JPH025810B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an aluminum alloy for magnetic disks, and particularly to an aluminum alloy for magnetic disks with excellent plating properties. [Prior Art] A magnetic disk is generally an aluminum alloy substrate whose surface is precisely polished and coated with a magnetic thin film, and signals are recorded by magnetizing the magnetic thin film. This magnetic disk substrate is required to have the following characteristics. (1) The surface accuracy after precision polishing or cutting is good; (2) there are few and small protrusions and holes on the substrate surface that can cause defects in the magnetic thin film; and (3) there is a certain degree of strength. (4) It is lightweight, non-magnetic, and has a certain degree of corrosion resistance. Conventionally, aluminum has been used as a magnetic disk substrate with these characteristics. -Mg-Mn-Cr alloy 5086 and its improved alloys have been used. In recent years, demands for higher density, larger capacity, etc. for magnetic disks have increased, and it is desired to develop an aluminum alloy suitable for this substrate and a method for coating the substrate with a magnetic thin film. Up until now, the main method for coating a substrate surface with a magnetic material has been a coating method, but in recent years, plating methods, sputtering methods, etc. have been developed, and their application to high-density magnetic disks is progressing. To manufacture a plating-type magnetic disk, in order to further improve the smoothness of the substrate before forming the magnetic material, a Ni--P intermediate layer plating is formed on the substrate and then polishing is performed again. However, when intermediate layer plating is directly performed on an aluminum substrate, the adhesion of the plating layer is poor, so pretreatment of the aluminum substrate is required to perform high-quality intermediate layer plating. Therefore, generally, the surface of the substrate is uniformly roughened by etching with an acidic solution, Zn plating is performed by a Zn substitution method, and a Ni--P intermediate layer is plated thereon. Therefore, the performance of a plated magnetic disk depends on the degree of uniform surface roughening used in the surface treatment, Zn plating properties, and Ni
Since it depends on the plating properties of the -P intermediate layer, it is necessary to perform Ni-P plating with no defects and excellent adhesion. To this end, it is necessary to consider the alloy composition and manufacturing method of the aluminum material that will serve as the substrate, taking plating properties into consideration. [Problems to be Solved by the Invention] The present invention provides an aluminum alloy for magnetic disks that has few defects during Ni-P plating, has good adhesion of the Ni-P plating layer, and is easy to manufacture. It is. [Means for Solving the Problems] The structure of the present invention for solving the above problems is as follows. Zn4~7%, Mg1.5~3.5%, Cu0.1~0.7%,
Contains Ti0.001~0.05%, further Mn0.05~0.5%,
A magnetic disk with excellent plating properties, containing one or more of 0.05 to 0.25% Cr and 0.05 to 0.25% Zr, and remaining aluminum impurities, and the impurities Fe and Si are Fe≦0.15% and Si≦0.10%. Aluminum alloy for. The reason for limiting the content of each component described in the above structure is as follows. Zn: Zn coexists with Mg to form MgZn ₂ compound,
This compound dissolves during pre-treatment pickling to form fine and uniform etching pits, imparting appropriate roughness to the substrate, not only improving the adhesion of the plating layer, but also allowing the zincate layer to adhere uniformly to the substrate. This is effective in improving the adhesion of the subsequent Ni-P plating layer. Below the lower limit, this effect is small, and above the upper limit, hot workability decreases. Mg: Mg not only contributes to improving strength, but also
Forms a compound of Zn and _MgZn , which contributes to the formation of uniform and fine etch pits by pretreatment pickling.
It is effective in improving the adhesion of the Ni-P plating layer and preventing defects. Below the lower limit, this effect is small, and above the upper limit, hot workability decreases. Cu: Like Zn and Mg, Cu improves strength, forms AlZnMgCu compounds, and contributes to the formation of etch pits during pretreatment pickling. In addition, in Al-Zn-Mg-Cu alloys such as this alloy, MgZn ₂ preferentially precipitates at grain boundaries, and this region is preferentially etched during pretreatment pickling, resulting in significant grain boundary etching. Sometimes. In such a case, the Ni--P plating becomes non-uniform and plating defects are likely to occur. When Cu is added, some of it precipitates at grain boundaries and has the effect of increasing the potential at the grain boundaries. Therefore, the addition of Cu has the effect of suppressing grain boundary etching and uniformly roughening the board surface during pretreatment pickling. Below the lower limit, this effect is small, and above the upper limit, this effect is saturated. On the other hand, when Cu is added, ingot cracks tend to occur, making it difficult to produce large ingots using the current semi-continuous casting method. Therefore, although alloys with a high Cu content have good plating properties, they cause casting cracks, making it extremely difficult to manufacture the material. When the amount of Cu is kept below the upper limit, this problem can be solved and a low-cost material can be manufactured. In addition, if the amount of Cu exceeds the upper limit, crystallization will occur.
AlZnMgCu-based compounds become coarse and form coarse etch pits during pretreatment etching, and Ni-P
The plating layer may become non-uniform and plating defects may occur. For the above reasons, the amount of Cu needs to be 0.1 to 0.7%. Ti: Makes the casting structure finer and helps prevent casting cracks. Below the lower limit, this effect is insufficient, and even above the upper limit, this effect is saturated. Mn, Cr, Zr: These elements precipitate as fine intermetallic compounds during homogenization treatment and contribute to grain refinement. If it is less than the lower limit, this effect will be insufficient, and if it exceeds the upper limit, a huge intermetallic compound will crystallize, which is not preferable. Fe, Si: Fe and Si hardly form a solid solution in aluminum and precipitate as intermetallic compounds.
When the amount of Si is large, Al-Fe system, Al-Fe-Si
Since there are many coarse intermetallic compounds such as metals, which cause plating defects, the amount of impurities is
Fe and Si should be Fe≦0.15% and Si≦0.10%. Other impurities are each less than 0.05%. Pretreatment pickling in the present invention is 50% HNO ₃ solution
This was carried out by immersing the sample in a solution at 30° C. to which g/g of acidic ammonium fluoride was added for 50 seconds. In the Zn plating method, for example, 300g of NaOH/
Zn is deposited on the surface of the substrate by immersing it in an aqueous solution of 80 g of ZnO at 20° C. for 90 seconds. In addition, the Ni-P plating method is an electroless Ni-P plating method that uses hypophosphorous acid as a ring agent.
A plating layer of 15 to 30 μm is formed by treatment at 90° C. for 2 to 4 hours. The film after Ni-P plating must be free of defects and have good adhesion. If coarse intermetallic compounds exist in aluminum, the compounds may remain after plating, or they may form coarse pits during pretreatment pickling and cause Ni-
Since this results in P plating defects, a good plating surface cannot be obtained. Furthermore, if the surface is not uniformly roughened during pretreatment pickling or the adhesion of zincate is poor, the adhesion of the Ni--P plating layer may decrease or plating defects may occur. This invention aims to uniformly roughen the surface during pretreatment pickling and improve the adhesion of zincate by adding appropriate amounts of Zn, Mg, Cu, etc., with the aim of improving the adhesion of the Ni-P plating layer. There is. Furthermore, we can control crystal grains by adding Mn, Cr, and Zr.
Plating defects are reduced by reducing coarse intermetallic compounds by controlling impurity elements such as Fe and Si. Furthermore, since this alloy suppresses the amount of Cu, it is easy to manufacture large ingots, making it possible to manufacture low-cost materials. Hereinafter, the present invention will be specifically explained with reference to Examples. In addition, the amount (%) of each chemical component described in the examples is weight %. Example 1 A large ingot with a thickness of 400 mm having the chemical components shown in Table 1 was produced by semi-continuous casting. This ingot
After homogenization treatment at 480°C for 24 hours, hot rolling was started at 430°C, and the sheet was rolled to a thickness of 6 mm. 370 hot rolled plates
It was annealed at ℃, cold rolled into a 2mm plate, and then
It was annealed at 220℃ for 2 hours to produce a semi-hard material. For this material, rough cutting, strain relief annealing (380
Table 2 shows the various properties when the specimens were mirror-finished by diamond-finish cutting, followed by Zn plating and Ni-P plating. However, Ni-P plating is commercially available electroless Ni-P
The test was carried out by immersing it in a plating solution at 90°C for 3 hours. Further, in both Tables 1 and 2, Nos. 1 to 7 are alloys of examples of the present invention, and Nos. 8 and after are alloys of comparative examples.

【table】

【table】

[Table] The above results and other findings are summarized as follows. No. 1 to 7: Few plating defects and good adhesion. No. 8: The amount of Cu is small and there are many plating defects. No. 9: The amount of Cu was large, and cracks occurred in the ingot. No. 10: Large amount of Fe and many plating defects. No. 11 to 12: Many plating defects and poor adhesion.
Also, the strength is low. Example 2 A large ingot with a thickness of 400 mm having the chemical components shown in Table 3 was produced by semi-continuous casting, and was made into a semi-hard material with a thickness of 2 mm using the same method as in Example 1. Table 4 shows the properties when this material was plated with Ni--P in the same manner as in Example 1. However, the Ni-P plating conditions, evaluation method, etc. are the same as in Example 1. Nos. 1 to 7 are examples, and Nos. 8 and after are comparative examples.

【table】

【table】

[Table] The above results and other findings are summarized as follows. No. 1 to 7: Few plating defects and good adhesion. No. 8: The amount of Cu is small and there are many plating defects. No. 9: The amount of Cu was large, and cracks occurred in the ingot. No. 10: Large amount of Fe and many plating defects. No. 11 to 12: Many plating defects and poor adhesion.
Also, the strength is low. [Effects of the Invention] As explained above, according to the present invention, uniform surface roughening can be achieved by pretreatment pickling, and as a result, Ni
- The adhesion of P plating is improved. Furthermore, since the formation of coarse intermetallic compounds can be suppressed, plating defects are reduced. On the other hand, since cracking of the ingot of the material is prevented, it is possible to provide a low-cost material that has a high yield and is easy to manufacture and process.

Claims (1)

[Claims] 1 Zn4~7%, Mg1.5~3.5%, Cu0.1~0.7%,
Contains Ti0.001~0.05%, further Mn0.05~0.5%,
Contains one or more of Cr0.05~0.25% and Zr0.05~0.25%, and the remainder consists of aluminum and impurities, and Fe and Si as impurities are Fe≦0.15% and Si≦0.10%. Excellent plating properties. Aluminum alloy for magnetic disks.