JP6506896B1 - Magnetic disk substrate, method of manufacturing the same, and magnetic disk - Google Patents

Abstract

A magnetic disk substrate capable of suppressing disk flutter and having excellent grinding processability, a method of manufacturing the same, and a magnetic disk manufactured from the magnetic disk substrate are provided.
SOLUTION: A magnetic disk substrate contains Fe: 0.005 to 0.600 mass%, Si: 0.4 mass% or less, and the balance is a chemical component consisting of Al and unavoidable impurities, and in an Al matrix. And a metal structure in which second phase particles are dispersed. Among the second phase particles, the number of second phase particles having a longest diameter of 1.5 μm or more is 50000 particles / mm ² or less.
[Selected figure] Figure 1

Description

  The present invention relates to a magnetic disk substrate, a method of manufacturing the same, and a magnetic disk.

  A hard disk drive (hereinafter referred to as "HDD") is widely used as a storage device in electronic devices such as computers and video recording devices. The HDD incorporates a magnetic disk for recording data. The magnetic disk has an annular magnetic disk substrate made of an aluminum alloy, a Ni-P plating film covering the surface of the magnetic disk substrate, and a magnetic layer laminated on the Ni-P plating film. . For example, JIS A5086 alloy or the like is used as an aluminum alloy constituting the magnetic disk substrate.

  In recent years, the amount of information to be recorded in the HDD has been increased in all business applications such as servers and data centers, and in household applications such as personal computers and video recording apparatuses. In order to increase the capacity of the HDD in response to such a situation, it is required to increase the number of magnetic disks incorporated per HDD and to increase the recording density of the individual magnetic disks. In order to increase the number of magnetic disks incorporated in one HDD, it is necessary to reduce the thickness of each magnetic disk. However, if the thickness of the magnetic disk is reduced, there is a problem that the rigidity is reduced.

  In addition, in order to read data from the HDD and write data to the HDD at high speed, it is desirable to increase the rotational speed of the magnetic disk. However, if the rotational speed of the magnetic disk is increased, the air flow formed between the magnetic disks tends to be destabilized. As a result, there is a problem that an excitation force resulting from the air flow acts on the magnetic disk, and the magnetic disk vibrates in the thickness direction, that is, so-called disk flutter is easily generated. If disk flutter occurs, the magnetic head may not be able to sufficiently follow the vibration of the magnetic disk. In this case, the position of the magnetic head on the magnetic disk is likely to deviate from the desired position, which may cause a read error or a write error.

  In particular, in a magnetic disk having a thin thickness as described above and a high recording density, the area occupied by one bit is narrow, so it is necessary to control the position of the magnetic head with high accuracy. However, since the rigidity decreases as the thickness of the magnetic disk decreases, disk flutter is more likely to occur, and the amplitude of the magnetic disk when the disk flutter occurs is likely to be large. Therefore, in order to increase the capacity of the HDD, it is important to suppress the occurrence of disk flutter.

  As a technique for suppressing the occurrence of disk flutter, for example, Patent Document 1 discloses a technique for providing a windbreak body at a specific position in a magnetic disk drive to restrict the collision of the air flow generated by the rotation of the magnetic disk with the magnetic head. Has been proposed.

  Also, for example, Patent Document 2 contains 0.5% by mass or more and 24.0% by mass or less of Si and 0.01% by mass or more and 3.00% by mass or less of Fe, and the balance is Al and unavoidable. An aluminum alloy substrate for a magnetic disk has been proposed which has a chemical component consisting of organic impurities.

Japanese Patent Application Laid-Open No. 2002-313061 International Publication WO 2016/068293

  When components for controlling air flow, such as the windscreen of Patent Document 1, are provided in the HDD, the number of components is increased. Furthermore, in this type of component, the effect of suppressing disk flutter largely varies depending on the distance from the magnetic disk, and therefore, it is necessary to increase the dimensional accuracy of the component. Therefore, in this case, there is a problem that the manufacturing cost of the HDD tends to increase.

  The aluminum alloy substrate for a magnetic disk disclosed in Patent Document 2 forms second phase particles containing Si in an Al matrix by the addition of Si. Then, the rigidity of the aluminum alloy substrate for a magnetic disk can be improved by the second phase particles containing Si. However, since the second phase particles are harder than the Al matrix, the processability of the grinding process performed in the process of producing the substrate may be deteriorated, which may result in an increase in the production cost of the substrate.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a magnetic disk substrate capable of suppressing disk flutter and having excellent grinding processability, a method of manufacturing the same, and a magnetic disk manufactured from the magnetic disk substrate. It is

One aspect of the present invention is a chemical containing Fe (iron): 0.005 to 0.600% by mass, Si (silicon): 0.4% by mass or less, with the balance being Al (aluminum) and unavoidable impurities. Ingredients,
A metallic structure in which second phase particles containing an element other than Al are dispersed in an Al matrix,
In the magnetic disk substrate, the number of second phase particles having a longest diameter of 1.5 μm or more among the second phase particles is 50000 particles / mm ² or less.

Another aspect of the present invention is a magnetic disk substrate according to the above aspect,
Ni-P (nickel-phosphorus) plating film covering the surface of the magnetic disk substrate;
And a magnetic disk having a magnetic layer laminated on the Ni-P plating film.

Yet another aspect of the present invention is a method of manufacturing a magnetic disk substrate according to the above aspect,
Producing an ingot with the above-mentioned chemical composition,
The hot-rolled sheet is subjected to hot rolling on the ingot under the condition that the temperature of the ingot during rolling is 200 to 430 ° C. and the time in which the temperature of the ingot is within the range is 30 minutes or more To make
Cold rolling is performed on the hot rolled sheet for one or more passes to produce a cold rolled sheet,
The cold rolled sheet is punched to produce a circular disc blank.
Heating and annealing the disc blank while pressing from both sides in the thickness direction
The present invention is a manufacturing method of a magnetic disk substrate, wherein the magnetic disk substrate is manufactured by sequentially performing cutting processing and grinding processing on the disk blank.

The magnetic disk substrate has a metal structure in which second phase particles containing an element other than Al are dispersed in the Al matrix, the amount of Fe dissolved in the Al matrix, thickness and loss. And a product with a coefficient . As a result, when an excitation force is applied to the disk substrate, the vibration of the magnetic disk substrate in the thickness direction can be reduced, and disk flutter can be suppressed. Although the reason why the second phase particles can suppress the disk flutter is not always clear at this time, for example, the magnetic disk is absorbed by the absorption of vibrational energy at the interface between the Al matrix and the second phase particles. The mechanism that the vibration to the thickness direction of is reduced is estimated.

In addition, the magnetic disk substrate can reduce the particle diameter of the second phase particles present in the Al matrix by setting the chemical component in the specific range. Then, among the second phase particles having various particle sizes, the number of second phase particles having a longest diameter of 1.5 μm or more is regulated to 50000 particles / mm ² or less, thereby obtaining an effect of suppressing the vibration. The deterioration of the grinding processability due to the coarse second phase particles can be avoided.

  As described above, according to the above aspect, it is possible to provide a magnetic disk substrate which can suppress disk flutter and has excellent grinding processability.

It is explanatory drawing of the evaluation method of a fluttering characteristic in an Example. It is a side view which shows the principal part of the measuring apparatus of a loss coefficient in an Example. It is an explanatory view showing an example of a waveform of damped free vibration in an example.

A. Magnetic Disk Substrate The chemical composition of the magnetic disk substrate, the metal structure, and the reasons for limitation are as follows.

-Fe (iron): 0.005 to 0.600 mass%
Some of Fe is contained in the second phase particles. As described above, since the second phase particles are dispersed in the Al matrix, it is possible to exhibit the function of suppressing the vibration of the magnetic disk substrate. Further, the balance of Fe is in solid solution in the Al matrix. Fe in solid solution in the Al matrix has the function of improving the strength of the aluminum alloy by solid solution strengthening.

  By setting the content of Fe to 0.005% by mass or more, the amount of Fe dissolved in the second phase particles and the Al matrix is sufficiently increased to suppress the disk flutter and to improve the strength of the magnetic disk substrate. It can be done. It is preferable to make content of Fe into 0.010 mass% or more from a viewpoint of raising these effects more. When the content of Fe is less than 0.005% by mass, the effect of suppressing the disk flutter and the effect of improving the strength may be reduced.

  On the other hand, when the content of Fe increases, coarse second phase particles are easily formed in the Al matrix. Since the second phase particles are harder than the Al matrix, when the ratio of coarse second phase particles increases, the magnetic disk substrate becomes difficult to cut during grinding. Therefore, in this case, the grinding processability may be deteriorated. In addition, when the large second phase particles are large, the rollability may be lowered in the process of manufacturing the magnetic disk substrate.

  Furthermore, coarse second phase particles are likely to come off, for example, during cutting or grinding performed in the process of manufacturing the magnetic disk substrate. In addition, such second phase particles are likely to come off during etching processing, zincate processing and the like performed in the subsequent manufacturing process of the magnetic disk. If the coarse second phase particles fall off in these steps, the surface roughness of the magnetic disk substrate may increase and the peeling of the Ni-P plating film may occur.

  By controlling the Fe content to not more than 0.600% by mass, preferably not more than 0.400% by mass, and more preferably not more than 0.200% by mass, these problems can be avoided while disc flutter is suppressed and magnetic The strength of the disk substrate can be improved.

  The amount of Fe in solid solution in the Al matrix is preferably 0.0010 to 0.0300 mass%. The strength of the magnetic disk substrate can be further improved by setting the amount of Fe in solid solution in the Al matrix to 0.0010 mass%, more preferably 0.0050 mass% or more. In addition, the number of second phase particles in the Al matrix is appropriately increased by setting the amount of Fe in solid solution in the Al matrix to 0.0300 mass% or less, more preferably 0.0200 mass% or less. can do. As a result, disk flutter can be suppressed more effectively.

  In the magnetic disk substrate, in addition to Fe as an essential component, Mn (manganese), Si (silicon), Mg (magnesium), Cu (copper), Ni (nickel), Cr (Cr) as an optional component are further added. , Zr (zirconium), Zn (zinc), Ti (titanium), B (boron), V (vanadium) and the like may be contained.

-Mn: 0.1-0.3 mass%
The magnetic disk substrate may contain Mn: 0.1 to 0.3% by mass as an optional component. Mn can form second phase particles containing Mn in an Al matrix. Similar to the second phase particles containing Fe, the second phase particles containing Mn have the function of suppressing disk flutter. Further, the second phase particles containing Mn have the function of improving the strength of the magnetic disk substrate.

  By setting the content of Mn to 0.1% by mass or more, the number of second phase particles containing Mn can be sufficiently increased. As a result, the effect of suppressing the disk flutter can be further enhanced, and the strength of the magnetic disk substrate can be further enhanced.

  On the other hand, when the content of Mn increases, coarse second phase particles are easily formed in the Al matrix. As a result, as in the case of Fe, problems such as deterioration in grinding processability, deterioration in rollability, increase in surface roughness of the magnetic disk substrate, and exfoliation of the Ni-P plating film may occur. By setting the content of Mn to 3.0% by mass or less, more preferably 1.0% by mass or less, the above-described effects can be obtained while avoiding these problems.

Si: 0.4 mass% or less The magnetic disk substrate may contain Si: 0.4 mass% or less as an optional component. The action effect by Si and the reason for limitation of the content are the same as Mn. That is, Si can form second phase particles containing Si in an Al matrix, thereby suppressing disk flutter and improving the strength of the magnetic disk substrate.

  The content of Si is preferably 0.1% by mass or more. In this case, the number of second phase particles containing Si can be sufficiently large. As a result, the effect of suppressing the disk flutter can be further enhanced, and the strength of the magnetic disk substrate can be further enhanced. Further, by setting the content of Si to 0.4 mass% or less, more preferably 0.3 mass% or less, formation of coarse second phase particles can be suppressed. As a result, the above-described effects can be obtained while avoiding problems such as the deterioration of the grinding processability, the reduction of the rollability, the increase of the surface roughness of the magnetic disk substrate and the peeling of the Ni-P plating film.

-Mg: 0.1 to 0.4% by mass
The magnetic disk substrate may contain Mg: 0.1 to 0.4% by mass as an optional component. The action effect by Mg and the reason for limitation of the content are the same as Mn. That is, Mg can form second phase particles containing Mg in an Al matrix, thereby suppressing disk flutter and improving the strength of the magnetic disk substrate.

  By setting the content of Mg to 0.1% by mass or more, the number of second phase particles containing Mg can be sufficiently increased. As a result, the effect of suppressing the disk flutter can be further enhanced, and the strength of the magnetic disk substrate can be further enhanced. Further, by setting the content of Mg to 0.4 mass% or less, more preferably 0.3 mass% or less, formation of coarse second phase particles can be suppressed. As a result, the above-described effects can be obtained while avoiding problems such as deterioration in grinding processability, reduction in rollability, increase in surface roughness of the magnetic disk substrate, and exfoliation of the Ni-P plating film.

Ni: 0.1 to 3.0% by mass
The magnetic disk substrate may contain Ni: 0.1 to 0.4% by mass as an optional component. The action effect by Ni and the reason for limitation of the content are the same as Mn. That is, Ni can form second phase particles containing Ni in an Al matrix, thereby suppressing disk flutter and improving the strength of the magnetic disk substrate.

  By setting the content of Ni to 0.1% by mass or more, the number of second phase particles containing Ni can be sufficiently increased. As a result, the effect of suppressing the disk flutter can be further enhanced, and the strength of the magnetic disk substrate can be further enhanced. In addition, by setting the content of Ni to 3.0% by mass or less, more preferably 1.0% by mass or less, formation of coarse second phase particles can be suppressed. As a result, the above-described effects can be obtained while avoiding problems such as the deterioration of the grinding processability, the reduction of the rollability, the increase of the surface roughness of the magnetic disk substrate and the peeling of the Ni-P plating film.

-Cr: 0.01 to 1.00 mass%
The magnetic disk substrate may contain, as an optional component, Cr: 0.01 to 1.00% by mass. The action effect by Cr and the reason for limitation of the content are the same as Mn. That is, Cr can form second phase particles containing Cr in an Al matrix to suppress disk flutter and improve the strength of the magnetic disk substrate.

  By setting the content of Cr to 0.01% by mass or more, more preferably 0.10% by mass or more, the number of Cr-containing second phase particles can be sufficiently increased. As a result, the effect of suppressing the disk flutter can be further enhanced, and the strength of the magnetic disk substrate can be further enhanced. In addition, by setting the content of Cr to 1.00 mass% or less, more preferably 0.50 mass% or less, the formation of coarse second phase particles can be suppressed. As a result, the above-described effects can be obtained while avoiding problems such as the deterioration of the grinding processability, the reduction of the rollability, the increase of the surface roughness of the magnetic disk substrate and the peeling of the Ni-P plating film.

· Zr: 0.01 to 1.00 mass%
The magnetic disk substrate may contain, as an optional component, Zr: 0.01 to 1.00% by mass. The effect of Zr and the reason for limitation of the content are the same as those of Mn. That is, Zr can form second phase particles containing Zr in an Al matrix, thereby suppressing disk flutter and improving the strength of the magnetic disk substrate.

  By setting the content of Zr to 0.01% by mass or more, more preferably 0.10% by mass or more, the number of second phase particles containing Zr can be sufficiently increased. As a result, the effect of suppressing the disk flutter can be further enhanced, and the strength of the magnetic disk substrate can be further enhanced. In addition, by setting the content of Zr to 1.00 mass% or less, more preferably 0.50 mass% or less, formation of coarse second phase particles can be suppressed. As a result, the above-described effects can be obtained while avoiding problems such as the deterioration of the grinding processability, the reduction of the rollability, the increase of the surface roughness of the magnetic disk substrate and the peeling of the Ni-P plating film.

Cu: 0.005 to 1.000% by mass
The magnetic disk substrate may contain Cu: 0.005 to 1.000% by mass as an optional component. Cu can form second phase particles containing Cu in an Al matrix. The second phase particles containing Cu have the function of suppressing disk flutter by increasing the Young's modulus of the magnetic disk substrate. Further, the second phase particles containing Cu have the function of improving the strength of the magnetic disk substrate.

  Furthermore, Cu can deposit a zincate film which is dense, thin, and small in thickness variation, on the surface of the magnetic disk substrate when zincate treatment is performed in the process of manufacturing the magnetic disk. And by forming such a zincate film, the Ni-P plating film with small surface roughness can be formed by the electroless Ni-P plating process performed later.

  By setting the content of Cu to 0.005% by mass or more, the number of second phase particles containing Cu can be sufficiently increased. As a result, the effect of suppressing the disk flutter can be further enhanced, and the strength of the magnetic disk substrate can be further enhanced. Furthermore, in this case, the surface roughness of the Ni-P plating film can be further reduced.

  On the other hand, when the content of Cu increases, coarse second phase particles are easily formed in the Al matrix. As a result, as in the case of Fe, problems such as reduction in rollability, deterioration in grinding processability, increase in surface roughness of the magnetic disk substrate, and exfoliation of the Ni-P plating film may occur. By setting the content of Cu to 1.000% by mass or less, more preferably 0.500% by mass or less, and further preferably 0.300% by mass or less, the above-described effects can be obtained while avoiding these problems. be able to.

Zn: 0.005 to 1.000% by mass
The magnetic disk substrate may contain Zn: 0.005 to 1.000% by mass as an optional component. Zn can form second phase particles comprising Zn in an Al matrix. The second phase particles containing Zn have the function of suppressing disk flutter by increasing the Young's modulus of the magnetic disk substrate. Further, the second phase particles containing Zn have the function of improving the strength of the magnetic disk substrate.

  Furthermore, Zn can reduce the amount of Al dissolved when zincate treatment is performed in the manufacturing process of the magnetic disk. Further, it is possible to attach a zincate film which is dense, thin, and small in thickness variation to the surface of the magnetic disk substrate. As a result of these, it is possible to form a Ni-P plating film having a small surface roughness by the electroless Ni-P plating treatment to be performed later.

  By setting the content of Zn to 0.005% by mass or more, more preferably 0.100% by mass or more, the number of second phase particles containing Zn can be sufficiently increased. As a result, the effect of suppressing the disk flutter can be further enhanced, and the strength of the magnetic disk substrate can be further enhanced. Furthermore, in this case, the surface roughness of the Ni-P plating film can be further reduced.

On the other hand, when the content of Zn increases, coarse second phase particles are easily formed in the Al matrix. As a result, as in the case of Fe, problems such as reduction in rollability, deterioration in grinding processability, increase in surface roughness of the magnetic disk substrate, and exfoliation of the Ni-P plating film may occur. By setting the content of Zn to 1.000% by mass or less, more preferably 0.700% by mass or less, the above-described effects can be obtained while avoiding these problems.
-Ti, B, V: A total of 0.005 to 0.500% by mass
The magnetic disk substrate may contain one or more of Ti, B, and V as optional components. When these elements are contained in the molten metal, second phase particles containing these elements are formed in the process of solidification of the ingot. These second phase particles become solidification nuclei when solidification of the molten metal proceeds, and the crystal grains of the magnetic disk substrate can be refined.

  Then, by reducing the crystal grains of the magnetic disk substrate, the variation in size of the second phase particles is reduced, and the variation in the strength of the magnetic disk substrate and the variation in the effect of suppressing the disk flutter are reduced. it can. In addition, by reducing the crystal grains of the magnetic disk substrate, the adhesion of the plating can be improved in the electroless Ni-P plating process performed in the process of manufacturing the magnetic disk. From the viewpoint of reliably obtaining these effects, the total content of Ti, B and V is preferably 0.005 mass% or more.

  On the other hand, when the total content of these elements exceeds 0.500% by mass, it is difficult to obtain the effects corresponding to the content. Therefore, it is preferable that it is 0.500 mass% or less, and, as for the sum total of content of Ti, B, and V, it is more preferable that it is 0.100 mass% or less.

Other Elements The magnetic disk substrate may contain elements other than the above-described elements. Examples of such an element include Ga (gallium) and Sn (tin). If the content of these elements is excessively large, the effects of the magnetic disk substrate may be impaired. From the viewpoint of avoiding such a problem, the content of each of Ga and Sn is regulated to less than 0.10 mass%, and the total of the content of Ga and the content of Sn is regulated to 0.20 mass% or less Is preferred.

Metal Structure The magnetic disk substrate has a metal structure in which second phase particles containing an element other than Al are dispersed in an Al matrix. The second phase particles are, for example, Al ₃ Fe, Al ₆ Fe, Al ₆ (Fe, Mn), Al-Fe-Si, Al-Fe-Mn-Si, Al-Fe-Ni, Al-Cu-Fe, etc. Al-Fe based intermetallic compounds, Mg-Si based intermetallic compounds such as Mg ₂ Si, Al-Mn based intermetallic compounds such as Al ₆ Mn, Al-Ni based intermetallic compounds such as Al ₃ Ni, Al ₂ It is composed of an Al—Cu based intermetallic compound such as Cu, an Al—Cr based intermetallic compound such as Al ₇ Cr, an Al—Zr based intermetallic compound such as Al ₃ Zr, an elemental Si, or the like. These intermetallic compounds or single substance Si as second phase particles may be a crystallized product or a precipitated product.

  The second phase particles dispersed in the Al matrix have various particle sizes. As described above, disc flutter can be suppressed by dispersing the second phase particles in the Al matrix. On the other hand, since the second phase particles are harder than the Al matrix, if the number of coarse second phase particles is large, the grinding processability may be deteriorated.

The magnetic disk substrate, of the second-phase particles having various particle sizes, by setting the number of second-phase particles having a maximum diameter of more than 1.5 [mu] m 50000 pieces / mm ² or less, grinding of The effect of suppressing disk flutter can be obtained while avoiding deterioration. From the viewpoint of more reliably avoiding the deterioration of the grinding processability, the number of second phase particles having a longest diameter of 1.5 μm or more is preferably 30,000 / mm ² or less, and 10,000 / mm ² or less It is more preferable to do.

From the viewpoint of obtaining the above-described effects, the number of second phase particles having a longest diameter of 1.5 μm or more in the Al matrix may be 0 / mm ² . In the magnetic disk substrate having the above-described chemical components, the number of second phase particles having a longest diameter of 1.5 μm or more, which are present in an Al matrix, is usually 100 / mm ² or more.

  In the Al matrix of the magnetic disk substrate, second phase particles having a longest diameter of less than 1.5 μm are dispersed. The presence of such relatively small second phase particles in the Al matrix can effectively suppress disk flutter. In addition, these second phase particles have less adverse effect on grinding processability than relatively large second phase particles having a longest diameter of 1.5 μm or more. Therefore, in the range of the second phase particles formed in the magnetic disk substrate having the chemical components described above, grinding is carried out even if a large number of second phase particles having a longest diameter of less than 1.5 μm are dispersed in the Al matrix. There is no risk of deterioration of processability.

The “number of second phase particles having a longest diameter of 1.5 μm or more” described above can be calculated as follows. First, the plate surface of the magnetic disk substrate is polished, and then a composition image of the plate surface is acquired using an electron beam microanalyzer. The view area of the composition image should be large enough to represent the metal structure of the entire magnetic disk substrate. Specifically, for example, by setting the visual field area to 1.0 mm ² or more, a composition image representing the metal structure of the entire magnetic disk substrate can be obtained.

The composition image obtained is analyzed using an image analysis device, and the outline of the second phase particles present in the field of view is extracted. Then, for each second phase particle, among the points on the contour line, two points whose distances from each other are the most distant are determined. The distance between these two points is taken as the longest diameter of each second phase particle. By thus determining the longest diameter of the second phase particles present in the field of view, the number of second phase particles having the longest diameter of 1.5 μm or more is counted and converted to the number per 1 mm ² , The “number of second phase particles having the longest diameter of 1.5 μm or more” described above can be obtained.

Further, “the number of second phase particles having a longest diameter of less than 1.5 μm” can also be obtained by the same method as the above-mentioned method. That is, after determining the longest diameter of the second phase particles present in the field of view based on the composition image, the number of second phase particles having the longest diameter of less than 1.5 μm is counted and converted to the number per 1 mm ² As a result, the “number of second phase particles having the longest diameter of 1.5 μm or more” described above can be obtained.

Thickness The thickness of the magnetic disk substrate can be appropriately selected, for example, from the range of 0.35 to 1.30 mm. By setting the thickness of the magnetic disk substrate to 0.35 mm or more, preferably 0.50 mm or more, the strength of the magnetic disk substrate can be sufficiently increased. As a result, when an impact is applied to the hard disk drive, it is possible to suppress the deformation of the magnetic disk. Further, by setting the thickness of the magnetic disk substrate to 1.30 mm or less, preferably 1.00 mm or less, more magnetic disks can be incorporated into the HDD. As a result, the capacity of the HDD can be further increased.

Loss Coefficient The value of the product of the thickness t [mm] of the magnetic disk substrate and the loss coefficient η is preferably 0.10 × 10 ⁻³ or more. As the magnetic disk substrate becomes thicker, the rigidity becomes higher, and disk flutter can be effectively suppressed. Further, the magnetic disk substrate can damp the vibration earlier as the value of the loss coefficient 大 き く becomes larger, and the disk flutter can be effectively suppressed.

Therefore, in the magnetic disk substrate, for convenience, the value of the product of the thickness t [mm] and the loss coefficient η can be used as an index representing the strength of the suppression effect of the disk flutter. The product of the thickness t [mm] and the loss coefficient に お け る in the magnetic disk substrate is 0.10 × 10 ⁻³ or more, more preferably 0.20 × 10 ⁻³ or more, and still more preferably 0.50 × 10 ⁻ By setting it to ³ or more, disk flutter can be suppressed more effectively. From the viewpoint of obtaining the above-described effects, there is no upper limit to the value of the product of the thickness t [mm] and the loss coefficient 効果. In the case of the magnetic disk substrate having the above-described chemical component, the product of the thickness t [mm] and the loss coefficient η is usually 10.0 × 10 ⁻³ or less.

Strength The magnetic disk substrate preferably has strength characteristics such that the proof stress after holding at 280 ° C. for 3 hours in the atmosphere is 70 MPa or more. In the magnetic disk manufacturing process, the temperature of the magnetic disk substrate may rise to about 280.degree. When the magnetic disk substrate is softened by the temperature rise, the magnetic disk may be easily deformed, for example, when an impact is applied to the HDD during transportation or attachment to an electronic device. By using the magnetic disk substrate having the specific strength characteristic, it is possible to suppress a decrease in the strength of the magnetic disk substrate in the process of manufacturing the magnetic disk. As a result, deformation of the magnetic disk can be suppressed.

  From the viewpoint of suppressing deformation of the magnetic disk more effectively, the magnetic disk substrate preferably has strength characteristics such that the proof stress after holding at 280 ° C. for 3 hours in the atmosphere is 80 MPa or more, and is 90 MPa or more. It is more preferable to have the strength characteristics that From the viewpoint of obtaining the above-described operation and effect, there is no upper limit to the yield strength of the magnetic disk after holding at 280 ° C. for 3 hours. In the case of a magnetic disk substrate having the above-described chemical components, the resistance of the magnetic disk after holding at 280 ° C. for 3 hours is usually 280 MPa or less.

B. Method of Manufacturing Magnetic Disk Substrate The magnetic disk substrate can be manufactured, for example, by the following method.

-Preparation of ingot First, an ingot having the above-mentioned chemical component is prepared. As a casting method, known methods such as continuous casting and semi-continuous casting can be adopted. In continuous casting, the melt is poured between a pair of spaced apart casting rolls. The molten metal can be rapidly cooled by a casting roll and solidified to continuously produce an ingot. In continuous casting, a belt caster or a block caster may be used instead of the casting roll. In semi-continuous casting, the molten metal is poured into a water-cooled cylindrical mold, and the ingot formed in the mold is drawn out of the mold while solidifying the molten metal, thereby forming the ingot semi-continuously. It can be carried out.

  Continuous casting can accelerate the cooling rate of molten metal compared to semi-continuous casting. Therefore, by producing an ingot by continuous casting, the particle size of the second phase particles can be reduced compared to semi-continuous casting.

Homogenization treatment After producing the ingot, if necessary, the ingot may be heated to perform homogenization treatment. When the homogenization treatment is performed, the holding temperature of the ingot is preferably in the range of 250 to 430 ° C., and more preferably in the range of 280 to 380 ° C. Further, the holding time of the ingot is preferably in the range of 0.5 to 60 hours, and more preferably in the range of 1 to 50 hours. By setting the holding temperature and the holding time in the homogenization treatment to the above-mentioned specific range, the ingot is sufficiently homogenized to make the variation of the adhesion of the Ni-P plating film to the magnetic disk substrate and the suppressing effect of the disk flutter more It can be effectively suppressed.

  If at least one of the holding temperature and the holding time in the homogenization treatment is below the specific range, the ingot may be insufficiently homogenized. When the holding temperature in the homogenization treatment exceeds the above-mentioned specific range, coarse second phase particles tend to be formed in the ingot. As a result, the grinding processability of the magnetic disk substrate may be deteriorated. When the holding time in the homogenization treatment exceeds the above-mentioned specific range, the productivity of the magnetic disk substrate may be deteriorated.

· Hot rolling Next, the ingot is hot-rolled under the condition that the temperature of the ingot during rolling is 200 to 430 ° C and the time in which the temperature of the ingot is within the range is 30 minutes or more To make a hot-rolled sheet. Thus, the formation of second phase particles in the Al matrix can be promoted, and the growth of second phase particles already present in the Al matrix can be suppressed. As a result, the number of coarse second phase particles can be reduced. It is preferable to hot-roll the ingot under the condition that the temperature of the ingot during rolling is 220 to 400 ° C. from the viewpoint of obtaining such effects more reliably. Moreover, it is preferable to hot-roll the ingot under the condition that the time when the temperature of the ingot is in the specific range is 60 minutes or more.

  If the temperature of the ingot is less than 200 ° C. during rolling, the deformation resistance of the ingot becomes excessively high, and therefore, the ingot may be cracked. In addition, if the temperature of the ingot exceeds 430 ° C. during rolling, the growth of second phase particles present in the Al matrix is promoted, so the number of coarse second phase particles tends to be large. As a result, the grinding processability of the magnetic disk substrate may be deteriorated.

  In addition, when the time in which the temperature of the ingot is within the above-mentioned specific range is less than 30 minutes, the precipitation of the element solid-solved in the Al matrix becomes insufficient, and the number of second phase particles tends to decrease. As a result, disk flutter may occur easily. There is no upper limit to the time during which the temperature of the ingot is within the above-mentioned specific range from the viewpoint of obtaining the above-mentioned effects, but from the viewpoint of avoiding the deterioration of productivity, the temperature of the ingot is the above-mentioned specific It is preferable to set the time within the range to 300 minutes or less.

Cold Rolling After hot rolling, the obtained hot rolled sheet is cold rolled for one or more passes to produce a cold rolled sheet. The thickness of the cold rolled sheet may be appropriately set according to the desired thickness of the magnetic disk substrate. For example, the thickness of the cold rolled sheet can be appropriately set from the range of 0.35 to 1.3 mm.

-Annealing In the manufacturing method of the said aspect, you may perform an annealing process as needed in at least 1 side before the 1st pass in cold rolling, and between passes. The annealing treatment may be performed using a batch heat treatment furnace or may be performed using a continuous heat treatment furnace. When using a batch type heat treatment furnace, it is preferable to hold | maintain a hot rolled sheet at the temperature of 300-500 degreeC for 0.1 to 30 hours, and to anneal. Moreover, when using a continuous-type heat treatment furnace, it is preferable to heat and anneal a hot-rolled sheet so that the residence time in a furnace may be less than 60 seconds, and temperature may be 400-600 degreeC. By performing the annealing treatment under such conditions, the workability at the time of cold rolling can be recovered.

Punching, pressure annealing, cutting, and grinding The cold-rolled sheet obtained as described above is punched to produce an annular disk blank. Thereafter, the disk blank is heated while being pressed from both sides in the thickness direction and pressure annealing is performed to reduce the distortion of the disk blank and improve the flatness. The holding temperature in pressure annealing can be suitably selected from the range of 100-380 degreeC, for example. Moreover, the holding time in pressure annealing can be made into 30 minutes or more, for example.

  After pressure annealing, cutting and grinding are sequentially performed on the disk blank to produce a magnetic disk substrate having a desired shape. After these processes, if necessary, a strain removing heat treatment may be performed to remove the strain during the process. In the strain removing heat treatment, for example, the magnetic disk substrate may be held at a temperature of 250 to 400 ° C. for 5 to 15 minutes.

C. Magnetic Disk The magnetic disk provided with the magnetic disk substrate has, for example, the following configuration. That is, the magnetic disk is a magnetic disk substrate,
Ni-P plating film covering the surface of the magnetic disk substrate;
And a magnetic layer laminated on the Ni-P plating film.

  The magnetic disk substrate further comprises a carbon-based material such as diamond like carbon, and has a protective layer laminated on the magnetic layer, and a lubricating layer consisting of lubricating oil and coated on the protective layer. It is also good.

· Fluttering property When the atmosphere in the HDD is air, the fluttering property of the magnetic disk, that is, the amplitude in the thickness direction of the magnetic disk when the disk flutter occurs is preferably 50 nm or less, and 30 nm or less It is more preferable that When the atmosphere in the HDD is helium, the fluttering property of the magnetic disk is preferably 30 nm or less, more preferably 20 nm or less. By regulating the fluttering characteristics as described above according to the atmosphere in the HDD, the positional deviation of the magnetic head at the time of disk flutter can be accommodated within the allowable range, and the occurrence of read errors and write errors can be suppressed.

  In order to reduce the amplitude in the thickness direction of the magnetic disk when the disk flutter occurs, it is preferable to use the magnetic disk incorporated in a helium-filled HDD. Helium has a viscosity of about 1/8 that of air. Therefore, when the magnetic disk is rotated in a helium atmosphere, the hydrodynamic force of helium can be reduced compared to that in air. As a result, the excitation force applied to the magnetic disk can be further reduced, and the occurrence of disk flutter can be suppressed more effectively.

D. Method of Manufacturing Magnetic Disk The magnetic disk can be manufactured, for example, by the following method.

-Pre-plating treatment Before forming the Ni-P plating film on the surface of the magnetic disk substrate described above, a pre-plating treatment including degreasing washing, etching and desmutting treatment is performed. Specifically, first, degreasing and cleaning are performed to remove oil components such as processing oil adhering to the surface of the magnetic disk substrate described above. After degreasing and cleaning, the magnetic disk substrate is etched using an acid. Thereafter, desmutting is performed to remove the smut generated by the etching from the magnetic disk substrate. The processing conditions in these processes can be appropriately set according to the type of processing liquid.

Zincate treatment After plating pretreatment, zincate treatment is performed to form a Zn film on the surface of the magnetic disk substrate. In zincate treatment, a Zn film can be formed by performing zinc substitution plating in which Al is substituted with Zn. As the zincate treatment, the so-called double zincate method in which the zinc coating formed on the surface of the magnetic disk substrate is once peeled off after performing the first zinc substitution plating, and the zinc substitution plating is performed again to form the Zn coating It is preferable to adopt. According to the double zincate method, a denser Zn film can be formed on the surface of the magnetic disk substrate as compared with the Zn film formed by the first zinc displacement plating. As a result, defects in the Ni-P plating film can be reduced in the electroless Ni-P plating treatment to be performed later.

-Formation of Ni-P plating film After forming a Zn film on the surface of a magnetic disk substrate by zincate treatment, the Zn film can be replaced with a Ni-P plating film by performing electroless Ni-P plating treatment . Thereafter, the surface of the Ni-P plating film is smoothed by polishing the Ni-P plating film.

Formation of Magnetic Material Layer, Protective Layer, and Lubricant Layer A magnetic material is deposited on the smoothed Ni-P plating film by sputtering to form a magnetic material layer. The magnetic layer may be composed of a single layer or may be composed of a plurality of layers having different compositions. After sputtering, a protective layer made of a carbon-based material is formed on the magnetic layer by CVD. Thereafter, lubricating oil is applied on the protective layer to form a lubricating layer. Thus, the magnetic disk can be obtained.

  An example of the magnetic disk and a method of manufacturing the same will be described. The specific aspects of the magnetic disk and the method of manufacturing the same according to the present invention are not limited to the aspects of the embodiments shown below, and the configuration is appropriately changed from the embodiments within the scope of the present invention. can do.

Preparation of Magnetic Disk Substrate Magnetic disk substrates (test materials A1 to A62) used for evaluation in this example can be prepared by the following method. First, a molten metal having chemical components shown in Tables 1 to 3 is prepared. The symbol "Bal." In Table 1 is a symbol indicating that the remainder is left.

  The molten metal is cast by either continuous casting (i.e. CC) or semi-continuous casting (i.e. DC) to produce an ingot. Specifically, as shown in Tables 4 to 7, when producing the test materials A40, A41, and A60, an ingot with a thickness of 15 mm is produced by continuous casting. Moreover, in producing test material A1-A39, A42-A59, A61-A62, after producing the ingot of thickness 230mm by semicontinuous casting, the surface of the range of 15 mm in depth is surface-cut from the surface of an ingot, Remove the segregation layer present on the surface of the ingot.

  Moreover, in producing test material A1-A2, A6-A62, after producing an ingot, an ingot is hold | maintained at the temperature of 370 degreeC for 10 hours, and a homogenization process is performed. Thereafter, the ingot is hot-rolled under the conditions shown in Tables 4 to 7 to produce a hot-rolled sheet. In preparing the test materials A1, A3 and A40, after hot rolling and before performing the first pass of cold rolling, the hot rolled sheet is heated to a temperature of 360 ° C. using a batch heat treatment furnace. Hold for a while and perform annealing.

  Thereafter, one or more passes of cold rolling are performed on the hot-rolled sheet to produce a cold-rolled sheet having a thickness of 0.8 mm. The cold-rolled sheet is punched to produce an annular disc blank having an outer diameter of 96 mm and an inner diameter of 24 mm.

  The obtained disk blank is held at a temperature of 280 ° C. for 3 hours while being pressurized from both sides in the thickness direction at a pressure of 0.5 MPa, and pressure annealing is performed. The outer peripheral end face and the inner peripheral end face of the disk blank after pressure annealing are subjected to cutting so that the outer diameter of the disk blank is 95 mm and the inner diameter is 25 mm. Thereafter, grinding is performed on each plate surface of the disk blank so that the grinding amount is 70 μm. Thus, the magnetic disk substrate (test materials A1 to A62) can be obtained.

  Evaluation method of metal structure in each test material, measurement method of amount of Fe dissolved in Al matrix, evaluation method of grinding processability, evaluation method of fluttering characteristics, measurement method of strength and measurement method of loss coefficient Explain to.

-Evaluation method of metal structure The plate surface of each test material after grinding processing is ground so that a grinding amount may be 10 micrometers. The plate surface is observed with an electron beam microanalyzer at a magnification of 1000 to obtain a composition image. An image analyzer is used to count the number of second phase particles having a longest diameter of 1.5 mm or more present in the composition image. Tables 5 to 7 show the number of second phase particles having a longest diameter of 1.5 mm or more in each test material.

Method of measuring the amount of Fe dissolved in the Al matrix In this example, a value obtained by subtracting the mass of Fe contained in the second phase particles from the total mass of Fe contained in each test material is added to the Al matrix. Let it be the amount of dissolved Fe. Tables 5 to 7 show the amount of Fe dissolved in the Al matrix in each test material. The mass of Fe contained in the second phase particles can be measured by the following method.

  First, 2 g of small pieces are collected from the test material. After pouring 50 ml of phenol into a beaker, the beaker is heated so that the temperature of phenol becomes 170 to 180 ° C. Next, small pieces are placed in a beaker, and the Al matrix is dissolved in phenol by stirring for about 30 minutes.

  After dissolving the Al matrix in phenol, stop heating the beaker and cool the phenol solution. Next, benzyl alcohol is added to the phenol solution to prevent solidification. By filtering this solution through a polytetrafluoroethylene membrane filter (pore diameter: 0.1 μm), the second phase particles can be recovered as a solid remaining on the filter.

  Next, 10% aqueous NaOH solution and aqua regia (that is, a solution in which concentrated hydrochloric acid and concentrated nitric acid are mixed in a volume ratio of 3: 1) are sequentially added to the second phase particles to dissolve the second phase particles. When Si is contained in the second phase particles, Si can be dissolved by a 10% aqueous NaOH solution. In addition, Fe in the second phase particles can be dissolved by aqua regia. The mass of Fe contained in the second phase particles can be measured by quantitatively analyzing the concentration of Fe in the aqueous solution thus obtained by inductively coupled plasma emission spectrometry (ICP).

-Evaluation method of grinding processability In the manufacturing process of a test material, after performing pressure annealing, the disk blank before cutting and grinding is extract | collected. The grinding processability can be evaluated based on the processing speed when the disk blank is subjected to grinding under the same conditions. In this example, these disc blanks are ground using a double-sided grinder ("DSM 9B-5L / P-V" manufactured by SpeedFam Co., Ltd.). Grinding is performed after dressing and the processing time is 5 minutes. The grinding speed (μm / min) can be calculated by dividing the amount of reduction in thickness (μm) by grinding by the processing time (minute).

  Tables 5 to 7 show the average value of the processing speeds obtained by grinding each test material five times. Moreover, in the "judgement" column in the grinding processability column in Tables 5 to 7, the symbol "A" when the average value of the processing speed is 10 μm / min or more, in the case of 5 μm / min or more and less than 10 μm / min. The symbol "B" and the symbol "D" were described in the case of less than 5 μm / min. In the evaluation of the grinding processability, the symbol A and the symbol B in which the average value of the machining speed is 5 μm / min or more are judged as pass because the machining speed is sufficiently fast, and the symbol D of less than 5 μm / min The case was judged to be unacceptable because the processing speed was slow.

Evaluation of fluttering characteristics In the evaluation of fluttering characteristics, first, a Ni-P plating film is formed on the surface of each test material, and a simulated disk simulating a magnetic disk is produced. The method of producing the simulated disk is as follows. First, as a pretreatment for plating, each test material is sequentially subjected to degreasing washing, etching and desmutting treatment to clean the surface of the test material. Next, a Zn film is formed on the surface of the test material by the double zincate method as zincate treatment. Thereafter, the Zn film is replaced with a 10.3 μm thick Ni-P plating film by electroless Ni-P plating treatment. Using a buff, the surface of the Ni-P plating film is polished so that the polishing amount is 1.1 μm.

  The plurality of simulated disks 12 obtained as described above are incorporated into the housing 11 ("ST2000" manufactured by Seagate) of the HDD 1 as shown in FIG. An observation window 13 for measuring the vibration of the simulation disk 12 is provided in the housing 11 of the HDD 1 of this example, and the simulation disk 121 disposed at the outermost side among the plurality of simulation disks 12 is observed. It is configured to be able to. Further, the squeeze plate is removed from the housing 11 of the HDD 1 in advance.

  Although not shown in the figure, a motor driver ("SLD 102" manufactured by Techno Alive Corporation) is directly connected to the spindle motor 14 of the housing 11 incorporating the simulated disk 12, and the simulated disk 12 is rotated at 7200 rpm. In this state, the laser beam L is irradiated from the laser doppler vibrometer 15 (“LV1800” manufactured by Ono Sokki Co., Ltd.) to the simulated disc 121 disposed on the outermost side, and the vibration of the simulated disc 121 is measured.

  The vibration waveform of the simulated disk 12 thus obtained is subjected to Fourier transform to obtain a spectrum of the vibration. Then, the maximum value of the amplitude within the frequency range of 300 to 1500 Hz, which is determined based on the spectrum of vibration, is taken as the value of the fluttering characteristic. It is also possible to measure fluttering characteristics using a magnetic disk provided with a magnetic layer, a protective layer and a lubricating layer instead of the simulated disk 12.

  The fluttering characteristics of each test material are shown in Tables 5 to 7. In the "fluttering characteristics" column in Tables 5 to 7, the symbol "A" when the maximum value of the amplitude is 30 nm or less, the symbol "B" when more than 30 nm and 40 nm or less, and 40 or more and 50 nm or less The symbol "C" and the symbol "D" above 50 nm are respectively described.

  The test materials A50 to A59 can not be evaluated for fluttering characteristics because the Ni-P plating film peels off from the magnetic disk substrate after the electroless Ni-P plating treatment. Therefore, the symbol "-" was described about these test materials.

  In the fluttering characteristics evaluation, the above-described maximum value of the amplitude can be used as an index of vibration not synchronized with the rotation of the magnetic disk called non-repeatable run out (NRRO). If the amplitude of this vibration becomes large, the position of the magnetic head is likely to be deviated from the desired position, which may cause the occurrence of a read error or a write error. In this example, in the case of symbols A to C in which the maximum value of the amplitude is 50 nm or less, NRRO is small, and disk flutter can be sufficiently suppressed, so it is judged as pass. In the case of symbol D exceeding 50 nm, NRRO Was judged to be a failure because the disk flutter was not sufficiently suppressed.

・ Evaluation method of strength In the manufacturing process of the test material, cold-rolled sheet after cold rolling is collected. This cold rolled sheet is held at a temperature of 280 ° C. for 3 hours, and heat treatment simulating pressure annealing is performed. Once the cold rolled sheet is cooled, the cold rolled sheet is again held at a temperature of 280 ° C. for 3 hours to perform heat treatment simulating heating in the process of manufacturing the magnetic disk.

  After these heat treatments, the No. 5 test piece specified in JIS Z2241: 2011 is taken from the cold-rolled sheet so that the longitudinal direction and the rolling direction become parallel. The tensile test is performed using the test piece obtained above according to the prescription | regulation of JIS Z2241: 2011. The proof stress of each test material can be calculated from the obtained stress-strain curve.

  In the tensile test, in addition to the No. 5 test piece made of a cold-rolled sheet, a test piece made of a magnetic disk can also be used. In this case, first, the Ni-P plating film on the magnetic disk and the layer laminated thereon are peeled off to separate the magnetic disk substrate. After grinding the surface of the magnetic disk substrate by 10 μm, heat treatment is performed by maintaining the temperature at 280 ° C. for 3 hours. Thereafter, a test piece having a shape according to the No. 5 test piece may be manufactured from the magnetic disk substrate. Specifically, the dimensions of the test piece are such that the width of the parallel portion is 5 ± 0.14 mm, the standard mark distance of the test piece is 10 mm, the radius of the shoulder is 2.5 mm, and the parallel portion length is 15 mm.

  Table 5-Table 7 perform a tension test twice for each test material, and show the average value of the yield strength obtained from each test result. Moreover, in the “judgment” column in the strength column in Tables 5 to 7, the symbol “A” when the average value of proof stress is 90 MPa or more, the symbol “B” when 80 MPa or more and less than 90 MPa, 70 MPa or more and less than 80 MPa In the case of, the symbol "C", and in the case of less than 80 MPa, the symbol "D" was described. In the evaluation of strength, in the case of symbols A to C in which the average value of the proof stress is 70 MPa or more, the strength is sufficiently high and it is determined to be acceptable. In the case of symbol D less than 70 MPa, the strength is low It was determined that.

Method of Measuring Loss Factor A strip test piece 60 mm long and 8 mm wide is produced from a cold-rolled plate or magnetic disk by the same method as the measurement of strength described above. In this example, the loss factor of this strip test piece is measured by the attenuation method.

  For measurement of the loss factor, a free resonance type internal friction measuring device ("JE-RT" manufactured by Nippon Techno Plus Co., Ltd.) can be used. As shown in FIG. 2, the measuring device 2 has a drive electrode 21 and an amplitude sensor 22 facing the drive electrode 21. The strip test piece S is horizontally disposed between the drive electrode 21 and the amplitude sensor 22, and the strip test piece S is fixed by the thin wire 23 at a position where it becomes a node of vibration. The strip test piece S can be vibrated by causing an alternating current to flow through the drive electrode 21 in this state and applying a coulomb force to the strip test piece S. Then, by measuring the amplitude of the strip test strip S using the amplitude sensor 22, a waveform of vibration can be obtained.

  In this example, after alternating current is supplied to the drive electrode 21 to forcibly vibrate the strip test piece S, the alternating current is stopped and the strip test piece S is freely vibrated by the restoring force. The vibration of the strip test strip S is a so-called damped free vibration in which the amplitude is exponentially damped while being periodically vibrated with a period T as shown in the waveform shown in FIG. In the damping free vibration, it is considered that the amplitude decreases exponentially because the loss of vibrational energy occurs due to the resistance by the atmosphere, the internal friction derived from the dislocation inside the strip specimen, etc. .

Based on the waveform of the damping free vibration obtained as described above, first, the logarithmic attenuation factor δ is calculated by the following method. Initially, the waveform of the attenuation free vibration, n-th cycle (wherein, n is a positive integer) and n + m-th cycle (wherein, m is an integer of 2 or more) optionally select, the n-th cycle of the amplitude a _n It acquires the value of n + m-th cycle a value of the amplitude a _{n + m.} The logarithmic decrement [delta], and the amplitude a _k of the k-th cycle, since the the next cycle of the amplitude a _{k + 1} and the natural logarithm ln value of the ratio (a _k / a k _{+ 1),} the amplitude a _n When the amplitude a _{n + m} with the natural ratio logarithm _{ln (a n / a n +} m) can be expanded as the following equation.
ln (a _n / a _{n + m} ) = ln {(a _n / a _{n + 1} ) × (a _{n + 1} / a _{n + 2} ) ×... x (a _{n + m−1} / a _{n + m} )} = mδ

Therefore, the value of logarithmic decrement δ can be expressed by the following equation using the value of the amplitude a _n of n-th cycle, the n + m th cycle a value of the amplitude a _{n + m.}
δ = (1 / m) · ln (a _n / a _{n + m} )

Then, the loss coefficient η can be calculated by dividing the value of the logarithmic attenuation factor δ by the circling factor π.
η = δ / π = (1 / πm) · ln (a n / a n + m)

  Tables 5 to 7 show values of the product of the thickness t [mm] and the loss coefficient に お け る in each test material.

  As shown in Tables 5 to 7, the test materials A1 to A47 have the specific chemical components and the metal structure. Therefore, these test materials have excellent grinding processability and sufficient strength, and can suppress disk flutter.

  In the test materials A48 to A49, since the content of Fe is smaller than the above-described specific range, it is difficult to suppress the disk flutter. Moreover, these test materials have lower strength than the test materials A1 to A47.

In the test material A50, since the content of Fe is larger than the above-mentioned specific range, peeling of the Ni-P plating film tends to occur. Therefore, it is difficult to use the test material A50 as a magnetic disk substrate.
Since the test material A51 contains a larger amount of Fe than the test material A50, peeling of the Ni-P plating film is likely to occur as in the case of the test material A50. In addition, in the test material A51, a large number of coarse second phase particles are formed in the Al matrix, which may cause deterioration in grinding processability.

In the test materials A52 to A59, since the content of any of Mn, Si, Ni, Cu, Mg, Cr, Zr, or Zn is larger than the above-mentioned specific range, peeling of the Ni-P plating film tends to occur. Therefore, it is difficult to use these test materials as magnetic disk substrates.
In the test materials A60 to A62, the time during which the temperature of the ingot is in the range of 200 to 430 ° C. is short, and the amount of heat input in hot rolling is insufficient, so the precipitation amount of second phase particles tends to be small. Therefore, these test materials are difficult to suppress disk flutter.

1 hard disk drive 11 housing 12 simulated disk 13 observation window 14 spindle motor 15 laser doppler vibrometer

Claims (10)

A chemical component containing Fe: 0.005 to 0.600% by mass, Si: 0.4% by mass or less, the balance being Al and unavoidable impurities,
A metal structure in which second phase particles are dispersed in an Al matrix,
Among the second-phase particles, Ri number der 50000 / mm ² or less of the second phase particles having a maximum diameter of more than 1.5 [mu] m,
The amount of Fe in solid solution in the Al matrix is 0.0010 to 0.0300 mass%,
A magnetic disk substrate , wherein the value of the product of the thickness t [mm] and the loss coefficient η is 0.10 × 10 ⁻³ or more . The magnetic disk substrate further comprises Mn: 0.1 to 3.0% by mass, Mg: 0.1 to 0.4% by mass, Ni: 0.1 to 3.0% by mass, Cr: 0.01 to 40%. The magnetic disk substrate according to claim 1, containing one or more of 1.00 mass% and Zr: 0.01 to 1.00 mass%. The magnetic disk substrate further, Cu: .005 to 1.000 containing mass%, the magnetic disk substrate according to claim 1 or 2. The magnetic disk substrate according to any one of claims 1 to 3 , wherein the magnetic disk substrate further contains Zn: 0.005 to 1.000% by mass. The magnetic disk substrate further contains one or more of Ti, B and V, and the total content of Ti, B and V is 0.005 to 0.500% by mass. A magnetic disk substrate according to any one of claims 1 to 4 . A magnetic disk substrate according to any one of claims 1 to 5 ;
Ni-P plating film covering the surface of the magnetic disk substrate;
And a magnetic disk having a magnetic layer laminated on the Ni-P plating film. A method of manufacturing a magnetic disk substrate according to any one of claims 1 to 5 , wherein
Producing an ingot with the above-mentioned chemical composition,
The hot-rolled sheet is subjected to hot rolling on the ingot under the condition that the temperature of the ingot during rolling is 200 to 430 ° C. and the time in which the temperature of the ingot is within the range is 30 minutes or more To make
Cold rolling is performed on the hot rolled sheet for one or more passes to produce a cold rolled sheet,
The cold rolled sheet is punched to produce a circular disc blank.
The disk blank is heated while being pressed from both sides in the thickness direction to perform pressure annealing,
A method of manufacturing a magnetic disk substrate, wherein the magnetic disk substrate is manufactured by sequentially performing cutting processing and grinding processing on the disk blank. After the ingot is produced, the ingot is maintained at a temperature of 250 to 430 ° C. for 0.5 to 60 hours for homogenization treatment, and then the ingot is subjected to the hot rolling to obtain the hot-rolled sheet The method of manufacturing a magnetic disk substrate according to claim 7 , wherein The hot-rolled sheet is annealed at a temperature of 300 to 500 ° C. for 0.1 to 30 hours in a batch heat treatment furnace at least one before and during the first pass in the cold rolling. The manufacturing method of the magnetic disc board | substrate as described in 7 or 8 . In at least one of the first pass and the pass between the cold rollings, using a continuous heat treatment furnace, the heat is maintained so that the residence time in the furnace is within 60 seconds and the temperature is 400 to 600 ° C. performing annealing by heating the rolled sheet, manufacturing method of a magnetic disk substrate according to claim 7 or 8.

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