Aluminum alloy substrate for magnetic disk and magnetic disk using said aluminum alloy substrate for magnetic disk

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]

[0001] The present invention relates to an aluminum alloy substrate for a magnetic disk having good impact resistance and energy saving properties, and a magnetic disk using the aluminum alloy substrate for a magnetic disk. [Background technology]

[0002] Hard disk drives (hereinafter referred to as "HDDs") are widely used as storage devices in electronic devices such as computers and video recorders. HDDs incorporate a magnetic disk for recording data. The magnetic disk has a circular 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.

[0003] In recent years, there has been a growing demand for larger capacity and higher density magnetic disk devices such as HDDs due to the needs of multimedia, etc. To achieve even greater capacity, the number of magnetic disks installed in storage devices is on the rise, and this has led to a demand for thinner magnetic disks.

[0004] However, there is a problem in that thinning magnetic disk substrates reduces their rigidity. A decrease in rigidity reduces the impact resistance, which indicates the degree to which the substrate is resistant to deformation, so there is a demand for improved impact resistance in substrates. Furthermore, increasing the number of substrates results in excessive power consumption when used in a magnetic disk device, so there is also a demand for power saving (hereinafter simply referred to as "energy saving"). In addition to the use of magnetic disk devices, reducing energy consumption during magnetic disk manufacturing (energy saving (hereinafter simply referred to as "energy saving")) is also becoming increasingly important.

[0005] In view of these circumstances, in recent years, there has been a strong demand for and investigation into magnetic disk substrates that have high rigidity and excellent energy-saving properties. For example, Patent Document 1 proposes a method of improving the rigidity of aluminum alloy substrates by adding large amounts of elements such as Fe, Mn, and Ni, which contribute to improving the rigidity of aluminum alloy substrates. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-186597

[0007] However, the method disclosed in Patent Document 1 of increasing the content of Fe, Mn, Ni, etc. to improve only the rigidity increases the density of the aluminum alloy substrate, and the targeted good energy saving performance has not been achieved at present. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above problems, and the inventors have investigated the effects of the content of various additive elements in an aluminum alloy and the density 、 Young's modulus and conductivity The present inventors have found that by controlling the above, an aluminum alloy substrate for a magnetic disk having good impact resistance and energy saving properties can be obtained, and have completed the present invention. [Means for solving the problem]

[0009] The present invention is, in claim 1, an aluminum alloy containing 1.00 to 3.50 mass% of Mg, the balance being Al and unavoidable impurities, and having a Young's modulus of 68.7 GPa or more and a density of 2.72 g / cm 3 Below , conductivity is 32.0%IACS or more The aluminum alloy substrate for magnetic disks is characterized by the above.

[0010] The present invention provides claim 2 according to claim 1, wherein the aluminum alloy further contains one or more elements selected from the group consisting of 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.

[0011] In claim 3 of the present invention, in claim 1 or 2, the aluminum alloy further contains one or more elements 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.

[0013] The present invention is 4 In the above, claims 1 to 3 The magnetic disk is characterized by having an electroless Ni-P plating layer on the surface of the aluminum alloy substrate for magnetic disk described in any one of the above, and a magnetic layer on the electroless Ni-P plating layer. [Effects of the Invention]

[0014] The aluminum alloy substrate for magnetic disks according to the present invention can achieve good impact resistance and energy saving properties by controlling the contents of various additive elements, density and Young's modulus. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a plan view showing a measurement sample for measuring Young's modulus in a direction of 0° from the rolling direction of an aluminum alloy substrate for a magnetic disk. [Figure 2] FIG. 2 is a plan view showing a measurement sample for measuring Young's modulus, taken at an angle of 45° from the rolling direction of an aluminum alloy substrate for a magnetic disk. [Figure 3] FIG. 2 is a plan view showing a measurement sample for measuring Young's modulus, taken at an angle of 90° from the rolling direction of an aluminum alloy substrate for a magnetic disk. DETAILED DESCRIPTION OF THE INVENTION

[0016] A. Aluminum alloy substrates for magnetic disks An aluminum alloy substrate for magnetic disks (hereinafter sometimes referred to as "aluminum alloy substrate" or "substrate") according to the present invention will be described. The aluminum alloy substrate is prepared by preparing an aluminum alloy plate using an aluminum alloy of a predetermined alloy composition, and then punching this into an annular shape to obtain an aluminum alloy disk blank for magnetic disks (hereinafter sometimes referred to as "aluminum alloy disk blank" or "disk blank"). The disk blank is then subjected to pressure annealing, further annealing, cutting and grinding in sequence, and, if necessary, stress relief heat treatment to obtain an aluminum alloy substrate.

[0017] The aluminum alloy of the aluminum alloy substrate contains, as an essential element, 1.00 to 3.50 mass% Mg (hereinafter simply referred to as "%"). It also contains, as a first optional element, one or more selected from the group consisting of 1.80% or less Fe, 1.80% or less Mn, 3.00% or less Ni, 0.40% or less Cu, 0.70% or less Zn, 0.40% or less Cr, 0.60% or less Si, and 0.0020% or less Be. It also contains, as a second optional element, one or more selected from the group consisting of 0.100% or less Sr, 0.100% or less Na, and 0.100% or less P. The aluminum alloy consists of the above essential elements, the first and second optional elements, and the balance being Al and unavoidable impurities. The 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 It has the following properties: Furthermore, it is preferable that this aluminum alloy substrate has a conductivity of 32.0% IACS or more.

[0018] 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 substrate has excellent impact resistance, which indicates the degree to which the substrate is difficult to deform.3 By having a substrate with a conductivity of 32.0% IACS or more, the weight of the substrate can be reduced, which reduces power consumption when used in a magnetic disk drive, resulting in excellent energy efficiency. Furthermore, by having a substrate with a conductivity of 32.0% IACS or more, the thermal conductivity is increased, allowing for a reduction in energy consumption during heat treatment, further improving energy efficiency. As a result, impact resistance and energy efficiency can be achieved at the same time.

[0019] A-1. Aluminum alloy composition The composition of the aluminum alloy used in the aluminum alloy substrate and the reasons for limiting it will be explained in detail below.

[0020] Mg: 1.00-3.50% Mg is an essential element in aluminum alloys, primarily present as solute Mg, and is effective in improving the strength of aluminum alloy substrates. Furthermore, it allows the zincate film formed during zincating of aluminum alloy substrates to be uniformly, thinly, and densely adhered, thereby improving the smoothness of the electroless Ni-P plating surface in the plating process that follows the zincating process. However, if the Mg content is less than 1.00%, the strength of the aluminum alloy substrate is insufficient and it deforms during cutting, grinding, and other processes. Furthermore, the zincate film formed during zincating becomes nonuniform, resulting in reduced plating adhesion and smoothness. On the other hand, if the Mg content exceeds 3.50%, the Young's modulus of Mg is lower than that of Al, resulting in a significant decrease in the Young's modulus. This results in a decrease in the rigidity of the substrate and a decrease in impact resistance. Therefore, in the aluminum alloy substrate of the present invention, the Mg content of the aluminum alloy is specified to be 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 even more preferably 1.80 to 2.50%, in view of the balance between strength and manufacturability.

[0021] The aluminum alloy may further contain, in addition to Mg, one or more first optional elements selected from the group consisting of Fe, Mn, Ni, Cu, Zn, Cr, Si, and Be. The aluminum alloy may also further contain, in addition to Mg or in addition to Mg and the first optional element, one or more second optional elements selected from the group consisting of Sr, Na, and P.

[0022] Each optional element will be described in detail below.

[0023] Fe:1.80% or less The aluminum alloy may contain Fe as a first optional element. Fe exists primarily as second-phase particles (e.g., Al-Fe intermetallic compounds), with a portion dissolved in the matrix. Both of these elements improve the Young's modulus and other properties of the aluminum alloy substrate. When the Fe content in the aluminum alloy exceeds 1.80%, numerous coarse Al-Fe intermetallic compound particles are generated. The coarse Al-Fe intermetallic compounds are harder than the aluminum matrix, making them difficult to cut, resulting in a lower grinding rate during grinding and increased production costs. Furthermore, these coarse Al-Fe intermetallic compound particles can fall off during etching, zincating, cutting, or grinding, creating large depressions and resulting in plating pits, which can reduce the smoothness of the plating surface and cause plating peeling. This also reduces workability during the rolling process. Furthermore, because Fe has a higher density than Al, excessive Fe content significantly increases the density, resulting in reduced energy efficiency. Therefore, the Fe content in the aluminum alloy is set to 1.80% or less, preferably 1.30% or less, and more preferably 1.00% or less. There is no particular lower limit for the Fe content, but since Fe is usually present in raw materials as an unavoidable impurity, in this case the lower limit is about 0.001%. The Fe content may be 0% (0.000%).

[0024] Mn: 1.80% or less The aluminum alloy may contain Mn as a first optional element. Mn exists primarily as second-phase particles (e.g., Al-Mn intermetallic compounds), with a portion dissolved in the matrix. Both of these elements improve the Young's modulus and other properties of the aluminum alloy substrate. If the Mn content in the aluminum alloy exceeds 1.80%, numerous coarse Al-Mn intermetallic compound particles are generated. The coarse Al-Mn intermetallic compounds are harder than the aluminum matrix, making them difficult to cut. This reduces the grinding rate during grinding, thereby increasing production costs. Furthermore, these coarse Al-Mn intermetallic compound particles may fall off during etching, zincating, cutting, or grinding, resulting in large depressions, which can lead to plating pits, reducing the smoothness of the plating surface, and causing plating peeling. This also reduces workability during the rolling process. Furthermore, because Mn has a higher density than Al, excessive Mn content significantly increases the density, resulting in reduced energy efficiency. Therefore, the Mn content in the aluminum alloy is set to 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%.

[0025] Ni: 3.00% or less The aluminum alloy may contain Ni as a first optional element. Ni exists primarily as second-phase particles (e.g., Al-Ni intermetallic compounds), with the remainder present as solid solution in the matrix. Both of these elements improve the Young's modulus and other properties of the aluminum alloy substrate. If the Ni content in the aluminum alloy exceeds 3.00%, numerous coarse Al-Ni intermetallic compound particles are generated. The coarse Al-Ni intermetallic compounds are harder than the aluminum matrix, making them difficult to cut, resulting in a decrease in the grinding rate during grinding and increased production costs. Furthermore, these coarse Al-Ni intermetallic compound particles may fall off during etching, zincating, cutting, or grinding, creating large depressions and resulting in plating pits, which reduce the smoothness of the plating surface and cause plating peeling. This also reduces workability during the rolling process. Furthermore, because Ni has a higher density than Al, excessive Ni content significantly increases the density, resulting in reduced energy efficiency. Therefore, the Ni content in the aluminum alloy is set to 3.00% or less, preferably 2.80% or less, and more preferably 2.50% or less. The lower limit of the Ni content is not particularly set, and may be 0%.

[0026] Cu: 0.40% or less The aluminum alloy may contain 0.40% or less Cu as a first optional element. Cu has the effect of suppressing Al elution from the aluminum alloy when zincating is performed in the magnetic disk manufacturing process. By setting the Cu content to 0.40% or less, a dense, thin Zn coating with little thickness variation can be adhered to the surface of the aluminum alloy substrate when zincating is performed in the magnetic disk manufacturing process. Furthermore, by forming such a Zn coating, a smooth electroless Ni-P plating layer can be formed in the subsequent electroless Ni-P plating process.

[0027] However, if the Cu content is too high, the corrosion resistance of the aluminum alloy substrate decreases, and localized areas where Al is easily dissolved are formed. Therefore, when zincating is performed in the manufacturing process of a magnetic disk, the amount of Al dissolved on the surface of the aluminum alloy substrate tends to be uneven, and the thickness of the Zn coating tends to vary greatly. As a result, the adhesion between the electroless Ni-P plating layer and the aluminum alloy substrate decreases, and the smoothness of the electroless Ni-P plating layer decreases.

[0028] By setting the Cu content in the aluminum alloy to 0.40% or less, preferably 0.30% or less, the formation of plating pits can be suppressed and the smoothness of the electroless Ni-P plating layer can be further improved. The lower limit of the Cu content is preferably 0.003%, more preferably 0.010%. The Cu content may be 0% (0.000%).

[0029] Zn: 0.70% or less The aluminum alloy may contain 0.70% or less Zn as a first optional element. Zn, like Cu, has the effect of suppressing Al elution from the aluminum alloy during zincate treatment. By setting the Zn content to 0.70% or less, a dense, thin Zn coating with little thickness variation can be adhered to the surface of the aluminum alloy substrate during zincate treatment in the magnetic disk manufacturing process. Furthermore, by forming such a Zn coating, a smooth electroless Ni-P plating layer can be formed in the subsequent electroless Ni-P plating process.

[0030] However, if the Zn content is too high, the corrosion resistance of the aluminum alloy substrate decreases and localized areas where Al is easily dissolved are formed. Therefore, when zincating is performed in the manufacturing process of a magnetic disk, the amount of Al dissolved on the surface of the aluminum alloy substrate tends to be uneven, which tends to increase the variation in the thickness of the Zn coating. As a result, the adhesion between the electroless Ni-P plating layer and the aluminum alloy substrate decreases and the smoothness of the electroless Ni-P plating layer decreases.

[0031] By setting the Zn content in the aluminum alloy to 0.70% or less, preferably 0.50% or less, the formation of plating pits can be suppressed and the smoothness of the electroless Ni-P plating layer can be further improved. The lower limit of the Zn content is preferably 0.005%, more preferably 0.010%. The Zn content may be 0% (0.000%).

[0032] Cr:0.40% or less The aluminum alloy may contain 0.40% or less of Cr as a first optional element. Part of the Cr is dispersed in the aluminum alloy substrate as fine intermetallic compounds formed during casting. Cr that does not form intermetallic compounds during casting dissolves in the Al matrix, improving the strength of the aluminum alloy substrate through solid solution strengthening.

[0033] In addition, Cr improves machinability and grindability and refines the recrystallized structure, thereby improving the adhesion between the aluminum alloy substrate and the electroless Ni-P plating layer and suppressing the occurrence of plating pits.

[0034] 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, and if such coarse Al-Cr intermetallic compounds fall off from the surface of the aluminum alloy substrate, plating pits are likely to be formed in the subsequent electroless Ni-P plating process.

[0035] By setting the Cr content in the aluminum alloy to 0.40% or less, preferably 0.30% or less, it is possible to suppress the formation of plating pits, form a smooth electroless Ni-P plating layer, and further improve the strength of the aluminum alloy substrate. The lower limit of the Cr content is not particularly set, and may be 0%.

[0036] Si:0.60% or less The aluminum alloy may contain 0.60% or less of Si as a first optional element. When the aluminum alloy contains Mg, Si forms an Mg-Si intermetallic compound with Mg.

[0037] If such Mg-Si intermetallic compounds fall off from the surface of the aluminum alloy substrate, plating pits are likely to form 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, and more preferably 0.01% or less, the amount of the above intermetallic compounds present in the aluminum alloy substrate can be further reduced. As a result, the formation of plating pits can be suppressed and the smoothness of the electroless Ni-P plating layer can be further improved.

[0038] In order to suppress the occurrence of plating pits due to the intermetallic compounds, it is preferable to reduce the Si content. However, Si is contained not only in base metals of ordinary purity but also in high-purity base metals with an Al purity of 99.9% or more. Therefore, if an aluminum alloy substrate containing almost no Si is to be produced, a special treatment to remove these elements during casting is required, which increases the production cost of the aluminum alloy substrate.

[0039] In particular, by using an aluminum alloy with a Si content of 0.01% or less, an aluminum alloy substrate can be produced without any special treatment for removing Si. As a result, the smoothness of the aluminum alloy substrate can be further improved while avoiding an increase in the manufacturing cost of the aluminum alloy substrate. Furthermore, if the Si content in the aluminum alloy is more than 0.01% but not more than 0.60%, an aluminum alloy substrate can be produced using a base metal with a lower purity. This allows the formation of the intermetallic compounds to be suppressed while further reducing the material cost of the aluminum alloy substrate.

[0040] Be: 0.0020% or less Be is an element added to the molten metal when casting an aluminum alloy containing Mg to suppress oxidation of Mg. Furthermore, by limiting the Be content in the aluminum alloy to 0.0020% or less, the Zn coating formed on the surface of the aluminum alloy substrate during the magnetic disk manufacturing process can be made denser and the thickness variation can be reduced. As a result, the smoothness of the electroless Ni-P treatment layer formed on the aluminum alloy substrate can be further improved.

[0041] However, if the Be content in the aluminum alloy is too high, Be-based oxides are likely to form on the surface of the aluminum alloy substrate when the aluminum alloy substrate is heated during its manufacturing process. Furthermore, if the aluminum alloy further contains Mg, Al-Mg-Be-based oxides are likely to form on the surface of the aluminum alloy substrate when the aluminum alloy substrate is heated. If the amounts of these Be-based oxides and Al-Mg-Be-based oxides are large, the thickness of the Zn coating becomes more variable, leading to the occurrence of plating pits.

[0042] 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 oxides and Al-Mg-Be-based oxides can be reduced, and the smoothness of the electroless Ni-P plating layer can be further improved. The lower limit of the Be content may be 0% (0.0000%), but is preferably 0.0001%.

[0043] Sr, Na and P: 0.100% or less each Sr, Na, and P have the effect of refining second-phase particles (mainly Si particles) in the aluminum alloy substrate and improving plating properties. They also have the effect of reducing the non-uniformity in the size of second-phase particles in the aluminum alloy substrate and reducing the variation in impact resistance. Therefore, the aluminum alloy may contain one or more elements selected from Sr, Na, and P, each of which is 0.100% or less.

[0044] However, even if the content of each of Sr, Na, and P exceeds 0.100%, the above effects saturate and no further significant effects are obtained. In order to obtain the above effects, it is preferable that the lower limit of each of Sr, Na, and P is set to 0.0005. However, each of Sr, Na, and P may be 0% (0.0000%).

[0045] Other elements The aluminum alloy may contain elements other than the above-mentioned essential components and the first and second optional elements that may be unavoidable impurities. These elements include Zr, Ti, B, Ga, etc., and the effects of the present invention are not impaired as long as the content of each element is 0.10% or less and the total content is 0.30% or less.

[0046] As mentioned above, in the present invention, Fe and Si can be actively added as optional elements, but they may also be contained as inevitable impurities without being actively added. Si and Fe are contained as inevitable impurities not only in ingots of ordinary purity but also in high-purity ingots with an Al purity of 99.9% or more. Even when they are contained as inevitable impurities, as in the case of optional elements, the effects of the present invention are not impaired as long as the Fe content is 1.80% or less, preferably 1.30% or less, and more preferably 1.00% or less, and the Si content is 0.60% or less, preferably 0.10% or less, and more preferably 0.01% or less.

[0047] A-2.Young's modulus: 68.7GPa or more Next, the Young's modulus of the aluminum alloy substrate will be described in detail below.

[0048] According to the inventors' investigations, increasing the Young's modulus of the aluminum alloy substrate has the effect of improving the impact resistance of the magnetic disk (which indicates the degree to which the substrate is resistant to deformation), and therefore the Young's modulus is specified to be 68.7 GPa or more. Although the magnetic disk deforms when the magnetic disk device is dropped, this deformation is within the elastic range, and therefore, the deformation can be suppressed by improving the Young's modulus. In this way, the impact resistance can be improved by improving the Young's modulus.

[0049] It is known that Young's modulus has in-plane anisotropy and varies depending on the angle from the rolling direction. The directions with the highest and lowest Young's modulus are usually either at 0°, 45°, or 90° from the rolling direction, and it is important that the Young's modulus in the lowest direction is 68.7 GPa or higher. Therefore, in the present invention, the Young's modulus in the lowest direction is specified to be 68.7 GPa or higher. If the Young's modulus is less than 68.7 GPa, the magnetic disk will be significantly deformed when the magnetic disk device is dropped, resulting in multiple collisions with other components (such as other magnetic disks or ramp roads where the head is retracted), generating dust and other particles that can cause recording errors.

[0050] In the present invention, the property of a magnetic disk that is difficult to deform is defined as impact resistance. To avoid a decrease in impact resistance, the Young's modulus of the aluminum alloy substrate is set to 68.7 GPa or more. This Young's modulus is preferably 69.5 GPa or more, and more preferably 70.0 GPa or more. The upper limit of the Young's modulus of the aluminum alloy substrate is not particularly limited, but is naturally determined by the material and composition of the aluminum alloy substrate and the manufacturing conditions, and in the present invention, it is preferably about 80 GPa.

[0051] A-3.Density: 2.72g / cm 3 below Next, the density of the aluminum alloy substrate will be described in detail below.

[0052] In the present invention, the weight of the aluminum alloy substrate for magnetic disks per magnetic disk is important for improving the energy saving performance. 3 This reduces the weight of each magnetic disk, thereby improving the energy efficiency. 3 If the weight exceeds this, the weight per magnetic disk will become heavier, which will increase the power consumption of the spindle motor used to rotate the magnetic disk, resulting in a lack of energy efficiency. Power consumption is related to power and can be expressed as the product of the rotation speed (rpm), torque (N·m), and a coefficient. As the weight of the magnetic disk increases, the torque also increases, which increases power consumption.

[0053] Although the magnetic disk is coated with plating and magnetic films, these only account for a small proportion of the total weight of the magnetic disk, so it is important to reduce the weight of the aluminum alloy substrate, i.e., to reduce its density. Therefore, the density of the aluminum alloy substrate is 2.72 g / cm 3 The density is preferably 2.71 g / cm 3 or less, more preferably 2.70 g / cm 3 The lower limit of this density is not particularly set, but it is set to 2.62 g / cm3 based on the composition of the aluminum alloy. 3 That's about it.

[0054] A-4. Electrical conductivity: 32.0%IACS or more Next, the electrical conductivity of the aluminum alloy substrate will be described in detail below.

[0055] It is known from the Wiedemann-Franz law that the higher the electrical conductivity of an aluminum alloy substrate, the higher its thermal conductivity. Therefore, by increasing the electrical conductivity of the aluminum alloy substrate to 32.0% IACS or higher, the thermal conductivity increases, allowing the desired temperature to be reached more quickly during heat treatment. As a result, the energy required during heat treatment can be reduced, leading to improved energy conservation.

[0056] Heat treatments in magnetic disk manufacturing processes include sputtering and plating of magnetic films. If the conductivity increases by 1.0% IACS, the time required to reach a predetermined temperature (100°C) during sputtering of magnetic films is calculated. For a single substrate with an outer diameter of 97 mm, an inner diameter of 25 mm, a thickness of 0.5 mm, and a surface plating thickness of 0.01 mm, the temperature will be reached approximately 0.1 seconds faster when sputtering with the same amount of heat. Therefore, increasing the conductivity is effective from the perspective of energy conservation when sputtering large quantities of aluminum alloy substrates. Conductivity can be measured using a conductivity meter (e.g., the AutoSigma 3000 manufactured by GE Sensing & Inspection Technologies, Inc.). Conductivity is measured using the eddy current method at 25°C on test specimens with a thickness of 1 mm to 2 mm.

[0057] If the electrical conductivity is less than 32.0% IACS, the thermal conductivity will be low, making it difficult to raise the temperature during heat treatment and reducing energy efficiency. Therefore, the electrical conductivity is preferably 32.0% IACS or more, and more preferably 33.0% IACS or more. Although there is no particular upper limit for this electrical conductivity, it is approximately 60.0% IACS depending on the material and composition of the aluminum alloy substrate.

[0058] A-5. Manufacturing method of aluminum alloy plate (1) Casting process Aluminum raw materials with a specified alloy composition are melted to produce molten metal, which is then cast to produce ingots. Casting methods include semi-continuous casting (DC casting), permanent mold casting, and continuous casting (CC casting). In DC casting, molten metal poured through a spout loses heat through the bottom block, the water-cooled mold walls, and cooling water directly sprayed onto the outer periphery of the ingot, solidifying and being drawn downward as an ingot. In permanent mold casting, molten metal poured into a hollow mold made of cast iron or other material loses heat through the mold walls, solidifying and producing an ingot. In CC casting, molten metal is supplied through a casting nozzle between a pair of rolls (or belt casters or block casters), and thin plates are directly cast by removing heat from the rolls.

[0059] In such a casting process, it is preferable to carry out in-line a degassing treatment to reduce the amount of gas dissolved in the molten metal and a filtration treatment to remove solids from the molten metal.

[0060] For example, the degassing process can be performed using a process known as the SNIF (Spinning Nozzle Inert Flotation) process or the Alpur process. In these processes, a process gas such as argon gas or a mixture of argon and chlorine is blown into the molten metal while stirring the molten metal at high speed using a rotor with blades, forming fine bubbles of the process gas into the molten metal. This allows hydrogen gas and inclusions dissolved in the molten metal to be removed in a short period of time. An in-line degassing device can be used for the degassing process.

[0061] For example, the filtration process can be performed using a cake filtration method, a filter medium filtration method, etc. For the filtration process, a filter such as a ceramic tube filter, a ceramic foam filter, or an alumina ball filter can be used.

[0062] (2) Homogenization process After the ingot is produced, and before hot rolling, the ingot may be subjected to facing and homogenization treatment as necessary. The holding temperature in the homogenization treatment can be appropriately set within the range of, for example, 500 to 570°C. The holding time in the homogenization treatment can be appropriately set within the range of, for example, 1 to 60 hours.

[0063] (3) Hot rolling process Next, the ingot is hot-rolled to produce a hot-rolled sheet. The rolling conditions for the hot rolling are not particularly limited, but for example, the hot rolling can be performed at a starting temperature in the range of 400 to 550°C and a finishing temperature in the range of 260 to 380°C.

[0064] (4) Cold rolling process After hot rolling, the resulting hot-rolled sheet can be subjected to one or more passes of cold rolling to obtain a cold-rolled sheet. The rolling conditions for cold rolling are not particularly limited and can be appropriately set depending on the desired thickness and strength of the aluminum alloy sheet. For example, the total reduction rate in cold rolling can be 20 to 95%. The thickness of the cold-rolled sheet can be appropriately set, for example, within the range of 0.2 to 1.9 mm.

[0065] (5) Annealing process In the manufacturing method of the above embodiment, annealing may be performed, if necessary, at least either before the first pass of cold rolling or between passes. The annealing may be performed using a batch-type heat treatment furnace or a continuous heat treatment furnace. When a batch-type heat treatment furnace is used, the holding temperature during annealing is preferably set to 250 to 430°C and the holding time is preferably set to 0.1 to 10 hours. When a continuous heat treatment furnace is used, the residence time in the furnace is preferably set to 60 seconds or less and the temperature in the furnace is preferably set to 400 to 500°C. By performing annealing under these conditions, it is possible to restore the workability during cold rolling. Through the above steps, an aluminum alloy plate is produced.

[0066] A-6. Manufacturing method of aluminum alloy substrate When producing an aluminum alloy substrate from the above-mentioned aluminum alloy plate, for example, the following method can be adopted. First, the aluminum alloy plate is punched to produce a disk blank having an annular shape. Then, the disk blank is subjected to pressure annealing by heating while being pressed from both sides in the thickness direction, thereby reducing distortion of the disk blank and improving flatness. The holding temperature and pressure in the pressure annealing can be appropriately selected, for example, from the ranges of 250 to 430°C and 1.0 to 3.0 MPa. Furthermore, the holding time in the pressure annealing can be, for example, 30 minutes or more.

[0067] After pressure annealing, annealing is preferably performed before cutting and grinding. The holding temperature during annealing is preferably 190 to 260°C, and the holding time is preferably in the range of 0.1 to 10 hours. The holding temperature during annealing is more preferably 190 to 240°C, and even more preferably 190 to 220°C. The holding time during annealing is more preferably 0.5 to 10 hours, and even more preferably 1 to 10 hours. By performing annealing treatment under these conditions, solute Mg and the like are precipitated, thereby increasing the electrical conductivity of the substrate.

[0068] After this annealing, the aluminum alloy disk blank is sequentially subjected to cutting and grinding, and then subjected to a stress relief heat treatment at 150 to 180°C for 0.1 to 10.0 hours as needed to remove stress generated during processing. Through these processing steps, an aluminum alloy substrate having a desired shape is produced.

[0069] B. Magnetic disk B-1. Magnetic Disk Configuration The magnetic disk having the aluminum alloy substrate has, for example, the following configuration: the magnetic disk has an aluminum alloy substrate, an electroless Ni-P plating layer covering the surface of the aluminum alloy substrate, and a magnetic layer laminated on the electroless Ni-P plating layer. The Ni-P plating layer is preferably an electroless Ni-P plating layer formed by electroless plating.

[0070] The magnetic disk may further have a protective layer made of a carbonaceous material such as diamond-like carbon and laminated on the magnetic layer, and a lubricating layer made of lubricating oil and applied on the protective layer.

[0071] B-2. Magnetic Disk Manufacturing Method When manufacturing a magnetic disk from an aluminum alloy substrate, for example, the following method can be used. First, the aluminum alloy substrate is degreased and cleaned to remove oils such as processing oils adhering to the surface of the aluminum alloy substrate. After degreased and cleaned, the aluminum alloy substrate may be etched using an acid, if necessary. If etching is performed, it is preferable to perform a desmutting treatment after etching to remove smut generated by etching from the aluminum alloy substrate. The treatment conditions for these treatments can be appropriately set depending on the type of treatment solution.

[0072] After these pre-plating treatments, a zincate treatment is performed to form a Zn coating on the surface of the aluminum alloy substrate. In the zincate treatment, a zinc immersion plating is performed to replace Al with Zn, thereby forming a Zn coating. A preferred zincate treatment is the so-called double zincate method, in which the Zn coating formed on the surface of the aluminum alloy substrate after the first zinc immersion plating is once stripped off and then another zinc immersion plating is performed to form a Zn coating. The double zincate method allows a denser Zn coating to be formed on the surface of the aluminum alloy substrate compared to the Zn coating formed by only the first zinc immersion plating. As a result, defects in the electroless Ni-P plating layer can be reduced in the subsequent electroless Ni-P plating process.

[0073] 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 at around 90° C. Then, by replacing such a Zn film with a Ni-P plating layer in the electroless Ni-P plating, a smooth Ni-P plating layer with few plating pits can be formed.

[0074] Increasing the thickness of the electroless Ni-P plating layer tends to reduce plating pits, allowing for the formation of 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. In practice, the upper limit of the plating thickness is approximately 40 μm.

[0075] By polishing the electroless Ni-P plated layer after the electroless Ni-P plating treatment, the smoothness of the surface of the electroless Ni-P plated layer can be further improved.

[0076] After electroless Ni-P plating (including polishing), a magnetic material is deposited on the electroless Ni-P plating layer by sputtering to form a magnetic layer. The magnetic layer may consist of a single layer or multiple layers with different compositions. Conventional sputtering temperatures are used, but high conductivity of the aluminum alloy substrate, particularly at sputtering temperatures of 100°C or less, can provide energy-saving benefits. After sputtering, a protective layer made of a carbon-based material is formed on the magnetic layer by CVD. Next, a lubricating oil is applied to the protective layer to form a lubricating layer. This completes the magnetic disk. [Example]

[0077] 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 below.

[0078] Specific aspects of these aluminum alloy plates and their manufacturing methods, as well as aluminum alloy substrates produced from these aluminum alloy plates and their manufacturing methods, are not limited to the aspects of the examples shown below, and the configurations can be appropriately changed from the examples within the scope that does not detract from the spirit of the present invention.

[0079] (1) Preparation of aluminum alloy plate The aluminum alloy sheets used for evaluation in the present examples were produced by the following method: First, a molten metal having the alloy composition shown in Table 1 was prepared in a melting furnace.

[0080] [Table 1]

[0081] Next, the molten metal in the melting furnace was transferred, and an ingot was produced using 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 chamfering, the ingot was subjected to homogenization treatment under the conditions shown in Table 2. Next, hot rolling was carried out under the conditions shown in Table 2 to obtain a hot-rolled plate with a thickness of 3 mm. Furthermore, as shown in Table 2, the hot-rolled plate was cold-rolled at a total reduction of 75% to obtain a cold-rolled plate with a thickness of 0.74 mm.

[0082] (2) Preparation of aluminum alloy substrate The aluminum alloy plate was punched to obtain an annular aluminum alloy disk blank with an outer diameter of 98 mm and an inner diameter of 24 mm. The obtained aluminum alloy disk blank was then subjected to pressure annealing by holding it at the temperature shown in Table 2 for 3 hours while applying pressure from both sides in the thickness direction. Further, annealing was performed at a temperature of 190 to 260°C for the time shown in Table 2. The outer peripheral end face and inner peripheral end face of each annealed aluminum alloy disk blank were then cut to obtain a disk blank with an outer diameter of 97 mm and an inner diameter of 25 mm. The plate surface of each aluminum alloy disk blank was then ground to a grinding depth of 10 μm. Thus, an aluminum alloy substrate was produced.

[0083] Measurement of Young's modulus A 60 mm x 8 mm sample was wire-cut from the annealed aluminum alloy disk blank and used as the measurement specimen to measure Young's modulus. The method for taking samples in the 0°, 45°, and 90° directions from the rolling direction is shown in Figures 1 to 3. Young's modulus measurements were performed at room temperature by the resonance method using a JE-RT type device manufactured by Nippon Technoplus Co., Ltd. In this way, Young's modulus measurements were performed in the 0°, 45°, and 90° directions.

[0084] Here, Young's modulus can also be measured using aluminum alloy substrates after cutting and grinding or after stress relief heat treatment, aluminum alloy substrates after plating, and magnetic disks after sputtering. However, it has been confirmed that there is no significant difference in the Young's modulus between an aluminum alloy disk blank after annealing and an aluminum alloy substrate after cutting and grinding or after stress relief heat treatment, an aluminum alloy substrate after plating, and a magnetic disk after sputtering. Therefore, in the present invention, an aluminum alloy disk blank after annealing was used to measure Young's modulus. When using an aluminum alloy substrate or a magnetic disk, the plating was removed and the surface was ground 10 μm to obtain a test piece, which was then used to measure and evaluate Young's modulus.

[0085] Density measurement For density measurements, samples of specified dimensions (length, width, and thickness) were taken by wire cutting from the annealed aluminum alloy disk blank that showed the lowest Young's modulus. The length, width, and thickness of the measurement sample were accurately measured using a micrometer and vernier calipers, and the weight of the measurement sample was measured using an electronic balance.

[0086] Conductivity measurement The conductivity (%IACS) of the annealed aluminum alloy disk blanks was measured using a conductivity meter (GE Sensing & Inspection Technologies, Inc., "AutoSigma 3000") at 25°C using the eddy current method. When the thickness of the measurement sample was less than 1 mm, two or more samples were stacked to a thickness of 1 mm to 2 mm, and the conductivity was measured.

[0087] The measurement results of Young's modulus, density and electrical conductivity are shown in Table 2.

[0088] [Table 2]

[0089] As shown in Tables 1 and 2, Examples 1 to 5、 No. 7 has a specific alloy composition defined in the present invention, and has a Young's modulus of 68.7 GPa or more and a density of 2.72 g / cm 3 Below , conductivity is 32.0%IACS or more Therefore, in these examples, good impact resistance and energy saving can be obtained.

[0090] On the other hand, Comparative Examples 1 to 4 So, alloy composition, Young's modulus 、 density and conductivity Since at least one of the above does not meet the requirements of the present invention, the impact resistance and energy saving performance will be poor. [Industrial Applicability]

[0091] According to the present invention, a specific alloy composition, Young's modulus 、 density and conductivity By having the above, it is possible to provide an aluminum alloy substrate for magnetic disks that has good impact resistance and energy saving properties, and a magnetic disk using the same.

Claims

1. An aluminum alloy containing 1.00 to 3.50 mass% Mg, 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 1. An aluminum alloy substrate for a magnetic disk, characterized in that the substrate has a conductivity of 32.0% IACS or more.

2. 2. The aluminum alloy substrate for magnetic disks according to claim 1, further comprising one or more elements selected from the group consisting of 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.

3. 3. The aluminum alloy substrate for magnetic disks according to claim 1, wherein the aluminum alloy further contains one or more elements 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.

4. A magnetic disk comprising an aluminum alloy substrate for a magnetic disk according to any one of claims 1 to 3, an electroless Ni-P plating layer on the surface thereof, and a magnetic layer on the electroless Ni-P plating layer.

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