Corrosion-resistant and low-brittle aluminum alloy coating on steel surfaces by magnetron sputtering

Abstract

To provide a coating having reduced porosity on a steel base material and having corrosion resistance.SOLUTION: The present invention provides an alloy coating for coating a steel base material, the alloy comprising: aluminum; and one or more of: about 1 wt.% to about 15 wt.% zinc based on the total weight of the alloy, about 1 wt.% to about 10 wt.% magnesium based on the total weight of the alloy, and about 0.1 wt.% to about 5 wt.% zirconium based on the total weight of the alloy, the alloy coating having a percent total pore volume of about 5% or less and an average pore diameter about 10 microns or less. The alloy coating is formed by magnetron sputtering.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Aspects of the present disclosure generally relate to aluminum alloy coatings for steel, methods for depositing aluminum alloys on substrates, magnetron sputtering targets, and substrates coated with aluminum alloys. [Background technology]

[0002] Steel is a high strength material and is used in many industries. Coatings can be placed on steel to improve its quality. For example, cadmium coated steel is the material used for aircraft components for aerospace and military applications in wet environments. Because cadmium protects the steel from moisture and deteriorates slowly, cadmium coatings are referred to in the industry as "sacrificial coatings." Other technologies are also being developed to provide other coatings. For example, low hydrogen embrittlement zinc-nickel (LHE Zn-Ni) (e.g., AlumiPlate TM ) coatings offer similar performance to cadmium-coated aluminum. Aluminum offers another alternative for coating aviation components. Aluminum-coated steel has traditionally been produced by ion vapor deposition (IVD) of aluminum onto the steel surface. Alternatively, ionic solution-based coating preparation methods have been developed to eliminate aqueous and organic solvents from coating preparation.

[0003] Nevertheless, there is a need for a protective coating for steel that has reduced porosity compared to coatings formed by ion vapor deposition and that has a wider range of metals used in the protective coating compared to Zn-Ni plating. There is also a need for a protective coating for steel that can be formed without the use of organic solvents and other non-ideal materials. Summary of the Invention

[0004] The present disclosure provides an alloy coating for coating a substrate, such as a steel substrate, comprising aluminum and one or more of about 1 wt % to about 15 wt % zinc, about 1 wt % to about 10 wt % magnesium, and about 0.1 wt % to about 5 wt % zirconium, based on the total weight of the alloy, wherein the alloy coating has a percent total pore volume of about 5% or less and an average pore size of about 10 microns or less.

[0005] In another aspect, a substrate, such as a steel substrate, has an aluminum alloy of the present disclosure disposed on a surface thereof.

[0006] The present disclosure further provides a magnetron sputtering target comprising the aluminum alloy of the present disclosure.

[0007] In another aspect, a method for magnetron sputtering an aluminum alloy onto a substrate includes flowing a sputter gas into a processing region of a process chamber containing an aluminum alloy sputter target containing one or more of: about 1 wt. % to about 15 wt. % zinc, based on the total weight of the alloy; about 1 wt. % to about 10 wt. % magnesium, based on the total weight of the alloy; and about 0.1 wt. % to about 5 wt. % zirconium, based on the total weight of the alloy. The alloy coating has a total pore volume fraction of about 5% or less and an average pore size of about 10 microns or less. The method includes supplying an energy pulse to the sputter gas and depositing the aluminum alloy onto the substrate.

[0008] So that the above-mentioned features of the present disclosure may be understood in detail, a more particular description of the present disclosure, briefly summarized above, will be had by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the present disclosure is also susceptible to other equally effective embodiments, and therefore, the accompanying drawings illustrate only typical embodiments of the disclosure and should not be considered as limiting its scope. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an aircraft comprising a steel substrate according to one aspect of the present disclosure. [Figure 2] FIG. 1 is a flow diagram of a method for depositing an aluminum alloy coating on a steel substrate in a magnetron sputtering chamber according to one aspect of the present disclosure. [Figure 3] 1 is a graph showing total pore volume fraction versus pore size for aluminum coatings deposited on steel substrates using ion vapor deposition or magnetron sputtering. [Figure 4A] 1 is a bar graph showing pore size versus pore distribution for an aluminum coating deposited on a steel substrate using ion vapor deposition. [Figure 4B] 1 is a bar graph showing pore distribution versus pore size for an aluminum coating deposited on a steel substrate using magnetron sputtering, according to one aspect of the present disclosure. [Figure 5] 1 is a graph showing the open circuit potential of Al-5Mg alloy in distilled water and in 3.5% NaCl solution, according to one embodiment of the present disclosure. [Figure 6] 1 is a graph showing the open circuit potential of an Al-5Zn-5Mg alloy in distilled water and in a 3.5% NaCl solution, according to one embodiment of the present disclosure. [Figure 7] 1 is a graph showing the open circuit potential of Al-9Zn-5Mg alloy in distilled water and in a 3.5% NaCl solution, according to one embodiment of the present disclosure. [Figure 8] 1 is a graph showing the open circuit potential of an Al-9Zn-5Mg-1Zr alloy in distilled water and in a 3.5% NaCl solution, according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] For ease of understanding, where possible, the same reference numerals have been used to designate identical elements that are common to multiple figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0011] The present disclosure provides an alloy for coating a steel substrate, the alloy comprising aluminum and one or more of: about 1 wt. % to about 15 wt. % zinc, based on the total weight of the alloy; about 1 wt. % to about 10 wt. % magnesium, based on the total weight of the alloy; and about 0.1 wt. % to about 5 wt. % zirconium, based on the total weight of the alloy. The alloy coating has a total pore volume fraction of about 5% or less and an average pore size of about 10 microns or less. The aluminum alloy of the present disclosure can be disposed on a substrate, such as a steel substrate (e.g., an aircraft component). The aluminum alloy of the present disclosure provides a coating having a corrosion resistance according to ASTM B 117 of at least 500 hours.

[0012] The aluminum alloys of the present disclosure may be disposed in components of propulsion structures such as aircraft, spacecraft, watercraft, engines and blow-off flaps, exhaust-exposed structures, thermally insulating structural components for high-performance supersonic / hypersonic / re-entry vehicle structures, and power generation turbines, vehicle engines, alternative energy delivery devices, and related technologies. For example, the aluminum alloys of the present disclosure may be disposed in steel-based landing gear and / or undersides of aircraft. FIG. 1 illustrates an aircraft having a steel structure (e.g., substrate) according to one embodiment of the present disclosure. As shown in FIG. 1, the aircraft 100 includes an aircraft structure 102, including aircraft components such as a narrow-shaped fuselage 104, wings 106 extending laterally from the fuselage 104, and a tail section 108 extending longitudinally from the fuselage 104. The aluminum alloys of the present disclosure may be disposed on one or more surfaces of the aircraft component(s) to form one or more corrosion-resistant aluminum alloy coatings on the aircraft component(s).

[0013] alloy: The aluminum (Al) alloys of the present disclosure include one or more of magnesium (Mg), zinc (Zn), and zirconium (Zr). In at least one embodiment, the aluminum alloys of the present disclosure include about 1 wt.% to about 10 wt.% (e.g., about 1 wt.% to about 5 wt.%) Mg based on the total weight of the alloy. In at least one embodiment, the aluminum alloys of the present disclosure include about 1 wt.% to about 15 wt.% (e.g., about 5 wt.% to about 12 wt.%, about 8 wt.% to about 10 wt.%, etc.) Zn based on the total weight of the alloy. In at least one embodiment, the aluminum alloys of the present disclosure include about 0.1 wt.% to about 5 wt.% (e.g., about 1 wt.% to about 3 wt.%, e.g., about 1 wt.%) Zr based on the total weight of the alloy. In at least one embodiment, the aluminum alloy has 5 wt.% Mg and 95 wt.% Al (referred to as Al-5Mg). Alternatively, the aluminum alloy has 5 wt% Mg, 5 wt% Zn, and 90 wt% Al (referred to as Al-5Zn-5Mg). In at least one embodiment, the aluminum alloy has 9 wt% Zn, 5 wt% Mg, and 86 wt% Al (referred to as Al-9Zn-5Mg). Alternatively, the aluminum alloy has 9 wt% Zn, 5 wt% Mg, and 1 wt% Zr (referred to as Al-9Zn-5Mg-1Zr).

[0014] In at least one embodiment, the alloy of the present disclosure is magnetron sputtered onto a steel substrate to form a coating that is disposed on the steel substrate. In at least one embodiment, the aluminum alloy coating of the present disclosure has a thickness of 0.1 μm to about 100 μm (e.g., 0.1 μm to about 70 μm, about 1 μm to about 50 μm, about 2 μm to about 30 μm, about 0.1 μm to about 5 μm, etc.).

[0015] Magnetron Sputtering In at least one embodiment, corrosion-resistant aluminum alloy coatings are formed on steel substrates using magnetron sputtering. Magnetron sputtering is ideal for depositing the coatings described herein because it does not require ionization of the target and target alloy to be deposited on the substrate. Magnetron sputtering involves removal of material from the target, which is then deposited on the substrate. Targets used in magnetron sputtering of the present disclosure include the aluminum alloys of the present disclosure. Aluminum alloy targets can be formed by conventional melting and casting methods. For example, if an aluminum-zinc-magnesium-zirconium alloy is desired, calculated amounts of each pure metal are melted together in a resistance-heated furnace using a graphite crucible to form the alloy. An ingot of the alloy is cast and machined into the shape of a cylindrical rod. Electrical discharge machining is used to machine the cylindrical rod into a target for subsequent magnetron sputtering. In at least one embodiment, the cylindrical rod is cut into 3" or 2" diameter disks having a thickness of 3 mm for use as targets.

[0016] Any suitable magnetron sputtering system may be used to deposit the aluminum alloys of the present disclosure onto a substrate, such as a multi-target magnetron sputtering system by Hind High Vac Pvt. Ltd. of Bengaluru, India. The magnetron sputtering system includes one or more targets. In at least one embodiment, one target has a surface area of ​​about 1,000 cm. 2 ~Approx. 2,000cm 2 Alternatively, the surface area of ​​one target is approximately 50 cm 2 ~about 500cm 2 In at least one embodiment, the substrate is placed on a rotating table within the chamber. In at least one embodiment, the substrate rotates at a speed of about 10 revolutions per minute (rpm) to about 400 rpm (e.g., about 20 rpm to about 200 rpm) during deposition of the aluminum alloy by magnetron sputtering.

[0017] In at least one embodiment, a bias is applied to the substrate during various phases of the deposition process. For example, a bias is provided from a source (e.g., a DC source and / or an RF source) to a bias electrode (or chuck electrode) of a rotatable substrate table. The substrate is thereby bombarded with ions formed in the plasma during one or more phases of the deposition process. In at least one embodiment, the bias is applied to the substrate after the aluminum alloy deposition process is performed. Alternatively, the bias is applied during the aluminum alloy deposition process. A more negative substrate bias tends to cause positive ions generated in the plasma to move toward the substrate (and vice versa). This results in the ions having a greater amount of energy when they impact the substrate surface.

[0018] In at least one embodiment, the pulsed DC power supply is configured to supply power impulses of short duration (about 10 μs to about 200 μs) with voltages of, for example, about 1 megavolt (MV) to about 8 MV. Typical power supplies can supply power impulses at high voltages for short durations to generate high-density, high-energy plasma in pulsed DC processes. The voltage can be about 100 V to about 12,000 V. However, for aluminum alloy targets, a negative voltage pulse having a voltage of about 200 V to about 1,000 V (e.g., about 500 V to about 1,000 V) at the target relative to the anode (such as the wall of the vacuum chamber) can be sufficient. The power impulses (or energy pulses) can be generated by the power supply with a duration (or pulse width) and pulse cycle time. In one embodiment, each power impulse has a duration of about 10 μs to about 40 μs, and the pulse cycle time is about 200 μs, which corresponds to a pulse repetition frequency of 5000 Hz (i.e., an interval between successive pulses of 160-190 μs). The power or energy delivered over the pulse cycle time can have a non-square waveform throughout the duration, such that the average power over the entire duration can be between about 2 kilowatts (kW) and about 40 kW (e.g., about 2 kW to 40 kW). In at least one embodiment, each power impulse delivered to the target has a uniform power amount and / or a uniform duration. Alternatively, each pulse delivered to the target has a different power amount and / or a different duration.

[0019] To achieve a large amount of reactive energy and a high degree of ionization of the sputtered material in a HIPIMS process, various processing parameters can be controlled to promote low porosity and low brittleness of the resulting sputtered material. In some aspects, the process parameters include controlling the magnetic field strength of a magnetron positioned adjacent to the target and the amount of power supplied to a power impulse over a duration to generate a plasma having a desired energy and plasma density.

[0020] Increasing plasma density increases the HIPIMS deposition rate and ionization rate of sputtered atoms passing through the plasma. Furthermore, the plasma density peak shifts to shorter pulse widths as the bias voltage increases. Thus, the peak plasma density is a function of the target bias voltage and pulse width. In one example, a 500 V target bias is applied in a power impulse with a 2 A current and a 70 KHz pulse frequency.

[0021] After cleaning the steel substrate with one or more cleaning procedures, the substrate is mounted on a support operable to rotate during deposition. The cleaning procedures include sandblasting the substrate surface with alumina particles, followed by removing dust particles by blowing with air and argon. The target surface may also be cleaned prior to deposition. A typical target cleaning involves ultrasonic surface cleaning with acetone. In at least one embodiment, the substrate is cleaned using an argon ion plasma by reversing the polarity of the substrate or applying an additional voltage. During deposition of the aluminum alloy, the minimum distance between a portion of the target and a portion of the steel substrate is about 3 cm to about 20 cm (e.g., about 6 cm to about 10 cm).

[0022] 2 is a flow diagram of a method for depositing an aluminum alloy coating on a steel substrate in a magnetron sputtering chamber. As shown in FIG. 2, the method 200 begins by introducing the substrate into the chamber, optionally cleaning the substrate, and then using a high vacuum pump to apply a 5×10- 4 Less than Torr (e.g., 5×10 6 The method includes evacuating 202 a chamber (e.g., vacuum deposition device 200) to a pressure of less than 100 Torr. In at least one embodiment, prior to deposition, the steel substrate is heated to a temperature of about 300°C to about 900°C (e.g., about 450°C to about 700°C, about 570°C to about 630°C, etc.).

[0023] The method 200 includes flowing 204 a sputter gas into a processing region of a process chamber, the process chamber having an aluminum alloy sputter target. The method 200 includes providing 206 an energy pulse to the sputter gas to create a sputtering plasma. The sputter gas is typically a gas inert to the substrate or sputter target. In one example, the sputtering gas is argon. A constant argon flow is used, and the chamber pressure is about 15 mTorr or less (e.g., about 1 mTorr to about 10 mTorr, about 3 mTorr to about 8 mTorr, etc.). Deposition is initiated in a sputtering gas, preferably pure argon. The gas is introduced at a constant flow rate, and this constant flow rate is maintained throughout deposition. A sputtering plasma is formed in the processing space adjacent to the aluminum alloy sputter target to form a sputtered aluminum alloy material. In one embodiment, the sputtering plasma has a constant sputtering duration, and the energy pulse is 2 W / cm. 2 ~12W / cm 2 The sputtering plasma is controlled by a magnetic field, which is less than 900 Gauss.

[0024] Typically, providing the energy pulses involves selecting a target bias voltage and pulse width to provide the desired plasma energy to form a plasma that imparts the desired amount of energy to provide a fast ionization rate and high order of ionization of the sputtered atoms, thereby resulting in the desired sputter deposition rate. In one aspect, the energy pulses used to form the sputtering plasma each have a pulse width of about 1 W / cm. 2 ~about 10W / cm 2 The magnetron magnetic field can be less than about 300 Gauss (e.g., about 200 Gauss). In at least one embodiment, the substrate is 6 inches by 6 inches, and the total power of the sputtering process is about 1 kW. In at least one embodiment, even larger substrates (e.g., substrates with a top surface area of ​​15 m) can be sputtered. 2A substrate (such as a tungsten or aluminum alloy substrate) is used. Suitable large area coaters are available, for example, from Hind High Vac Pvt. Ltd. of Bengaluru, India. The method 200 includes sputtering 208 an aluminum alloy target to form a sputtered aluminum alloy, and depositing 210 the aluminum alloy on a substrate, such as a steel substrate.

[0025] In another embodiment, the magnetron sputtering method described above can be used to form one or more intermediate layers. Once the intermediate layer is formed, an aluminum alloy material is deposited onto the steel substrate containing the one or more intermediate layers. In at least one embodiment, the intermediate layer includes a second layer having metal oxides, nitrides, carbides, and metal oxynitrides.

[0026] example: To deposit the coating, a multi-target magnetron sputtering system from Hind High Vac Pvt. Ltd., Bengaluru, India, was used. This sputtering system has the capability to deposit on flat substrates with rotation and a vacuum device adapted for rotation to coat steel substrates.

[0027] Electrolytic grade aluminum ingots (99.9%), electrolytic grade Zn (99.9%), >99% pure Mg, and 99% pure Zr rods were used to produce aluminum and aluminum alloy targets for magnetron sputtering. The Al alloys were produced by a melting and casting process. A predetermined amount of pure metal was taken and melted in a resistance-heated furnace using a graphite crucible. The cast ingots were then machined into cylindrical rods, from which targets were machined using electrical discharge machining. The following alloy targets were produced by this process: i) Al-5Mg (5% Mg by weight, balance Al) ii) Al-5Zn-5Mg (5% Zn, 5% Mg, balance Al by weight) iii) Al-9Zn-5Mg (9% Zn, 5% Mg, balance Al by weight) iv) Al-9Zn-5Mg-1Zr (9% Zn, 5% Mg, 1% Zr, balance Al, by weight)

[0028] The cylindrical rod was cut into disk shapes with a thickness of 3 mm and a diameter of 3" and 2" to be used as a target. The target was attached to the cathode of a water-cooled chamber. The surface of the aluminum alloy target was ultrasonically cleaned with acetone and sputtered for 1 hour before deposition onto the substrate.

[0029] The substrate (4130 high strength steel) was sandblasted with alumina particles, blown with air and argon to remove dust particles, and then placed on a base plate attached with a shutter (to avoid any pre-sputtering contamination of the target).

[0030] The vacuum chamber is maintained at 1–2 × 10 pressure using a turbopump attached to the system. -6 The target was pumped down to 100 mbar. After sputter cleaning the target, aluminum or aluminum alloy was sputter deposited onto the substrate. The size of the substrate varied from 1 in. x 3 in. to 3 in. x 3 in. The coating thickness of the aluminum or aluminum alloy coating varied with the deposition time and deposition power. A typical deposition rate was calculated to be 2-3 micrometers per hour at a power of 300 watts (DC).

[0031] To deposit the aluminum alloy onto the flat steel substrate, the DC power, the argon flow rate into the chamber, and the deposition pressure (4–6 × 10) were adjusted so that each coating was formed on the respective steel substrate. -3Deposition parameters such as pressure (MPa) (mbar) and target-to-substrate distance (10 cm) were kept constant. Four substrates were coated simultaneously in this chamber. During deposition, the flat substrate rotated at 20 RPM. To deposit the alloy on the surface of 4340 high-strength steel, the sample rotated in the deposition chamber at 200 RPM. The target-to-substrate distance was 6 cm, and all other parameters were kept constant. During the sputtering process, the presence of oxygen in the chamber was minimized by evacuating the deposition chamber to obtain a sufficiently bright coating.

[0032] All coated samples received a conversion coating such as a chromate coating (e.g., ALODINE 1200). The stabilized samples were tested for corrosion protection performance by open circuit potential measurements in a salt spray chamber (according to ASTM B 117).

[0033] Porosity: The porosity of the samples was measured using a mercury porosimeter (AMP-60-KA-1, PMI, USA). The porosity was measured at a maximum mercury injection pressure of 30,000-60,000 PSI. The coated samples were ~10 -2 The chamber is evacuated to a vacuum level of 1000 mbar, and then mercury is introduced into the pores by applying water pressure. The amount of mercury injected into the pores is measured to determine the porosity of the coating. The solid metal substrate is considered to be free of any pores on the surface where the deposition took place.

[0034] In at least one embodiment, the aluminum alloy coatings of the present disclosure have a total pore volume fraction of about 5% or less and an average pore size of about 10 microns or less. For example, the aluminum alloy coatings may have a total pore volume fraction of about 0.1% to about 5% (e.g., about 1% to about 3%) and an average pore size of about 1 micron to about 10 microns (e.g., about 3 microns to about 7 microns). FIG. 3 is a graph showing the total pore volume fraction versus pore size for aluminum coatings deposited on steel substrates using ion vapor deposition or magnetron sputtering. As shown in FIG. 3, the aluminum coatings deposited using ion vapor deposition (and the aluminum alloy coatings of the present disclosure) have about 20% of their total pore volume due to the presence of pores greater than 5 microns in diameter (line 302). In comparison, the aluminum coatings deposited using magnetron sputtering (and the aluminum alloy coatings of the present disclosure) have only 5% of their total pore volume due to pores greater than 5 microns in diameter (line 304).

[0035] 4A and 4B are bar graphs showing pore size versus pore distribution for aluminum coatings deposited on steel substrates using ion vapor deposition or magnetron sputtering. As shown in FIG. 4A, more than 40% of the total pores in the aluminum coating (deposited by a conventional ion vapor deposition process) have a pore size greater than 0.5 microns. In comparison, as shown in FIG. 4B, less than 10% of the total pores in the aluminum coating (deposited by magnetron sputtering as described above) have a pore size greater than 0.5 microns.

[0036] Salt spray test (ASTM B 117) After 500 hours of salt spray exposure, sputter-deposited Al-5Mg coatings on steel substrates were found to have no visible red rust formation. Similarly, sputter-deposited Al-9Zn-5Mg coatings on steel substrates also had no red rust formation after 500 hours of salt spray testing. However, after 1,000 hours of salt spray testing, small spots of red rust were observed on the sputter-deposited Al-9Zn-5Mg coating. Ion vapor deposition is limited to pure Al coatings. Furthermore, IVD involving multiple elements is very difficult. Therefore, magnetron sputtering facilitates manipulation of the alloy composition. Current practice in the aerospace industry uses pure Al coatings by IVD, but these coatings do not provide sacrificial corrosion protection in pure water. Therefore, magnetron sputtering and Al alloy deposition offer advantages over conventional methods and corrosion-resistant materials. Furthermore, Al alloys offer better corrosion resistance than pure Al.

[0037] For Al-9Zn-5Mg-1Zr coatings sputter-deposited on steel substrates, no red rust formation is observed after 500 hours of salt spray testing (or even after 1,000 hours of salt spray testing). Alloys with Zn contents less than 9% can withstand shorter salt spray times. Similarly, alloys with Zn contents greater than 10% may experience increased hydrogen embrittlement due to the alloy's reactivity with chlorides in aqueous media. The corrosion-resistant alloy coatings described above have corrosion resistance similar to that of Zn-Ni plating, which has a corrosion resistance of greater than 500 hours according to ASTM B 117.

[0038] Wet Test Wet testing was also performed on steel substrates having sputter-deposited alloys of the present disclosure, for which scribed test panels were exposed to 100°F to 115°F (38 to 46°C) and a minimum relative humidity of 95% for 500 hours.

[0039] A steel substrate coated with sputter-deposited 100% aluminum has no visible red rust formation after 500 hours of wet testing. Similarly, a steel substrate coated with sputter-deposited Al-5Mg also has no visible red rust formation after 500 hours of wet testing. Similarly, a steel substrate coated with sputter-deposited Al-9Zn-5Mg-1Zr also has no visible red rust formation after 500 hours of wet testing.

[0040] Open circuit potential: The open-circuit potential was used as a quantitative measure of the corrosion protection ability of the disclosed aluminum alloy coatings disposed on steel substrates. The open-circuit potential of the coating should be negative relative to the steel, thereby indicating that the coating provides sacrificial corrosion protection to the steel. The open-circuit potential is a parameter that indicates the thermodynamic tendency of a material toward electrochemical oxidation in a corrosive medium. The open-circuit potential of the above aluminum alloy coatings was measured in distilled water and 3.5% NaCl solution over a period of 14 days according to ASTM G 82. An electrochemical cell was constructed with the coated surface as the working electrode, and a calomel electrode was used as the reference electrode. The temperature during the open-circuit potential measurements was maintained at approximately 30°C.

[0041] A comparative study of aluminum-coated steel substrates formed by magnetron sputtering versus conventional ion vapor deposition was performed. i) The open circuit potential of the pure aluminum coating is negative relative to the 4130 steel substrate in a 3.5% NaCl solution; ii) It was determined that the open circuit potential of the sputter-deposited and ion-vapor-deposited aluminum coatings was positive relative to the 4130 substrate in distilled water, indicating that the aluminum coatings were not sacrificial for the steel substrate.

[0042] Thus, the sputter-deposited aluminum alloy coatings of the present disclosure can be used to overcome the open circuit potential limitations of 100% Al coatings in distilled water, and may also provide improved corrosion resistance.

[0043] 100% aluminum, manganese (Mn)-containing aluminum alloys, magnesium (Mg)-containing aluminum alloys, and Mg-silicon (Si)-containing alloys have excellent corrosion resistance in water. However, the addition of copper (Cu) to these aluminum alloys increases the corrosion rate. Adding Mg to these aluminum alloys improves their corrosion resistance in seawater. Furthermore, Al-Mg alloys have better corrosion resistance in seawater than Al-Mg-Si alloys. At room temperature, Mg has a solid solubility of 2% in Al alloys, and when the Mg content exceeds 5%, the susceptibility of the aluminum alloy to stress corrosion increases. Therefore, it was decided to examine the maximum Mg content of Al alloys at 5%.

[0044] Increasing the zinc content improves the corrosion resistance of Al alloys. Furthermore, adding Mg to Al-Zn alloys further improves corrosion resistance. Al-Zn-Mg coatings offer better corrosion resistance than Al-Zn coatings. Furthermore, improvements in the mechanical properties and stress corrosion resistance of Al-Zn-Mg alloys can be achieved by including Zr in the alloy.

[0045] Figure 5 is a graph showing the open-circuit potential of Al-5Mg alloy in distilled water and 3.5% NaCl solution. As shown in Figure 5, the straight solid line represents the residual potential of steel in 3.5% NaCl solution (502) or pure water (504). The residual potential is the open-circuit potential if the circuit is open and allowed to equilibrate with the surrounding environment (such as seawater or pure water). The curved line represents the open-circuit potential value of Al-5Mg-coated steel in 3.5% NaCl solution (506) or pure water (508). The more negative the open-circuit potential value compared to steel in saltwater, the more sacrificial corrosion protection the aluminum alloy coating can provide to the steel. In pure water, the coating is more noble than steel, thus providing barrier protection.

[0046] Figure 6 is a graph showing the open-circuit potential of Al-5Zn-5Mg alloy in distilled water and 3.5% NaCl solution. As shown in Figure 6, the open-circuit potential of Al-5Zn-5Mg alloy is cathodic relative to steel in both media (water: line 602; 3.5% NaCl: line 604). The straight solid lines represent the residual potential of steel in 3.5% NaCl solution (606) or pure water (608). Again, the more negative the open-circuit potential value compared to steel in saltwater, the greater the degree of sacrificial corrosion protection the aluminum alloy coating can provide to the steel.

[0047] Figure 7 is a graph showing the open circuit potential of Al-9Zn-5Mg alloy in distilled water and 3.5% NaCl solution. As shown in Figure 7, Al-9Zn-5Mg alloy provides a lower open circuit potential than steel substrate in distilled water and saltwater media (lines 706 and 708, respectively) when compared to Al-5Zn-5Mg. The straight solid lines represent the residual potential of steel in 3.5% NaCl solution (704) or pure water (702).

[0048] Figure 8 is a graph showing the open circuit potential of Al-9Zn-5Mg-1Zr alloy in distilled water and 3.5% NaCl solution. As shown in Figure 8, the curved lines represent the open circuit potential values ​​of the Al-9Zn-5Mg-1Zr coated substrate in pure water (802) and 3.5% NaCl solution (804). The aluminum alloy coating provides sacrificial corrosion protection to steel. In pure water, the coating is less susceptible to corrosion than steel, thus providing barrier protection.

[0049] Hydrogen embrittlement Hydrogen embrittlement (HE) testing was performed in accordance with ASTM F 519 using notched Type 1a.1 specimens. In the HE test, a load is applied to a notch in a high-strength steel 4340 specimen (Type 1a.1) without any coating to determine an average notch fracture strength (NFS) value based on three uncoated samples. The average NFS for the high-strength steel 4340 samples was determined to be 3,953 kg at 200 hours. No failures per ASTM F 519 were observed.

[0050] The above-mentioned alloy was sputter-deposited onto a new high-strength steel 4340 specimen (Type 1a.1). The specimen was then subjected to a load of 75% of the average NFS value (75% of 3,953 kg = 2,964.75 kg, approximately 2,965 kg) and held for 200 hours. No fractures were observed, indicating that the coating passed the HE test. Alloy coatings deposited on high-strength steel 4340 specimens using a conventional ion vapor deposition process were also confirmed to pass this test; however, as noted above, the ion vapor deposition samples did not pass corrosion tests (especially the OCP test). Furthermore, the IVD coating required an additional shot peening step to reduce porosity and pass corrosion tests (i.e., salt spray).

[0051] Overall, the aluminum alloys of the present disclosure can be disposed on substrates such as steel substrates (e.g., aircraft components). The aluminum alloys of the present disclosure offer reduced porosity compared to coatings formed by ion vapor deposition. Additionally, compared to Zn-Ni plating, which cannot form coatings with two or more dissimilar metals, the aluminum alloys of the present disclosure allow for the use of a wider range of metals in corrosion-resistant coatings. The aluminum alloys of the present disclosure provide coatings with corrosion resistance equal to or greater than that of Zn-Ni plating, which has a corrosion resistance of 500 hours or more according to ASTM B 117. The alloys of the present disclosure can be formed without the use of organic solvents and other undesirable materials.

[0052] The description of various aspects of the present disclosure has been presented for illustrative purposes and is not intended to be exhaustive or to be limiting to the disclosed aspects. Numerous modifications and variations will be apparent to those skilled in the art that do not depart from the scope and spirit of the described aspects. The terminology used herein has been chosen to best explain the principles of the aspects, practical applications, or technical improvements over existing technology in the market, or to enable others skilled in the art to understand the aspects disclosed herein. While the foregoing is directed to aspects of the present disclosure, other and further aspects of the present disclosure may be devised without departing from its basic scope.

Claims

1. 1. An alloy coating for coating a steel substrate, the alloy comprising: Aluminum and 1 wt % to 15 wt % zinc, based on the total weight of the alloy; 1 wt % to 10 wt % magnesium based on the total weight of the alloy; and 0.1 wt % to 5 wt % zirconium based on the total weight of the alloy; An alloy coating having a total pore volume fraction of 0.1% to 5% and an average pore size of 10 microns or less.

2. The alloy coating of claim 1 , wherein the alloy comprises 5 wt % to 12 wt % zinc.

3. 3. The alloy coating of claim 1, wherein the alloy comprises 1 wt % to 5 wt % magnesium based on the total weight of the alloy.

4. 4. The alloy coating of claim 3, wherein the alloy comprises 5 wt% magnesium based on the total weight of the alloy.

5. 5. The alloy coating of claim 4, wherein the alloy comprises 9 wt% zinc based on the total weight of the alloy.

6. 6. The alloy coating of claim 5, wherein the alloy comprises 1 wt% Zr based on the total weight of the alloy.

7. The alloy is an alloy comprising 5 wt% Mg and 95 wt% Al; an alloy comprising 5 wt% Zn, 5 wt% Mg, and 90 wt% Al; an alloy comprising 9 wt% Zn, 5 wt% Mg, and 86 wt% Al; or 7. The alloy coating of any one of claims 1 to 6, wherein the alloy comprises 9 wt% Zn, 5 wt% Mg, 1 wt% Zr, and 85 wt% Al.

8. 8. The alloy coating of claim 7, wherein the alloy comprises 9 wt% Zn, 5 wt% Mg, 1 wt% Zr, and 85 wt% Al.

9. 9. The alloy coating of any one of claims 1 to 8, wherein no more than 10% of the total pores of the alloy have a pore size greater than 0.5 microns.

10. 10. A steel substrate having an alloy coating according to any one of claims 1 to 9 disposed on a surface thereof.

11. The steel substrate of claim 10, wherein the alloy coating has a thickness of from 1 μm to 50 μm.

12. The steel substrate of claim 11, wherein the alloy coating has a thickness of from 2 μm to 30 μm.

13. 12. The steel substrate of claim 10 or 11, wherein the alloy coating has an open circuit potential at 30°C in both distilled water and 3.5% sodium chloride solution according to ASTM G 82 that is lower than an aluminum coating of identical porosity.

14. 14. The steel substrate of any one of claims 10 to 13, wherein the alloy coating does not fracture at a load of 2,965 kg for 200 hours according to ASTM F 519.

15. 15. The steel substrate of claim 10, further comprising a second layer disposed between the steel substrate and the alloy, the second layer comprising a metal oxide, nitride, carbide, or oxynitride.

16. 1. A method for magnetron sputtering an alloy coating onto a substrate, comprising: flowing a sputter gas into a processing region of a process chamber, the process chamber having a sputter target made of an aluminum alloy, the aluminum alloy including one or more of: 1 wt % to 15 wt % zinc based on a total weight of the aluminum alloy; 1 wt % to 10 wt % magnesium based on a total weight of the aluminum alloy; and 0.1 wt % to 5 wt % zirconium based on a total weight of the aluminum alloy; providing an energy pulse to the sputter gas; depositing the alloy coating on a steel substrate; The alloy coating has a total pore volume fraction of 0.1% to 5% and an average pore size of 10 microns or less.

17. The method of claim 16 wherein the sputter gas is argon.

18. Providing an energy pulse to the sputter gas is greater than 2 W / cm ２ ~12 W / cm ２ 18. The method of claim 16 or 17, comprising providing an average power of

19. 19. The method of any one of claims 16 to 18, wherein supplying the energy pulse to the sputter gas comprises supplying a maximum sputter current of 0.1 A to 2 A and a maximum power of 0.3 kW to 5 kW.

20. 20. The method of any one of claims 16 to 19, wherein deposition is carried out at a DC power of 300 watts and a deposition rate of 2 micrometers / hour to 3 micrometers / hour.

21. Before providing the sputtering gas, a high vacuum pump was used to -４ 21. The method of any one of claims 16 to 20, further comprising evacuating the process chamber to a pressure below Torr.

22. 22. The method of any one of claims 16 to 21, wherein depositing comprises applying a magnetic field of less than 300 Gauss to the process chamber.

23. 23. The method of any one of claims 16 to 22, wherein the substrate rotates at 20 rpm to 200 rpm during deposition, and the distance between the surface of the sputter target and the surface of the substrate is 6 cm to 10 cm.

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