thickness) increased continuously. 2A and 2D show the surface and cross-sectional shape of the anodized oxide film for 1 hour. The average pore diameter, pore spacing, and thickness of the film are about 9.65 nm, 57.6 nm and 1.85 μm, respectively. A retained aluminum oxide film was formed. In addition, as the time increased, the pore diameter, pore spacing, and film thickness all increased continuously. When anodizing was performed for 12 hours, the average pore diameter, pore diameter and film thickness were up to about 15.49 nm and 95.89 nm, respectively, and It was grown as an anodized film with 9.15 μm.

It was confirmed that the growth rate of the film thickness decreased after 6 hours, and this was confirmed that after a certain period of time, further thickness growth could not occur due to the dissolution reaction of the uppermost part of the film in contact with the electrolyte. It appears that the thickness growth has decreased.

Meanwhile, the porosity is directly related to the pore diameter and the spacing between the pores and can be calculated by the following equation (1).

(1)

(One)

Here, P is the porosity, D _p is the pore diameter, and D _int is the interpore distance.

Table 2 below shows the diameter of pores after anodization, pore distance and porosity, and the composition of the oxide film analyzed through EDS according to the change of the anodization time under the voltage condition of 40V.

2 is a spectrum showing the result of component analysis through EDS for the composition of an aluminum oxide film generated under a voltage condition of 40V.

(40V) time Porosity Composition of oxide film (EDS) D _p (nm) D _int (nm) P (%) O K(at%) Mg K(at%) Al K(at%) Example 7 1 hour 9.6±1.32 57.6±0.19 2.81 62.92 0.54 36.54 Example 9 6 hour 12.3±0.64 75.3±3.27 2.66 64.78 0.52 34.70 Example 11 12 hour 15.5±0.52 95.9±5.87 2.37 65.94 0.48 33.58

The porosity was the lowest at 2.37% when anodized for 12 hours.

As a result of analyzing the composition of the oxide film, aluminum and oxygen were detected as main components, and a trace amount of magnesium was detected. It seems that a trace amount of magnesium present in the aluminum 5052 alloy was incorporated when an anodizing film was formed through an oxalic acid solution. Therefore, it was confirmed that aluminum, oxygen, and a trace amount of magnesium were present on the surface, and through this, it was confirmed that an aluminum oxide film was formed on the surface.

< Experimental example 2> Electrochemical test analysis

The problem of surface treatment through coating is that there are pores or pin holes. This lowers the interfacial bonding strength and adhesion between the coating layer and the metal material, and plays a role in which ions and water easily penetrate into the base material. Therefore, porosity is important in measuring corrosion resistance. The porosity of the coating layer having such pores can be quantitatively calculated using an electrochemical method.

To evaluate the electrochemical properties, a potentiodynamic polarization test was performed in a 3.5wt% NaCl solution at room temperature. The copper potential polarization test was performed by connecting the anodized specimens of Examples 1 to 19 as a working electrode and platinum (Pt) as a counter electrode, and a three-electrode system using a silver-silver chloride electrode (Ag/AgCl) as a reference electrode. It was carried out by configuring. Measurement conditions were measured in the range of -1.0V to +2.0V (vs. Ag/AgCl) at a scanning speed of 1 mV/sec.

Among the various methods through electrochemical experiments, the porosity was evaluated using Equation (2) proposed by A. Matthews.

(2)

(2)

는 모재와 산화피막사이의 부식전위 차이를 나타내며

는 모재의 양극 Tafel상수를 나타낸다.Here, P is the total porosity, R _pm is the polarization resistance of the base material, and R _p is the polarization resistance of the anodized specimen.

Represents the difference in corrosion potential between the base metal and the oxide film

Represents the positive Tafel constant of the base material.

In addition, the protective efficiency for the coating can be calculated by the following equation (3).

(3)

(3)

Here, I _corr ° and I _corr represent the corrosion current density of the base metal and the corrosion current density of the anodized film, respectively.

3 is an image showing the dynamic potential polarization curves of the anodized films of Examples 7, 9 and 11 according to the anodization treatment time under a voltage condition of 40V.

In Table 3 below, corrosion potential (E _corr ) and corrosion current density (I _corr ), which are electrochemical factors of the aluminum anodized film of Examples 7, 9, 11 and 17 to 19, respectively, produced under voltage conditions of 40V and 50V The electrochemical factors of are shown.

40V 50V E _corr (mV) I _corr (A/cm ² ) E _corr (mV) I _corr (A/cm ² ) control -651 5.76×10 ^-7 -651 5.76×10 ^-7 1hr -156 2.01×10 ^-7 27 1.10×10 ^-7 6hr 324 9.28×10 ^-8 336 7.36×10 ^-8 12hr 341 1.86×10 ^-9 352 6.34×10 ^-8

It was found that all the anodized specimens produced over time had higher corrosion potential and corrosion current density than the base material. This indicates that the resulting oxide film serves to protect the base material surface from corrosion. In particular, it was confirmed that the oxide film, which was anodized for 12 hours under the voltage condition of 40V, had a high corrosion potential of 341 mV and the lowest corrosion current density of 1.86×10 ^-9 A/cm ² . This means that the specimen that was anodized for 12 hours under a voltage condition of 40V has the best corrosion resistance.

In addition, the corrosion current density (I _corr ), polarization resistance (R _p ), total porosity (P) and protection factor (P _i ) of Examples 1 to 19 are shown in Table 4 below.

Voltage (V) Time (hr) I _corr
(A/cm ² ) R _p
(Υ10 ⁶ Ωcm ² ) Porosity Pritective efficiency (%) control - - 5.76Х10 ^-7 0.047 - - Example 1 30 One 2.39Х10 ^-7 0.042 4.30Х10 ^-5 58.51 Example 2 30 6 2.01Х10 ^-7 0.129 3.81Х10 ^-6 65.10 Example 3 30 12 1.67Х10 ^-7 2.519 1.02Х10 ^-7 71.01 Example 4 35 One 2.15Х10 ^-7 0.124 1.24Х10 ^-6 62.67 Example 5 35 6 1.03Х10 ^-7 5.624 5.67Х10 ^-7 82.12 Example 6 35 12 7.25Х10 ^-8 10.138 4.56Х10 ^-7 87.42 Example 7 40 One 2.01Х10 ^-7 0.201 3.78Х10 ^-8 65.07 Example 8 40 3 1.42Х10 ^-7 7.285 2.84Х10 ^-10 75.24 Example 9 40 6 2.28Х10 ^-9 37.903 5.08Х10 ^-17 99.60 Example 10 40 10 2.01Х10 ^-9 38.024 3.62Х10 ^-17 99.65 Example 11 40 12 1.86Х10 ^-9 38.597 2.89Х10 ^-17 99.76 Example 12 40 15 5.15Х10 ^-8 38.601 2.26Х10 ^-17 91.06 Example 13 40 18 6.87Х10 ^-8 38.912 1.95Х10 ^-17 88.07 Example 14 45 One 1.25Х10 ^-7 4.945 2.35Х10 ^-10 78.39 Example 15 45 6 7.12Х10 ^-8 28.416 2.54Х10 ^-17 87.64 Example 16 45 12 5.78Х10 ^-8 33.527 2.02Х10 ^-17 89.97 Example 17 50 One 1.10Х10 ^-7 11.248 4.38Х10 ^-11 80.87 Example 18 50 6 7.74Х10 ^-8 24.125 2.62Х10 ^-17 87.22 Example 19 50 12 6.34Х10 ^-8 31.843 1.89Х10 ^-17 88.99

As shown in Table 4, it was confirmed that the polarization resistance increased and the porosity decreased as time increased in each voltage treatment condition. This is demonstrated by the results of the pore diameter and the porosity obtained through the pore spacing. In general, corrosion resistance is known to be inversely proportional to corrosion rate, and corrosion current density is known to be proportional. Therefore, it was confirmed that the polarization resistance increased with the increase of time and the corrosion rate was also decreased due to the low corrosion current density. In addition, it was confirmed that when the oxide film was exposed to the corrosive environment, the corrosive environment such as water and ions penetrated into the base material, so that the lower the porosity, the higher the corrosion resistance.

In Table 3, the highest corrosion potential value was observed under the voltage condition of 50V, but as shown in Table 4, overall higher corrosion current density and lower polarization resistance value than 40V were observed. Through this, it was found that the corrosion rate of the oxide film subjected to anodization at 50 V was faster than that of the oxide film subjected to anodization at 40 V. Through this, it was confirmed that resistance to corrosion is affected by corrosion rate as well as porosity.

As a result, it was confirmed that the oxide film of Example 10, which was anodized for 3 to 18 hours, in particular, 6 to 12 hours, at a voltage of 40V showed the best film protection rate.

So far, the present invention has been looked at around its preferred embodiments. Those of ordinary skill in the art to which the present invention pertains will be able to understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative point of view rather than a limiting point of view. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

Claims (12)

A method for improving the corrosion resistance of a surface of a 5000 series aluminum alloy comprising the step of anodizing an aluminum 5000 series alloy at 30-50V for 1-18 hours.
The method of claim 1,
The anodization treatment is a method for improving the corrosion resistance of the surface of the 5000 series aluminum alloy, characterized in that the anodization treatment for 4-18 hours at 35-45V.
The method of claim 2,
The anodizing treatment is a method for improving the corrosion resistance of the surface of the 5000 series aluminum alloy, characterized in that the anodization treatment for 5-16 hours at 37-43V.
The method of claim 1,
The anodization treatment is characterized in that using 0.1-0.5M oxalic acid as an electrolyte, a method of improving the corrosion resistance of the surface of the 5000 series aluminum alloy.
The method of claim 1,
The anodization treatment is a method for improving the corrosion resistance of the surface of the 5000 series aluminum alloy, characterized in that performed at a temperature of -5 to 5 ℃.
The method of claim 1,
The 5000 series aluminum alloys are Al 5005, Al 5023, Al 5042, Al 5052, Al 5054, Al 5056, Al 5082, Al 5083, Al 5084, Al 5086, Al 5154, Al 5182, Al 5252, Al 5352, Al 5383 , Al 5454, Al 5456, Al 5457, Al 5657 and Al 5754, characterized in that at least one selected from the group consisting of, a method for improving the corrosion resistance of the surface of the 5000 series aluminum alloy.
The method of claim 1,
A method for improving corrosion resistance of a surface of a 5000 series aluminum alloy, characterized in that an anodized film having a pore diameter of 10 to 17 nm and a pore distance of 65 to 105 nm is formed on the surface of the aluminum alloy by the anodization treatment.
A 5000 series aluminum alloy having corrosion resistance manufactured by the method of claim 1.
Structures for ships, aviation, trains, or vehicles containing the 5000 series aluminum alloy of claim 8.
Construction material containing the 5000 series aluminum alloy of claim 8.
A structure for home appliances comprising the 5000 series aluminum alloy of claim 8.
A gasket containing the 5000 series aluminum alloy of claim 8.

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