JP2023032361A - Aluminum alloy substrate for magnetic disks, and magnetic disk including the same - Google Patents

Abstract

To provide an aluminum alloy substrate for magnetic disks that achieves excellent impact resistance and energy saving, and a magnetic disk including the same.SOLUTION: An aluminum alloy substrate for magnetic disks contains an aluminum alloy containing Mg: 1.00-3.50 mass%, with the balance being Al and inevitable impurities, the aluminum alloy substrate having a Young's modulus of 68.7 GPa or more and a density of 2.72 g/cm3 or less. A magnetic disks has, on the surface of the aluminum alloy substrate for magnetic disks, an electroless Ni-P plated layer, and a magnetic layer over the electroless Ni-P plated layer.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an aluminum alloy substrate for a magnetic disk having good impact resistance and energy saving, and a magnetic disk using the aluminum alloy substrate for a magnetic disk.

2. Description of the Related Art Hard disk drives (hereinafter abbreviated as “HDD”) are widely used as storage devices in electronic devices such as computers and video recorders. The HDD incorporates a magnetic disk for recording data. The magnetic disk has an annular aluminum alloy substrate made of an aluminum alloy, a Ni—P plating layer covering the surface of the aluminum alloy substrate, and a magnetic layer laminated on the Ni—P plating layer. ing.

By the way, in recent years, due to needs such as multimedia, there is an increasing demand for large capacity and high density magnetic disk devices such as HDDs. The number of magnetic disks mounted in a storage device tends to increase in order to further increase the capacity, and along with this, there is a demand for thinner magnetic disks.

However, when the thickness of the magnetic disk substrate is reduced, there is a problem that the rigidity is lowered. If the rigidity is lowered, the impact resistance, which indicates the extent to which the substrate is difficult to deform, is lowered. In addition, as the number of substrates increases, power consumption becomes too large when used as a magnetic disk device, so power saving (hereinafter simply referred to as "energy saving") is also required. In addition to the use of magnetic disk devices, energy reduction (energy saving (hereinafter simply referred to as "energy saving")) during magnetic disk manufacturing is also becoming more important.

Under such circumstances, in recent years, a magnetic disk substrate having high rigidity and excellent energy saving has been strongly desired and studied. For example, Patent Literature 1 proposes a method of increasing the rigidity of an aluminum alloy substrate by adding a large amount of elements such as Fe, Mn, and Ni that contribute to the improvement of the rigidity of the aluminum alloy substrate.

JP 2017-186597 A

However, in the method disclosed in Patent Document 1, in which the content of Fe, Mn, Ni, etc. is increased to improve only the rigidity, the density of the aluminum alloy substrate is increased, and the desired good energy saving property is not achieved. The current situation was that there was none.

The present invention has been made in view of the above problems, and the present inventors have found that by controlling the content of various additive elements, the density and the Young's modulus of the aluminum alloy, good impact resistance and energy saving can be achieved. The inventors have found that an aluminum alloy substrate for a magnetic disk can be obtained, which has led to the completion of the present invention.

According to claim 1, the present invention comprises an aluminum alloy containing Mg: 1.00 to 3.50 mass%, the balance being Al and unavoidable impurities, having a Young's modulus of 68.7 GPa or more and a density of 2.72 g / An aluminum alloy substrate for a magnetic disk is provided, which is characterized by having a surface area of 1 cm ³ or less.

In claim 2 of claim 1, the aluminum alloy comprises Fe: 1.80 mass% or less, Mn: 1.80 mass% or less, Ni: 3.00 mass% or less, Cu: 0.40 mass% or less, Zn : 0.70 mass% or less, Cr: 0.40 mass% or less, Si: 0.60 mass% or less, and Be: 0.0020 mass% or less. .

According to claim 3 of the present invention, in claim 1 or 2, the aluminum alloy is selected from the group consisting of Sr: 0.100 mass% or less, Na: 0.100 mass% or less, and P: 0.100 mass% or less. It shall further contain a seed or two or more.

According to claim 4 of the present invention, in any one of claims 1 to 3, the electric conductivity of the magnetic disk aluminum alloy substrate is 32.0%IACS or more.

In claim 5, the present invention provides an electroless Ni—P plating layer and the electroless Ni—P plating layer on the surface of the aluminum alloy substrate for a magnetic disk according to any one of claims 1 to 4. and a magnetic layer on the magnetic disk.

The magnetic disk aluminum alloy substrate according to the present invention can achieve good impact resistance and energy saving by controlling the content of various additive elements, density and Young's modulus.

FIG. 2 is a plan view showing a measurement sample in the direction of 0° from the rolling direction of the magnetic disk aluminum alloy substrate for measuring Young's modulus. FIG. 3 is a plan view showing a measurement sample in the direction of 45° from the rolling direction of the magnetic disk aluminum alloy substrate for measuring the Young's modulus. FIG. 3 is a plan view showing a measurement sample in the direction of 90° from the rolling direction of the magnetic disk aluminum alloy substrate for measuring the Young's modulus.

A. Magnetic Disk Aluminum Alloy Substrate The magnetic disk aluminum alloy substrate (hereinafter sometimes referred to as "aluminum alloy substrate" or "substrate") according to the present invention will be described. The aluminum alloy substrate is produced by using an aluminum alloy having a predetermined alloy composition to produce an aluminum alloy plate, which is punched into an annular shape to obtain an aluminum alloy disk blank for a magnetic disk (hereinafter, "aluminum alloy disk blank" or "disk blank"). ). Next, the disk blank is subjected to pressure annealing, followed by further annealing, followed by cutting and grinding, and if necessary, heat treatment for stress relief to form an aluminum alloy substrate.

The aluminum alloy of the aluminum alloy substrate contains Mg: 1.00 to 3.50 mass% (hereinafter simply referred to as "%") as an essential element. Further, as the first optional element, Fe: 1.80% or less, Mn: 1.80% or less, Ni: 3.00% or less, Cu: 0.40% or less, Zn: 0.70% or less, Cr : 0.40% or less, Si: 0.60% or less, and Be: 0.0020% or less. Furthermore, as a second optional element, one or more selected from the group consisting of Sr: 0.100% or less, Na: 0.100% or less, and P: 0.100% or less . The aluminum alloy is composed of the above essential elements, the first and second optional elements, and the remainder Al and unavoidable impurities. An aluminum alloy substrate made of such an aluminum alloy has a Young's modulus of 68.7 GPa or more and a density of 2.72 g/cm ³ or less. Furthermore, it is preferable that the aluminum alloy substrate has an electrical conductivity of 32.0% IACS or more.

When the Young's modulus of the aluminum alloy substrate is 68.7 GPa or more, the rigidity of the substrate is improved, and the impact resistance indicating the extent to which the substrate is difficult to deform can be excellent. In addition, since the density of the substrate is 2.72 g/cm ³ or less, the weight of the substrate can be reduced, so that the power consumption can be reduced when used as a magnetic disk device, and the energy saving performance is excellent. can be Furthermore, since the conductivity of the substrate is 32.0% IACS or more, the thermal conductivity is increased and the energy required for heat treatment can be reduced, thereby further improving the energy saving. As a result, both impact resistance and energy saving can be achieved.

A-1. Alloy Composition of Aluminum Alloy The composition of the aluminum alloy used for the aluminum alloy substrate and the reasons for its limitation will be described in detail below.

Mg: 1.00-3.50%
Mg is contained as an essential element in aluminum alloys, exists mainly as solid solution Mg, and exhibits the effect of improving the strength of aluminum alloy substrates. In addition, since the zincate film during the zincate treatment of the aluminum alloy substrate is uniformly, thinly and densely adhered, the smoothness of the plating surface made of electroless Ni—P can be achieved in the plating process, which is the next step after the zincate treatment process. improve. However, if the Mg content is less than 1.00%, the strength of the aluminum alloy substrate is insufficient, and deformation occurs during processing such as cutting and grinding. Furthermore, the zincate film formed by the zincate treatment becomes non-uniform, and the adhesion and smoothness of the plating deteriorate. On the other hand, when the Mg content exceeds 3.50%, the Young's modulus of Mg is lower than that of Al, resulting in a significant decrease in Young's modulus. As a result, the rigidity of the substrate is lowered and the impact resistance is lowered. Therefore, in the aluminum alloy substrate of the present invention, the Mg content of the aluminum alloy is specified as 1.00 to 3.50%. In addition, the Mg content is preferably 1.30 to 3.30%, more preferably 1.60 to 3.00%, and still more preferably 1.80%, from the balance between strength and manufacturability. ~2.50%.

In addition to Mg, the aluminum alloy may further contain one or more selected from the group consisting of Fe, Mn, Ni, Cu, Zn, Cr, Si and Be as a first arbitrary element. . In addition, the aluminum alloy contains one or more selected from the group consisting of Sr, Na, and P as a second optional element, in addition to Mg, or in addition to Mg and the first optional element It may further contain:

Each arbitrary element will be described in detail below.

Fe: 1.80% or less The aluminum alloy may contain Fe as the first optional element. Fe mainly exists as second-phase particles (such as Al—Fe-based intermetallic compounds), and other part exists in a solid solution in the matrix. When the Fe content in the aluminum alloy exceeds 1.80%, a large number of coarse Al—Fe intermetallic compound particles are produced. Coarse Al—Fe intermetallic compounds are harder to grind than the aluminum matrix and are difficult to cut, causing a reduction in the grinding rate during grinding and an increase in production costs. In addition, such coarse Al-Fe-based intermetallic compound particles fall off during etching, zincate treatment, cutting or grinding to generate large depressions, and plating pits occur, resulting in smoothness of the plating surface. decrease and peeling of plating. Moreover, the workability in the rolling process is also deteriorated. Furthermore, since Fe has a higher density than Al, if the amount of Fe is too large, the density will increase significantly, resulting in a decrease in energy saving performance. Therefore, the Fe content in the aluminum alloy should be 1.80% or less, preferably 1.30% or less, and more preferably 1.00% or less. Although the lower limit of the Fe content is not particularly set, since Fe is usually present in raw materials as an unavoidable impurity, the lower limit is about 0.001% in this case. Note that the Fe content may be 0% (0.000%).

Mn: 1.80% or less The aluminum alloy may contain Mn as the first optional element. Mn mainly exists as second-phase particles (Al—Mn intermetallic compounds, etc.), and the other part exists in a solid solution in the matrix. When the Mn content in the aluminum alloy exceeds 1.80%, a large number of coarse Al—Mn intermetallic compound particles are produced. Coarse Al—Mn intermetallic compounds are harder to grind than the aluminum matrix and are difficult to grind, causing a reduction in the grinding rate during grinding and an increase in production costs. In addition, such coarse Al-Mn-based intermetallic compound particles fall off during etching, zincate treatment, cutting or grinding to generate large dents, and the smoothness of the plating surface due to the generation of plating pits. decrease and peeling of plating. Moreover, the workability in the rolling process is also deteriorated. Furthermore, since Mn has a higher density than Al, if the amount of Mn is too large, the density will increase significantly, resulting in a decrease in energy saving performance. Therefore, the Mn content in the aluminum alloy should be 1.80% or less, preferably 1.30% or less, and more preferably 1.00% or less. The lower limit of the Mn content is not particularly set, and may be 0%.

Ni: 3.00% or less The aluminum alloy may contain Ni as the first optional element. Ni mainly exists as second-phase particles (Al—Ni system intermetallic compound, etc.), and other part exists as a solid solution in the matrix, and both exhibit the effect of improving the Young's modulus and the like of the aluminum alloy substrate. When the Ni content in the aluminum alloy exceeds 3.00%, a large number of coarse Al—Ni intermetallic compound particles are produced. Coarse Al—Ni based intermetallic compounds have a higher hardness than the aluminum matrix, and are therefore difficult to grind, causing a reduction in the grinding rate during grinding and an increase in production costs. In addition, such coarse Al-Ni intermetallic compound particles fall off during etching, zincate treatment, cutting or grinding to generate large dents, and plating pits occur, resulting in the smoothness of the plating surface. decrease and peeling of plating. Moreover, the workability in the rolling process is also deteriorated. Furthermore, since Ni has a higher density than Al, if the amount of Ni is too large, the density will increase significantly, resulting in a decrease in energy saving performance. Therefore, the Ni content in the aluminum alloy should be 3.00% or less, preferably 2.80% or less, more preferably 2.50% or less. The lower limit of the Ni content is not particularly set, and may be 0%.

Cu: 0.40% or less The aluminum alloy may contain 0.40% or less of Cu as the first optional element. Cu has the effect of suppressing the elution of Al from the aluminum alloy during the zincate treatment in the manufacturing process of the magnetic disk. By reducing the Cu content to 0.40% or less, a dense, thin, and thin Zn film with little thickness variation is attached to the surface of the aluminum alloy substrate when the zincate treatment is performed in the manufacturing process of the magnetic disk. can be made By forming such a Zn film, it is possible to form a smooth electroless Ni--P plated layer by electroless Ni--P plating in a post-process.

However, if the Cu content is too high, the corrosion resistance of the aluminum alloy substrate is lowered, and local areas where Al easily dissolves are formed. Therefore, when the zincate treatment is performed in the manufacturing process of the magnetic disk, the amount of Al dissolved on the surface of the aluminum alloy substrate becomes uneven, and the thickness of the Zn film tends to vary greatly. As a result, the adhesion between the electroless Ni--P plated layer and the aluminum alloy substrate is lowered, and the smoothness of the electroless Ni--P plated layer is lowered.

By setting the Cu content in the aluminum alloy to 0.40% or less, preferably 0.30% or less, the formation of plating pits is suppressed and the smoothness of the electroless Ni—P plating layer is further enhanced. can be done. The lower limit of the Cu content is preferably 0.003%, more preferably 0.010%. Note that the Cu content may be 0% (0.000%).

Zn: 0.70% or less The aluminum alloy may contain 0.70% or less of Zn as the first optional element. Zn, like Cu, has the effect of suppressing the elution of Al from the aluminum alloy during zincate treatment. By setting the Zn content to 0.70% or less, a dense, thin, and less-thickness Zn coating adheres to the surface of the aluminum alloy substrate when the zincate treatment is performed in the manufacturing process of the magnetic disk. can be made By forming such a Zn film, it is possible to form a smooth electroless Ni--P plated layer by electroless Ni--P plating in a post-process.

However, if the Zn content is too high, the corrosion resistance of the aluminum alloy substrate is lowered, and regions where Al is likely to dissolve locally are formed. Therefore, when the zincate treatment is performed in the manufacturing process of the magnetic disk, the amount of Al dissolved on the surface of the aluminum alloy substrate becomes uneven, and the thickness of the Zn film tends to vary greatly. As a result, the adhesion between the electroless Ni--P plated layer and the aluminum alloy substrate is lowered, and the smoothness of the electroless Ni--P plated layer is lowered.

By setting the Zn content in the aluminum alloy to 0.70% or less, preferably 0.50% or less, the formation of plating pits is suppressed and the smoothness of the electroless Ni—P plating layer is further enhanced. can be done. The lower limit of the Zn content is preferably 0.005%, more preferably 0.010%. Note that the Zn content may be 0% (0.000%).

Cr: 0.40% or less The aluminum alloy may contain 0.40% or less of Cr as the first optional element. Part of Cr is dispersed in the aluminum alloy substrate as fine intermetallic compounds generated during casting. Cr that does not form an intermetallic compound during casting dissolves in the Al matrix and has the effect of improving the strength of the aluminum alloy substrate by solid-solution strengthening.

Moreover, Cr has the effect of further enhancing the machinability and grindability and further refining the recrystallized structure. As a result, the adhesion between the aluminum alloy substrate and the electroless Ni—P plating layer is enhanced, and the formation of plating pits is suppressed.

However, if the Cr content in the aluminum alloy is too high, coarse Al—Cr intermetallic compounds are likely to be formed in the aluminum alloy substrate. When such coarse Al--Cr-based intermetallic compound falls off from the surface of the aluminum alloy substrate, plating pits are likely to be formed in the subsequent electroless Ni--P plating process.

By setting the Cr content in the aluminum alloy to 0.40% or less, preferably 0.30% or less, the formation of plating pits is suppressed, a smooth electroless Ni—P plating layer is formed, and aluminum The strength of the alloy substrate can be further improved. The lower limit of the Cr content is not particularly set, and may be 0%.

Si: 0.60% or less The aluminum alloy may contain 0.60% or less of Si as the first optional element. Si forms an Mg—Si intermetallic compound with Mg when Mg is contained in an aluminum alloy.

When such an Mg--Si intermetallic compound falls off from the surface of the aluminum alloy substrate, plating pits are likely to be formed in the subsequent electroless Ni--P plating process. By setting the Si content in the aluminum alloy to 0.60% or less, preferably 0.10% or less, more preferably 0.01% or less, the amount of the intermetallic compound present in the aluminum alloy substrate is further reduced. can do. As a result, the formation of plating pits can be suppressed, and the smoothness of the electroless Ni—P plating layer can be improved.

In order to suppress the formation of plating pits due to the intermetallic compound, it is preferable to reduce the Si content. However, Si is contained not only in ordinary pure ingots but also in high-purity ingots with an Al purity of 99.9% or more. Therefore, when trying to produce an aluminum alloy substrate containing little Si, it is necessary to perform a special treatment to remove these elements during casting, which increases the production cost of the aluminum alloy substrate.

In particular, by using an aluminum alloy with a Si content of 0.01% or less, an aluminum alloy substrate can be produced without special treatment for removing Si. As a result, the smoothness of the aluminum alloy substrate can be improved while avoiding an increase in manufacturing cost. Also, if the Si content in the aluminum alloy exceeds 0.01% but is 0.60% or less, the aluminum alloy substrate can be produced using a base metal with lower purity. As a result, it is possible to further reduce the material cost of the aluminum alloy substrate while suppressing the formation of the intermetallic compound.

Be: 0.0020% or less Be is an element added to the molten metal for the purpose of suppressing oxidation of Mg when casting an aluminum alloy containing Mg. In addition, by making the Be contained in the aluminum alloy 0.0020% or less, the Zn film formed on the surface of the aluminum alloy substrate in the manufacturing process of the magnetic disk is made more dense and the thickness variation is further reduced. can be made smaller. As a result, the smoothness of the electroless Ni—P treatment layer formed on the aluminum alloy substrate can be further enhanced.

However, if the Be content in the aluminum alloy is too high, Be-based oxides are likely to be formed on the surface of the aluminum alloy substrate when the aluminum alloy substrate is heated during the manufacturing process of the aluminum alloy substrate. Further, when the aluminum alloy further contains Mg, Al--Mg--Be-based oxides are likely to be formed on the surface of the aluminum alloy substrate when the aluminum alloy substrate is heated. When the amount of these Be-based oxides and Al--Mg--Be-based oxides increases, the variation in thickness of the Zn film increases, leading to the generation of plating pits.

By setting the Be content in the aluminum alloy to 0.0020% or less, preferably 0.0010% or less, the amounts of the Be-based oxide and the Al-Mg-Be-based oxide are reduced, and the electroless Ni- The smoothness of the P-plated layer can be further enhanced. The lower limit of the Be content may be 0% (0.0000%), but is preferably 0.0001%.

Sr, Na and P: Each of 0.100% or Less Sr, Na and P have the effect of refining the second phase particles (mainly Si particles) in the aluminum alloy substrate and improving the plating properties. In addition, the non-uniformity of the size of the second phase particles in the aluminum alloy substrate is reduced, and the effect of reducing the variation in the impact resistance property is exhibited. Therefore, the aluminum alloy may contain one or more elements selected from Sr, Na and P, each of which is 0.100% or less.

However, even if each of Sr, Na and P is contained in excess of 0.100%, the above effect is saturated and no further significant effect is obtained. Moreover, in order to obtain the above effect, it is preferable to set the lower limit of each of Sr, Na and P to 0.0005. Note that each of Sr, Na and P may be 0% (0.0000%).

Other Elements The aluminum alloy may contain elements that are unavoidable impurities other than the essential components described above and the first and second optional elements. These elements include Zr, Ti, B, Ga, and the like, and the content of each element is 0.10% or less, and the total content is 0.30% or less, so that the effects of the present invention are not impaired. .

Further, as described above, in the present invention, Fe and Si can be positively added as optional elements, but they may be included as unavoidable impurities without being positively added. Si and Fe are contained as unavoidable impurities not only in ordinary pure ingots but also in high-purity ingots with an Al purity of 99.9% or higher. And when it is contained as an unavoidable impurity in this way, the Fe content is 1.80% or less, preferably 1.30% or less, more preferably 1.00% or less, as in the case of an arbitrary element. If the content of Si is 0.60% or less, preferably 0.10% or less, more preferably 0.01% or less, the effect of the present invention is not impaired.

A-2. Young's modulus: 68.7 GPa or more Next, the Young's modulus of the aluminum alloy substrate will be described in detail below.

According to studies by the present inventors, increasing the Young's modulus of the aluminum alloy substrate has the effect of improving the impact resistance of the magnetic disk (indicating the extent to which the substrate is less likely to deform). is defined as 68.7 GPa or more. The magnetic disk is deformed when the magnetic disk drive is dropped, but since this deformation is within the elastic region, the deformation can be suppressed by improving the Young's modulus. Thus, the improvement of Young's modulus can improve the impact resistance.

It is known that Young's modulus has in-plane anisotropy and varies depending on the angle from the rolling direction. The direction with the highest Young's modulus and the direction with the lowest Young's modulus are usually one of the 0° direction, 45° direction and 90° direction from the rolling direction, and the Young's modulus in the lowest direction is 68.7 GPa or more. It is important to have Therefore, in the present invention, the Young's modulus in the lowest direction is specified to be 68.7 GPa or more. If the Young's modulus is less than 68.7 GPa, the magnetic disk will be greatly deformed when the magnetic disk drive is dropped, etc., and many collisions will occur with other members (such as other magnetic disks and the ramp road where the head is withdrawn). , dust, etc., may be generated and cause recording errors.

In the present invention, the characteristic of resistance to deformation of the magnetic disk is defined as impact resistance. In order to avoid a decrease in impact resistance, the Young's modulus of the aluminum alloy substrate should be 68.7 GPa or more. This Young's modulus is preferably 69.5 GPa or more, more preferably 70.0 GPa or more. Although the upper limit of the Young's modulus of the aluminum alloy substrate is not particularly limited, it is naturally determined by the material and composition of the aluminum alloy substrate and the manufacturing conditions, and in the present invention, it is about 80 GPa. preferable.

A-3. Density: 2.72 g/cm ³ or less Next, the density of the aluminum alloy substrate will be described in detail below.

In the present invention, the weight of the magnetic disk aluminum alloy substrate per magnetic disk is important for improving the energy saving, and the density is defined to be 2.72 g/cm ³ or less. As a result, the weight per magnetic disk is reduced, so that the energy saving can be improved. If the density exceeds 2.72 g/cm ³ , the weight per magnetic disk increases, and the power consumption of the spindle motor for rotating the magnetic disk increases, resulting in a lack of energy saving. Power consumption is related to power and can be expressed as the product of rotation speed (rpm), torque (N·m), and a coefficient. As the weight of the magnetic disk increases, the torque increases, resulting in increased power and power consumption.

Plating, magnetic films, etc. are attached to the magnetic disk, but since these parts account for a small proportion of the total weight of the magnetic disk, it is important to reduce the weight of the aluminum alloy substrate, that is, to reduce the density. be. Therefore, the density of the aluminum alloy substrate should be 2.72 g/cm ³ or less. This density is preferably 2.71 g/cm ³ or less, more preferably 2.70 g/cm ³ or less. Although the lower limit of this density is not particularly set, it is about 2.62 g/cm ³ considering the composition of the aluminum alloy and the like.

A-4. Electrical conductivity: 32.0% IACS or more Next, the electrical conductivity of the aluminum alloy substrate will be described in detail below.

It is known from the Wiedemann-Franz law and the like that the higher the electrical conductivity of an aluminum alloy substrate, the higher the thermal conductivity. Therefore, by setting the electrical conductivity of the aluminum alloy substrate to 32.0% IACS or higher, the thermal conductivity is increased, and the desired temperature can be reached quickly during the heat treatment. As a result, energy during heat treatment can be reduced, leading to improvement in energy saving.

The heat treatment in the magnetic disk manufacturing process includes sputtering and plating of the magnetic film. When the electrical conductivity increases by 1.0% IACS, the time required for the magnetic film to reach a predetermined temperature (here, 100° C.) in the sputtering process is calculated. When a single substrate having a thickness of 0.5 mm and a surface plating thickness of 0.01 mm is sputter-heated with the same amount of heat, the substrate reaches a predetermined temperature about 0.1 second faster. Therefore, when a large amount of aluminum alloy substrates are subjected to sputtering, increasing the electrical conductivity is effective from the viewpoint of energy saving. For example, a conductivity meter (“AutoSigma 3000” manufactured by GE Sensing & Inspection Technologies, Inc.) can be used to measure the conductivity. Conductivity is measured on a test material having a thickness of 1 mm or more and 2 mm or less by an eddy current method in an environment of 25°C.

If the electrical conductivity is less than 32.0% IACS, the thermal conductivity is low, the temperature is difficult to rise during the heat treatment, and the energy saving performance is lowered. Therefore, the electrical conductivity is preferably 32.0%IACS or more, more preferably 33.0%IACS or more. Although the upper limit of this conductivity is not particularly set, it is about 60.0% IACS from the material and composition of the aluminum alloy substrate.

A-5. Method for producing an aluminum alloy plate (1) Casting step A raw material of an aluminum material having a predetermined alloy composition is melted to produce a molten metal, which is then cast to produce an ingot. For casting, a semi-continuous casting (DC casting) method, a die casting method, or a continuous casting (CC casting) method is used. In the DC casting method, the molten metal poured through the spout is cooled by cooling water discharged directly to the bottom block, the water-cooled wall of the mold, and the outer periphery of the ingot (ingot). and pulled downward as an ingot. In the mold casting method, molten metal poured into a hollow mold made of cast iron or the like loses heat to the walls of the mold and solidifies to form an ingot. In the CC casting method, a molten metal is supplied through a casting nozzle between a pair of rolls (or a belt caster or a block caster), and heat is removed from the rolls to directly cast a thin plate.

In such a casting process, it is preferable to perform in-line a degassing treatment for reducing dissolved gas in the molten metal and a filtering treatment for removing solids in the molten metal.

As the degassing process, for example, a processing method called SNIF (Spinning Nozzle Inert Flotation) process, a processing method called Alpur process, or the like can be employed. In these processes, a process gas such as argon gas or a mixed gas of argon and chlorine is blown into the molten metal while stirring the molten metal at high speed by means of a rotor equipped with blades to form fine bubbles of the process gas in the molten metal. As a result, hydrogen gas and inclusions dissolved in the molten metal can be removed in a short period of time. An in-line degasser can be used for degassing.

As the filtration process, for example, a cake filtration method, a filter media filtration method, or the like can be adopted. Filters such as ceramic tube filters, ceramic foam filters, and alumina ball filters can be used for filtration.

(2) Homogenization treatment step Before hot rolling is performed after the production of the ingot, the ingot may be chamfered and homogenized as necessary. The holding temperature in the homogenization treatment can be appropriately set, for example, within the range of 500 to 570°C. Also, the holding time in the homogenization treatment can be appropriately set, for example, within the range of 1 to 60 hours.

(3) Hot Rolling Step Next, the ingot is hot rolled to produce a hot rolled plate. The rolling conditions for hot rolling are not particularly limited. For example, hot rolling can be performed with a starting temperature in the range of 400 to 550°C and an ending temperature in the range of 260 to 380°C.

(4) Cold Rolling Step After hot rolling, the obtained hot rolled sheet is subjected to one or more cold rolling passes to obtain a cold rolled sheet. The rolling conditions for the cold rolling are not particularly limited, and may be appropriately set according to the desired thickness and strength of the aluminum alloy plate. For example, the total rolling reduction in cold rolling can be 20 to 95%. Also, the thickness of the cold-rolled plate can be appropriately set within a range of, for example, 0.2 to 1.9 mm.

(5) Annealing Step In the manufacturing method of the above aspect, at least one of before the first pass in cold rolling and between passes, annealing may be performed as necessary. The annealing treatment may be performed using a batch heat treatment furnace or a continuous heat treatment furnace. When a batch type heat treatment furnace is used, it is preferable that the holding temperature during annealing is 250 to 430° C. and the holding time is 0.1 to 10 hours. When a continuous heat treatment furnace is used, it is preferable that the residence time in the furnace is 60 seconds or less and the temperature in the furnace is 400 to 500.degree. By performing the annealing treatment under such conditions, the workability during cold rolling can be recovered.
An aluminum alloy plate is produced by the above steps.

A-6. Method for Producing Aluminum Alloy Substrate In producing the aluminum alloy substrate from the above aluminum alloy plate, for example, the following method can be employed. First, an aluminum alloy plate is punched to produce a disc blank having an annular shape. Thereafter, the disk blank is heated while being pressed from both sides in the thickness direction to perform pressure annealing, thereby reducing the distortion of the disk blank and improving the flatness. The holding temperature and pressure in pressure annealing can be appropriately selected, for example, from the range of 250 to 430° C. and 1.0 to 3.0 MPa. Moreover, the holding time in the pressure annealing can be, for example, 30 minutes or longer.

After performing pressure annealing, it is preferable to perform annealing before cutting and grinding. It is preferable that the holding temperature during the annealing is 190 to 260° C. and the holding time is 0.1 to 10 hours. Further, the holding temperature during annealing is more preferably 190 to 240°C, still more preferably 190 to 220°C. The holding time during annealing is more preferably 0.5 to 10 hours, more preferably 1 to 10 hours. By performing the annealing treatment under such conditions, solid solution Mg or the like is precipitated, so that the electrical conductivity of the substrate can be increased.

After performing this annealing, the aluminum alloy disk blank is subjected to cutting and grinding in sequence, and then under the conditions of 150 to 180 ° C. for 0.1 to 10.0 hours, strain relief heat treatment to remove strain during processing. as necessary. Through these processing steps, an aluminum alloy substrate having a desired shape is produced.

B. Magnetic disk B-1. Configuration of Magnetic Disk A magnetic disk having the aluminum alloy substrate has, for example, the following configuration. That is, the magnetic disk has an aluminum alloy substrate, an electroless Ni--P plated layer covering the surface of the aluminum alloy substrate, and a magnetic layer laminated on the electroless Ni--P plated layer. The Ni—P plating layer is preferably an electroless Ni—P plating layer formed by electroless plating.

The magnetic disk may further include a protective layer made of a carbon-based material such as diamond-like carbon and laminated on the magnetic layer, and a lubricating layer made of lubricating oil and coated on the protective layer. good.

B-2. Magnetic Disk Manufacturing Method In manufacturing a magnetic disk from an aluminum alloy substrate, for example, the following method can be adopted. First, the aluminum alloy substrate is degreased and washed to remove oils such as working oil adhering to the surface of the aluminum alloy substrate. After degreasing and cleaning, if necessary, the aluminum alloy substrate may be etched using an acid. When etching is performed, it is preferable to perform a desmutting treatment after etching to remove smut generated by the etching from the aluminum alloy substrate. Processing conditions in these treatments can be appropriately set according to the type of treatment liquid.

After performing these pre-plating treatments, a zincate treatment is performed to form a Zn film on the surface of the aluminum alloy substrate. In the zincate treatment, a Zn film can be formed by performing zinc displacement plating in which Al is substituted with Zn. As the zincate treatment, a so-called double zincate method is used in which, after performing the first zinc substitution plating, the Zn film formed on the surface of the aluminum alloy substrate is once peeled off, and zinc substitution plating is performed again to form a Zn film. preferably adopted. According to the double zincate method, a denser Zn film can be formed on the surface of the aluminum alloy substrate than the Zn film formed only by the first zinc substitution plating. As a result, defects in the electroless Ni—P plating layer can be reduced in the subsequent electroless Ni—P plating process.

After forming a Zn film on the surface of an aluminum alloy substrate by zincate treatment, the Zn film can be replaced with an electroless Ni-P plating layer by performing electroless Ni-P plating treatment at around 90°C. . By replacing such a Zn film with a Ni--P plating layer in the electroless Ni--P plating process, a smooth Ni--P plating layer with few plating pits can be formed.

Increasing the thickness of the electroless Ni--P plating layer tends to reduce plating pits, making it possible to form a smooth electroless Ni--P plating layer. Therefore, the plating thickness is preferably 7 μm or more, more preferably 18 μm or more, and even more preferably 25 μm or more. Practically, the upper limit of the plating thickness is about 40 μm.

After the electroless Ni--P plating treatment, the surface smoothness of the electroless Ni--P plating layer can be further improved by polishing the electroless Ni--P plating treatment layer.

After electroless Ni—P plating (including polishing), a magnetic layer is formed by depositing a magnetic material on the electroless Ni—P plating layer by sputtering. The magnetic layer may be composed of a single layer, or may be composed of a plurality of layers having compositions different from each other. A conventional method is applied to the sputtering temperature and the like, but when the sputtering temperature is 100° C. or less, the high electrical conductivity of the aluminum alloy substrate exhibits an energy-saving effect. After sputtering, a protective layer made of a carbon-based material is formed on the magnetic layer by CVD. Next, lubricating oil is applied onto the protective layer to form a lubricating layer. As described above, a magnetic disk can be obtained.

An example of an aluminum alloy plate, a method for producing the same, and an aluminum alloy substrate produced from the aluminum alloy plate will be described.

Specific aspects of these aluminum alloy plates and methods for producing the same, and aluminum alloy substrates made from these aluminum alloy plates and methods for producing the same are not limited to the aspects of the examples shown below, and the present invention The configuration can be changed as appropriate from the embodiment within the scope that does not impair the gist of the above.

(1) Production of aluminum alloy plate Aluminum alloy plates used for evaluation in the present examples were produced by the following method. First, a molten metal having an alloy composition shown in Table 1 was prepared in a melting furnace.

Next, the molten metal in the melting furnace was transferred, and an ingot was produced by the casting method shown in Table 2. Next, the surface of the ingot was chamfered to remove the segregation layer present on the surface of the ingot. After facing, the ingot was homogenized under the conditions shown in Table 2. Then, hot rolling was performed under the conditions shown in Table 2 to obtain a hot rolled sheet with a thickness of 3 mm. Furthermore, as shown in Table 2, the hot-rolled sheet was cold-rolled at a total rolling reduction of 75% to obtain a cold-rolled sheet with a thickness of 0.74 mm.

(2) Fabrication of Aluminum Alloy Substrate The above aluminum alloy plate was punched to obtain an aluminum alloy disc blank having an annular shape with an outer diameter of 98 mm and an inner diameter of 24 mm. Then, the obtained aluminum alloy disk blank was pressure-annealed at the temperature shown in Table 2 for 3 hours while being pressed from both sides in the thickness direction. Furthermore, annealing was performed at a temperature of 190 to 260° C. for the time shown in Table 2. Then, the outer and inner peripheral end faces of each aluminum alloy disk blank after annealing were machined to obtain disk blanks having an outer diameter of 97 mm and an inner diameter of 25 mm. After that, the plate surface of each aluminum alloy disk blank was ground so that the grinding amount was 10 μm. As described above, an aluminum alloy substrate was produced.

Measurement of Young's Modulus Young's modulus was measured using a 60 mm×8 mm sample obtained by wire cutting from an aluminum alloy disk blank after annealing. The method of collecting samples in the 0° direction, 45° direction and 90° direction from the rolling direction is as shown in FIGS. The Young's modulus was measured at room temperature by a resonance method using a JE-RT type apparatus manufactured by Technoplus Japan Co., Ltd. In this way, the Young's moduli in the 0°, 45° and 90° directions were measured.

Here, the Young's modulus is measured using an aluminum alloy substrate after cutting, grinding, or subjected to strain relief heat treatment, an aluminum alloy substrate after plating, and a magnetic disk after sputtering. can also However, each Young's modulus of an aluminum alloy disk blank after annealing, an aluminum alloy substrate after cutting/grinding or heat treatment for strain relief, an aluminum alloy substrate after plating, and a magnetic disk after sputtering. It was confirmed that there was no significant difference in Therefore, in the present invention, an annealed aluminum alloy disk blank was used to measure the Young's modulus. When an aluminum alloy substrate or a magnetic disk was used, the plating was peeled off and the surface was ground by 10 μm, and a test piece was taken from the substrate to measure and evaluate the Young's modulus.

・Measurement of density Density is measured by wire-cutting a sample of predetermined dimensions (length, width, thickness) from the aluminum alloy disk blank after annealing that showed the lowest Young's modulus. board. The length, width, and thickness of the measurement sample were measured accurately using a micrometer and vernier calipers, and the weight of the measurement sample was measured using an electronic balance.

- Measurement of electrical conductivity Electrical conductivity (%IACS) was measured using an aluminum alloy disk blank after annealing as a measurement sample. For the measurement, a conductivity meter (“AutoSigma 3000” manufactured by GE Sensing & Inspection Technologies, Inc.) was used to measure under an environment of 25° C. by an eddy current method. When the plate thickness of the measurement sample was less than 1 mm, two or more of these were stacked to have a thickness of 1 mm or more and 2 mm or less, and the electrical conductivity was measured.

Table 2 shows the measurement results of Young's modulus, density and conductivity.

As shown in Tables 1 and 2, Examples 1 to 7 had a specific alloy composition specified in the present invention, and had a Young's modulus of 68.7 GPa or more and a density of 2.72 g/cm ³ or less. rice field. Therefore, in these examples, good impact resistance and energy saving can be obtained.

On the other hand, in Comparative Examples 1 to 3, at least one of the alloy composition, Young's modulus and density is out of the scope of the present invention, resulting in poor impact resistance and energy saving performance.

ADVANTAGE OF THE INVENTION By having a specific alloy composition, a Young's modulus, and a density, the present invention can provide an aluminum alloy substrate for a magnetic disk having good impact resistance and energy saving, and a magnetic disk using the same.

Claims (5)

An aluminum alloy containing Mg: 1.00 to 3.50 mass%, the balance being Al and unavoidable impurities, having a Young's modulus of 68.7 GPa or more and a density of 2.72 g/cm ³ or less. An aluminum alloy substrate for a magnetic disk. The aluminum alloy contains Fe: 1.80 mass% or less, Mn: 1.80 mass% or less, Ni: 3.00 mass% or less, Cu: 0.40 mass% or less, Zn: 0.70 mass% or less, and Cr: 0.40 mass%. % or less, Si: 0.60 mass% or less, and Be: 0.0020 mass% or less, further containing one or more selected from the group consisting of 0.0020 mass% or less. 1 or 2, wherein the aluminum alloy further contains one or more selected from the group consisting of Sr: 0.100 mass% or less, Na: 0.100 mass% or less, and P: 0.100 mass% or less 3. The aluminum alloy substrate for a magnetic disk according to 2. 4. The aluminum alloy substrate for a magnetic disk according to claim 1, which has a conductivity of 32.0%IACS or more. An electroless Ni—P plating layer and a magnetic layer on the electroless Ni—P plating layer are formed on the surface of the magnetic disk aluminum alloy substrate according to any one of claims 1 to 4. A magnetic disk, comprising:

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