JP2008001946A - Method of manufacturing aluminum alloy substrate for magnetic disk and aluminum alloy substrate for magnetic disk manufactured by this manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an aluminum alloy substrate for magnetic disk which is superior in productivity and which can make the surface of an NiP-plated film of magnetic disk substrate highly smooth, and an aluminum alloy substrate for magnetic disk manufactured by this manufacturing method. <P>SOLUTION: The method of manufacturing an aluminum alloy substrate for magnetic disk which is formed by sticking a skin material of an aluminum alloy onto the both sides of a core material includes: a melting step for melting a metal for the skin material containing a prescribed amount of Mg, Si, Fe and Cr, and further containing a prescribed amount of at least one kind of Cu and Zn, and the balance being Al with inevitable impurities; a casting step for manufacturing an ingot for the skin material; a slicing step for slicing the ingot for the skin material into pieces having a prescribed thickness; a superposing step for manufacturing a superposed material by superposing the core materials and sliced skin materials; a homogenizing heat treating step for subjecting the superposed material to homogenizing heat treatment; a hot rolling step; and a cold rolling step. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an aluminum alloy substrate for a magnetic disk and an aluminum alloy substrate for a magnetic disk manufactured by the manufacturing method.

Generally, a magnetic disk device (Hard Disk Drive) which is one of external recording devices includes a magnetic disk for recording (storing) information and a magnetic head for writing or reproducing information on the magnetic disk. I have.
As a magnetic disk substrate, an aluminum alloy substrate is used because it is lightweight and non-magnetic and has excellent workability. However, since an aluminum alloy substrate alone has a side face that it is difficult to obtain the surface hardness required for a magnetic disk substrate, generally, an aluminum alloy substrate having a NiP plating film formed thereon is used. Yes.

  By the way, recently, the performance of the magnetic disk and the magnetic head constituting the magnetic disk device has been greatly improved, and the recording density of the magnetic disk has been improved. Here, in order to increase the recording density of the magnetic disk, it is necessary for the magnetic head to stably float on the magnetic disk with a low flying height. For this purpose, the surface of the NiP plating film on the magnetic disk substrate is highly smooth. There must be.

In order to obtain such high smoothness of the NiP plating film surface, it is necessary to reduce the size of the Al—Fe compound or the Mg—Si compound that causes the smoothness to be impaired. For that purpose, Fe, Si, etc. It is necessary to reduce the impurities.
However, in order to reduce such impurities, it is necessary to use a high-purity bare metal, and therefore, in manufacturing a magnetic disk substrate having high smoothness on the surface of the NiP plating film, the material cost becomes high. There was a problem.

In order to reduce the material cost, a method for manufacturing an aluminum alloy substrate in which a high purity skin material is clad on a low purity core material has been proposed (for example, Patent Documents 1 and 2).
Here, the skin material used for such an aluminum alloy substrate is generally formed into a predetermined thickness by hot rolling after casting a metal for the skin material (for example, Patent Document 1).
JP-A-10-310836 (paragraphs 0009 to 0020) JP 2004-332068 A (paragraphs 0015 to 0031)

However, such a conventional method for producing a general aluminum alloy substrate has the following problems.
In the conventional technique, since a hot-rolled sheet is used as a skin material (see Patent Document 1), there are many manufacturing processes of an aluminum alloy substrate, and the number of hot-rolling operations increases, resulting in a decrease in productivity. There was a problem.

When a hot rolled material is used as the skin material, the surface state and flatness of the rolled plate (particularly the flatness in the longitudinal direction) are controlled only by the rolling roll. Since an oxide film is formed on the surface, it is difficult to control the surface state and flatness, and there is a problem in that poor adhesion between the core material and the skin material cannot be prevented. And in order to improve the adhesiveness of a core material and a skin | leather material, the multipass rolling under a light pressure is needed in a clad hot rolling, and the productivity in a clad hot rolling will fall.
For these reasons, it has been difficult to produce an aluminum alloy substrate having high productivity on the surface of the NiP plating film and excellent productivity in the conventional method for producing an aluminum alloy substrate.

  The present invention has been made in view of the above problems, and its object is to provide a method for producing an aluminum alloy substrate for a magnetic disk, which has excellent productivity and the surface of the NiP plating film of the magnetic disk substrate has high smoothness. An object of the present invention is to provide an aluminum alloy substrate for a magnetic disk manufactured by this manufacturing method.

  In order to solve the above problems, the method for manufacturing an aluminum alloy substrate for a magnetic disk according to claim 1 is a method for manufacturing an aluminum alloy substrate for a magnetic disk in which an aluminum alloy skin material is bonded to both surfaces of a core material. : Less than 5% by mass, Si: 0.005% by mass to 0.1% by mass, Fe: 0.005% by mass to 0.1% by mass, Cr: 0.01% by mass to 0.35% by mass In addition, Cu: 0.01% by mass or more and 0.2% by mass or less, Zn: 0.01% by mass or more and less than 0.5% by mass, and the balance is Al. And a melting step for melting the skin metal made of inevitable impurities, a casting step for casting the skin metal melted in the melting step to produce a skin material ingot, and the skin material ingot Slice into a predetermined thickness A superposition step of superposing the core material and the sliced skin material in a predetermined arrangement to produce a superposition material, a homogenization heat treatment step of subjecting the superposition material to a homogenization heat treatment, and the homogenization It includes a hot rolling process in which hot rolling is performed after the heat treatment process, and a cold rolling process in which cold rolling is performed after the hot rolling process.

According to such a manufacturing method, by limiting the Mg content of the skin material to a predetermined range, the strength of the aluminum alloy substrate for a magnetic disk is improved, and the Cu and Zn contents are limited to a predetermined range. As a result, the NiP plating property is improved. In addition, by limiting the content of the predetermined element to a predetermined range, the fineness of the intermetallic compound of the substrate and the smoothness of the substrate are improved.
In addition, since the skin material sliced on the aluminum alloy substrate is used, there is no need to reduce the thickness of the skin material by hot rolling as in the case of conventional clad materials, and the number of hot rolling operations is reduced compared to the conventional case. The work process can be omitted. Moreover, the surface state and flatness can be easily controlled, the thickness of the oxide film is reduced, and the adhesion is improved.

The method for producing an aluminum alloy substrate for a magnetic disk according to claim 2 is characterized in that a homogenized heat treatment is further performed on the cast ingot for skin material after the casting step.
According to such a manufacturing method, the internal stress of the aluminum alloy substrate is removed, and the internal structure becomes uniform.

The method for producing an aluminum alloy substrate for a magnetic disk according to claim 3 is characterized in that after the slicing step, a surface smoothing treatment is further performed on the surface of the sliced skin material.
According to such a manufacturing method, the surface state and flatness of the skin material are improved, and the adhesion with the core material is improved. In addition, the crimping performance is improved and the number of crimping passes is reduced.

The method for producing an aluminum alloy substrate for a magnetic disk according to claim 4 is characterized in that the thickness of the skin material on one side of the aluminum alloy substrate after the cold rolling is 30 to 150 μm.
According to such a manufacturing method, it is possible to obtain an alloy substrate in which the core material does not appear on the surface after grinding for smoothing performed in the pre-process of NiP plating.

In the method of manufacturing an aluminum alloy substrate for a magnetic disk according to claim 5, the core material is Mg: 3 mass% to 6 mass%, Cu: 0.01 mass% to 0.8 mass%, Zn: 0.01 It contains at least one or more of mass% or more and 1 mass% or less.
According to such a manufacturing method, the strength of the core material and the NiP plating property at the end of the core material are improved.

The aluminum alloy substrate for a magnetic disk according to claim 6 is manufactured by the manufacturing method described above.
According to such an aluminum alloy substrate for magnetic disks, the NiP plating film surface of the aluminum alloy substrate for magnetic disks has high smoothness.

According to the method for manufacturing an aluminum alloy substrate for a magnetic disk according to the present invention, since the sliced skin material is used, it is not necessary to reduce the thickness of the skin material by hot rolling unlike the conventional aluminum alloy substrate. Therefore, the number of hot rolling operations is reduced as compared with the conventional case, the work process can be omitted, and the productivity can be improved. Moreover, the usage-amount of the high purity metal | metal | money required in order to obtain the smooth NiP plating surface can be reduced.
According to the aluminum alloy substrate for magnetic disks according to the present invention, a NiP plating film surface excellent in smoothness can be obtained.

  Next, a method for manufacturing an aluminum alloy substrate for a magnetic disk according to the present invention and an aluminum alloy substrate manufactured by this method will be described in detail with reference to the drawings. In the drawings to be referred to, FIG. 1 is a cross-sectional view showing the structure of an aluminum alloy substrate, FIG. 2 is a diagram showing a flow of a method for manufacturing an aluminum alloy substrate for a magnetic disk, and FIG. FIG. 4 is a schematic diagram showing an outline of the process of slicing the skin material, FIG. 5A is a schematic diagram showing the configuration of the overlapping material, and FIG. It is a schematic diagram which shows the outline of a hot rolling process.

As shown in FIG. 1, an aluminum alloy substrate 1 for a magnetic disk (hereinafter referred to as “aluminum alloy substrate 1” as appropriate) has an aluminum alloy skin material 3 bonded to both surfaces of a core material 2.
As shown in FIG. 2, in the method of manufacturing an aluminum alloy substrate for a magnetic disk, first, the skin metal is melted by the melting step (S1a). The skin metal melted in the melting step (S1a) is cast in the casting step (S2a) to become a skin material ingot, and this skin material ingot is subjected to a homogenization heat treatment step (S3a) as necessary. ) And then sliced to a predetermined thickness in the slicing step (S4a). In addition, you may perform a surface smoothing process by a surface smoothing process process (S5a) after a slice process (S4a) as needed.
Next, in the superimposing step (S2), the core material manufactured in the core material manufacturing step (S1b) and the sliced skin material are overlapped to manufacture an overlapping material, and the overlapping material is subjected to a homogenization heat treatment step. In (S3), after the homogenization heat treatment, hot rolling is performed in the hot rolling step (S4), and then cold rolling is performed in the cold rolling step (S5).
The aluminum alloy substrate according to the present invention is obtained by the manufacturing method including the above-described steps.
Next, each process in the manufacturing method of an aluminum alloy substrate is demonstrated.

<Dissolution process>
The melting step (S1a) contains a predetermined amount of Mg, Si, Fe, Cr, further contains at least one of a predetermined amount of Cu, Zn, and the balance is made of Al and inevitable impurities. This is a step of dissolving the metal for skin material.
The reason why the content of each component is limited to the numerical values will be described below.

[Mg: less than 5% by mass]
Mg has the effect of improving the strength of the aluminum alloy substrate. However, when the Mg content is 5% by mass or more, the oxide film becomes thick, the press-bonding property is lowered, the number of hot rolling passes is increased, the strength is increased, and the surface is heated during hot rolling. Cracks are likely to occur. Therefore, the Mg content is less than 5% by mass.

[Si: 0.005% by mass or more and 0.1% by mass or less]
Si is usually mixed into the aluminum alloy as a metal base impurity, and in the casting step (S2a) or the like, an Mg—Si intermetallic compound is generated in the ingot. When the Si content exceeds 0.1% by mass, a coarse Mg-Si intermetallic compound is generated in the ingot, and the aluminum alloy substrate produced from the ingot has a coarse Mg-Si on its surface. It will have an intermetallic compound. When a magnetic disk substrate is produced using this aluminum alloy substrate, this coarse Mg-Si intermetallic compound falls off from the blank surface during so-called mirror surface processing such as blank grinding, and aluminum In the pre-plating treatment of the alloy substrate, it dissolves from the aluminum alloy substrate. Therefore, a depression is generated in the aluminum alloy substrate, and pits are generated on the surface of the NiP plating film, which causes a decrease in smoothness. At the same time, even when only Mg is dissolved and Si remains undissolved, since the zinc substitution reaction does not occur on Si in the zincate process of the plating pretreatment, the NiP plating film is formed on Si even in the electroless NiP plating treatment. Does not grow. For this reason, the adhesion of the NiP plating film is insufficient, and the NiP plating film is blistered by heating such as a sputtering process of the magnetic film, thereby reducing the smoothness. Further, if the Si content is less than 0.005% by mass, the metal becomes highly pure and the cost becomes high. Therefore, the Si content is in the range of 0.005 mass% to 0.1 mass%.

[Fe: 0.005% by mass or more and 0.1% by mass or less]
Fe is also usually mixed into the aluminum alloy as a metal base impurity, and an Al—Fe intermetallic compound is generated in the ingot in the casting step (S2a) or the like. This Al—Fe-based intermetallic compound is dissolved from the aluminum alloy substrate in the pretreatment for plating, and a depression is generated in the aluminum alloy substrate, causing pits on the surface of the NiP plating film. When the Fe content exceeds 0.1% by mass, coarse Al—Fe-based intermetallic compounds increase and fall off from the blank surface during so-called mirror surface processing such as grinding, resulting in a depression in the aluminum alloy substrate. Pits are generated on the plating film surface. Further, if the Fe content is less than 0.005% by mass, the metal becomes highly pure and the cost becomes high. Therefore, the Fe content is in the range of 0.005 mass% to 0.1 mass%.

[Cr: 0.01% by mass or more and 0.35% by mass or less]
Cr is precipitated as a fine compound in the casting step (S2a) and the homogenization heat treatment step (S3a), and has the effect of suppressing crystal grain growth. In particular, when Cr is added in an amount of 0.01% by mass or more, there is an effect of suppressing the crystal grain growth in the homogenizing heat treatment and hot rough rolling, and suppressing the abnormal growth of recrystallized grains and homogenizing the structure. If the Cr content is less than 0.01% by mass, the above effect cannot be expected. Also, if the Cr content exceeds 0.35 mass%, the effect of stabilizing the crystal grains is too great, so when annealed after the cold rolling step (S5), it does not become an equiaxed recrystallized structure, Since the deformed structure extending in the rolling direction becomes a remaining structure, the anisotropy of the structure increases and the smoothness of the NiP plating film surface deteriorates. At the same time, coarse Al—Fe—Cr intermetallic compounds and Al—Cr intermetallic compounds are crystallized as primary crystals, and fall off by so-called mirror finishing such as grinding during the production of aluminum alloy substrates. Causes surface pits. Therefore, the Cr content is in the range of 0.01% by mass to 0.35% by mass.

The metal for skin material contains the aforementioned Mg, Si, Fe, and Cr as essential components, and further contains at least one of the following Cu and Zn.
[Cu: 0.01% by mass or more and 0.2% by mass or less]
Cu is an effective element for improving NiP plating properties. Cu is uniformly dissolved in the aluminum alloy, and has the effect of finely depositing Zn ions in the zincate bath uniformly on the surface of the aluminum alloy substrate in the zincate step of the plating pretreatment. Thereby, generation | occurrence | production of the nodule of the NiP plating film surface can be suppressed. If the Cu content is less than 0.01% by mass, the above effect cannot be expected. Further, if the Cu content exceeds 0.2 mass%, Cu precipitates at the grain boundary in the pretreatment for plating, the grain boundary part is over-etched, and the generation of nodules on the NiP plating film surface becomes significant. . Therefore, the Cu content is in the range of 0.01% by mass to 0.2% by mass.

[Zn: 0.01% by mass or more and less than 0.5% by mass]
Zn is also an effective element for improving plating properties. Zn, as well as Cu, is uniformly dissolved in the aluminum alloy, and has the effect of uniformly and finely depositing Zn ions in the zincate bath on the surface of the aluminum alloy substrate in the zincate process. Further, as the content is increased, Zn is uniformly deposited in the aluminum alloy substrate and becomes an etching starting point in the acid etching process during the plating pretreatment and a Zn ion precipitation base in the zincate process. For this reason, it has the effect of suppressing the level | step difference by a crystal grain. If the Zn content is less than 0.01% by mass, the above effect cannot be expected. In addition, when the Zn content is 0.5% by mass or more, the etching pits formed during the pre-plating process increase as the Zn precipitation nuclei increase, causing the pits on the NiP plating film surface. It becomes. Therefore, the Zn content is in the range of 0.01 mass% or more and less than 0.5 mass%.

Moreover, if content of Ti, V, B, etc. as an unavoidable impurity is 0.01 mass% or less, respectively, it will not affect the characteristic of the aluminum alloy substrate of this invention.
In addition, after melt | dissolving the metal for skin materials, you may perform a dehydrogenation process, filtration, etc. as needed.

<Casting process>
The casting step (S2a) is a step of manufacturing the skin material ingot by casting the metal for skin material dissolved in the melting step (S1a).
As a casting method, a semi-continuous casting method can be used.
In the semi-continuous casting method, a casting apparatus 10 as shown in FIG. 3 is used, and a molten metal M (here, metal for skin material) is poured into a metal water-cooled mold 11 having an open bottom from above, the metal solidifies from the bottom of the water-cooled mold 11 is continuously taken out, thereby obtaining a cladding material for an ingot 17 having a predetermined thickness T _1. At this time, the molten metal M is supplied from the trough 12 to the water-cooled mold 11 through the nozzle 13, the float 14 and the glass screen 15. The molten metal M supplied to the water-cooled mold 11 is solidified by being in contact with the inner wall surface of the water-cooled mold 11 cooled by the cooling water W to become a solidified shell 16. Further, the cooling water W is directly sprayed from the lower part of the water-cooled mold 11 onto the surface of the solidified shell 16 to continuously produce the skin material ingot 17.
Here, the thickness T ₁ of the skin material ingot 17 is preferably 200 to 700 mm.
The semi-continuous casting method may be performed either vertically or horizontally.

<Slicing process>
The slicing step (S4a) is a step of slicing the ingot for skin material produced by the casting step (S2a) to a predetermined thickness.
As the slicing method, a slab slicing method can be used.
In the slab slicing method, as shown in FIG. 4, the skin material ingot 17 manufactured by the semi-continuous casting method is sliced by a band saw cutting machine or the like (not shown), so that the skin material 35 having a predetermined thickness T ₂ is obtained. Is to be manufactured. Here, the thickness _{T 2} of the cladding material 35, 5～120Mm is preferred. If the _second thickness T ₂ is outside the range, easy cladding of the aluminum alloy substrate becomes inadequate.
As a slicing method, it may be cut by a circular saw cutter, or may be cut by a laser or water pressure.

Before slicing the ingot produced in the casting step (S2a), a homogenization heat treatment may be performed as necessary.
<Homogenization heat treatment process>
The homogenizing heat treatment step (S3a) is a step of homogenizing heat treatment of the ingot produced in the casting step (S2a).
The homogenization heat treatment is for the purpose of removing internal stress and homogenizing the internal structure, and is performed by maintaining at a treatment temperature of 200 to 570 ° C. for 1 hour or longer according to a conventional method.

  If the treatment temperature of the homogenization heat treatment is less than 200 ° C., the amount of internal stress removed is small, and the solute elements segregated during casting are not sufficiently homogenized, so that the effect of the heat treatment is small. Therefore, the processing temperature is set to 200 ° C. or higher. Further, when the processing temperature exceeds 570 ° C., a phenomenon called burning in which a part of the ingot surface is melted is likely to cause a surface defect of the aluminum alloy substrate. Therefore, the processing temperature is set to 570 ° C. or lower. Further, if the treatment time is less than 1 hour, the effect of removing internal stress is small, and the solid solution of the intermetallic compound becomes insufficient, and it tends to precipitate. Therefore, processing time shall be 1 hour or more. The treatment time is preferably 24 hours or less from the viewpoint of productivity.

The skin material 35 manufactured by the above manufacturing method may be subjected to a surface smoothing treatment for removing crystallized substances and oxides formed on the surface, if necessary, before overlapping with the core material. Good.
<Surface smoothing process>
The surface smoothing treatment step (S5a) is a step of smoothing the surface of the skin material sliced by the slicing step (S4a).
As the surface smoothing treatment method, a cutting method such as end mill cutting or diamond bite cutting, a grinding method in which the surface is ground with a grindstone, a polishing method such as buffing, or the like can be used, but it is not limited thereto. .

  Thus, by performing the slicing of the skin material ingot 17 and the surface smoothing treatment, in the evaluation of flatness, the flatness per 1 m in the rolling direction is 1 mm or less / 1 m length, desirably 0.5 mm or less / A skin material having a length of 1 m and a surface roughness of 0.05 to 1 μm in terms of arithmetic average roughness (Ra) can be obtained. If the flatness exceeds the above range, adhesion failure tends to occur on the aluminum alloy substrate. If the surface roughness is less than the above range, wrinkles are likely to occur, and processing tends to be difficult. When the surface roughness exceeds the above range, adhesion failure tends to occur on the aluminum alloy substrate.

In addition, the skin material of the one side in an aluminum alloy board | substrate may be manufactured by the said manufacturing method, and the skin material of the other surface may be manufactured by the conventional manufacturing method.
The skin material manufactured in this way is bonded to both surfaces of the core material manufactured in the core material manufacturing process.

<Core production process>
As shown in FIG. 2, the core material manufacturing process S1b includes a melting process for melting the core metal, and a casting process for manufacturing the core metal ingot by casting the core metal dissolved in the melting process. It is characterized by including. In addition, you may perform a surface smoothing process by a surface smoothing process process as needed.

(Dissolution process)
In the melting step, the core metal having a different component composition from the skin material is dissolved.
As the core metal, 2000 series Al-Cu series aluminum alloy, 3000 series Al-Mn series aluminum alloy, 5000 series Al-Mg series aluminum alloy, 7000 series Al-Mg-Zn series aluminum alloy, etc. Although it can be used, it is not limited to these, and any alloy can be applied as long as it is an alloy used as a core material.
In particular, at least one of Mg: 3 mass% and 6 mass%, Cu: 0.01 mass% and 0.8 mass%, and Zn: 0.01 mass% and 1 mass% is contained It is preferable to do.
The reason why the contents of Mg, Cu, and Zn are limited numerically will be described below.

[Mg: 3% to 6% by mass]
Mg has the effect of improving strength. If the Mg content is less than 3% by mass, the strength increasing effect tends to be small, and a sufficient concentration gradient in the direction of the skin material is not formed, and the Mg concentration in the surface portion where electroless NiP plating is performed is low. It becomes easy to wrinkle in the pretreatment process of electroless NiP plating performed later. If the Mg content exceeds 6% by mass, the core material is increased in strength, and problems such as cracking are likely to occur during rolling. Therefore, the Mg content is preferably in the range of 3% by mass to 6% by mass.

[Cu: 0.01% by mass or more and 0.8% by mass or less]
Cu is an element that affects plating properties. The surface of the core material is covered with the skin material, but the end portion is exposed. In order to improve the electroless NiP plating property at the end of the core material, addition of Cu is effective. If the Cu content is less than 0.01% by mass, the above effect cannot be expected. Moreover, when Cu content exceeds 0.8 mass%, the corrosion resistance as a core material will be reduced significantly. Therefore, the Cu content is preferably 0.01% by mass or more and 0.8% by mass or less.

[Zn: 0.01% by mass or more and 1% by mass or less]
Zn is an element that affects the plating property like Cu, and has the effect of increasing the electroless NiP plating property at the end of the core material. If the Zn content is less than 0.01% by mass, the above effect cannot be expected. Moreover, even if Zn contains more than 1 mass%, the effect beyond this will not be acquired. Therefore, the Zn content is preferably 0.01% by mass or more and 1% by mass or less.

(Casting process)
As the casting method, the semi-continuous casting method described above can be used.
Here, the thickness T ₁ (see FIG. 3) of the core material ingot 25 is preferably 200 to 700 mm. When the thickness T ₁ is out of the above range, the clad rate of the aluminum alloy substrate tends to be inappropriate. Further, if necessary, the surface smoothing treatment for removing crystallized substances and oxides formed on the surface may be performed by a grinding machine before the superposition with the above-described skin material 35. By doing so, a core having a flatness of 1 mm or less / 1 m length, desirably 0.5 mm or less / 1 m length, and a surface roughness of 0.05 to 1.5 μmRa in terms of arithmetic average roughness (Ra). A material can be obtained. If the surface roughness is less than the above range, processing tends to be difficult, and if the flatness and the surface roughness exceed the above range, poor adhesion tends to occur on the aluminum alloy substrate.

The core material manufactured in this way is superposed on the sliced skin material in the superposition process.
<Overlay process>
In the overlapping step S2, as shown in FIG. 5A, the overlapping material 40 is manufactured by overlapping the skin material 35 in a predetermined arrangement on both surfaces of the core material 26 manufactured in the above step. As the overlaying method, a conventionally known method, for example, a method of banding both ends of the core material 26 and the skin material 35 is used. There is no problem even if a method such as welding is used in addition to the banding method.
Each gap when overlapped is preferably within 10 mm at maximum, desirably within 5 mm.

<Homogenization heat treatment process>
The laminated material 40 thus manufactured is subjected to homogenization heat treatment in the homogenization heat treatment step (S3) in order to make the internal structure uniform and to make it soft so that hot rolling can be easily performed.
Here, the homogenization heat treatment is preferably performed at a temperature of 500 to 570 ° C. for 4 hours or longer in order to sufficiently dissolve the Mg—Si compound precipitated or coarsened in the skin material before heating and during temperature rise.

<Hot rolling process>
In the hot rolling step S4, as shown in FIG. 5B, the band of the overlapping material 40 is cut, and the overlapping material 40 is hot-rolled to produce an aluminum alloy plate before cold rolling. It is. Here, the hot rolling method is performed by a conventionally known rolling method. As the rolling mill to be used, the four-stage rolling mill 50 is described in FIG. 5B, but a two-stage rolling mill or a rolling mill having four or more stages (not shown) may be used. Moreover, although the rolling mill 50 provided with the roll stand of 1 row was described in FIG.5 (b), the aluminum alloy plate of predetermined thickness was used using the rolling mill provided with the roll stand of the multiple rows which is not shown in figure. You may repeat hot rolling until it is obtained.

<Cold rolling process>
The aluminum alloy sheet thus manufactured is then subjected to a cold rolling process in the cold rolling step (S5). As an example, the cold rolling treatment can be performed at a rolling reduction of 30 to 99%.
Here, it is preferable that the thickness of the single-sided skin material after the cold rolling is 30 to 150 μm.
When the thickness of the single-sided skin material after cold rolling is less than 30 μm, the core material is likely to be exposed on the surface of the aluminum alloy substrate, so the smoothness of the NiP plating surface is likely to be reduced, and when it exceeds 150 μm, The amount of aluminum alloy that uses high-purity bullion increases, which may be disadvantageous in terms of material costs.

  In addition, in order to impart desired mechanical properties as required, heat treatment (annealing treatment), distortion correction treatment, age hardening treatment, or the like is performed by a conventional method, or a predetermined shape is processed, or a predetermined shape is obtained. It may be cut into sizes. As an example, as annealing treatment, rough annealing performed before cold rolling, intermediate annealing performed during cold rolling, and final annealing performed after final cold rolling are performed at 200 to 500 ° C. × 0 to 10 hours in a continuous furnace or batch furnace. However, the present invention is not limited to these, and it goes without saying that the conditions can be appropriately changed as long as the effects (mechanical characteristics) obtained by these treatments are exhibited.

  Since the aluminum alloy substrate for magnetic disk manufactured by the above-described method for manufacturing an aluminum alloy substrate for magnetic disk is excellent in the smoothness of the NiP plating film surface, the recording density of the magnetic disk can be improved.

Next, the effect of the embodiment that satisfies the claims of the present invention will be specifically described in comparison with a comparative example that departs from the claims of the present invention.
First, after the aluminum alloy for skin materials and core materials adjusted to the compositions shown in Table 1 was dissolved, dehydrogenation treatment was performed by blowing inert gas, and casting was performed to produce an ingot having a thickness of 500 mm. After chamfering both sides of the manufactured ingot, slice or hot-skin the ingot for skin to the specified sheet thickness so that the thickness of the skin on one side after cold rolling becomes the thickness shown in the table The skin material before rolling was produced by rolling. Some sliced materials were subjected to chamfering (surface smoothing treatment) on the surface after slicing, and some were annealed (homogenized heat treatment) at the temperatures shown in Table 1 before slicing. Then, after superposing the skin material and the core material to obtain a superposed material, it was heated at 540 ° C. for 8 hours and homogenized and heat-rolled so that the final thickness was 3 mm, and finally Cold rolling was performed until the plate thickness reached 1 mm.

  After cold rolling, it was punched into a 3.5-inch size by a conventional method and subjected to pressure annealing at 340 ° C. for 3 hours to produce a 3.5-inch type aluminum alloy substrate (blank) for a magnetic disk. Thereafter, both surfaces were mirror-finished by 10 μm on each surface by grinding with a grindstone (GR processing) to produce a GR substrate.

  The GR substrate thus prepared was first degreased with AD-68F at 50 ° C. for 5 minutes, then subjected to acid etching with AD-101F at 68 ° C. for 2 minutes, and desmutted with 30% nitric acid. Thereafter, a zincate treatment at 20 ° C. for 30 seconds was performed with AD-301F-3X, and Zn was once dissolved with 30% nitric acid, and then a zincate treatment at 20 ° C. for 15 seconds was performed again. Thereafter, an electroless NiP plating treatment at 90 ° C. for 2 hours was performed using the HDX-7G solution to form a NiP plating film having a thickness of about 10 μm on one side. The surface of the NiP plating substrate thus obtained was polished to produce a NiP plating substrate. Thereafter, the NiP plating substrate was annealed at 300 ° C. for 1 h. The AD-68F, AD-101F, and AD-301F-3X are plating pretreatment solutions, and the HDX-7G solution is a NiP plating solution, all of which are manufactured by Uemura Kogyo.

The following evaluation was performed on the aluminum alloy substrate obtained as described above.
<Productivity>
Evaluation of productivity was performed based on the total number of passes of hot rolling after the superposition of the skin material. When the skin material is manufactured by slicing, there is no hot rolling at the time of manufacturing the skin material, so only the number of hot rolling of the laminated material is obtained. The evaluation standard is that productivity is excellent when the total number of passes is 15 or less (◎), productivity is good when 20 passes or less (◯), and productivity is poor when 21 passes or more (×) It was.

<Smoothness of NiP plating film surface>
The smoothness of the NiP plating film surface was evaluated when the pits with a depth of 1 μm or more or the bulge with a height of 1 μm or more did not appear on the surface of the NiP plating substrate. In this case, the smoothness of the NiP plating film surface was judged as poor (x).
In some cases, the core material is exposed on the surface after GR processing, the NiP plating film surface is somewhat poor in smoothness, and scratches are likely to occur during handling, and defects occur after NiP plating on some substrates. What was made was set as ((triangle | delta)).
These evaluation results are shown in Table 1.
In Table 1, those that do not satisfy the configuration of the present invention are underlined in numerical values and the like.

As shown in Table 1, Examples 1-4 were the scope of the present invention, and all evaluations were good. Particularly, in Examples 2 and 4, the flatness after slicing is good due to the effect of annealing (homogenization heat treatment) before slicing the ingot. Since the surface smoothing treatment was performed, the adhesion with the core material was good, and in particular, the hot rolling productivity was excellent.
Example 5 is within the scope of the present invention. However, since the thickness of the skin material is thinner than specified, the core material is exposed on the surface after GR processing on some substrates, and the smoothness of the NiP plating film surface is slightly poor. Met.
Example 6 was within the scope of the present invention, but the plating was not uniform on the end face of the substrate because Cu and Zn in the core material were low. Further, since Mg in the core material is less than the lower limit value, the diffusion of Mg into the skin material is small, and the strength of the skin material is small, so that the surface is easily scratched.

  In Comparative Example 1, since the skin material was prepared by hot rolling, the number of hot rolling passes was large and the productivity was poor. In Comparative Example 2, since the Si of the skin material exceeded the upper limit value, a coarse Mg—Si intermetallic compound was generated, and the smoothness of the NiP plating film surface was poor. In Comparative Example 3, since the Fe of the skin material exceeded the upper limit value, a coarse Al—Fe-based intermetallic compound was generated, and the smoothness of the NiP plating film surface was poor. In Comparative Example 4, since the Mg of the skin material exceeds the upper limit value, the oxide film becomes thick, the press-bonding property is lowered, and the number of hot rolling passes is increased, so the hot rolling productivity is poor. . Moreover, since the pit resulting from the crack generate | occur | produced at the time of hot rolling generate | occur | produced on the NiP plating film surface, the smoothness of the NiP plating film surface was also bad.

  In Comparative Example 5, since the Cu of the skin material exceeded the upper limit, nodules were generated on the surface of the NiP plating film, and the smoothness of the NiP plating film surface was poor. In Comparative Example 6, since Zn of the skin material exceeded the upper limit value, pits were generated on the NiP plating film surface, and the smoothness of the NiP plating film surface was poor. In Comparative Example 7, since both Cu and Zn of the skin material are less than the lower limit, the effect of uniformly finely depositing Zn ions in the zincate bath on the surface of the aluminum alloy substrate cannot be obtained, and the surface of the NiP plating film is smooth. The nature was bad. In Comparative Example 8, since Cr exceeded the upper limit, coarse Al—Fe—Cr intermetallic compounds and Al—Cr intermetallic compounds were generated, and the smoothness of the NiP plating film surface was poor.

  As mentioned above, although the manufacturing method of the aluminum alloy substrate for magnetic discs concerning this invention and the aluminum alloy substrate for magnetic discs manufactured by this manufacturing method were demonstrated, the meaning of this invention is not limited to these description. Therefore, it should be broadly interpreted based on the description of the claims of the present application. It goes without saying that the technical scope of the present invention can be widely changed and modified without departing from the spirit of the present invention.

It is sectional drawing which shows the structure of an aluminum alloy board | substrate. It is a figure which shows the flow of the manufacturing method of the aluminum alloy board | substrate for magnetic discs. It is a schematic diagram which shows the outline of a skin material casting process or a core material casting process. It is a schematic diagram which shows the outline of the process of slicing a skin material. (A) is a schematic diagram which shows the structure of a laminated material, (b) is a schematic diagram which shows the outline of a hot rolling process.

Explanation of symbols

S1a Melting step S2a Casting step S3a Homogenizing heat treatment step S4a Slicing step S5a Surface smoothing step S1b Core material manufacturing step S2 Overlapping step S3 Homogenizing heat treatment step S4 Hot rolling step S5 Cold rolling step 1 Aluminum alloy for magnetic disk Substrate 2 Core material 3 Skin material 17 Skin material ingot 25 Core material ingot 26 Core material 35 Skin material 40 Superposition material

Claims (6)

A method of manufacturing an aluminum alloy substrate for a magnetic disk in which an aluminum alloy skin material is bonded to both surfaces of a core material,
Mg: less than 5% by mass, Si: 0.005% by mass to 0.1% by mass, Fe: 0.005% by mass to 0.1% by mass, Cr: 0.01% by mass to 0.35% by mass Contains:
Furthermore, Cu: 0.01% by mass or more and 0.2% by mass or less, Zn: 0.01% by mass or more and less than 0.5% by mass, and the balance is Al and inevitable impurities A melting step of melting a metal for skin material comprising:
A casting process for producing a skin material ingot by casting the skin metal melted in the melting step;
A slicing step of slicing the ingot for skin material into a predetermined thickness;
A superposition step of superposing the core material and the sliced skin material in a predetermined arrangement to produce a superposition material;
A homogenizing heat treatment step of performing a homogenizing heat treatment on the laminated material;
A hot rolling step of performing hot rolling after the homogenizing heat treatment step;
A method of manufacturing an aluminum alloy substrate for a magnetic disk, comprising: a cold rolling step of performing cold rolling after the hot rolling step.   2. The method for producing an aluminum alloy substrate for a magnetic disk according to claim 1, wherein after the casting step, the cast skin material ingot is further subjected to a homogenization heat treatment.   3. The method of manufacturing an aluminum alloy substrate for a magnetic disk according to claim 1, wherein after the slicing step, a surface smoothing process is further performed on the surface of the sliced skin material.   4. The aluminum alloy substrate for a magnetic disk according to claim 1, wherein the thickness of the skin material on one side of the aluminum alloy substrate after the cold rolling is 30 to 150 μm. 5. Production method.   The core material contains at least one of Mg: 3 mass% to 6 mass%, Cu: 0.01 mass% to 0.8 mass%, Zn: 0.01 mass% to 1 mass% 5. The method for producing an aluminum alloy substrate for a magnetic disk according to claim 1, wherein:   An aluminum alloy substrate for a magnetic disk manufactured by the manufacturing method according to any one of claims 1 to 5.

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