JPS635459B2 - - Google Patents

Description

[Detailed description of the invention]

The invention relates to magnetic tape contact parts, e.g.
VTR (video tape recorder) cylinder,
The present invention relates to an aluminum alloy with excellent corrosion resistance suitable for parts of magnetic recording devices that come into direct contact with magnetic tape, such as fixed or rotating tape guide drums and head drums. A VTR consists of a rotating magnetic head for magnetically recording and reproducing video signals on a magnetic tape, and a stationary or rotating tape guide drum for stably running the magnetic tape. Parts that come into direct contact with the magnetic tape, such as the rotating magnetic head or the tape guide drum, play an extremely important function in maintaining stable tape running without damaging the tape surface that has magnetic particles attached. It is known that the accuracy of the reproduced image (image clarity, color unevenness, etc.)
In order to improve the performance of magnetic tape, there is a strong demand for improvements in materials for magnetic tape contact parts. Conventionally, VTR tape contact parts have been made of, for example, a copper alloy with Cr hard plating on the surface, an austenitic SUS material, or the like. However, recently, aluminum alloy castings or ingots have been cut or plastic processed (particularly forged) by taking advantage of the advantages of aluminum alloys, such as their light weight, excellent workability, and non-magnetic properties. ,
Magnetic tape contact parts such as VTR drums began to be manufactured. The properties of the aluminum alloy required for the material for magnetic tape contact parts include the following items. 1. Good abrasion resistance against tape. 2. The coefficient of dynamic friction with the tape is small and the tape has good running properties. 3. Excellent mechanical strength. 4. Excellent machinability and smooth finished surface. 5. Excellent plastic workability, especially cold forgeability. 6. Good corrosion resistance in a high temperature and humid atmosphere. Conventionally, JISA2218 wrought alloy, for example, has been used as an aluminum alloy for magnetic tape contact parts, but although this alloy is excellent in properties 1) to 5) above, it is difficult to use in a high temperature and humid atmosphere as described in 6). There are the following problems with corrosion resistance. If you leave magnetic tape wrapped around the rotating drum of a VTR for a long time in a hot and humid atmosphere,
Moisture condensed between the magnetic tape and the cylinder corrodes the cylinder and causes rust, which not only causes the cylinder surface to lose its smoothness, but also
This rust may become embedded in the magnetic coating of the magnetic tape, causing the magnetic coating to peel off when the tape is peeled off. As a countermeasure to this problem, Japanese Patent Application Laid-Open No. 1984-19472 describes
A technique has been disclosed in which a chemically treated film is applied to the surface of a metal or an alloy, and the film is covered with a sputtered film of chromium or stainless steel. However, this method has the disadvantage that the cost is high because the steps of surface treatment and sputter film coating are added to the normal steps. In view of the current situation, the present inventors have undertaken various technical tasks to develop an aluminum alloy with excellent mechanical properties and excellent corrosion resistance in a humid atmosphere for use in magnetic tape contact parts. As a result of research, we discovered that the Si content in particular has a large effect on corrosion in the JIS A2218 alloy for wrought materials, which has been widely used so far, and completed the present invention. That is, the gist of the present invention is that Si
0.05~0.4%, Cu 3.0~5.0%, Mg 0.3~2.0%,
This is an aluminum alloy for magnetic tape contact parts with excellent corrosion resistance, containing 0.5-3.0% Ni, 0.005-0.3% Ti, and the remainder being Al containing ordinary impurities. The reason for limiting the composition range of the alloy of the present invention will be explained below. In the description of this specification, the contents of all included elements are expressed in weight %. Si: Si forms Mg ₂ Si-based precipitates together with Mg,
Increases the strength of the alloy. This effect is not sufficient when Si is less than 0.05%, and when Si exceeds 0.4%, corrosion resistance in a high temperature and humid atmosphere is significantly deteriorated. For these reasons, the content of Si is 0.05 to 0.4%, more preferably 0.1 to 0.3%. Cu: Cu increases the strength of the alloy base and improves machinability. If the effect is less than 3.0%, it is insufficient, and if it exceeds 5.0%, the forgeability decreases. Therefore, Cu is in the range of 3.0 to 5.0%. Mg: Mg not only improves the mechanical strength of the alloy, especially its yield strength, but also further ensures machinability due to its additive effect with Cu. If it is less than 0.3%, mechanical strength will not be sufficient, and if it exceeds 2.0%, castability will deteriorate and it will be difficult to obtain a homogeneous alloy ingot. Therefore,
Mg is in the range of 0.3 to 2.0%. Ni: Ni improves wear resistance and machinability. If it is less than 0.5%, no effect will be observed, and if it exceeds 3.0%, coarse intermetallic compounds will be formed.
Forging workability and machinability deteriorate. Therefore, Ni
shall be in the range of 0.5 to 3.0%. Ti: Ti is effective for refining the structure, but 0.005
If it is less than 0.3%, no effect will be observed, and if it exceeds 0.3%, not only will the effect be saturated, but the forging processability will decrease. Therefore, Ti should be in the range of 0.005 to 0.3%. In carrying out the present invention, 0.0004 to 0.002% of B may be added in addition to the above-mentioned additional elements.
As a result, coexistence with Ti enhances the miniaturization effect and improves workability. When manufacturing a tape contact part made of the alloy of the present invention, the starting material is not a sand mold or metal mold casting, but rather a long ingot produced by a direct cooling continuous casting method with a high cooling rate, and then forged by a long ingot. Most preferably, it is plastically worked and then shaped and finished by mechanical cutting means. In this case, JP-A-56-
Applying the manufacturing method of aluminum alloy for forging described in Publication No. 69348, the cooling rate (cooling rate of the solid-liquid interface during continuous casting) is maintained at 25°C/second or more (especially when the diameter
If a narrow diameter pillaret of 100 mm or less is suitable for this condition), castability will be greatly improved, and long ingots can be directly forged without extrusion, improving productivity. The structure has become significantly finer, and the second phase particles made of intermetallic compounds are finely and uniformly dispersed. For this reason, it has high strength and wear resistance, and in addition, it has an extremely excellent surface roughness after being processed to a precise, smooth surface, so-called mirror finishing, which is required for VTR tape contact parts. In general, it has been found that when a precision finished surface is required, such as mirror finish processing of metal using a cutting tool having a diamond cutting edge, it is necessary to adjust the structure of the alloy ingot. A long, narrow-diameter ingot of the alloy satisfies these requirements. It is truly an ideal alloy material. However, the alloy material of the present invention is not limited to the above-mentioned continuous casting ingots, but also metal molds, sand molds,
Compared to conventional alloy materials, even if the ingot is formed by a casting method such as die casting and then processed as it is or after heat or cold forging and then cut and formed to produce VTR tape contact parts, the present invention is better than conventional alloy materials. The characteristic effects of are fully exhibited. The present invention will be explained below based on Examples.
Within the scope of the gist, the present invention is not limited to the following examples. Examples and Comparative Examples Table 1 shows the alloy compositions of Example Alloys No. 1 to 7 and Comparative Example Alloys No. 8 to 13. In the classification of alloy ingots shown in this table, alloy ingot A is produced by the vertical semi-continuous casting method. The cooling rate was maintained at 28°C/sec, and the ingot was manufactured into a long cylindrical ingot with a diameter of 73 mm. The distance between dendrite arms in the internal structure of the obtained ingot was narrow, and the second phase particles were fine. It was also observed that the particles were uniformly dispersed. Alloy ingot B was obtained by extruding a cylindrical ingot with a diameter of 200 mm obtained by a vertical semi-continuous casting method into a round bar with a diameter of 70 mm. The alloy ingot C was formed into the shape shown in FIG. 1 by die casting. The test pieces for tensile strength and elongation were ingots for alloy materials A and B, and boat bottom mold ingots for alloy C.
After T6 heat treatment (500℃ x 4 hours, water-cooled quenching, then artificial aging treatment at 180℃ x 8 hours), JIS4
It was processed into a No. 1 test piece. For the test pieces for cold castability evaluation, the ingots of both alloy materials A and B were subjected to annealing heat treatment (370°C x 4 hours, furnace cooling).
After that, the wedge test piece (L=
150 mm, t ₀ = 3 mm, t ₁ = 15 mm, W = 20 mm). Test specimens for hardness, machinability, surface roughness, tape running performance, coefficient of dynamic friction, and corrosion resistance were prepared by cold casting for alloy materials A and B, and by die casting for alloy material C, respectively, as shown in Figure 1. Molded into a shape. After rough-machining these alloy materials, they were subjected to T6 heat treatment under the same conditions as above, and then mirror-finished using a cutting tool with a diamond cutting blade. ₁ = 40mm, _d2 = 20mm,
The VTR rotating drum was made up of H ₁ = 16 mm and H ₂ = 7 mm. The cutting conditions for the outer peripheral surface of the drum on which the tape slides were a cutting speed of 150 m/min, a depth of cut of 0.05 mm, and a cutting tool feed rate of 0.05 mm/rotation. A specimen for specific wear loss test was cut out from a part of the VTR rotating drum. Table 2 shows the characteristic values of these specimens.

【table】

【table】

[Table] A summary of each test method is as follows. (a) Tensile strength and (b) Elongation A test was conducted using a JIS No. 4 test piece using an Olzen type 50-ton universal testing machine. C. Cold casting properties The wedge test piece 1 shown in Fig. 2a is placed on the anvil 2 shown in Fig. 2b, forged with a 1/2 ton hammer 3, and the test piece 4 cracks after forging. Evaluation was made by comparing the location of occurrence. D. Hardness The hardness directly below the tape sliding surface was measured using a Bitkers hardness meter. E. Cutting property Cutting was performed using a compact diamond cutting tool at a cutting speed of 150 m/min and a depth of cut of 0.15 mm, and the shapes of cutting chips were compared and evaluated. The cutting type and flow-cutting type have good processing properties for cutting waste, while the coil type has poor processing properties. F. Surface Roughness The surface roughness of the drum in the axial direction was measured using a stylus type roughness tester. G Wear resistance Using the Ohkoshi type abrasion tester, the opponent was FC30.
Friction speed 3m/sec, load 18.2Kg, friction distance 600
The test was conducted without lubrication, and the specific wear amount per kg of unit area was measured. H Tape running properties After running magnetic tape for VTR for 1500 hours,
The stability of the reproduced images was tested using a VTR. Coefficient of Dynamic Friction Using the same running method as a VTR, a reverse tension (Wp) of 50 gr is applied to one side of the magnetic tape, and the specimen is rotated at a relative speed of 18.0 cm/sec. The acting load (WT) was measured and the coefficient of dynamic friction was calculated. Corrosion resistance A VTR drum is wrapped with magnetic tape loaded with 60gr and placed in an atmosphere of 40℃ and 85% humidity.
After holding for a week, the condition of the parts where the drum and magnetic tape were in contact with each other was observed. The evaluation was in four stages. That is, ◎: No change in drum or magnetic tape. ○: Small corrosion occurred on the drum, no abnormality on the magnetic tape. △: Corrosion occurred on the drum, and magnetic powder was peeled off in some places on the magnetic tape. ×: The drum was severely corroded, and the magnetic powder on the magnetic tape was noticeably peeled off. In the above evaluation, ◎ and ○ indicate that there is no problem in practical use. Figure 3 shows the alloy obtained by the semi-continuous casting method.
Microscopic microstructure photographs (magnification: 630x) of the ingots of No. 2 (Fig. 3 a) and Alloy No. 8 (Fig. 3 b) are shown. Alloy No.
There are many black grains of Mg ₂ Si in the grain boundaries of Alloy No. 8, and this is because the Si content is higher than that of Alloy No. 2. A sketch of the drum surface obtained from the corrosion resistance test is shown in FIG. 4, and a corresponding sketch of the magnetic tape is shown in FIG. In both Figures 4 and 5, a
corresponds to alloy No. 2, and b corresponds to alloy No. 8. Figure 4b
The black dots on the tape surface are corroded parts, and the black dots on the tape surface in Figure 5b are the parts where the magnetic powder has peeled off due to drum corrosion. When the structure of the cross section of the corroded area shown in FIG. 4b was observed, it became clear that the corrosion was intergranular corrosion that propagated to the grain boundaries. FIG. 6 shows a micrograph of the cross section of the corroded portion of the drum shown in FIG. 4b. Therefore, corrosion resistance when the VTR drum and magnetic tape are statically left in contact with each other under high temperature and high humidity can be achieved by controlling the Si content. As seen in the characteristic values in Table 2, the alloy of the present invention has excellent mechanical properties required for magnetic tape contact parts, and also has excellent corrosion resistance without special treatment such as coating on the part surface. Therefore, it is extremely suitable as a material for magnetic tape contact parts.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a rotating drum-shaped test piece for VTR, Figure 2a is the shape of a wedge test piece for forgeability evaluation, Figure 2b is an explanatory diagram of the forgeability test method, and Figure 3 The figures are microscopic photographs of semi-continuously cast ingots, in which a is alloy No. 2 and b is alloy No. 8. Figures 4 and 5 show the drum surface (No. 4) obtained by a corrosion resistance test under a high temperature and high humidity atmosphere.
Fig. 5) and the corresponding magnetic tape (Fig. 5), in which a is alloy No. 2 and b is alloy No. 2, respectively.
Corresponds to No.8. FIG. 6 is a micrograph of a cross section of the corroded portion of the drum of FIG. 4b.

Claims (1)

[Claims] 1 Si 0.05-0.4%, Cu 3.0-5.0%, Mg by weight
An aluminum alloy for magnetic tape contact parts with excellent corrosion resistance, containing 0.3 to 2.0% Ni, 0.5 to 3.0%, and 0.005 to 0.3% Ti, with the remainder being Al containing ordinary impurities.