JPH0339454A - Production of cast aluminum alloy bar for vtr cylinder - Google Patents

Abstract

PURPOSE:To inexpensively produce an Al alloy bar for VTR cylinder excellent in forgeability, wear resistance, and hardness by casting a molten Al alloy with a specific composition under specific cooling conditions and then carrying out homogenizing treatment, annealing treatment, and slow cooling at the time of producing a cast Al alloy bar for VTR cylinder. CONSTITUTION:At the time of producing an Al alloy bar for VTR cylinder with ease by means of casting, a molten Af alloy, as raw material, having a composition containing, by weight, 3-4.5% Cu, 0.3-1.8% Mg, 0.5-2.5% Ni, 0.1-0.9% Si, and 0.1-0.7% Fe is cast into a shape of a bar of <=phi80mm, cooled at >=50 deg.C/sec average cooling rate, heated up to 450-520 deg.C for >=8hr to undergo homogenizing treatment, successively annealed at 330-390 deg.C for >=2hr, and cooled slowly from the annealing temp. down to <=250 deg.C at <=20 deg.C/hr average cooling rate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for making an aluminum alloy cast rod for vRT cylinders.

[Conventional technology] Traditionally, forged products made from extruded aluminum alloy rods have often been used for vRT cylinders, but in order to reduce costs, it has been desired to switch to a manufacturing method for cast rods that does not require an extrusion process, and this has been implemented. It is being done. However, unlike extruded rods, cast rods cannot improve the workability of the material through extrusion processing, and therefore have the problem of being susceptible to cracking and cracking during forging. In addition, when cold forging a material into a product shape, conventionally, the material is forged twice, that is, forged twice to bring the material closer to the product shape, and then the work-hardened material during forging is annealed, making it easier to forge. Previously, a method was used in which the forging was re-forged and finished into the product shape, but in order to streamline the process, single-step forging was desired, and as VTR cylinders were becoming lighter and cheaper, , product shapes are becoming thinner and more complex, and the forgeability required of materials is becoming more demanding.

For this reason, when a cast bar is forged, cracks and cracks are likely to occur, which is a major problem in using the cast bar.

For this reason, when a cast bar is forged, cracks and cracks tend to occur, which is a major problem in using the cast bar.

[Problems to be Solved by the Invention] Under these circumstances, an object of the present invention is to provide a method for manufacturing an aluminum alloy cast bar for a VTR cylinder that is less likely to break or crack during forging.

[Means for solving the three problems] The present invention solves the above problems and provides a VTR with good forgeability.
The present invention provides a method for manufacturing an aluminum alloy cast rod for cylinders, and its gist is that Cu 3
~4.5 if [41%, MgO03~1.8 ffi
amount%, Ni0.5-2.5ffi amount%, S i O,
1-0.9ffi amount%, F e O, 1-0.7 f
After casting an aluminum alloy consisting of the remaining aluminum and impurities at an average cooling rate of 5 o''C/see or more to a diameter of 80 mm or less, the aluminum alloy is homogenized at 450 to 520 °C for 8 hours or more, and then 330 to 390 °C. The method of manufacturing an aluminum alloy cast bar for a VTR cylinder is characterized by annealing the bar for 2 hours or more and then slowly cooling it from that temperature to 250°C or less at an average cooling rate of 20'C/hr or less.

The reasons for limiting the alloy components and manufacturing method in the present invention are as follows.

Cu: Cu is an element originally added to increase the strength of the VTR cylinder through processing (T6 quenching, tempering) performed after forging, but it has the following effects during forging.

That is, Cu present in Al mainly forms deposits and precipitates, and some of it is dissolved in Al. Among these, crystallized substances are coarse compounds formed together with other elements during casting, and become the starting point of forging cracks. Therefore, after casting, as much crystallized material as possible is injected (solid solution) through homogenization treatment.
It is desirable to Precipitates can be broadly divided into two types depending on their function.

One is the stable phase (θ: A12 C
u%S: A12 CuMg), and one is a metastable phase or G8P band that improves hardness and strength. this house,
The G and P bands are formed in a short period of time even when left naturally due to the supersaturated solid solution of Cu after casting or homogenization treatment, increasing the hardness of the material. The forgeability of the material improves as the hardness decreases, so before forging, softening treatment is performed to
It is desirable to precipitate a large amount of Cu, which has become a supersaturated solid solution during casting or homogenization, in the form of a stable phase rather than a G, P band or metastable phase. Therefore, it is desirable to reduce the amount of crystallized substances and increase the number of stable phases in order to improve forgeability.

However, when the content exceeds 4.5 wt%, the amount of crystallized substances that become the starting point of forging cracks increases significantly, and when this is infiltrated by homogenization treatment, a significantly large amount of Cu dissolved in supersaturated solid solution is accommodated. For this reason, it becomes difficult to precipitate most of it in the form of a stable phase during the softening treatment, resulting in insufficient reduction in hardness. In addition, if it is less than 3 wt%, metastable phases and G precipitate during processing (T6 quenching, tempering).

Pll), sufficient strength cannot be obtained.

Therefore, the content should be in the range of 3 to 4.5 wt%.

Mg: Like Cu, Mg is an element added to increase the strength of VTR cylinders during the T6 process, but before forging, a softening process precipitates a large amount of stable phase to reduce the hardness of the material. can improve sex.

However, if it exceeds 1.8% by weight, the reduction in hardness will be insufficient, and if it is less than 0.3% by weight, sufficient strength will not be obtained after T6 treatment. Therefore, the content should be in the range of 0.3 to 1.8% by weight.

Si: Similar to Cu and Mg, Si is an element added to increase the strength of VTR cylinders in the T6 process, but before forging, a softening process precipitates a large amount of stable phase and reduces the hardness of the material. , it is possible to improve forgeability.

However, if it exceeds 0.9 ffl amount %, the reduction in hardness will be insufficient, and if it is less than 0.111 t %, sufficient strength will not be obtained after T6 treatment. Therefore, 0.1-0.9% by weight
The range shall be .

Ni: The amount of Ni dissolved in solid solution in AI is extremely small, and most of the added amount remains in AI as a crystallized substance, making it almost impossible to dissolve it even in a homogenization treatment. This crystallized material contributes to improving the wear resistance and machinability of the VTR cylinder, but during forging, it acts as a starting point for cracks, resulting in a decrease in forgeability. If it is less than 0.5% by weight, the contribution to wear resistance and machinability will be small, and if it exceeds 2.5% by weight, forgeability will be significantly reduced. Therefore, the content should be in the range of 0.5 to 2.5% by weight.

Fe: When Fe is cast, it combines with Ni to form a Fe-Ni compound, which contributes to the wear resistance of VTR cylinders.

However, since the Fe-N1 compound hardly penetrates during the homogenization process, it becomes a starting point for cracks during forging. 0.1
If it is less than 0.7ff, sufficient wear resistance cannot be obtained.
If the content exceeds i%, forgeability will be significantly reduced. Therefore, 0
．． The range is 1 to 0.7 ffi amount%.

Casting Cooling Rate When a two-component alloy solidifies, primary crystals A1 grow in a dendritic shape, and then compounds mainly consisting of alloying elements crystallize between the dendrites. This compound is very brittle and increases in proportion to the dendritic spacing (DAS), so the greater the DAS, the lower the forgeability. In particular, when the average value of DAS exceeds 15 μm, forgeability is significantly reduced. By the way, DAS has a relationship with the cooling rate as shown in the following formula: C-ni/D'' C: cooling rate ('C/5ee) D: DAS (μm) m, ni: constant In the case of a book-based alloy, Km 7 .8XlG', m-2,
It is 7. Therefore, in order to make the average DAS value 15 μm or less, a cooling rate of 50° C./sec or more is required on average.

Casting size; In addition, in order to make the average cooling rate 50 ° C / sec or more,
It is necessary that the diameter is 80 mm or less.

If it exceeds φ80+gm, the average cooling rate should be reduced to 50℃/se.
This is because it becomes difficult to achieve a rating of C or higher.

Casting speed is 450mm/win or more, cooling water amount is 30
It is desirable to set it to 1/sin or more.

Homogenization treatment: During forging, the starting point of cracks is mainly crystallized substances. Therefore, the greater the amount of crystallized substances, the lower the forgeability. In the case of the present alloy, when the crystallized material content exceeds 20%, the forgeability is significantly reduced. However, since the crystallized content of this alloy exceeds 20% after casting, it is necessary to infiltrate the product through homogenization treatment. Treatment for 8 hours or more is required. At lower temperatures, it is impossible to reduce the crystallized content of all alloys having the above-defined components to 20% or less.

In addition, the higher the temperature, the faster the crystallized content can be reduced to 20%.
However, in the case of 450°C, more than 8 hours are required.

Furthermore, if the processing temperature exceeds 520° C., eutectic melting occurs and the material deteriorates significantly. Therefore, the homogenization process is 450
-520°C for 8 hours or more.

Softening treatment (sintered pongee): The hardness of the rope material has a large effect on its forgeability. If the hardness is high, the elongation of the material will be small and the forgeability will be significantly reduced. Therefore, the hardness before forging must be as low as possible, and in order to forge a water-based alloy into a VTR cylinder, the Vickers hardness (Hv) must be 55 or less. In order to reduce the hardness, the main hardening components (Cu, Mg, etc.) are dissolved in solid solution.

St) must be precipitated in large amounts in the form of a stable phase,
Usually carried out softening treatment (1 to 35° to 450°C)
Hold for 2 hours, then cool in the furnace to approximately 300'C (approximately 0°C/hr)
) After air cooling or air cooling without furnace cooling), the hardness is Hv≦55.
It is difficult to do so. To achieve this 330~3
It must be maintained at 90"C for at least 2 hours and slowly cooled at an average cooling rate of 20"C/hr or less. Furthermore, since this alloy has a considerable amount of solid solution even at low temperatures, slow cooling must be carried out to 250'C or lower. If slow cooling is stopped at a higher temperature than this, the hardness will significantly increase due to natural age hardening after the softening process is completed. Therefore, in the softening treatment, it is necessary to maintain the temperature at 330 to 390°C for 2 hours or more and slowly cool it to 250°C or less at an average cooling rate of 20°C or less.

After passing through the above steps, the cast material is forged into a predetermined shape for a VTR cylinder, subjected to T6 treatment to increase strength and hardness, and finally finished into a product by cutting.

[Example] The present invention will be explained in more detail by giving examples below.

Example 1 After melting an alloy having the chemical components shown in Coating 1 below, the melt was treated to remove inclusions and degas, and 0.02 ffl and 0.004 wt% of Tt and B were added, respectively. ,
Casting speed 510mm/m1n, average cooling rate 120℃/
It was cast to φ65 in sec. After this cast bar was homogenized at 480° C. for 18 hours, the content of crystallized substances was measured.

Thereafter, as a softening treatment, it was maintained at 380°C for 6 hours, and slowly cooled to 150°C at a cooling rate of 10°C/hr. A forging test was conducted using this softened material. The results are shown in Table 2. In addition, the material after softening is subjected to T6 treatment (500'CX 1
Table 2 also shows the results of examining the wear resistance and hardness.

In the width of the alloys in Table 1, Nos. 1 to 5 are alloys having the chemical composition of the present invention, and Nos. 8 to 8 are comparative materials. No,
Nos. 1 to 5 are excellent in forgeability, wear resistance after T6 treatment, and hardness.

However, No. 6 has a large amount of Cu and Mg1l, so the hardness after softening is high, and furthermore, there are many coarse crystallized substances that become the starting point of forging cracks, and the forgeability is poor.

No. 7 has a large amount of N1Et, so there are many coarse pieces that become the starting point of forging cracks, and the forgeability is poor.

In addition, No. 8 has a small amount of Cu1Mg and Ni, so T
6 Poor hardness and wear resistance after treatment.

In addition, forgeability and wear resistance were evaluated using Haggi's method.

Forgeability: A cylindrical test piece of φ20X L 3hm was subjected to various full compressions at a compression speed of 10mm/+gln while both bottoms were restrained, and the forgeability was evaluated by the deformation rate (critical deformation rate) at which cracks occurred on the sides. did. If the critical deformation rate is 50% or more, forging into a VTR cylinder is fully possible.

Abrasion resistance: Abrasion resistance was evaluated by an ultra-thickness abrasion test. The test conditions were: Friction distance: 200m Friction speed: 2.38m/sec Final load: 2.1)cg Compatible material: 550C (Hv=750) φ30XL3ms+ No lubrication. If the specific wear amount is 8+n/kg or less and the Vickers hardness is 120 or more, the wear resistance and hardness as a VTR cylinder are sufficient.

Table 1 Chemical composition (vt%) of the alloy used in Example 1 Table 2 Various characteristics of Example 4 FlJ2 Cu 4.0% by weight, Mg 1.5ffiffi%, S
i0.3ffi amount%, Ni1. effi amount%, Fe
An aluminum alloy containing 25% by weight of O and the remaining aluminum and impurities is melted and treated as a molten metal to obtain T.
After adding iO,02ffi amount % and B O,004 weight%, casting speed 500817 gin% Average cooling rate 10
It was cast to φ65 am at 0°C/sec.

This ingot was heated at 300 to 510°C for 10 to 10 minutes under the conditions listed in Table 3.
After homogenization for 24 hours, the crystallized material content was measured.

Thereafter, as a softening treatment, it was maintained at 250 to 380°C for 4 to 30 hours, and cooled to 150°C at a cooling rate of 10 to iooo°C/hr. However, no.

Only No. 15 was slowly cooled to 280° C. at 10° C./hr and then air-cooled. Table 3 shows the results of forging tests conducted using the above materials. The hardness after softening in Table 3 is the hardness measured about one month after the softening treatment, when the hardness increases due to natural age hardening and the hardness reaches its peak.

Among the alloys in Table 3, No. 1 to 8 are examples of the present invention, and No.
, 9 to 15 are comparative examples. No, compared to 1-8
, 9. Because the homogenization process for IO is insufficient, there are many coarse products that become the starting point of forging cracks, and the forgeability is poor, resulting in No.
, Nos. 11 to 15 were insufficiently softened, so their hardness before forging was high and their forgeability was poor. In addition, No, T of 1 to 15
The Vickers hardness after the 6 treatments was all 120 or more, and the specific wear amount was all 8.8 g. Note that the evaluation method for forgeability is the same as in Example 1.

Table 3 Characteristics of Example 2 () Shows the cooling rate ("C/hr") up to 150°C, hardness after softening treatment is completed one month after cooling to 260°C,
Air Cooling [Effects of the Invention] As explained above, according to the present invention, it is possible to obtain an aluminum alloy cast rod that has excellent forgeability, wear resistance, and hardness, and is extremely suitable for use in VTR cylinders.

Claims (1)

[Claims] Cu: 3-4.5% by weight, Mg: 0.3-1.8% by weight
, Ni; 0.5 to 2.5% by weight, Si; 0.1 to 0.9
After casting an aluminum alloy containing 0.1 to 0.7 wt% of Fe; the remainder consisting of aluminum and impurities to a diameter of 80 mm or less at an average cooling rate of 50° C./sec or more,
Homogenization treatment at 450-520℃ for 8 hours or more, 330-520℃
A method for producing an aluminum alloy cast bar for a VTR cylinder, which comprises annealing at 390°C for 2 hours or more, and then gradually cooling from that temperature to 250°C or less at an average cooling rate of 20°C/hr or less.