JPH07331397A - Production of aluminum alloy sheet for magnetic disk substrate - Google Patents

Abstract

PURPOSE:To provide a method for producing a substrate for a magnetic disk excellent in flatness after mirror finishing, furthermore good in the adhesion of an Ni-P plated layer and free from surface flaws. CONSTITUTION:The ingot of an Al alloy having a chemical componental compsn. contg., by weight, 3.0 to 5.0% Mg, 0.10 to 0.30% Zn, 0.05 to 0.20% Cu and 0.01 to 0.10% Fe, in which the content of Si as impurities is limited to <=0.05%, furthermore contg., at need, at least one or more kinds among 0.001 to 0.03% Ti, 0.05 to 0.15% Cr and 0.05 to 0.15% Zr and the balance Al with other inevitable impurities is subjected to homogenizing treatment in the temp. range of 500 to 560 deg.C for 4 to 24Hr and is thereafter subjected to hot rolling and cold rolling. Next, the Al alloy sheet prepd. in the above-mentioned manner is heated to 400 to 560 deg.C temp. range as process annealing, is held for >0 to 30sec, is thereafter cooled and is moreover subjected to final cold rolling at 30 to 70% rolling ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an Al alloy plate for a magnetic disk substrate which is excellent in flatness and plating property.

[0002]

2. Description of the Related Art Generally, as a substrate material for a magnetic disk, it is lightweight, non-magnetic, and has sufficient strength to withstand the mechanical processing at the time of manufacturing the substrate and the high-speed rotation at the time of using the disk. Since it is necessary that
-A Mg-based alloy plate is used. That is, the alloy plate was punched into a doughnut-shaped disk, pressure-annealed, and then mirror-finished by cutting, grinding and polishing the disk surface, and then the alloy plate thus prepared was The method of hot-treatment, Ni-P electroless plating, and polishing has become the mainstream of recent methods for manufacturing magnetic disk Al alloy substrates. Therefore, the following characteristics are further required for such a magnetic disk substrate.

Although the distance between the magnetic disk substrate and the magnetic head is extremely narrow, the distance must be kept constant when the magnetic disk rotates at a high speed. Therefore, the flatness of the disk after mirror finishing is an important characteristic. Adhesion between the Ni-P plating layer and the underlying Al alloy is good, and there are no surface defects such as pits after plating.

In recent years, the demand for higher density in magnetic disks has become stronger and stronger, and it has become necessary to further miniaturize the magnetized area per bit and to reduce the distance between the magnetic head and the magnetic disk. It was Further, the thickness of the magnetic disk is being reduced, and the deformation of the magnetic disk due to its own weight cannot be ignored. Therefore, the requirement for the flatness of the substrate is very strict.

[0005] In response to such requirements, the JIS5086 alloy plate used as an Al alloy plate for a magnetic disk substrate and its improved alloy plate have been invented. For example, an invention in which the waviness on the surface of a magnetic disk substrate is improved is disclosed in Japanese Patent Publication No. 5-40016 (hereinafter referred to as prior art).

According to the prior art, as an Al alloy for magnetic disks, Mg: 3.0-6.0 wt%, Ti: 0.0
3 to 0.15 wt%, and Zn: 0.1
2.0 wt% and Cu: 0.01 to 0.5 wt%, containing 1 or 2 types, and further containing F as an impurity.
It is described that e, Si, B, Zr and Cr are limited to a predetermined value or less (see the claims of the specification of the same publication), and an ingot having such a chemical composition is 530
After holding at 8 ° C for 8 hours, hot rolling was started at 470 ° C, and then cold rolling was performed to a plate thickness of 2 mm, punching was performed into a hollow disc, and then annealing was performed at 350 ° C for 2 hours. , An example using a substrate for a magnetic disk is described. That is, the crystal grains are made finer by the addition of Ti (see the same publication, column 8, line 3), and the temperature at the start of hot rolling is set to less than 500 ° C. to suppress macrostructure coarsening ( The same column, lines 20 to 22) suggests a technique for improving the waviness of the surface of the magnetic disk substrate by optimizing the component composition of the Al alloy and the hot rolling temperature.

[0007]

However, in the method of manufacturing an aluminum alloy plate for a magnetic disk substrate according to the above-mentioned prior art, the flatness of the magnetic disk substrate is insufficient, and further improvement is desired. That is, in the manufacturing method according to the prior art, the intermediate annealing is not performed, and the manufacturing method by combining the aluminum alloy having an appropriate chemical composition with the appropriate intermediate annealing condition has not been clarified. Therefore, the subject of this invention is
The production of coarse intermetallic compounds is suppressed, to produce a hot-rolled sheet having a homogeneous and fine recrystallized grain structure, and further, after intermediate annealing and subsequent final cold rolling, the crystal grain size is equiaxed grains. It is to produce a cold-rolled sheet having a uniform recrystallization structure.

Therefore, an object of the present invention is to provide a method for producing a magnetic disk substrate which has excellent flatness after mirror finishing, good adhesion of the Ni-P plating layer and no surface defects. .

[0009]

In order to achieve the above object, the present inventors have optimized the chemical composition of an aluminum alloy for a magnetic disk substrate, adopted an intermediate annealing step, and cast an aluminum alloy. As a result of repeated studies on the optimization of each condition of homogenizing treatment conditions of the piece or the ingot, the intermediate annealing condition and the cold rolling reduction condition at the final cold rolling,
The following invention has been reached.

A method for manufacturing an aluminum alloy plate for a magnetic disk substrate according to the present invention is as follows: magnesium (Mg): 3.0 to 5.0 wt%, zinc (Zn): 0.10 to 0.30 wt%, copper (Cu) : 0.05 to 0.20 wt% and iron (Fe): 0.01 to 0.10 wt.%, And the content of silicon as an impurity is limited to silicon (Si): 0.05 wt% or less. Furthermore, if necessary, titanium (Ti): 0.001 to 0.03 wt.%, Chromium (Cr): 0.05 to 0.15 wt%, and zirconium (Zr): 0.05 to 0. In the range of 500 to 560 ° C for an ingot of an aluminum alloy that contains at least one of 15 wt% and has the chemical composition that the balance is aluminum (Al) and other unavoidable impurities. After performing a homogenizing treatment within a range of 4 to 24 hours for a period of time, hot rolling and cold rolling are performed, and then the aluminum alloy sheet thus prepared is subjected to intermediate annealing at a temperature of 400 to 560.
It is characterized in that it is heated in the range of ° C, kept for a time in the range of more than 0 to 30 sec, cooled, and then subjected to final cold rolling at a rolling rate of 30 to 70%.

[0011]

The reason why the chemical composition of the aluminum alloy for a magnetic disk substrate of the present invention is limited to the above range will be described. Mg: Mg is an element effective for imparting a predetermined strength to the magnetic disk substrate. However, if the content is less than 3.0 wt%, the desired strength cannot be obtained, while
If it exceeds 5.0 wt%, the hot rolling property of the Al alloy plate is significantly reduced. Therefore, the Mg content is 3.0 to 5.0 wt%
Should be limited to within the range.

Zn and Cu: Zn and Cu are Al
It uniformly forms a solid solution in the alloy and forms a uniform fine and dense treatment film during the zincate treatment before plating. Therefore, Zn and Cu have the effect of forming a sound Ni—P plating layer having excellent adhesion to the base Al alloy, few fine defects, and uniform on the surface of the disk substrate. In order to obtain such effects, Zn and Cu are
Coexistence in the 1-alloy is an essential condition. However, if the Zn content is less than 0.10 wt% and the Cu content is less than 0.05 wt%, the above effect cannot be obtained. On the other hand, when the Zn content exceeds 0.30 wt% and the Cu content exceeds 0.20 wt%, not only the corrosion resistance is significantly deteriorated, but also Al-Cu-Mg-based precipitates are formed, resulting in the donut. During pressure annealing performed after punching the circular disk, stress is generated due to their solid solution / precipitation, which deteriorates the flatness of the substrate. Therefore, in order to ensure the flatness of the substrate, it is particularly important that the Zn and Cu contents do not exceed the above values. From the above, the Zn content is 0.10 to 0.30 wt.
%, Cu content should be within the range of 0.05 to 0.20 wt%. In order to further exert the above-mentioned effects and further prevent the above-mentioned harmful effects, Zn + C
The content of u is preferably within the range of 0.3 to 0.4 wt%.

Ti, Cr and Zr: Ti, Cr and Zr do not crystallize the Al--Fe intermetallic compound and Mg ₂ Si, and form a uniform recrystallized grain structure, so that the planarity of the substrate is improved. Improve. Further, it also has the function and effect of improving the strength. However,
If the Ti content is less than 0.001 wt% and the Cr and Zr contents are less than 0.05 wt%, the above-described action and effect are not exhibited. On the other hand, the Ti content exceeds 0.03 wt%, Cr
If the content of each of Zr and Zr exceeds 0.15 wt%, Al ₇
Coarse intermetallic compounds such as Cr and Al ₃ Zr are generated, and protrusions or drop pits are generated on the substrate surface, which causes plating defects. Therefore, the Ti content is 0.001 to 0.0.
Within the range of 3 wt%, each content of Cr and Zr is 0.
It should be in the range of 05 to 0.15 wt%.

Fe: When Fe is contained in the Al alloy, its machinability is improved. Further, Fe is Al-
Generates Fe-based intermetallic compound, pretreatment for plating and Ni
It becomes the core of the film formation in the -P plating process and is effective for fine and uniform deposition of the plating layer. However, if the Fe content is less than 0.01 wt%, the grindstone is likely to be clogged when the substrate is ground, and the productivity is significantly reduced. On the other hand, if the content exceeds 0.10 wt%, a coarse Al—Fe-based intermetallic compound is generated, which causes protrusions or drop dents on the surface of the substrate, which causes plating defects. Therefore, Fe
The content should be within the range of 0.01-0.10 wt%.

Si: Si hardly forms a solid solution in the Al alloy and is crystallized as Mg ₂ Si. Then, by the pretreatment of plating, Mg ₂ Si dissolves and falls off from the surface of the substrate, which easily causes a pit defect after plating. Therefore, it is necessary to make the Si content as low as possible. However, Si
Since it takes a high cost to reduce the content, the Si content is limited to 0.05 wt% or less in consideration of both of the above.

Next, the reason why the manufacturing conditions are limited as described above in the present invention will be described.

Homogenizing treatment: The homogenizing treatment of a slab or ingot is performed by the effect of homogenizing Mg, Cu or Si components which are easily segregated during casting, and Cr and Zr for refining recrystallization.
Is sufficiently precipitated. However, if the heating temperature in the homogenization treatment is less than 500 ° C, the homogenization effect is insufficient, and in particular Mg _{2 which} causes pit defects.
It is not possible to reduce the density and size of Si crystallisates. On the other hand, if the heating temperature exceeds 560 ° C,
Eutectic melting occurs. Also, the heating time for homogenization treatment is 4
If the time is less than the time, the homogenizing effect is small, while if the time exceeds 24 hours, the homogenizing effect is saturated, which has no industrial meaning, and further, the manufacturing cost is increased and it is uneconomical. Therefore, the conditions for homogenizing the slab or ingot should be such that the heating temperature is in the range of 500 to less than 560 ° C and the holding time is in the range of 4 to 24 hours.

Intermediate annealing: When the intermediate annealing is performed, the recrystallized structure of the plate after pressure annealing of the doughnut-shaped disk is prevented from becoming elongated grain structure in the rolling direction, and hot rolling is performed. Due to the non-uniform distribution of temperature and working degree in the plate thickness direction at the time, it is possible to prevent a difference in crystal grain size between the surface layer and the central part of the plate, and therefore a donut-shaped circle after pressure annealing. The flatness of the plate is improved. As intermediate annealing, there is no directionality by adopting short-time heating by rapid heating (10 to 50 ° C / sec) and rapid cooling (10 to 50 ° C / sec) using a continuous annealing heating furnace. A recrystallized structure close to the axial grains and having a relatively uniform crystal grain size distribution in the plate thickness direction is formed, and thus the flatness after pressure annealing is improved. However, the heating temperature (annealing temperature) is 400 ° C.
If it is less than 5,000, the effect of improving the flatness is insufficient, while if it exceeds 560 ° C, eutectic melting occurs. Therefore, the heating temperature should be in the range of 400-560 ° C. If the heating temperature holding time exceeds 30 seconds, the crystal grains become coarse and the flatness deteriorates. Therefore, the holding time should be 30 seconds or less.

Rolling ratio of final cold rolling: By rolling to a predetermined plate thickness by final cold rolling after intermediate annealing, the crystal grains of the plate after pressure annealing are refined and the flatness is improved.
However, if the rolling ratio of the final cold rolling is less than 30%, the grain size is not sufficiently refined, while if it exceeds 70%, the effect of intermediate annealing becomes insufficient. Therefore, the rolling rate of the final cold rolling should be within the range of 30 to 70%.

[0020]

EXAMPLES The present invention will now be described with reference to examples. Table 1
Of alloy No. A, B or C of No. 1 having a chemical composition within the range of the present invention was continuously cast, and each ingot was chamfered by 10 mm on each side. Next, Table 2
The homogenization treatment was carried out under the conditions shown below. Then, this was hot-rolled to a thickness of 6 mm and cold-rolled to a predetermined plate thickness of 1.12 to 4.25 mm according to a conventional method. Next, the aluminum alloy sheet thus prepared was rapidly heated to a predetermined temperature using a continuous annealing furnace, held for a predetermined period of time, and then forced air-cooled for intermediate annealing.
The cooling rate during forced air cooling was about 20 ° C./sec. Then, final cold rolling was performed at a rolling ratio of 30 to 70% to manufacture an aluminum alloy plate for a magnetic disk substrate having a thickness of 0.85 mm.

[0021]

[Table 1]

Table 2 shows the manufacturing conditions of the above-mentioned aluminum alloy plate. That is, the present invention specimens No. 1 to 6 in which all the conditions are within the scope of the present invention, and the comparative specimens No. 1 to 5 in which at least one condition is outside the scope of the present invention.
For alloy No., and homogenization treatment conditions, intermediate annealing conditions and final cold rolling rate.

[0023]

[Table 2]

Each of the aluminum alloy sheets thus produced was punched to prepare a doughnut-shaped disc having a diameter of 89 mm, which was then subjected to pressure annealing at 350 ° C. for 2 hours, The surface was mirror finished by cutting, grinding and polishing. With respect to the doughnut-shaped disc (blank) of each sample No. mirror-finished in this way, a flatness measurement test of the plate was performed by analyzing interference fringes using a laser interferometer. A distribution measurement test of the Mg ₂ Si intermetallic compound was carried out by observing the plate surface with an optical microscope. The results of the above tests are also shown in Table 2 above.

From Table 1 and Table 2, the following matters are clear. Since the heating temperature of the homogenizing treatment was low outside the range of the present invention (460 ° C.), the homogenizing effect of Comparative Sample No. 1 was insufficient, and Mg, which causes pit defects in particular, was
It was not possible to reduce the density and size of the ₂ Si crystallized products.

Since the heating temperature of the intermediate annealing was low outside the range of the present invention (360 ° C.) in the comparative sample No. 2, the effect of the intermediate annealing was insufficient, and the sheet after pressure annealing was The recrystallized structure became an elongated grain structure, and the flatness was deteriorated due to the difference in crystal grain size between the surface layer and the central part of the plate due to the uneven distribution of temperature and workability in the plate thickness direction during hot rolling.

Since the final cold rolling ratio of the comparative sample No. 3 was too small outside the range of the present invention, the crystal grains of the plate were not sufficiently refined, and therefore the flatness was poor. On the other hand, since the final cold rolling rate of the comparative sample No. 4 was too large outside the range of the present invention, the effect of the intermediate annealing was not sufficiently exhibited and the flatness was poor.

Since the heating time of the homogenization treatment was too short for the comparative sample No. 5 outside the scope of the present invention, the density and size of the Mg ₂ Si crystallized substances causing pit defects were reduced. In addition, since the segregation of the components could not be made sufficiently uniform, the uniformity of the crystal grains was insufficient and the flatness was poor.

On the other hand, all the samples of the present invention are
The donut-shaped disc was excellent in flatness, and the distribution density of large Mg ₂ Si crystallized substances that could cause pit defects was small, and it was desirable as an aluminum alloy plate for a magnetic disk substrate.

As described above, none of the comparative specimens had the desired characteristics as an aluminum alloy plate for a magnetic disk substrate, but the specimen of the present invention has a chemical composition of the aluminum alloy sheet. Since all the manufacturing conditions were within the scope of the present invention, the aluminum alloy plate had excellent flatness and excellent characteristics without surface defects.

[0031]

The present invention is configured as described above, and particularly in the manufacture of an aluminum alloy plate for a magnetic disk substrate, an intermediate annealing step is incorporated, and further, the alloy components are optimized and the intermediate annealing conditions are optimized. It is possible to provide an excellent aluminum alloy plate for a magnetic disk substrate, which has excellent flatness, which has not been obtained in the past, and has no surface defects, by combining it with Can bring.

Claims (2)

[Claims] 1. Magnesium (Mg): 3.0-5.
0 wt%, zinc (Zn): 0.10 to 0.30 wt%, copper (Cu): 0.05 to 0.20 wt%, and iron (Fe): 0.01 to 0.10 wt.%, Further, the content of silicon as an impurity is limited to silicon (Si): 0.05 wt% or less, and the balance is aluminum alloy ingot having a chemical composition of aluminum (Al) and other unavoidable impurities. Then, after subjecting to a homogenizing treatment in a temperature range of 500 to 560 ° C. for a time of 4 to 24 hours, hot rolling and cold rolling are performed, and then the aluminum alloy sheet thus prepared is subjected to On the other hand, as intermediate annealing, rapid heating is performed within a temperature range of 400 to 560 ° C., time is maintained within a range of more than 0 to 30 seconds, followed by rapid cooling, and further final cold rolling is performed at a rolling rate of 30 to 70%. This Wherein the manufacturing method of an aluminum alloy plate for a magnetic disk substrate. 2. Magnesium (Mg): 3.0-5.
0 wt%, zinc (Zn): 0.10 to 0.30 wt%, copper (Cu): 0.05 to 0.20 wt%, and iron (Fe): 0.01 to 0.10 wt%, The content of silicon as an impurity is limited to silicon (Si): 0.05 wt% or less, and further, titanium (Ti): 0.001 to 0.03 wt.%, Chromium (Cr): 0.05 to 0 .15 wt% and zirconium (Zr): 0.05 to 0.15 wt% of an aluminum alloy containing at least one kind and a balance of aluminum (Al) and other unavoidable impurities. The ingot was subjected to a homogenizing treatment in a temperature range of 500 to 560 ° C. for a time in a range of 4 to 24 hours, followed by hot rolling and cold rolling, and then prepared in this manner. Al Relative bromide alloy plate, temperature of intermediate annealing 400-560
An aluminum alloy for a magnetic disk substrate, which is characterized in that it is heated in a range of ° C, kept for a time of more than 0 to 30 sec, then cooled, and further subjected to final cold rolling at a rolling rate of 30 to 70%. Method of manufacturing a plate.