JPH0239578B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides corrosion resistance suitable for parts of magnetic recording devices that directly contact magnetic tape, such as VTR (video tape recorder) cylinders, fixed or rotating tape guide drums, and head drums. It concerns an excellent aluminum alloy. 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. It is known that 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 to which magnetic particles are attached. Therefore, in order to improve the accuracy of reproduced images (image clarity, color unevenness, etc.), 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 runs well. 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, as aluminum alloys for magnetic tape contact parts, for example, JIS2000 series alloys for plastic working have been used.
Al--Cu alloys, JIS AC5A casting alloys, and 8-type Al--Si--Cu--Mg alloys are widely used, but these alloys do not have the properties listed in 1) to 5) above. Although it is excellent, it has the following problems in 6) corrosion resistance in a high temperature and humid atmosphere. If you leave magnetic tape wrapped around a VCR cylinder in a hot and humid atmosphere for a long time,
Moisture condensed between the magnetic tape and the cylinder causes the cylinder to corrode and rust, which not only causes the cylinder surface to lose its smoothness, but also to
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 inventors of the present invention have conducted various researches to develop an aluminum alloy with excellent mechanical properties and excellent corrosion resistance in a high temperature and humid atmosphere for use in magnetic tape contact parts. As a result, in the JIS 2000 series Al-Cu alloys, which are alloys for plastic working, and the JIS AC5A series, which are alloys for casting, and the Al-Si-Cu-Mg series 8 series, which have been widely used so far, Si and Mg The present invention was completed based on the discovery that the content has a large effect on corrosion. That is, the object of the present invention is to improve wear resistance, coefficient of dynamic friction,
The object of the present invention is to provide an aluminum alloy for magnetic tape contact parts that has improved machinability and also improved corrosion resistance, and these technical problems are solved by the following configuration. The gist of the present invention is that Si exceeds 5% and 12% by weight.
up to, Cu over 2% up to 5%, Mg 0.2 to 0.8%,
Ni0.5~2.5%, Fe0.1%~1.0%, Ti0.005~0.2%
, and further contains one or more elements among Mn0.2-1.2%, Cr0.2-1.2%, and one or more elements among Pb, Bi, Sn, and Sb in a total amount of 0.5-2%, The remaining part is made of Al containing ordinary impurities to provide an aluminum alloy for magnetic tape contact parts with excellent corrosion resistance. 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 %. Cu: Cu increases the strength of the alloy base metal and improves machinability. If it is less than 2%, the effect will be insufficient, and if it exceeds 5%, castability, forgeability, and corrosion resistance will deteriorate. Therefore, Cu should be in a range of more than 2% and up to 5%. Si and Mg: Forms Si and Mg ₂ Si-based precipitates to increase alloy strength. Mg improves the mechanical strength and yield strength of the alloy. In particular, the synergistic effect with Cu further ensures machinability. Si has a remarkable effect on improving wear resistance. Si5% or less, Mg0.2%
If the amount is less than that, these effects will not be sufficient. When Si exceeds 12%, primary silicon crystallizes, and cold forgeability and smoothness of the cut surface deteriorate. For this reason, Si should be in a range of more than 5% and up to 12%. Within the range of Si in the present application, Mg has a significant effect on corrosion resistance in a high temperature and humid atmosphere. That is, if Mg exceeds 0.8%, corrosion resistance will deteriorate significantly. For this reason, Mg should be in the range of 0.2 to 0.8%. Fe: Fe is effective in improving wear resistance and machinability. The effect is not recognized at less than 0.1%,
If it exceeds 1.0%, plastic workability will deteriorate. Accordingly
Fe is in the range of 0.1 to 1.0%. Ni: Ni improves wear resistance and machinability. The effect is not recognized below 0.5%, and 2.5%
If it exceeds this, coarse intermetallic compounds will be formed and forging workability and machinability will deteriorate. Therefore, the range of Ni is 0.5
~2.5%. Mn, Cr: Addition of Mn and/or Cr improves wear resistance. If it is less than 0.2%, the crystallization that contributes to wear resistance will not be sufficient, and if it exceeds 1.2%, the crystallized substances will become coarse and will impair machinability. Therefore, Mn and Cr are
It should be in the range of 0.2 to 1.2%. Pb, Bi, Sn, Sb: These elements improve the machinability of the alloy. Improving machinability means reducing cutting resistance, fragmenting chips into fine particles, and improving the accuracy of the cut surface, and two or more types are more effective than using them alone. If it is less than 0.5%, it has no effect on the above properties, and if it exceeds 2.0%, the plastic workability and toughness will be extremely reduced, which is not a good idea. If the content of these elements (total amount if two or more types) is less than 0.5%, there is little effect on the above properties, and if it exceeds 2.0%, plastic workability and mechanical strength, especially toughness, will be extremely reduced. . The preferred content is 0.8-1.4%. Ti: Ti is effective in refining the structure, but
If it is less than 0.005%, the effect is not recognized, and if it exceeds 0.2%, not only the effect is saturated, but also the forging workability decreases. Therefore, Ti should be in the range of 0.005 to 0.2%. 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. If B is less than 0.0004%, the refinement effect due to coexistence with Ti will not be exhibited. If B exceeds 0.002%, a coarse hard intermetallic compound is formed with Ti, and if this appears on the tape contact surface, there is a risk of damaging the tape surface during running. Therefore, B is 0.0004%
The range shall be ~0.002%. When manufacturing tape contact parts 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 manufactured 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 pillar 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. It is generally known that when a precision finished surface is required, such as mirror finishing of metal using a cutting tool having a diamond cutting edge, it is necessary to prepare the structure of the alloy ingot. A long, narrow-diameter ingot of the alloy satisfies these requirements. 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, the present invention can be made by molding ingots using a casting method such as die casting, and then manufacturing VTR tape contact parts by cutting or forming the ingots as they are or by applying heat or cold forging. 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 Example Alloys No. 1 to 9 and Comparative Example Alloys.
The alloy compositions of Nos. 10 to 12 are shown. 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 mechanical property test pieces were T6 ingots for alloy materials A and B, and boat bottom mold ingots for alloy C.
Heat treatment (500℃ x 4 hours, water cooling quenching, then
After undergoing artificial aging treatment at 180°C for 8 hours, it was processed into JIS No. 4 test pieces. For the test pieces for forgeability 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 pieces for hardness, machinability, surface roughness, coefficient of dynamic friction, and corrosion resistance were formed into the shapes shown in Figure 1 by cold forging for alloy materials A and B, and by die casting for alloy material C. . After rough cutting 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, and the dimensions in Fig. 1 were D = 63 mm, d ₁ = 40mm, _d2 =20mm, _H1 =16mm, _H2
= 7mm VTR rotating drum. The cutting conditions for the outer peripheral surface of the drum on which the tape slides are the cutting speed.
150m/min, depth of cut 0.05mm, cutting tool feed rate
It was 0.05mm/rotation. The specific wear amount test piece is as above.
It was cut out from a part of a 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 Tests were conducted using JIS No. 4 test pieces using an Olzen 50-ton universal testing machine. c) Forgeability The wedge test piece 1 shown in Fig. 2a is
Place it on the anvil 2 shown in the figure, and use the 1/2 ton hammer 3.
The evaluation was made by comparing the crack occurrence positions of the test piece 4 after forging and elongation. The evaluation results are indicated as ◎: good, 〇: normal, and △: slightly poor. d) Hardness The hardness directly below the tape sliding surface was measured using a Bitkers hardness meter. e) Chip disposal properties Cutting was performed using an artificial sintered diamond cutting tool at a cutting speed of 150 m/min and a depth of cut of 0.15 mm, and the shape of the chips was compared and evaluated. The evaluation results are displayed as ◎: good, 〇: normal, and △ slightly poor. f) Surface roughness The surface roughness of the drum in the axial direction was measured using a stylus roughness tester. g) Abrasion resistance Using an Okoshi type abrasion tester, the test material was FC30.
Friction speed 3m/sec, load 2.1Kg, friction distance 600m,
The test was conducted without lubrication, and the specific wear resistance per kg of unit area was measured. H) Coefficient of Dynamic Friction Using the same running method as a VTR, a reverse length force (Wp) of 50gr was applied to one side of the magnetic tape, and the magnetic tape was rolled at 18.0cm/
The test material was rotated at a relative speed of sec, and the acting load (WT) was measured on one side facing the magnetic tape load to calculate the dynamic friction coefficient. li) Corrosion resistance After wrapping a magnetic tape with a load of 60gr around a VTR drum and keeping it in an atmosphere of 40℃ and 85% humidity for one week, the condition of the parts where the drum and magnetic tape were in contact with each other was determined. 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. A sketch of the drum surface obtained from the corrosion resistance test is shown in FIG. 3, and a corresponding sketch of the magnetic tape is shown in FIG. In both Figures 3 and 4, a
corresponds to alloy No. 2, and b corresponds to alloy No. 10. The black dots on the drum surface in FIG. 3b are corroded areas, and the black dots on the tape surface in FIG. 4b are areas 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. 3b was observed, it became clear that the corrosion was intergranular corrosion that propagated to the grain boundaries. FIG. 5 shows a micrograph of the cross section of the corroded portion of the drum shown in FIG. 3b. 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 and Mg contents. 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 drawings]

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 Figures 4 and 4 show the drum surface (Third
Fig. 4) and the corresponding magnetic tape (Fig. 4), where a is alloy No. 2 and b is alloy No. 2, respectively.
Corresponds to No.14. FIG. 5 is a micrograph of a cross-section of the corroded portion of the drum of FIG. 3b.

Claims (1)

[Claims] 1. Si is more than 5% and up to 12% by weight, and Cu is 2% by weight.
up to 5%, Mg0.2~0.8%, Ni0.5~2.5%,
Contains Fe0.1%~1.0%, Ti0.005~0.2%, and further,
Contains a total of 0.5-2% of one or more elements among Mn0.2-1.2%, Cr0.2-1.2%, and one or more elements among Pb, Bi, Sn, and Sb, and the remainder is normal impurities. An aluminum alloy for magnetic tape contact parts with excellent corrosion resistance. 2 Si over 5% and up to 12% by weight, Cu 2%
up to 5%, Mg0.2~0.8%, Ni0.5~2.5%,
Fe0.1%~1.0%, Ti0.005~0.2%, B0.0004~
Contains 0.002%, additionally Mn0.2~1.2%, Cr0.2~
1.2% of one or more elements and Pb, Bi, Sn,
An aluminum alloy for magnetic tape contact parts with excellent corrosion resistance, containing a total amount of 0.5 to 2% of one or more elements among Sb, and the remainder being Al containing ordinary impurities.