DE102014201761A1 - A method of producing a hardened aluminum material by a cross-coupling reaction - Google Patents

Abstract

[OBJECT] It is an object to provide a method for producing a hardened aluminum material which has a thick hardened layer which is extremely hard on the surface and whose hardness steadily decreases from the surface into the interior. [MEASURES TO SOLVE THE PROBLEM] The method for producing a hardened aluminum material is a method in which an aluminum alloy material including Mg elements is surface hardened, and includes a first step and a second step. In the first step, a nickel layer 20 of 15 μm is formed on a surface of an aluminum alloy material 10. In the second step, the aluminum alloy material 10 having the nickel layer 20 formed thereon is heated to 550 ° C. and held there for 60 to 90 minutes. In this way, Mg elements in a base material (the aluminum alloy material 10) serve as a catalyst that causes Mg ions and Al ions to diffuse to a surface of the nickel layer 20. A hardened layer of high hardness of intermetallic components of Al and Ni can thus be formed.

Description

Technical area

The present invention provides a processing method which shows that when a nickel layer of suitable thickness is formed on a surface of an aluminum alloy material containing Mg elements and the aluminum alloy material is heated to 500 ° C to 600 ° C, a coating of high hardness intermetallic compounds such as AlNi, Al3Ni, Al3Ni2, AlNi3 and Al3Ni5 (hereinafter referred to as AlmNin, if necessary) on a surface layer of the aluminum alloy material by a cross-coupling reaction catalyzed by Mg ions.

Relevant prior art

Automotive components have mostly been formed of iron and steel parts which have a relatively high specific gravity. However, in order to improve fuel efficiency, a lightweight base material having a small specific gravity has been sought to replace the iron and steel parts. Aluminum alloy materials, which have a specific gravity of about one third of that of iron, have attracted attention as alternative materials. Although having a low specific gravity, aluminum alloy materials are significantly inferior in strength and other properties to iron and steel materials even after being subjected to ordinary heat treatment. In addition, it is difficult to perform a surface hardening process such as nitriding in an aluminum alloy material in the air because an inert oxide coating is formed on the outermost surface. Surface hardening methods to improve the surface hardness of aluminum alloy materials have also been developed. An example of these methods is shown below.

The following Patent Document 1 describes a surface hardening method which performs an ion (plasma) nitriding process. In this surface hardening method, first, an iron-chromium alloy plating layer is formed on the surface of an aluminum alloy material by a plating process, and then an ion nitriding process is performed on the galvanized aluminum alloy material. With this glow-discharge ion nitriding process, high-energy nitrogen ions strike the surface of a workpiece. Upon impact, the nitrogen ions react with the iron-chromium and diffuse into the surface of the workpiece to form a hardened (nitride) layer of 5 μm to 20 μm, which consists of chromium nitride. Accordingly, the Vickers hardness of the surface of the hardened aluminum alloy material can be increased up to 700 HV to 1200 HV.

Documents on the state of the art

Patent documents

• [Patent Document 1] Japanese Patent Application Publication No. 06-235096 ( JP6-235096 A )

Summary of the invention

Technical problem

The ion nitriding method in Patent Document 1 has the following problems. First, it is difficult to form the extremely hard hardened layer to a thickness of 20 μm or more, and the hardened layer is extremely thin. The reason for this is that chromium nitride formed on the surface makes it difficult to continue the glow discharge of activating nitrogen ions and further makes it difficult for nitrogen ions to diffuse into the workpiece. In the portion in which nitrogen ions do not diffuse, that is, the portion in which the hardened layer is not formed, the hardness abruptly decreases as compared with the hardened layer. Therefore, the hardness of the hardened aluminum material in Patent Document 1 does not steadily decrease from the surface to the inside, and the hardened aluminum material is extremely hard only in the vicinity of the surface, and also thin. In the case where the hardened aluminum material is used in Patent Document 1 at a position where sliding friction is extremely large, the thin hardened layer soon wears away. This fact is not desirable in terms of product safety. When torsion or the like acts on the hardened aluminum material in Patent Document 1, cracking or separation may occur at the boundary of the hardened layer.

In order to solve the aforementioned problems, it is an object of the present invention to provide a method of producing a hardened aluminum material having a thick, hardened layer which is extremely hard on the surface and whose hardness steadily decreases from the surface to the inside to deliver.

the solution of the problem

The present invention provides a process for the production of a hardened aluminum material, in which a Aluminum alloy material, including magnesium elements, surface hardened. The method comprises a first step of removing an oxide film on a surface of the aluminum alloy material and then forming a nickel film of 10 μm or more, and a second step of depositing the aluminum alloy material having the nickel film formed thereon a temperature of not lower than 500 ° C and not higher than 600 ° C is heated and the aluminum alloy material is kept at the temperature for a predetermined time. In the second step, it is required that the aluminum alloy material be kept at the temperature for a predetermined time, based on a thickness of the nickel layer and the temperature of heating, until magnesium ions and aluminum ions in a base material diffuse toward a surface of the nickel layer to diffuse to form an intermetallic component in a surface layer of the aluminum alloy material by a cross-coupling reaction.

According to the present invention, Mg (magnesium) elements having a low vapor pressure ionize and actively diffuse to the surface layer because of a high temperature environment in which the heating temperature during a heat treatment is not less than 500 ° C and not more than 600 ° C is. During diffusion, the ionized Mg elements carry the ionized Al (aluminum) elements in the environment to move toward the surface layer of the aluminum alloy material. The Al ions which have been carried to the surface layer are coupled with the Ni (nickel) elements which are ionized in the surface layer to form high hardness intermetallic compounds (AlmNin) such as AlNi, Al3Ni, Al3Ni2, AlNi3, and Al3Ni5. That is, in a high temperature range, Mg elements act as a catalyst to react the ionized Al elements with the ionized Ni elements to produce high hardness intermetallic components. Consequently, the depth of the hardened layer is more than 1.5 times higher than that of a hardened layer formed by, for example, regular plating, so that a hardened aluminum material having the thick hardened layer can be produced in such a manner in that the hardness steadily decreases towards the inside.

In the method for producing a hardened aluminum material according to the present invention, in the second step, heating can be performed in a vacuum chamber at a low vacuum state of 100 Pa or less. In this case, a hardened aluminum material having a clean surface can be produced because the heating process is performed in a state of low oxygen concentration. Furthermore, the reaction process time can be reduced because the function of the ionized Mg elements becomes active as a catalyst. In the second step, the heating by a glow discharge can be performed by using an external ion vacuum furnace with heating.

Advantageous effects of the invention

According to the present invention, a hardened aluminum material can be produced which has a thick hardened layer which is extremely hard on the surface and in which the hardness steadily decreases from the surface to the inside. Even if the hardened aluminum material is used in portions in which sliding friction in automobile parts and other parts is extremely high, the hardened layer does not wear off quickly, which is desirable in terms of product safety. Even if torsion or the like is exerted, occurrence of cracking or separation at the boundary of the hardened layer is unlikely. For use in wristwatches or wristwatch cases, ideal products that are lightweight and resistant to damage can be expected.

BRIEF DESCRIPTION OF THE DRAWINGS

1 Fig. 10 is a schematic diagram showing an aluminum alloy material serving as a base material.

2 Fig. 10 is a schematic diagram showing the aluminum alloy material having a nickel layer and a chromium layer formed by a first step.

3 Fig. 10 is a schematic diagram showing a hardened aluminum material having a hardened layer formed by a second step.

4 is a state diagram of a binary alloy of aluminum and magnesium.

5 Fig. 10 shows a hardness transition curve of hardened aluminum material in the present embodiment.

6 FIG. 12 is a component table showing the weight percentages of the metal elements in each spectrum of the hardened aluminum material in the present embodiment. FIG.

7 Fig. 12 is an electron microscopic image of a surface portion when the aluminum alloy material containing magnesium elements involves undergoing a surface hardening process.

8th is a binary state diagram of aluminum and nickel.

9 is a hardness transition curve of a hardened aluminum material in a comparative example.

10 FIG. 15 is a component table showing the weight percent of metal elements in each spectrum of the hardened aluminum material in the comparative example.

11 Fig. 12 shows an electron microscopic image of a surface portion when an aluminum alloy material containing no magnesium is subjected to a surface hardening process.

Description of the embodiments

Embodiments of a method for producing a hardened aluminum material according to the present invention will be described below with reference to the drawings. 1 FIG. 12 is a schematic diagram showing an aluminum alloy material. FIG 10 shows, which serves as a base material for the production of a hardened aluminum material. The aluminum alloy material 10 is that of JIS 6061 and contains 0.8 to 1.2 wt.% Mg, 0.4 to 0.8 wt.% Si, 0.7 wt.% Fe, 0.15 to 0.40 wt.% Cu, 0.15 wt .-% Mn, 0.04 to 0.35 wt .-% Cr, 0.15 wt .-% Ti, with Al as the remainder. Here, the aluminum alloy material 10 any material containing Mg elements, for example one of JIS 5000 or 6000 series , This aluminum alloy material 10 is subjected to a surface hardening process by a first step and a second step as shown below.

First step

2 FIG. 12 is a schematic diagram showing the aluminum alloy material. FIG 10 shows which is a nickel layer 20 and a chrome layer 30 , which are formed by a first step, has. Here is the aluminum alloy material 10 which is in 1 is shown to have a strong affinity for oxygen, and therefore has a thin oxide coating (alumina layer) of about 100 angstroms on the surface. Because of the oxide layer, a plating layer which has good adhesion can not be directly on the surface of the aluminum alloy material 10 be formed. In the first step, the aluminum alloy material 10 first soaked in a zincate solution to remove the oxide coating. The aluminum alloy material 10 from which the oxide coating has been removed is placed in a plating solution in the next step, so that no new oxide coating is formed on the surface. A nickel layer 20 of 15 μm is then formed on the surface of the aluminum alloy material by an electroless plating method. A chrome layer 30 of 0.2 microns is then on the surface of the nickel layer 20 formed by a galvanizing process. The aluminum alloy material 10 which is the nickel layer 20 and the chrome layer 30 which is formed on this has (hereinafter called "the alloy material 10A with the electroplating layer ") is formed in this way. Although the chrome layer 30 is formed to prevent the oxidation of the outermost surface in the present embodiment, the chromium layer 30 not be provided in practice. The process to the nickel layer 20 is not limited to an electroless plating process and may be changed as appropriate. The nickel layer 20 can be formed by a plating method or a nickel powder adhering method.

Second step

3 FIG. 12 is a schematic diagram showing a hardened aluminum material. FIG 10B which is a hardened layer T1 formed by a second step. In the second step, first, a vacuum chamber (vacuum oven) is evacuated with a vacuum pump to reduce the pressure in the vacuum chamber to 0.1 torr (about 13.3 Pa) or less in order to reduce the oxygen partial pressure inside. The pressure in the vacuum chamber is then restored to about 500 torr (about 66,500 Pa) with an inert gas of nitrogen. In this condition, the temperature is raised to 450 ° C to 500 ° C. This is done because heat conduction by gas convention is much faster than heating by radiation in a vacuum. After raising the temperature to 450 ° C to 500 ° C by heating the environment, the pressure in the vacuum chamber is reduced to a low vacuum state of about 20 Pa (about 2 x 10 ^-4 atm). This is a preparatory step for a cross-coupling reaction. Then, the temperature in the reduced pressure chamber in the reduced pressure atmosphere is raised to 550 ° C (in mass production, allowed to 600 ° C) and held for 60 minutes to 90 minutes. Meanwhile, Mg elements ionize in the aluminum alloy material 10A and diffuse to the nickel layer 20 in the surface layer of the aluminum alloy material 10A together with the ionized Al ions in the environment. In the surface layer of the aluminum alloy material 10A Both Al ions, which are guided by Mg ions and Ni ions, undergo a cross-coupling reaction to be continuous to produce intermetallic components. After the oven is held at 550 ° C for the holding time of 60 minutes to 90 minutes, it is cooled down to 500 ° C to 450 ° C under the vacuum atmosphere. The continuous cooling serves to prevent separation of the produced intermetallic components. More specifically, because of the cooling, a considerably high tensile stress must be exerted between the hard intermetallic compound layer produced by the cross-coupling reaction and the core base material which has thermally expanded. To reduce the tension between them, the cooling rate of the workpiece must be set small. When the furnace temperature reaches approximately 500 ° C to 450 ° C, the pressure is restored to 500 Torr and the furnace is cooled by a fan to room temperature and then the pressure is restored to atmospheric pressure. The recovered hardened aluminum material 10B is then taken out. When an ion vacuum oven is used to perform a glow discharge glow process, it is desirable to use an external ion vacuum oven with heating in which the inside of a vacuum chamber is heated from the outside. In a conventional ion vacuum furnace, a small mass workpiece is heated only to a predetermined temperature for the duration of ion sputtering, at which electricity is dissipated on the surface of the workpiece during the glow discharge, and it is difficult to keep the set temperature steady. An ion vacuum oven having a heating element on the outside of the vacuum vessel is therefore necessary for heat-treating mass-produced parts having a small mass. In this case, the workpiece to be heated (the alloy material 10A with the plating layer) are heat-treated without being cooled, so that the heating process can stably be performed. The heating process may also be carried out using an atmosphere furnace instead of a conventional vacuum furnace or an ion vacuum furnace, as long as the surface oxidation and the length of the heat treatment time do not matter.

Here, the reason why the heating temperature is set to 550 ° C, with reference to 4 explained. 4 is a state diagram of a binary alloy of aluminum and magnesium. First, the heating temperature has to be a temperature above the solidus line SL, which in 4 and under a liquidus line LL which is shown in FIG 4 will be shown. That is, the temperature is not lower than 450 ° C and not higher than 660 ° C. The reason for this is that the solid phase of Mg and Al is melted and the movement of ionized Mg and Al in the base material (the aluminum alloy material 10 ) is facilitated. The melting point of Al is 660 ° C. Therefore, Al changes from the solid to the liquid state when the alloy material 10A is heated with the galvanizing layer near 660 ° C, and the base material is plastically deformed. The inventors have experimentally determined that cracking is likely to occur when the alloy material 10A with the plating layer with the conditions described above is heated to 480 ° C. The inventors have therefore found that it is desirable in the present embodiment that the alloy material 10A is heated with the galvanizing to a temperature of not less than 500 ° C and not more than 600 ° C.

The reason why the pressure in the negative pressure chamber is reduced to about 20 Pa is that the heating process, which is performed at a low oxygen concentration, is the hardened aluminum material 10B can produce with a clean surface. Another reason is that the Mg ions that are ionized in the base material are able to move actively more easily than they evaporate, thereby reducing the reaction process time. However, the heating process need not necessarily be performed in a low vacuum state such as 100 Pa or less, and the heat treatment may be performed even under the atmospheric condition, although a longer process time and some surface oxidation are unavoidable.

The components of metal elements in the produced hardened aluminum material 10B be related to 6 and 7 described. The hardened aluminum material 10B is analyzed by using a scanning electron microscope and an energy dispersive X-ray analyzer (SEM-EDX). 7 FIG. 12 is an electron micrograph of a surface portion of the hardened aluminum material. FIG 10B , and 6 is a component table showing the weight% of metal elements in each spectrum of the hardened aluminum material 10B in the current embodiment. Hitachi-Hitec S-4800 & Horiba EX 350-act is used for SEM-EDX. As an analysis condition, the acceleration voltage is set to 20 kV.

In 7 has a first layer S1 on the surface of the hardened aluminum material 10B that is, the range of spectra 1 to 3, a darker color than a second layer S2 below. This first layer S1 is an extremely hard section. The second layer S2 below the first layer S1, that is, the region of the spectra 4 to 8, has a lighter color. The second layer S2 is a portion where properties of the nickel layer 20 are left largely. A third layer S3 under the second layer S2, that is, the range of spectrum 9 to 11, has a darker color. The third layer S3 is a portion where properties of the base material (the aluminum alloy material 10 ) and properties of the nickel layer 20 are mixed.

6 shows the depth (μm) of the surface and the weight% of metal elements for each spectrum. Here, the first layer S1, in particular the weight% of Mg, Al and Ni, will be described. The first layer S1 is a portion in the range of spectra 1 to 3, in which the depths from the surface are 0.00 μm to about 3.73 μm. The first layer S1 is a portion in which the chromium layer 30 of 0.2 mm is formed on the surface and the nickel layer 20 of 15 microns under the chrome layer 30 is formed before it is subjected to the second step. The weight% of Cr is ignored because of the chrome layer 30 an extremely thin layer. Before undergoing the second step, the first layer S1 contains an extremely high amount (for example, 80% or more) of Ni due to the nickel layer 20 , However, as a result of undergoing the second step, the Ni is reduced to 20% or less in the first layer S1, whereas Al is increased up to 70% or more, as in FIG 6 shown. These phenomena may occur because Mg elements evaporate from the interior of the base material to the surface layer while acting as a catalyst (Mg ions) and remain in the surface layer in the amount of 5% or more. Further discussion will be given below.

The reason why 5% or more of Mg, which would have hardly existed before it undergoes the second step, exists in the first layer S1 is supposed to be that ionized Mg from the inside of the base material moves to the surface layer in the second step. The reason why 70% or more of Al, which would have hardly existed before being subjected to the second step, is that Mg moving from the inside of the base material in the second step to the surface simultaneously acts as a catalyst which accelerates that ionizes Al inside the material and diffuses to the surface layer. Ni, which would exist in excess before undergoing the second step, is reduced to 20% or less after the second step. This is because Ni in the second step simultaneously diffuses with the movement of Mg and Al toward the inside of the base material, and is coupled with Al in the base material to produce intermetallic compounds (Almin) such as AlNi, Al3Ni, Al3Ni2, AlNi3, and Al3Ni5. Here is 8th a binary state diagram of aluminum and nickel showing the relationship between Al and Ni, wherein the horizontal axis shows the ratio of each of Al and Ni in weight%, and the vertical axis shows the temperature. Like the binary state diagram, which is in 8th 5, five intermetallic components as described above (AlNi, Al3Ni, Al3Ni2, AlNi3, and Al3Ni5) are prepared.

The second layer S2, in particular the weight% of Mg, Al and Ni, will be described. The second layer S2 is a portion in the region of the spectra 4 to 8, in which the depths from the surface are 5.53 μm to 26.9 μm. This second layer S2 is a section in which the nickel layer 20 is formed in the upper portion S2a (in the spectra 4 and 5), and the lower portion S2b (in the spectra 6 to 8) is the base material before undergoing the second step. Therefore, the upper portion S2a of the second layer S2 includes an extremely large amount of Ni due to the nickel layer before undergoing the second step 20 , The lower portion S2b of the second layer S2 includes an extremely large amount of Al due to the base material before undergoing the second step. However, as a result of undergoing the second step, the second layer S2 includes 30% or more and 50% or less of Ni elements, 70% or less, and 50% or more Al elements, and 5% or less of Mg elements, as in 6 shown. A discussion based on this result will be made below.

The reason why the amount of Mg in the second layer S2 is lower than that in the first layer S1 is that in the second step, a large amount of Mg moves from the base material to the first layer. The reason why the upper portion S2a of the second layer S2 contains 70% or less and 50% or more Al elements, which would hardly exist before undergoing the second step, is that Al differs from the base material and the lower portion S2b of FIG second layer S2 moves in the second step. The reason why the lower portion S2b of the second layer S2 contains 30% or more and 50% or less of Ni, which would hardly exist before undergoing the second step, is that Ni is different from the first layer S1 and the upper portion S2a the second layer S2 moves in the second step.

The third layer S3, in particular the weight% of Mg, Al and Ni will now be described. The third layer S3 is a portion in the range of the spectra 9 to 11, in which the depths from the surface are 30.44 to 38.9 μm. The third layer S3 is a portion which is a base material before undergoing the second step. Therefore, the third layer S3 includes an extremely large amount of Al before undergoing the second step. However, as a result of undergoing the second step, the weight% of Al increases toward the inner side (from spectrum 9 to spectrum 11) in FIG third layer S3, and Al is 90% or more in spectrum 11, as in 6 shown. As in 7 As shown, the weight% of Ni decreases toward the inner side in the third layer S3, and Ni is 1% or less in the spectrum 11. On the basis of this, the third layer S3 approximates the base material in terms of its properties and is less influenced by the surface hardening process in the second step towards the inner side.

The relationship between the Vickers hardness (HV) and the depth (μm) of the surface of the hardened aluminum material 10B will now be referring to 5 described. The hardness transition curve of the hardened aluminum material 10B , what a 5 is produced by the following method. First, the hardened aluminum material 10B cut vertically to the surface, and the cut surface is polished to serve as a test surface. At positions to be measured on the test surface, a measurement is made sequentially by Vickers hardness tests, while the hardened aluminum material 10B is moved. The hardness transition curve is generated in this way.

As in 5 showed this hardened aluminum material 10B a Vickers hardness of 84 HV as the base material and a Vickers hardness of 95 HV at a depth of 75 μm. The hardened layer T1 of the hardened aluminum material 10B is a layer in which the intermetallic components (AlNi, Al3Ni, Al3Ni2, AlNi3, Al3Ni5) are produced. The surface portion is very hard because the Vickers hardness at the surface is 780 HV and the Vickers hardness at a depth of 20 μm from the surface is 742 HV. This can be assumed from the distribution state of Al and Ni in the region of the first layer S1 (spectrum 1 to spectrum 3), which in 6 is shown. The hardened layer T1 is thick and its hardness steadily decreases from the surface to the inside because the Vickers hardness is 237 HV at a depth of 50 μm from the surface. That is, the weight% of Ni ions for the production of an intermetallic component (AlmNin) becomes 30% or less in a range exceeding 20 μm from the extremely possible surface, and the hardness then decreases.

The inventors contemplated that the reason why the hardened layer T1 is formed as described above is related to Mg elements included in the aluminum alloy material 10 are included. The inventors then performed the same surface hardening process as described in the first step and second step above, using an aluminum alloy material 40 which does not contain Mg elements, instead of the aluminum alloy material 10 containing Mg elements is used, whereby a hardened aluminum material was prepared as a comparative example (hereinafter, the hardened aluminum material 40B called). The aluminum alloy material 40 which was used as a base material, this is out JIS 2011 and contains 0.40% by weight of Si, 0.7% by weight of Fe, 5.0% to 6.0% by weight of Cu, 0.3% by weight of Zn, and 0.2 to 0.6% by weight % Pb or 0.2-0.6 wt% Bi, where Al is the excess. The components of metal elements in the hardened aluminum material 40B be related to 10 and 11 described.

In 11 has a first layer U1 on the surface of the hardened aluminum material 40B , that is, the range of spectra 1 to 3, a bright color. With reference to spectra 1 to 3 in 10 is an extremely high amount of Ni, whereas no Al is contained. In 11 has a second layer U2 below the first layer U1, that is, spectrum 4, a darker color than the first layer U1. With reference to spectrum 4 in 10 For example, the amount of Ni is less than that in the first layer U1, whereas the amount of Al is larger than that in the first layer U1. With reference to spectra 5 and 6 in 10 is hardly contained Ni, with an extremely high proportion of Al is included. Based on these, Al diffuses in the hardened aluminum material 40B not from the base material to the surface as in the hardened aluminum material 10B and a large amount of Ni, which is the nickel layer, remains on the surface side.

The relationship between the Vickers hardness (HV) and the depth (μm) of the surface of the hardened aluminum material 40B is related to 9 described. As in 9 shown has the hardened aluminum material 40B a Vickers hardness of 73 HV to 79 HV as the base material and has a Vickers hardness of 64 HV at a depth of 20 microns. The hardened aluminum material 40B Therefore, it has a hardened layer which is harder than the base material to a depth of about 15 μm from the surface. The hardened aluminum material 40B however, originally has a nickel layer of 15 μm, and the hardness of the hardened layer is equivalent to the hardness of the nickel layer. The hardened layer is therefore not the one newly formed by the second step, but the nickel layer is left as it is.

The operation and effects of the present embodiment will be described. According to the present embodiment, which has been heated in a high-temperature atmosphere, Mg elements having a low vapor pressure ionize and actively diffuse toward the surface layer. During diffusion, the ionized Mg elements cause the ionized Al elements in the environment to move toward the surface layer. The Al ions, which to Surface layer are coupled with Ni elements which have been ionized in the surface layer to produce high hardness intermetallic components (AlmNin). That is, Mg elements act as a catalyst in a high-temperature atmosphere and allow the ionized Al elements and Ni elements to undergo cross-coupling reaction to produce high-hardness intermetallic compounds. As a result, the depth of the hardened layer T1 is more than 1.5 times as thick as the thickness of a hardened layer obtained by, for example, conventional plating, so that the hardened aluminum material 10B having the thick hardened layer T1 can be made in such a manner that the hardness decreases toward the inside.

The hardened aluminum material 10B , which is manufactured according to the present embodiment, can be used for automotive components such as cylinders and valves, which are exposed to friction due to sliding or the like. The surface portion of the hardened aluminum material 10B is very hard because the Vickers hardness is 750 HV or more at the surface, and the Vickers hardness is 700 HV or more at a depth of at least 20 μm from the surface. In particular, the hardened layer T1 is thick because the Vickers hardness is 200 HV or more at a depth of at least 50 μm from the surface, and the hardness of the hardened layer T1 steadily decreases from the surface to the inside. Accordingly, even if this is hardened aluminum material, it will wear out 10B is used in places where sliding friction is extremely high, the hardened layer T1 does not degrade quickly, which is desirable in terms of product safety. Even if torsion or the like is applied, cracking or separation at the boundary of the hardened layer is unlikely to occur. Although stainless steel wristbands made of austenitic stainless steel materials have been conventionally used, they are relatively heavy and soft on the surface so that they are easily damaged. When the prepared hardened aluminum material 10B For wrist watch bands, ideal goods which are lightweight and resistant to damage can be expected because the surface has a Vickers hardness of 750 HV or more because of the intermetallic components (AlmNin).

The inventors conducted the surface hardening process in the second step with an aluminum alloy material 10 which only the chrome layer 30 of 15 μm instead of the aluminum alloy material 10 through which the nickel layer 20 of 15 microns and the chromium layer 30 of 0.2 μm. In this case, though the Vickers hardness became the outermost surface of the chrome layer 30 1048 HV, the hardened layer of the produced hardened aluminum material is destroyed by separation. The inventors thereby have the validity of the surface hardening process in the second step in the aluminum alloy material 10 which is the nickel layer 20 own formed on this confirms.

When the thickness of the nickel layer 20 As the temperature rises and the heating temperature drops, the time required for the Mg ions and Al ions in the base material to increase toward the surface of the nickel layer increases 20 to diffuse. A predetermined time for heating and holding the alloy material 10A with the plating layer is therefore selected based on the thickness of the nickel layer 20 and the heating temperature, taking into account the time it takes for the Mg and Al ions in the base material to reach the surface of the nickel layer 20 to diffuse, and for Ni ions in the nickel layer 20 to diffuse towards the inside of the base material.

Although the method for producing a hardened aluminum material according to the present invention has been described above, the present invention is not limited thereto, and various modifications can be made in a range not departing from the scope of the invention. For example, the method of removing the oxide layer on the aluminum alloy material 10 is not limited to a method in which it is soaked in a zincate solution, and the oxide layer can be removed by, for example, a sputtering process.

The thickness of the chrome layer 30 (0.2 μm), the heating temperature (550 ° C), the pressure in the vacuum chamber (about 20 Pa), and the process time of the second step (60 minutes to 90 minutes) are not limited to the numerical values described above and can be changed appropriately. The nickel layer 20 which has a thickness of 15 μm is formed in the present embodiment. However, as long as the nickel layer 20 has a thickness of 10 μm or more, a hardened layer of 15 μm intermetallic component is formed, which is at least 1.5 times thicker. Therefore, the thickness of the nickel layer 20 can be appropriately changed as long as it is 10 μm or more.

The time and thickness in which the hardened layer having high hardness of intermetallic components is produced are determined by the heat treatment time (the temperature of not less than 500 ° C and not more than 600 ° C), and the holding time should be set , Although the thermal expansion and shrinkage rate of the aluminum alloy material used as the base material When used, the thermal expansion and shrinkage rate of the produced cured layer are extremely small. Accordingly, a tensile strength A1 of the surface layer and a tensile stress B1 due to shrinkage of the uncured portion between the surface layer (the hardened layer) which has been hardened and the uncured portion of the base material are exerted when the heat treatment is finished, and the workpiece is cooled down to room temperature. If the tensile stress B1 is greater than the tensile strength A1, the hardened layer may be separated. Therefore, the thickness of the nickel layer to be formed on the surface of the aluminum alloy material is determined by calculating the tensile stress B1 at half the thickness of the aluminum alloy material and calculating the tensile strength A1 exceeding the tensile stress B1.

LIST OF REFERENCE NUMBERS

10

Aluminum alloy material

10A

Alloy material with galvanizing layer

10B

hardened aluminum material

T1

hardened layer

S1

first shift

S2

second layer

S3

third layer

20

nickel layer

30

chromium layer

40

Aluminum alloy material

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 6-235096 A [0004]

Cited non-patent literature

• JIS 6061 [0022]
• JIS 5000 or 6000 series [0022]
• JIS 2011 [0036]

Claims (4)

A method of producing a hardened aluminum material in which an aluminum alloy material containing magnesium elements is surface-hardened, characterized by comprising: a first step of removing an oxide layer on a surface of the aluminum alloy material and thereafter forming a nickel layer of 10 μm or more ; and a second step of heating the aluminum alloy material having the nickel layer formed thereon to a temperature of not less than 500 ° C and not more than 600 ° C and heating the aluminum alloy material at the temperature for a predetermined time Time is kept. A method of producing a hardened aluminum material according to claim 1, characterized in that in the second step, the aluminum alloy material is held at the temperature for a predetermined time, based on a thickness of the nickel layer and the temperature of heating, up to magnesium ions and aluminum ions in a base material diffuse to a surface of the nickel layer. A method of producing a hardened aluminum material according to claim 1 or 2, characterized in that in the second step, the heating is carried out in a vacuum chamber in a low vacuum state of 100 Pa or less. A method for producing a hardened aluminum material according to any one of claims 1 to 3, characterized in that in the second step, the heating is carried out with a glow discharge, wherein an external ion vacuum furnace is used with heating.

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