JPH024672B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to an aluminum alloy for magnetic disks. More specifically, the present invention relates to an aluminum alloy for plated magnetic disks used as storage media for electronic computers. 2. Description of the Related Art Magnetic disks are generally made by precisely polishing the surface of an aluminum alloy substrate and then coating it with a magnetic thin film. Signals are recorded by magnetizing this magnetic film. A magnetic disk substrate is required to have the following characteristics. (1) Good surface accuracy after precision polishing or cutting. (2) There are fewer and smaller protrusions and holes that can cause defects in the magnetic thin film coated on the substrate surface. (3) It must have a certain degree of mechanical strength and be able to withstand machining during substrate manufacturing and high-speed rotation during polishing. (4) It must be lightweight, non-magnetic, and have a certain degree of corrosion resistance. Conventionally, Al-Mg-Mn-Cr alloy 5086 has been used as a magnetic disk substrate having such characteristics. Recently, there has been an increasing demand for higher density, larger capacity, etc. for magnetic disks, and there is a desire for the development of coating methods with aluminum materials and magnetic thin films suitable for these demands. In the case of conventional 5086 alloy, intermetallic compounds (Al-Fe,
Al−Fe−Si, Al−Mn, Al−Mn−Fe, Al−Si,
(Mg-Si system, etc.), these coarse intermetallic compounds fall off from the substrate during machining and polishing, forming holes or remaining as protrusions on the surface, making it difficult to maintain a good surface condition during polishing. I can't get it.
Therefore, even if the surface is coated with a magnetic thin film, the magnetic substance is not uniformly coated on the surface defects, causing storage errors, which is problematic as a substrate for high-density magnetic disks. Furthermore, as a method for coating the surface of a substrate with a magnetic material, coating methods have been the main method so far, but plating methods, sputtering methods, etc. have been developed in recent years, and their application to high-density magnetic disks is progressing. In this case, the conventional 5086 alloy has poor plating properties and is problematic in its application as a high-density magnetic disk for plating. Problems to be Solved by the Invention The present invention solves the above-mentioned problems of the 5086 alloy conventionally used as a substrate for magnetic disks, and provides an aluminum alloy for magnetic disks with excellent plating properties, especially Ni-P plating properties. This is what we provide. Means for solving the problem Generally, aluminum alloys are not suitable for plating due to their basic properties. For example, aluminum is electrochemically active and forms a strong oxide film;
Depending on the amount and distribution of alloying elements, the surface of aluminum may become chemically and electrochemically non-uniform, and its large coefficient of thermal expansion may cause tension between the plating layer and the aluminum, causing defects and damage to the plating layer. There are problems such as easy peeling. In plating type magnetic disks, in order to further improve the smoothness of the substrate before forming the magnetic material, a Ni-P intermediate plating layer is formed on the substrate and then polished again. In the case of direct plating, there is a problem that the adhesion of the plating layer is poor. Pre-treatment of the aluminum substrate is required to achieve good plating, and generally galvanization is performed using the zinc substitution method, and then
A Ni-P based intermediate layer is formed by plating. Therefore, the properties of a plated magnetic disk depend on the zinc plating properties of the base treatment and the plating properties of the Ni-P intermediate layer, and it is necessary to perform uniform and defect-free Ni-P plating and zinc plating with excellent adhesion. Therefore, it is necessary to consider the alloy composition and optimal manufacturing method for the aluminum material used as the substrate, taking plating properties into consideration. The present invention provides an alloy for magnetic disks having excellent Ni-P and galvanizing properties in accordance with the above-mentioned objects, and the gist thereof is as follows. Contains Mg2~5%, Zn0.2~2.9%, Be0.1~50ppm, and further includes Mn0.05~0.5%, Cr0.05~0.25%,
Contains one or more of Zr0.05-0.25%, Fe×Si as an impurity, Cu is Fe<0.40%,
Aluminum alloy with Si<0.25% and Cu<0.02%. The significance of component addition and the reason for its limitation are as follows. Mg: The addition of Mg improves the strength and provides the necessary strength as a magnetic disk material.
If it is less than 2%, this effect is insufficient and the workability during cutting and polishing of the magnetic disk material decreases. 5
%, hot rolling properties deteriorate. Accordingly
The amount of Mg added is 2 to 5%. Zn: The addition of Zn not only weakens the oxide film on the aluminum surface, but also contributes to improving the adhesion of the galvanized layer by imparting appropriate roughness to the substrate through pretreatment pickling, and also helps to spread the zincate layer over the entire surface of the substrate. This is effective for improving the adhesion of the Ni--P plating layer applied afterwards and for preventing defects. If it is less than 0.2%, this effect will not be sufficient, and if it exceeds 2.9%, hot workability will decrease. Therefore, the amount of Zn added is
Set at 0.2-2.9%. Mn: Mn precipitates as a fine intermetallic compound during homogenization treatment and has the effect of refining recrystallized grains, stabilizing the finish of the polished surface of the substrate and the layered structure of the Ni-P plating layer. Effective for improving adhesion, etc. If it is less than 0.05%, this effect is insufficient, and if it exceeds 0.5%, a huge intermetallic compound will crystallize, which is not preferable. Therefore, the amount of Mn added is set to 0.05 to 0.5%. Cr: Cr also has the same effect as Mn and is effective in refining crystal grains. If the amount added is less than 0.05%, this effect is insufficient, and if it exceeds 0.25%, a huge intermetallic compound will crystallize, which is not preferable. Therefore, the amount of Cr added should be 0.05 to 0.25%. Zr: Like Mn and Cr, Zr is effective in refining crystal grains. If the amount added is less than 0.05%, this effect will be insufficient, and if it exceeds 0.25%, a huge intermetallic compound will crystallize, which is not preferable. Therefore, the amount of Cr added should be 0.05 to 0.25%. Be: Be is effective in preventing oxidation and improving hot workability of Al-Mg alloys. If it is less than 0.1 ppm, this effect is insufficient, and if it exceeds 50 ppm, there is a problem in terms of toxicity, so the amount added should be 0.1 to 50 ppm. Ffe・Si: Fe and Si hardly dissolve in solid solution in aluminum and precipitate as intermetallic compounds.
When the amount of Fe/Si is large, Al-Fe system, Al-Fe system
-There are many coarse intermetallic compounds such as Si-based,
Since it is a question of quality, it is used as an impurity element.
The amount of Fe and Si shall be Fe<0.40% and Si<0.25%. Cu: If there is a large amount of Cu, the potential becomes noble and the appropriate roughness cannot be imparted to the substrate by pre-treatment pickling, so Cu as an impurity element is less than 0.02%.
shall be. The galvanizing method applied to the present invention is, for example,
15~ dissolved NaOH300gr/, Zn080gr/
Zinc is deposited on the surface of the substrate by immersing it in an aqueous solution at 20°C for several seconds to several minutes. In addition, the Ni-P plating method that is applied after zinc plating is an electroless Ni-P plating method that uses hypophosphorous acid as a reducing agent, and is usually treated at 80 to 90°C for 2 to 4 hours to form a layer of 15 to 30 μm. A plating layer is formed. There should be no defects in the film after Ni-P plating,
Good adhesion is required, but if there are large inclusions or defective parts of zincate in the aluminum substrate, those defects will still exist after Ni-P plating, and the adhesion of zincate will be poor. If the properties are poor, the adhesion of the Ni-P plating film will decrease. This invention aims to improve the adhesion of the Ni--P plating film and prevent defects by weakening the surface oxide film and improving the adhesion of zincate by adding Zn. By adding selective components such as Mn, Cr, and Zr, the crystal grains are made finer in order to make the Ni--P plating layer more uniform and to improve its adhesion. Examples Example 1 A 100 mm thick ingot having the chemical components shown in Table 1 was manufactured. Cu and Ti in the table are impurities. After homogenizing the ingot at 500°C for 24 hours, hot rolling was started at 480°C, and the ingot was rolled to a thickness of 6 mm. Approximately 66% of the hot-rolled plate is cold-rolled into a 2mm plate, and then heated at 220°C.
It was annealed for ×2 hours to produce a semi-hard material. Rough cutting and strain relief annealing (400℃) for this material.
x 2 hours) and then subjected to abrasive polishing. Next, zinc plating was performed as a base treatment, followed by Ni-P plating and various performances were evaluated. Table 2 shows the results. In addition, zinc plating is NaOH300gr/,
The test was carried out by immersing for 30 seconds in a 20°C aqueous solution containing 80gr of ZnO, and the Ni-P plating was carried out by immersing it in a commercially available electroless Ni-P plating solution (90°C) for 3 hours. Examples Nos. 1 to 10 have good performance. No. 11 has low strength and is difficult to polish with abrasive particles. No. 12 has a problem with plating properties because the amount of Zn is low. No. 13 to 14 have a high amount of added Mn + Zr, etc., and there are large intermetallic compounds, so there are many defects on the plating surface. No. 15 has a lot of impurities Fe and Si, so there are many defects on the plating surface.

【table】

【table】

[Table] Effects of the Invention According to the aluminum alloy of the present invention, an excellent plating type magnetic disk substrate having a uniform plating surface and no defects and good adhesion of the plating layer can be obtained.

Claims (1)

[Claims] 1 Mg2~5%, Zn0.2~2.9%, Be0.1~50ppm
Contains Mn0.05~0.5%, Cr0.05~0.25%,
Contains one or more of Zr0.05 to 0.25%, and the remainder consists of aluminum and impurities, and the impurities include Fe, Si, and Cu, Fe<0.40%, Si<0.25%,
An aluminum alloy for magnetic disks with excellent plating properties, characterized by Cu<0.02.