JP2019091515A - Magnetic disk substrate made of aluminum alloy and method of manufacturing the same, and magnetic disk - Google Patents

Abstract

To provide a magnetic disk substrate made of aluminum alloy with less defects on a Ni-P plating surface and less swelling on the Ni-P plating surface, a method of manufacturing the same, and a magnetic disk using the same.SOLUTION: The present invention are a magnetic disk substrate made of aluminum alloy, a method of manufacturing the same, and a magnetic disk using the magnetic disk substrate made of the aluminum alloy, the magnetic disk substrate made of aluminum alloy is characterized in that an aluminum alloy base material made of aluminum alloy having a predetermined composition, and an electroless Ni-P plating layer formed on the surface of the same are comprised, and in the surface of the electroless Ni-P plating layer of the aluminum alloy base material, existence density of a chemical compound having a maximum diameter of 3-6 μm is equal to or less than 300 pieces/mm, and when opening diameter is (X)μm and depth is (Y)μm, 80 pieces/cm or more holes in which Y/X is 0.8-3.0 exist at a radial position.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an aluminum alloy magnetic disk substrate, and more particularly, to an aluminum alloy magnetic disk substrate which is excellent in adhesion of plating and in which defects and swelling of the electroless Ni-P plating surface are reduced and its manufacture The present invention relates to a method and a magnetic disk using the aluminum alloy magnetic disk substrate.

  An aluminum alloy magnetic disk substrate used for a storage device of a computer or data center is manufactured using a substrate having excellent plating properties and excellent mechanical characteristics and processability. For example, JIS 5086 (Mg of 3.5 mass% or more and 4.5 mass% or less, Fe of 0.50 mass% or less, Si of 0.40 mass% or less, Mn of 0.20 mass% or more and 0.70 mass% or less, 0.05 mass% or more Manufactured from a substrate based on an aluminum alloy consisting of 0.25 mass% or less of Cr, 0.10 mass% or less of Cu, 0.15 mass% or less of Ti, 0.25 mass% or less of Zn, the balance of Al and unavoidable impurities) It is done.

  A general aluminum alloy magnetic disk is manufactured by first producing an annular aluminum alloy substrate, plating the aluminum alloy substrate, and then depositing a magnetic material on the surface.

  For example, an aluminum alloy magnetic disk made of the aforementioned JIS 5086 alloy is manufactured by the following manufacturing process. First, an aluminum alloy having a desired chemical composition is cast, the ingot is homogenized, hot rolled, and then cold rolled to produce a rolled material having a thickness necessary for a magnetic disk. Do. The rolled material is preferably annealed during cold rolling as needed. Next, this rolled material is punched into an annular shape, and in order to remove distortion and the like caused by the manufacturing process up to that time, aluminum alloy sheets punched into an annular shape are laminated, and annealing is performed while pressing from both upper and lower sides. By applying and planarizing pressure annealing, an annular aluminum alloy disk blank is produced. An aluminum alloy substrate for a magnetic disk is manufactured by sequentially applying cutting, grinding, and strain-removing heating as pretreatment to the disk blank thus manufactured.

  Next, the aluminum alloy substrate for a magnetic disk manufactured in this manner is sequentially subjected to degreasing treatment, etching treatment, desmutting treatment, and zincate treatment (Zn substitution treatment). Furthermore, a magnetic disk substrate made of an aluminum alloy is manufactured by electrolessly plating Ni-P, which is a hard nonmagnetic metal, as a surface treatment.

  Finally, the surface of the Ni-P electroless plating is smoothened by polishing, and then the magnetic material is sputtered to produce an aluminum alloy magnetic disk.

  By the way, in recent years, a new storage device, SSD, has appeared, and in particular, in notebook PCs, HDDs are being replaced with SSDs. HDDs are being used in larger capacity, higher density, and higher speeds, and are being applied to data centers and the like, which are increasing their storage capacity year by year, to compete with SSDs. For increasing the capacity of the HDD, there are methods such as an increase in the number of magnetic disks mounted in a storage device and an increase in storage capacity per magnetic disk. If defects such as pits are present on the electroless Ni-P plated surface, reading and writing of data must be performed excluding the defect periphery. As a result, the storage capacity per magnetic disk decreases in proportion to the number of defects. Thus, in order to increase the storage capacity per magnetic disk, it is essential to reduce defects on the electroless Ni-P plating surface.

  Recently, as a new issue of the surface quality of the magnetic disk, prevention of microblurring on the electroless Ni-P plating surface has been mentioned. If there is a minute bulging, the head, which is a reading unit, can not follow the bulging shape and contacts, and reading and writing become impossible, resulting in a failure of the HDD. In particular, in order to expand the demand for the HDD in the future, it is essential to solve the microblurring, since the influence at the time of the high speed rotation accompanying the speeding up is large.

  From the above situation, recently, it is strongly desired to simultaneously achieve the reduction of defects and micro blisters on the surface of electroless Ni-P plating. In order to solve both problems, it is effective to reduce the content of Fe and Si. However, the reduction of these elements can not avoid the cost increase, and the reduction of the content makes it impossible to ignore the adverse effects such as the deterioration of the grinding property. Therefore, there is a limit to the countermeasure only with the alloy composition, and it is necessary to develop a new method.

  For example, Patent Document 1 discloses a technique in which a smooth electroless Ni-P plated surface can be obtained by adjusting an etching solution in order to omit the polishing step of the electroless Ni-P plated surface. Moreover, the technique which suppresses a plating defect is disclosed by patent document 2 by adding a sulfate ion to the wash water in an electroless Ni-P plating process.

Unexamined-Japanese-Patent No. 5-247659 gazette Patent No. 5872322

  However, in the aluminum alloy substrate disclosed in Patent Document 1, the purpose is to omit the step of polishing the electroless Ni-P plating surface, and it is possible to solve the minute defects and swelling that are the current problems. Absent. In addition, since the technique of Patent Document 2 is not a technique for removing a compound, there is no effect on micro swelling, and additionally, when the number of compounds increases, the removal effect of all the compounds can not be expected.

  The present invention has been made in view of the above situation, and an aluminum alloy magnetic disk substrate in which the occurrence of defects and blisters on an electroless Ni-P plating surface are simultaneously suppressed, a method of manufacturing the same, and the aluminum alloy An object of the present invention is to provide a magnetic disk using a magnetic disk substrate manufactured by

  The inventors of the present invention conducted intensive studies on the compounds in the aluminum alloy substrate, the relationship between defects and blisters on the surface of the electroless Ni-P plating, and the removability of the compounds. As a result, by removing the compound of the aluminum alloy substrate in the compound removing step, defects of the electroless Ni-P plating surface are reduced, and the adhesion of the electroless Ni-P plating is improved by the holes from which the compound is removed. It was found that swelling can be suppressed by doing. The present inventors have further found that, even when the number of compounds is large, the compound removal step can suppress defects and blisters on the surface of the electroless Ni-P plating, thereby completing the present invention. The

That is, in the present invention, in claim 1, Mg: 2.5 to 10.0 mass%, Cu: 0.003 to 0.200 mass%, Zn: 0.05 to 0.60 mass% and Be: 0.00001 to 0. .00200 mass%, Si: 0.001 to 0.500 mass%, Fe: 0.001 to 0.500 mass%, Cr: 0.30 mass% or less and Mn: 0.50 mass% or less, balance Al And an electroless Ni-P plating layer of the aluminum alloy base material, and an electroless Ni-P plating layer formed on the surface of the aluminum alloy base material. in the surface side, the density of the compound having a maximum diameter of 3~6μm is 300 pieces / mm ² or less, and the aperture diameter (X) mu And a magnetic disk substrate made of an aluminum alloy characterized in that at least 80 holes / cm at a radial position where Y / X is 0.8 to 3.0 when the depth is (Y) μm did.

  According to a second aspect of the present invention, in the first aspect, the depth Y is 1.0 to 5.0 μm.

The present invention according to claim 3 is the method of manufacturing an aluminum alloy magnetic disk substrate according to claim 1 or 2, wherein the casting step, the hot rolling step and the cold rolling step of the aluminum alloy are performed in this order. An aluminum alloy including a step of preparing an aluminum alloy sheet containing the material; a pressure flattening annealing step of an annular aluminum alloy plate obtained by punching the aluminum alloy plate into an annular shape, a cutting / grinding step and a strain removing heat treatment step in this order A substrate preparation step; an alkaline degreasing treatment step, an acid etching treatment step, a desmutting treatment step and a zincate treatment step of the aluminum alloy substrate in this order; and an aluminum subjected to the plating pretreatment step. An electroless Ni-P plating process for performing electroless Ni-P plating on the surface of the alloy substrate; Before after at a by zincate treatment stage of the serial cutting and grinding stages, mixing of _HNO 3 / HF containing HF of 10～60Mass% of HNO ₃ solution at a by 10 to 80 g / L of 10 to 30 ° C. A method of manufacturing a magnetic disk substrate made of an aluminum alloy, further comprising a compound removing step of immersing the aluminum alloy substrate in a solution for 5 to 60 seconds.

  According to the present invention, in claim 4 according to claim 4, one or both of the homogenization treatment step and the annealing treatment step before or during the cold rolling step are performed between the casting step and the hot rolling step. It was further provided.

  According to a fifth aspect of the present invention, there is provided a magnetic disk comprising a magnetic material layer on the electroless Ni-P plating layer of the aluminum alloy magnetic disk substrate according to the first or second aspect.

  The magnetic disk substrate made of aluminum alloy according to the present invention is characterized in that defects and blisters on the surface of the electroless Ni-P plating are reduced, and the upper limit of the content of Fe and Si can be relaxed. As a result, the aluminum alloy magnetic disk according to the present invention can increase the storage capacity per sheet and reduce the defect rate, contribute to increasing the capacity of the HDD, and can be provided inexpensively.

It is explanatory drawing of the process of pre-plating treatment of a magnetic disc board | substrate made from aluminum alloy, and electroless-Ni-P plating.

  Hereinafter, the present invention will be described in detail based on the embodiments. Electroless Ni--A magnetic disk substrate made of aluminum alloy according to the present invention (hereinafter sometimes referred to simply as "magnetic disk substrate"), aluminum alloy substrate from which compounds present on the surface have been removed by compound removing step A P plating layer is provided, and by removing the compound on the surface of the aluminum alloy substrate, generation of defects on the electroless Ni-P plating surface is suppressed, and at the same time, a hole having a predetermined structure along with the compound removal It is possible to suppress the occurrence of blistering on the electroless Ni-P plated surface by forming. Below, the effect and the detailed mechanism about these are explained. In addition, "electroless Ni-P plating" may only be described as "Ni-P plating" below.

1. Compound plating surface defects on aluminum alloy substrate surfaces are associated with the dissolution of aluminum alloy substrates. Dissolution of the aluminum alloy base material is caused by a battery reaction between the compound and a matrix phase around the compound in a process of electroless Ni-P plating treatment described later. The potential of the Al-Fe-based compound and the Al-Si-based compound present on the surface of the aluminum alloy substrate is nobler than that of the matrix phase. That is, a local battery is formed in which these compounds become cathode sites and the matrix around the compounds becomes anode sites. If such a local cell reaction occurs during the electroless Ni-P plating process, it results in defects on the plating surface. If the aluminum alloy substrate is exposed during the electroless Ni-P plating process, dissolution of the matrix around the compound proceeds by the local cell reaction, and local gas generation occurs continuously, so that the aluminum alloy is formed. It becomes a defect of a plating surface with a large aspect ratio which extends from a substrate to a Ni-P plating surface.

  If the maximum diameter of the compound present on the surface on the electroless Ni-P plating layer side of the aluminum alloy substrate is less than 3 μm, it is not large enough to function as a cathode site, and the speed of the local cell reaction is small. . Therefore, the dissolution of the matrix phase around the compound proceeds and the defects of the plating surface having a large aspect ratio due to the continuous occurrence of the local gas generation can not be formed. On the other hand, if the maximum diameter of the compound exceeds 6 μm, it is large enough to function as a cathode site, the local cell reaction speed between the compound and the mother phase is large, and dissolution of the mother phase around the compound proceeds However, by providing the compound removal step, compounds having such a large maximum diameter are easily removed. From these facts, the above compound is intended for those having a maximum diameter of 3 to 6 μm. The maximum diameter defined in the present invention means that in the planar image of the intermetallic compound, first, the maximum value of the distance between one point on the outline and the other point on the outline is measured, and then this maximum value is All points on the contour line are measured, and finally, it is defined by the largest one selected from among these total maxima.

If the existing density of such a compound having a maximum diameter of 3 to 6 μm is 300 pieces / mm ² or less, there is no problem in applying as an aluminum alloy substrate. This presence density is preferably 150 pieces / mm ² or less. The lower limit value of the presence density is not particularly limited, but it depends on the composition of the aluminum alloy to be used and the production method. The lower the existing density, the better, but the lower limit is about 80 pcs / mm ² .

2. Irregularities on the Surface of Aluminum Alloy Substrate For example, when the compound is removed in a compound removal step described later, holes are formed on the surface of the aluminum alloy substrate. Also in the inside of the formed hole, if a zincate film is formed, Ni-P precipitates and becomes plating. When plating is applied to the inside of such a hole, the adhesion between the plating and the aluminum alloy base is usually improved by the anchor effect, which is the same as in the magnetic disk substrate. In the magnetic disk substrate, if the adhesion between the Ni—P plating and the aluminum alloy substrate is high, it is possible to suppress the swelling defect, so it is effective to enhance the anchor effect.

  In the present invention, since the anchor effect of Ni-P plating acts on the pores on the surface of the aluminum alloy substrate as described above, the structure and the existing density at the interface between the aluminum alloy substrate and the Ni-P plating layer are specified. It is As described above, since the inside of the hole needs to be plated, it is necessary to confirm from the cross section that the inside of the hole is also plated after plating. At this time, the number of holes per unit length may be defined at the radial position. That is, the relationship Y / X between the opening diameter (X) μm and the depth (Y) μm present at the radial position on the surface on the Ni-P plating layer side of the aluminum alloy base material is 0.8 to 3.0. It is defined that holes are present at 80 / cm or more. The radial position on the surface on the Ni-P plating layer side of the aluminum alloy base defined in the present invention means the circle in the cross section along the thickness direction passing through the circle center of the disk-shaped aluminum alloy base It is defined as a surface on the Ni-P plated layer side of an aluminum alloy substrate extending from the center to one circumferential end. Further, the opening diameter (X) defined in the present invention is defined by the maximum width of each hole measured in the above-mentioned cross section. Moreover, the depth (Y) prescribed | regulated by this invention is defined by the maximum depth in each hole measured in the said cross section.

When the value of Y / X is less than 0.8, the above-mentioned anchor effect is not sufficiently expressed. On the other hand, when the value of Y / X exceeds 3.0, the zincate reaction does not proceed at the bottom of the hole, and as a result, the zincate film is not formed, so Ni-P plating does not precipitate, and the cavity at the bottom of the hole Will be formed. If such a cavity exists, it will expand when heated and the Ni-P plating surface will swell. Therefore, Y / X is in the range of 0.8 to 3.0, preferably in the range of 1.0 to 2.5.

  As for Y, if it is less than 1.0 μm, it is shallow and not sufficient for the expression of the anchor effect, and if it exceeds 5.0 μm, the plating inside of the holes is uneven because it is deep and the cavity Even if the above Y / X relationship is satisfied, a sufficient anchor effect may not be obtained in order to cause occurrence and swelling. Therefore, Y is preferably in the range of 1.0 to 5.0 μm.

  Further, the existence density of the holes having Y / X of 0.8 to 3.0 present at the above radial position is preferably 120 / cm or more. When this existing density is less than 80 pieces / cm, sufficient adhesion between the plating due to the anchor effect and the aluminum alloy substrate can not be obtained. The upper limit value of the presence density is not particularly limited.

3. Alloy Composition of Aluminum Alloy Substrate The aluminum alloy substrate used in the present invention is Mg: 2.5 to 10.0 mass% (hereinafter simply referred to as “%”), Cu: 0.003 to 0.200%, Zn: 0.05 to 0.60% and Be: 0.00001 to 0.00200%, Si: 0.0005 to 0.500%, Fe: 0.0005 to 0.500%, Cr: 0 .30% or less and Mn: 0.50% or less, and consists of an aluminum alloy composed of the balance Al and unavoidable impurities.

Mg: 2.5 to 10.0%
Mg mainly has the effect of improving the strength of the aluminum alloy substrate. Further, Mg exerts the function of adhering the zincate film uniformly, thinly and precisely at the time of zincate treatment, and therefore, in the electroless Ni-P plating step, the generation of defects on the plating surface is suppressed to perform Ni-P plating. Improve surface smoothness. The Mg content is defined as 2.0 to 10.0 mass%. If the Mg content is less than 2.5%, the strength is insufficient, and if it exceeds 10.0%, rolling is difficult and industrial production can not be achieved. The preferred Mg content is 4.0 to 6.0% because of the combination of strength and ease of manufacture.

Cu: 0.003 to 0.200%
Cu has the effect of adhering the zincate coating uniformly, thinly and precisely. As a result, in the electroless Ni-P plating step, the generation of defects on the plated surface is suppressed, and the smoothness of the Ni-P plated surface is improved. The Cu content is defined as 0.003 to 0.200%. If the Cu content is less than 0.003%, the above effect can not be sufficiently obtained. On the other hand, if the Cu content exceeds 0.200%, the potential of the matrix becomes noble, and the potential difference between the compound and the matrix decreases in the compound removal step, whereby the speed of the local cell reaction decreases and the matrix Dissolution does not proceed and removal of large compounds becomes difficult. The preferred Cu content is 0.010 to 0.100%.

Zn: 0.05 to 0.60%
Zn, like Cu, has the effect of adhering the zincate coating uniformly, thinly and densely. As a result, in the electroless Ni-P plating step, the generation of defects on the plated surface is suppressed, and the smoothness of the Ni-P plated surface is improved. The Zn content is defined as 0.05 to 0.60%. If the Zn content is less than 0.05%, the above effects can not be sufficiently obtained. On the other hand, when the Zn content exceeds 0.60%, the potential of the matrix becomes negative and the potential difference between the compound and the matrix in the compound removal step becomes too large, so that the speed of the local cell reaction becomes large. In addition to the progress of the dissolution of the matrix phase, the dissolution of the entire surface proceeds, so that the formed holes do not become deep and the above equation can not be satisfied. The preferred Zn content is 0.10 to 0.35%.

Be: 0.00001 to 0.00200%
Be has the effect of suppressing the oxidation of the Mg melt at the time of casting. However, since Be is a metal having a potential lower than that of Al, when a Be-enriched phase is formed on the surface of the aluminum alloy substrate, a local cell is formed of the Be-enriched phase and the matrix. As a result, dissolution of the Be-condensed phase makes the substitution reaction of Ni-P non-uniform, and local gas generation continuously occurs to cause defects on the plated surface. The Be content is defined as 0.00001 to 0.00200%. If the Be content is less than 0.00001%, the effect of suppressing the molten metal oxidation of Mg during casting can not be obtained sufficiently and casting becomes difficult. On the other hand, when the Be content exceeds 0.00200%, a large amount of Be-condensed phase is formed, which causes generation of defects on the plating surface. The preferred Be content is 0.00003 to 0.00100%.

Cr: 0.30% or less Cr forms a fine Al-Cr based intermetallic compound at the time of casting, but a part thereof forms a solid solution in the matrix and contributes to the improvement of strength. In addition, it has the effect of improving the machinability and the abradability, and further refining the recrystallized structure to improve the adhesion of the plating layer. The Cr content is regulated to 0.30% or less. When the Cr content exceeds 0.30%, an excess is crystallized at the time of casting and at the same time a coarse Al-Cr intermetallic compound is formed. Then, the crystallized excess causes non-uniformity of the reaction during zincate treatment and causes defects on the plating surface. The preferred Cr content is 0.20% or less.

Si: 0.001 to 0.500%
Since Si combines with Al to form an Al-Si based intermetallic compound which causes defects on the plating surface, it is not preferable that Si be contained in the aluminum alloy, but the compound removing step of the present invention It is removable by applying. However, when the Si content exceeds 0.500%, coarse Al-Si based intermetallic compounds are formed, which adversely affects cutting and grinding. On the other hand, if the Si content is less than 0.001%, the production cost is high and industrial production becomes difficult. Therefore, the Si content is defined as 0.001 to 0.500%. The Si content is preferably 0.010 to 0.200%.

Fe: 0.001 to 0.500%
Fe combines with Al to form an Al-Fe-based intermetallic compound which causes defects on the plating surface, and therefore, it is not preferable that Fe is contained in the aluminum alloy. However, since the Al-Fe-based intermetallic compound has a dressing effect to suppress clogging of the grindstone, it has an effect to improve the grinding speed. Therefore, by dispersing the Al-Fe-based intermetallic compound, the grinding speed can be improved, and after the grinding, if the Al-Fe-based intermetallic compound is removed by the compound removing step of the present invention, this intermetallic compound Can eliminate the negative effects of However, when the Fe content exceeds 0.500%, a coarse Al-Fe intermetallic compound is formed, and the pores formed by removing this compound are filled with Ni-P plating. It becomes a defect of the plating surface. On the other hand, if the Fe content is less than 0.001%, the production cost is high and industrial production becomes difficult. In addition, the grinding performance can not be secured. Therefore, the Fe content is defined as 0.001 to 0.500%. The Fe content is preferably 0.010 to 0.200%.

Mn: 0.50% or less Mn is an Al-Fe-based intermetallic compound and an Al-Si-based intermetallic compound precipitated in an aluminum alloy base material, respectively, the Al-Fe-Mn-based intermetallic compound and Al-Si- It precipitates as a Mn type | system | group intermetallic compound. Since these intermetallic compounds have a small potential difference with the matrix phase, they suppress the occurrence of plating defects with a large aspect ratio, which are formed by the local cell reaction during the Ni-P plating process. In addition, the potential difference between these compounds and the mother phase does not affect the reaction in the compound removal step. When the Mn content exceeds 0.50%, the above-mentioned coarse intermetallic compound is formed, and the pores formed by removing this compound can not be filled with Ni-P plating and defects on the plating surface It becomes. Therefore, the Mn content is regulated to 0.50% or less. The Mn content is preferably regulated to less than 0.35%, and may be 0%.

Other Elements The balance of the aluminum alloy base according to the embodiment of the present invention consists of Al and unavoidable impurities. As unavoidable impurities, Pb, Ga, Sn, etc. may be mentioned, and if each is less than 0.1% and less than 0.2% in total, the characteristics as an aluminum alloy base material used in the present invention can be obtained. There is no loss.

4. The process of the pre-plating process in the magnetic disc board | substrate made from electroless-Ni-P plating aluminum alloy is shown in FIG. In the stage-0 pre-treatment sample, an annular disk blank of an aluminum alloy substrate is subjected to pressure flattening annealing, then subjected to cutting and grinding, and is further subjected to strain removing heat treatment. is there. In this sample before treatment, dirt adheres to the surface, and the thickness of the oxide film is different for each sample.

  Next, in the stage of alkaline degreasing treatment of stage-1, dirt adhering to the surface of the material is removed. In the stage-2 acid etching process, the oxide film on the surface of the aluminum alloy substrate is removed. In the stage-3 desmutting step, a thin oxide film is formed on the surface of the aluminum alloy substrate, and the thickness of the oxide film in each sample is made approximately constant. By the steps up to this point, the surface of each aluminum alloy base is uniformly adjusted.

  Next, at the stage of 1st zincate at stage 4, after depositing fine Fe on the surface of the aluminum alloy substrate, the aluminum alloy substrate is dissolved by a battery reaction of Fe and the aluminum alloy substrate, and a substitution reaction is performed. Precipitate Zn (zinccate coating). In the stage of Zn stripping in stage 5, the Zn deposited in stage 4 is dissolved to leave Fe. The same reaction as the 1st zincate occurs in the 2nd zincate stage of stage-6, but Fe precipitation again increases the starting point of the cell reaction, whereby the precipitated Zn becomes fine and uniform zincate coating Is formed. In the step of electroless Ni-P plating in the final step-7, the substitution reaction of Zn and Ni-P on the surface of the aluminum alloy substrate first proceeds, and when the surface is covered with Ni-P, it is autocatalytic. Ni-P precipitates on Ni-P.

5. Compound Removal Step In the acid etching step of the above-mentioned Step-2, only the etching power to the extent that the oxide film on the surface of the aluminum alloy substrate is removed and a small amount of the matrix is dissolved is exhibited. In conventional aluminum alloy substrates with very small amounts of Fe and Si added, the compounds are small and the existing density is low, so if the compounds are removed in such an acid etching step, electroless Ni-P There were no defects or swelling problems on the plating surface.

  However, recently, with the increase in the accuracy of disk surface inspection machines, it has become possible to detect defects and bulges that could not be detected so far, thereby improving the performance of magnetic disks, such as increasing the capacity. Is advancing. Therefore, the compound removal is insufficient only by the etching step, and in order to reduce defects on the electroless Ni-P plating surface, it is necessary to reduce the compound remaining on the surface of the aluminum alloy substrate. It is necessary to have a removal step. Here, the compounds referred to in the present invention refer to intermetallic compounds such as Al-Fe, Al-Si, Al-Fe-Si, Al-Fe-Mn, and Al-Si-Mn.

In the compound removal step, the compound remaining on the surface of the aluminum alloy substrate is removed by a chemical solution. The chemical solution to be used is a 10 to 60 mass% (hereinafter abbreviated as “%”) HNO ₃ solution at 10 to 30 ° C. and a mixed solution of HNO ₃ / HF containing 10 to 80 g / L of HF Hereinafter, simply referred to as “mixed solution” is used. This mixed solution is strong in etching power, and in particular increases the dissolution rate of the aluminum alloy substrate around the compound. The compound is removed by dissolving the aluminum alloy substrate around the compound, and it is possible to selectively remove only the compound on the surface of the aluminum alloy substrate.

In the mixed solution, if the concentration of HF is less than 10 g / L and the concentration of HNO ₃ is less than 10%, the etching power is weak and the compound on the surface of the aluminum alloy substrate can not be sufficiently removed. On the other hand, when the concentration of HF exceeds 80 g / L and the concentration of HNO ₃ exceeds 60%, the etching power is too strong and dissolution of the matrix phase of the aluminum alloy base proceeds. As a result, the irregularities on the surface of the aluminum alloy substrate become large, and the smoothness of the electroless Ni-P plated surface can not be obtained. The HF concentration is preferably 20 to 60 g / L and the HNO ₃ concentration is preferably 25 to 50%.

  In addition, the temperature of the mixed solution is 10 to 30 ° C. If it is less than 10 ° C., the reaction rate is slow and the compounds on the surface of the aluminum alloy substrate can not be removed sufficiently. On the other hand, when the temperature exceeds 30 ° C., the reaction rate is too fast, and the dissolution of the matrix of the aluminum alloy substrate progresses, so that the irregularities on the surface of the aluminum alloy substrate become large. The temperature of the mixed solution is preferably 15 to 25 ° C. Furthermore, the processing time in the compound removal step is 5 to 60 seconds. If it is less than 5 seconds, the reaction time is too short to sufficiently remove the compound on the surface of the aluminum alloy substrate. On the other hand, if the reaction time exceeds 60 seconds, the reaction time is too long, and the dissolution of the matrix of the aluminum alloy base proceeds, whereby the surface of the aluminum alloy base becomes rough. The treatment time is preferably 10 to 30 seconds.

  The compound removal step is performed after the cutting and grinding step and before the zincate step. For example, it may be performed before the 1st zincate step in FIG. 1 and after the desmut step of the step-3, or may be performed instead of the desmut step. Furthermore, for example, it may be performed after the cutting / grinding step and before the alkaline degreasing step of the step-1. In this case, the oxide film on the surface of the aluminum alloy substrate may be removed by providing the same step as the acid etching step of Step-2 before the compound removal step.

6. Magnetic Disk Substrate and Method of Manufacturing Magnetic Disk Next, a method of manufacturing an aluminum alloy magnetic disk substrate according to the present invention will be described. In the magnetic disk substrate made of aluminum alloy according to the present invention, first, a molten metal adjusted to have a predetermined alloy composition is cast, and any homogenization treatment stage, hot rolling stage, cold rolling stage and optional annealing An aluminum alloy sheet is produced by applying a process including steps. Next, this is punched into an annular shape to obtain an annular aluminum alloy plate, which is subjected to steps including a pressure flattening annealing step, a cutting / grinding step and a strain removing heat treatment step, thereby producing aluminum for a magnetic disk. Make an alloy substrate. This is then subjected to a pre-plating step which includes an alkaline degreasing step, an acid etching step, a desmutting step and a zincate step. Further, the surface of the aluminum alloy base material subjected to the pre-plating treatment is subjected to a step of electroless Ni-P plating treatment as a base plating treatment to obtain a magnetic disk substrate made of an aluminum alloy. Below, each process is demonstrated in detail.

6-1. Casting Stage First, a molten aluminum alloy is prepared by heating and melting according to a conventional method so as to achieve a predetermined alloy composition range. The molten aluminum alloy thus prepared is cast according to a conventional method such as a semi-continuous casting (DC casting) method. The cooling rate at the time of casting is preferably in the range of 0.1 to 1000 ° C./s.

6-2. Homogenization Step Next, homogenization treatment is performed on the cast aluminum alloy as required. The conditions of the homogenization treatment are not particularly limited, and for example, a one-stage heat treatment at 450 ° C. or more and 0.5 hours or more can be used. The upper limit of the heating temperature at the time of the homogenization treatment is not particularly limited, but if it exceeds 650 ° C., the upper limit may be 650 ° C. because melting of the aluminum alloy may occur.

6-3. Hot rolling stage The ingot of the aluminum alloy which has been subjected to the homogenization treatment or not is processed into a sheet material by hot rolling. In the hot rolling step, when homogenization treatment is performed, the hot rolling start temperature is preferably 300 to 550 ° C., and the hot rolling finish temperature is preferably less than 380 ° C., 300 ° C. or less It is more preferable to The lower limit of the hot rolling finish temperature is not particularly limited, but the lower limit is set to 100 ° C. in order to prevent occurrence of defects such as edge cracking. On the other hand, when the homogenization treatment is not performed, the hot rolling start temperature is preferably less than 380 ° C., and more preferably less than 350 ° C. The hot rolling completion temperature is not particularly limited, but the lower limit is set to 100 ° C. in order to prevent occurrence of defects such as edge cracking.

6-4. Next, the hot-rolled sheet is processed into a cold-rolled sheet of about 0.45 to 1.8 mm by cold rolling. Thus, the hot-rolled sheet is finished to the required product thickness by cold rolling. The conditions of the cold rolling step are not particularly limited, and may be determined according to the required product plate strength and plate thickness, and the rolling reduction is preferably 10 to 95%. Before cold rolling or in the middle of cold rolling, an annealing treatment step may be provided to secure cold rolling workability. When carrying out the annealing treatment, for example, in batch-type annealing, it is preferable to carry out at a temperature of 200 ° C. or more and less than 450 ° C. for 0.1 to 10 hours. On the other hand, continuous annealing is preferably performed under the conditions of holding at 400 to 500 ° C. for 0 to 60 seconds, and more preferably under the conditions of holding at 450 to 500 ° C. for 0 to 30 seconds. In this case, 0 seconds means cooling immediately after reaching a desired annealing temperature.

6-5. Production of Magnetic Disk Substrate The aluminum alloy plate produced as described above is punched into an annular shape to prepare an annular aluminum alloy plate. Then, the annular aluminum alloy sheet is subjected to a pressure flattening annealing step at 250 to 450 ° C. for 30 minutes or more to prepare a flattened disk blank. The flattened disk blank is then subjected in this order to a processing step consisting of a cutting and grinding step and a strain removal heat treatment step preferably at a temperature of 250 to 400 ° C. for 5 to 30 minutes. In this way, an aluminum alloy substrate for a magnetic disk is prepared.

  Next, the aluminum alloy substrate for the magnetic disk is subjected to an alkaline degreasing step, an acid etching step, a desmutting step, and a zincate step in this order as a pretreatment for plating.

In the degreasing step, it is preferable to carry out degreasing under the conditions of a temperature of 40 to 70 ° C., a treatment time of 3 to 10 minutes, and a concentration of 200 to 800 mL / L using a commercially available AD-68F (manufactured by Kamimura Kogyo) degreasing solution or the like. In the acid etching process step, acid etching is performed at a temperature of 50 to 75 ° C., a treatment time of 0.5 to 5 minutes, and a concentration of 20 to 100 mL / L using a commercially available AD-107F (made by Kamimura Kogyo) etching solution or the like Is preferred. In the case where the compound removal step has already been applied after the acid etching treatment, HNO ₃ is used as a normal desmutting treatment at a temperature of 15 to 40 ° C., a treatment time of 10 to 120 seconds, and a concentration of 10 to 60%. Desmutting is preferably performed. When the compound removal step is not applied, the above-mentioned compound removal treatment may be performed instead of or in addition to the desmutting treatment.

The 1st zincate treatment step is carried out under conditions of a temperature of 10 to 35 ° C., a treatment time of 0.1 to 5 minutes, and a concentration of 100 to 500 mL / L using a zincate treatment solution of AD-301F-3X (made by Kamimura Kogyo) commercially available. Is preferred. After the 1st zincate treatment step, it is preferable to perform Zn peeling treatment using HNO ₃ under conditions of a temperature of 15 to 40 ° C., a treatment time of 10 to 120 seconds, and a concentration of 10 to 60%. Thereafter, the 2nd zincate treatment step is carried out under the same conditions as the 1st zincate treatment. An electroless Ni-P plating process is performed as a base plating process on the surface of the 2nd zincate-treated aluminum alloy substrate. Electroless Ni-P plating treatment is carried out using a commercially available Nimden HDX (made by Uemura Kogyo) plating solution, etc., under conditions of temperature 80-95 ° C., treatment time 30-180 minutes, Ni concentration 3-10 g / L It is preferred to carry out the treatment.

  By the above-described pre-plating treatment step and the electroless Ni-P plating step, a magnetic disk substrate subjected to the base plating treatment can be obtained.

7. Finally, the surface of the underlayer-plated magnetic disk substrate is smoothed by polishing, and a magnetic medium comprising an underlayer, a magnetic layer, a protective film, a lubricating layer and the like is attached to the surface by sputtering to form a magnetic disk.

  EXAMPLES The present invention will be described in more detail based on examples given below, but the invention is not meant to be limited by these.

  First, each aluminum alloy having the component composition shown in Table 1 was melted according to a conventional method to melt a molten aluminum alloy. Next, a molten aluminum alloy was cast by a DC casting method to produce an ingot. 15 mm on both sides of the above ingot was chamfered and subjected to homogenization treatment at 520 ° C. for 1 hour. Next, hot rolling was performed at a hot rolling start temperature 460 ° C. and a hot rolling finish temperature 280 ° C. to obtain a hot-rolled sheet having a thickness of 3.0 mm. The hot-rolled sheet was rolled to a thickness of 0.8 mm by cold rolling (rolling ratio 73.3%) without intermediate annealing to form a final rolled sheet. The aluminum alloy plate thus obtained was punched into an annular shape having an outer diameter of 96 mm and an inner diameter of 24 mm to produce an annular aluminum alloy plate.

  The annular flat aluminum alloy sheet obtained as described above was subjected to pressure flattening annealing at 300 ° C. for 3 hours under a pressure of 1.5 MPa to obtain a disc blank. The end face of this disc blank was cut to an outer diameter of 95 mm and an inner diameter of 25 mm. Furthermore, the grinding process which grinds the surface 10 micrometers was performed, and distortion removal heat processing were performed at 350 degreeC for 10 minutes.

  Thereafter, the aluminum alloy base material subjected to the strain removing and heat treatment was subjected to treatment up to electroless Ni-P plating under the conditions shown in Table 2. Finally, finish polishing (polishing amount: 4 μm) with feather cloth was performed to obtain a sample for evaluation of the magnetic disk substrate. In Table 2, the process No. In C1 to C9 and D1 to D8, a compound treatment step was provided before the alkaline degreasing step. On the other hand, process No. For C10 to C18 and D9 to D16, a compound treatment step was provided before the 1 St zincate treatment step and after the desmutting treatment step. In D17, the compound treatment step was not performed.

The following evaluation was performed using the sample for evaluation produced as mentioned above.
Evaluation 1: Compound density on the surface of the aluminum alloy substrate The sample after the compound removal step was cut into strips, and the sample surface was photographed from the top surface by SEM with a magnification of 500 times for 15 fields of view. 53,600 μm ² ). About the measured photograph, the maximum diameter and number of compounds were measured by "image A" which is image analysis software, and the density was calculated as the number per 1 mm ² . The arithmetic mean of 15 fields of view was taken as the measurement density. The results are shown in Tables 3-5.

Evaluation 2: Shape and density of holes on the surface on the Ni-P plated layer side of the aluminum alloy base material by cross-sectional observation The above-described sample for evaluation of the magnetic disk substrate was resin-filled to prepare a resin sample for cross-sectional observation. The resin sample was mirror-polished, and a cross-sectional observation sample of the radial position on the surface on the electroless Ni-P plated layer side of the aluminum alloy substrate was obtained by SEM. For cross-sectional observation, 10 fields of view were taken with a 5000 × secondary electron image (the area of one field of view was 536 μm ² ). About the image of each field of view taken, the opening diameter and the depth of the hole which exists in the radial position in the surface at the side of an electroless Ni-P plating layer of an aluminum alloy substrate were measured. Next, the number of holes satisfying the above relational expression was counted, and the existing density was calculated as the number per 1 mm. The arithmetic mean value of 10 fields of view was taken as the measurement existing density. The results are shown in Tables 3-5.

Evaluation 3: Plating smoothness (defects)
The sample for evaluation was immersed in 50 vol% nitric acid at 50 ° C. for 3 minutes to etch the Ni-P plated surface. The Ni-P plating surface after etching was photographed for 5 fields of view at a magnification of 5000 using an SEM (the area of one field of view was 536 μm ² ). The number of plating defects was measured from images taken in 5 fields of view, and the arithmetic mean value of 5 fields of view was determined. The arithmetic mean value is less than 5 per field of view, 5 or more and less than 10 per field of view, 10 or more per field of view. ◎ and を were accepted, and x was rejected. The results are shown in Tables 3-5.

Evaluation 4: Plating smoothness (bulge)
The sample for evaluation was cut out and the surface shape was measured using AFM (manufactured by JEOL: JSPM-5200). The measurement of five places was implemented arbitrarily (the area of one place was 625 micrometers ² ), and the number of objects of a convex part over 10 nm was counted in each place. The arithmetic mean of 5 places of this number is calculated | required, 0 was set as (double-circle), 1 or more and less than 5 pieces as (circle), and 5 or more as x. ◎ and を were accepted, and x was rejected. The results are shown in Tables 3-5.

  Examples 1 to 36 and Comparative Examples 1 to 28 are examples in which the aluminum alloy composition used for the aluminum alloy substrate is changed, and Examples 37 to 52 and Comparative Examples 29 to 45 are examples of the aluminum alloy substrate. This is an embodiment in which the conditions of the treatment process are changed.

  In Examples 1 to 52, since the conditions of the alloy composition and the compound removal step are within the scope of the present invention, the evaluation results for both defects and blisters on the electroless Ni-P plated surface were acceptable.

  On the other hand, in Comparative Examples 1 to 45, at least one of the evaluation results of defects and blisters on the electroless Ni-P plating surface was rejected.

  Specifically, in Comparative Example 1 and Comparative Example 15, although the plating smoothness was a pass, the content of Mg is small and the strength is insufficient, so that the disk deformation during handling can not be suppressed and it is used as a magnetic disk I could not.

  In Comparative Example 2 and Comparative Example 16, since the content of Mg was large, cracking occurred during rolling, and a sample could not be manufactured.

  In Comparative Example 3 and Comparative Example 17, since the content of Cu was small, the zincate coating became uneven, many defects and blisters occurred on the plating surface, and any plating smoothness was also rejected.

  In Comparative Example 4 and Comparative Example 18, since the content of Cu was large, the potential of the matrix became noble, and the potential difference with the compound became small, so that the compound became difficult to remove. As a result, many defects and blisters occurred on the plated surface, and any plating smoothness was also rejected.

  In Comparative Example 5 and Comparative Example 19, since the content of Zn was small, the zincate coating became nonuniform, many defects and swelling occurred on the plating surface, and any plating smoothness was also rejected.

  In Comparative Example 6 and Comparative Example 20, since the content of Zn was large, the potential of the matrix became wrinkles, and the dissolution rate of the matrix increased. As a result, it was difficult to form holes exhibiting an anchor effect, many defects and blisters occurred on the plated surface, and any plating smoothness was also rejected.

  In Comparative Example 7 and Comparative Example 21, since Be was not contained, the surface of the molten metal was oxidized at the time of casting, and a sound ingot could not be produced, and a sample could not be produced.

  In Comparative Example 8 and Comparative Example 22, since the content of Be was large, it was difficult to form a hole in which the dissolution of the matrix significantly exerts the anchor effect. As a result, many defects and blisters occurred on the plated surface, and in all cases the plating smoothness was also rejected.

  In Comparative Example 9 and Comparative Example 23, a coarse compound was formed because the content of Cr was large, and the holes formed in the compound removing step were not filled by plating. As a result, many defects of the plating surface were generated, and the plating smoothness (defects) was rejected.

  In Comparative Example 10 and Comparative Example 24, since the content of Si was large, a coarse compound was formed, and the holes formed in the compound removing step were not filled by plating. As a result, many defects of the plating surface were generated, and the plating smoothness (defects) was rejected.

  In Comparative Example 11 and Comparative Example 25, coarse compounds were formed due to the large content of Fe, and the holes formed in the compound removing step were not filled with the plating. As a result, many defects of the plating surface were generated, and the plating smoothness (defects) was rejected.

  In Comparative Example 12 and Comparative Example 26, since the content of Mn was large, a coarse compound was formed, and the holes formed in the compound removing step were not filled by plating. As a result, many defects of the plating surface were generated, and the plating smoothness (defects) was rejected.

  In Comparative Example 13 and Comparative Example 27, since the content of Si was small, the plating smoothness of the defect was acceptable, but the formation of the holes was small and the swelling was generated and the plating smoothness of the blister was not acceptable. . In addition, since the Si content in the raw material is extremely low, the cost is industrially high and application to mass production is difficult.

  In Comparative Example 14 and Comparative Example 28, since the content of Fe was small, the plating smoothness of the defect was acceptable, but the formation of the holes was small, and the swelling was generated and the plating smoothness of the blister was not acceptable. . In addition, since the Si content in the raw material is extremely low, the cost is industrially high and application to mass production is difficult.

  In Comparative Example 29 and Comparative Example 37, the compound was not sufficiently removed because the HF concentration of the drug solution used in the compound removing step was low. As a result, many defects and blisters occurred on the plated surface, and any plating smoothness was also rejected.

  In Comparative Example 30 and Comparative Example 38, since the HF concentration of the chemical solution used in the compound removing step was too high, the substrate was strongly dissolved and a large number of irregularities were generated. As a result, many defects of the plating surface were generated, and the plating smoothness (defect) was a failure.

In Comparative Example 31 and Comparative Example 39, the compound was not sufficiently removed because the HNO ₃ concentration of the drug solution used in the compound removing step was low. As a result, many defects and blisters occurred on the plated surface, and any plating smoothness was also rejected.

In Comparative Example 32 and Comparative Example 40, the compound was not sufficiently removed because the HNO ₃ concentration of the drug solution used in the compound removing step was too high. As a result, many defects and blisters occurred on the plated surface, and any plating smoothness was also rejected.

  In Comparative Example 33 and Comparative Example 41, since the temperature of the chemical solution used in the compound removing step was low, the reaction rate was slow, and the compound was not sufficiently removed. As a result, many defects and blisters occurred on the plated surface, and any plating smoothness was also rejected.

  In Comparative Example 34 and Comparative Example 42, the reaction speed was fast because the temperature of the chemical solution used in the compound removing step was high, and the substrate was strongly dissolved, and a large number of irregularities were generated. As a result, many blistering arrows were generated on the plating surface, and the plating smoothness (blistering) was rejected.

  In Comparative Example 35 and Comparative Example 43, the reaction time was not sufficient because the time for the compound removal step was short, and the compound was not sufficiently removed. As a result, many defects and blisters occurred on the plated surface, and any plating smoothness was also rejected.

  In Comparative Example 36 and Comparative Example 44, the reaction progressed excessively due to the long time of the compound removing step, and the substrate was strongly dissolved and a large number of irregularities were generated. As a result, many defects of the plating surface were generated, and the plating smoothness (defects) was rejected.

  In Comparative Example 45, the compound was not sufficiently removed because it was the conventional electroless Ni-P plating step to which the compound removal step was not applied. As a result, many defects and blisters occurred on the plated surface, and any plating smoothness was also rejected.

  According to the present invention, it is possible to increase the storage capacity per sheet and to reduce the defect rate, to contribute to increase the capacity of the HDD, and to obtain a magnetic disk made of an aluminum alloy which can be manufactured inexpensively.

Claims (5)

Mg: 2.5 to 10.0 mass%, Cu: 0.003 to 0.200 mass%, Zn: 0.05 to 0.60 mass% and Be: 0.00001 to 0.00200 mass%, Si: 0.001 to An aluminum alloy containing 0.500 mass%, Fe: 0.001 to 0.500 mass%, Cr: 0.30 mass% or less, and Mn: 0.50 mass% or less, the balance being Al and an unavoidable impurity An alloy base material and an electroless Ni-P plating layer formed on the surface of the aluminum alloy base material, and the surface of the aluminum alloy base material on the side of the electroless Ni-P plating layer has a maximum of 3 to 6 μm The existence density of the compound having a diameter is 300 / mm ² or less, and the opening diameter is (X) μm and the depth is (Y) μm A magnetic disk substrate made of an aluminum alloy, wherein 80 or more holes having a Y / X of 0.8 to 3.0 exist at a radial position.   The aluminum alloy magnetic disk substrate according to claim 1, wherein the depth Y is 1.0 to 5.0 μm. 3. A method of manufacturing an aluminum alloy magnetic disk substrate according to claim 1, wherein the step of preparing the aluminum alloy plate includes the casting step, the hot rolling step and the cold rolling step of the aluminum alloy in this order. A step of preparing an aluminum alloy base material comprising, in this order, a pressure flattening annealing step, a cutting / grinding step and a strain removing heat treatment step of an annular aluminum alloy plate obtained by punching the aluminum alloy plate into an annular shape; A step of pre-plating treatment including an alkaline degreasing step, an acid etching step, a desmutting step and a zincate step in this order of the aluminum alloy base material; and electroless Ni on the surface of the aluminum alloy base member subjected to the plating pre-treatment step. -Electroless Ni-P plating process step to carry out P plating process; and after the cutting and grinding step There in front of zincate treatment stage, the aluminum alloy base in a mixed solution of _HNO 3 / HF containing HF of 10～60Mass% of HNO ₃ solution at a by 10 to 80 g / L of 10 to 30 ° C. 5 A method of manufacturing a magnetic disk substrate made of an aluminum alloy, further comprising a compound removal step of immersion for 60 seconds.   The aluminum alloy according to claim 3, further comprising one or both of a homogenization treatment step between the casting step and the hot rolling step, and an annealing treatment step before or during the cold rolling step. Method of manufacturing a magnetic disk substrate.   A magnetic disk comprising a magnetic layer on the electroless Ni-P plating layer of the aluminum alloy magnetic disk substrate according to claim 1 or 2.