JPS594204B2 - High-temperature isostatic extrusion method for aluminum alloy containing Mg and Cu as alloying elements - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for isostatically extruding an aluminum alloy containing Mg and Cu as alloying elements at high temperatures.

It is well known that aluminum alloys can be extruded by isostatic extrusion, and it is also well known that if the billet is heated to a high temperature and extruded, it can be extruded at a higher extrusion ratio and at a higher speed than conventional methods. In order to achieve good results, a special die shape is required, and an expensive mixture of peace wax and castor oil must be used as the pressure medium.

What is important in high-width isostatic extrusion of aluminum alloys is to prevent the die and billet from seizing even when processed at a high extrusion ratio, since aluminum alloys have a tendency to seize at high temperatures. In addition, a slight break in the lubricant film causes seizure, and as the machining progresses, the seizure grows, resulting in a product with partial seizure scratches.

Conventionally, in high-width isostatic extrusion, if a billet heated to high temperature is placed in a container and extruded using castor oil as a pressure medium, seizure will occur, so chromic acid and fluoride are applied to the surface of the aluminum alloy. Treated with a solution containing (
It is said that seizure can be reduced by applying JP-A-5O-149570), but the surface treatment is complicated and seizure cannot necessarily be prevented even with this treatment.

On the other hand, the inventors have already experienced that it is sufficient to use a multistage die for high-temperature extrusion of an aluminum alloy, and to use a viscoplastic material as the pressure medium.

However, in order to develop high-temperature extrusion technology for aluminum alloy in an even more stable state and without seizure, in 2017
．． After processing an aluminum alloy such as 2024.7075.5056.3003 into a billet shape for extrusion, it is heated at 350°C to 480°C in an oxidizing atmosphere with some 02 gas added.
Interesting results were obtained as a result of conducting high-width isostatic extrusion experiments under heating.

In addition, in aluminum alloys containing Mg and Cu as alloying elements such as 2017.2024.7075, the seizure phenomenon observed on the die surface after extrusion may occur when the billet surface is on the floor of the heating furnace, depending on the heating width. Oxidation was observed in areas that were in contact with the surface and had little oxidation, but no oxidation occurred in most areas where oxidation progressed due to exposure to the atmosphere.

In addition, in the case of materials such as 5056 and 3003 that do not contain Mg and Cu as alloying elements, seizure occurred even if an oxide film was formed.

Therefore, as a result of performing oxidation treatment under various heating conditions in an oxidizing atmosphere and conducting an extrusion experiment, the following was discovered.

1. Mg can prevent seizure by forming an oxide film.
and aluminum alloy containing Cu as an alloying element.

2. Depending on the oxide film, it may not be possible to reliably prevent seizure.

In other words, it depends on the remains of the oxide film attached to the billet surface.

3. The amount of oxide film that adheres to the billet surface is sufficient even when heated in the atmosphere, provided that the extruded material is heated under conditions for homogenization.

By the way, even in conventional extrusion of aluminum alloys, the billet is heated and then extruded, so an oxide film is more or less formed on the billet surface.

However, in direct ram extrusion without lubrication, the cast skin is extruded, so the lubricity of the oxide film on the surface is not a problem, and in indirect ram extrusion without lubrication,
After removing the surface of the homogenized cast billet, it is heated for a short time and subjected to extrusion, so an oxide film is formed, but the amount of oxide film deposited is insufficient.
The lubrication effect has not yet been discussed, and there are no reports that this effect has been recognized.

On the other hand, when performing high-temperature isostatic extrusion of aluminum alloys,
First of all, if you heat the billet to 250-350℃ and extrude it, the product will not crack, and the temperature will be 200-300℃.
It can be extruded at m/min.

This hot water temperature is much lower than the billet heating temperature in conventional direct and indirect non-lubricated extrusion.

Furthermore, if the surface of the billet used for extrusion is cast as it is, the alloy components may segregate, and this cannot be allowed to become the product surface. It is necessary to extrude after deleting.

Therefore, conventional high-temperature isostatic extrusion involves casting billet → homogenization → external machining/cutting, processing to extruded billet → heating →
It is carried out through a process called extrusion.

However, in the conventional process, an oxide film is formed on the billet surface only during heating before extrusion. There are some notes that cannot be done.

This is because the heating temperature of the billet subjected to high-temperature isostatic extrusion is 250 to 350°C, which is lower than other high-width extrusion methods.
The reason for this is that this heating takes place in a relatively short period of time.

Therefore, the inventors decided to pursue a rational process of high-temperature isostatic extrusion in order to generate a sufficient oxide film without complicating the billet processing process.

In other words, the present invention improves lubricity by forming an oxide film on the billet surface, and provides a high-temperature hydrostatic pressure treatment for an aluminum alloy containing Mg and Cu as alloying elements, which can produce a healthy product without seizure. providing an extrusion method;
Furthermore, the purpose of the present invention is to provide a method that can effectively generate an oxide film on the billet surface without complicating the billet treatment process. is for external machining of cast billets.
After cutting and processing into a billet shape for extrusion, the material is heated under homogenization treatment conditions to generate an oxide film on the billet surface at the same time as the homogenization treatment of the extrusion billet, and then the oxide film is removed. It is used as a lubricant by hydrostatic extrusion at high widths.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 1 shows an embodiment of the present invention. In FIG. 1, 1 is a container, and a die 3 supported by a die receiver 2 is fitted into an opening at one end of the container. A stem 4 is slidably fitted into the opening at the other end.

5 is a billet and 6 is a pressure medium.

The effects of the present invention will be easily understood by showing various experimental results using the high-temperature isostatic extrusion apparatus shown in FIG. 1 below.

First, a billet of 2024 aluminum alloy with a diameter of 40 mrIL and a length of 200 mm was heated at 350° C. with a humidity of 4.0° C. using bentonite grease A and bentonite grease B with 9 weight percent polyethylene powder added as pressure media. It was extruded into a 5iiφ product at a stem speed of 20 mm/sec.

After the billet was machined into a predetermined shape, it was placed in a heating furnace at 470°C for 8 hours to form an oxide film on the surface.
On the surface of the billet, three parts were provided where the oxide film was removed over the entire length, and then the billet was heated to extrusion temperature.

The pressure medium is the above two types A and B, and the die is:
The presence or absence of seizure after extrusion was investigated for two types of hot work tool steel with different surface roughness: A hot work tool steel surface roughness l~3μ (Rmax) and B hot work tool steel surface roughness lO~15μ (Rmax).

The results are summarized in Table 1.

Reference photo 1 shows the surface condition of the deformed part of the billet at this time. In reference photo 1, the darkened part shows the part with the oxide film, and the whitish part shows the part where the oxide film has been removed. Reference photo 2 taken from the right side of l (
According to the product (from the product side), it can be seen that seizure has occurred in the area where the oxide film was removed (white area in the photo), and according to reference photo 3, which shows the die approach area at that time. Similarly, you can see that burn-in occurs in areas where the oxide film has been removed (white scratch-like areas in the photo).

The following can be seen from the results in Table 1.

In other words, the surface roughness of the die was changed in the part that was treated with an oxide film (470℃xshr), and even if bentonite grease alone was used as the pressure medium, or bentonite grease with good lubricity and polyethylene powder was used as the pressure medium, seizure did not occur. However, in the part where the oxide film was removed after the oxide film treatment at 470°C x 8 hrs and then heated to 350°C and extruded, when bentonite grease was used, neither die A nor die B1 When 9 wt % polyethylene was added to bentonite grease, seizure occurred in die A and partial seizure occurred in die B.

This difference indicates that lubrication improves when the surface roughness of the die is increased to some extent.

In other words, Table 1 shows that if a billet with a sufficient oxide film is used, extrusion with extremely good lubricity can be achieved, and that heating the billet before extrusion alone is not enough to form an oxide film. confirmed.

Next, after machining the cast billet into the desired shape,
Billets having oxide films of various thicknesses were prepared by heating in the air at various hot water temperatures and times, and the billets were heated and subjected to high-width isostatic extrusion.

A billet made of 2024 aluminum alloy with a diameter of 40 mm and a length of 200 m was used, the die had a hole diameter of 4.5 mm, and bentonite grease was used as the pressure medium.
Wide isostatic extrusion was carried out at a billet heating temperature of 50°C.

The results are shown in Table 2. Furthermore, Table 2 shows the degree of seizure in the Zhengma die approach.

As is clear from Table 2, in the case of 2024 aluminum alloy, it is heated to 470°C or higher in the atmosphere and held for 3
The degree of burn-in becomes 1 to 2 at hrs, and no burn-in is seen at 4 hrs.

Similarly, when heated to 490°C, seizure during extrusion was reduced even if the holding time was short.

It is also effective to treat the billet surface with an oxide film by blowing air or oxygen into the heating furnace to accelerate oxidation.

Although the oxide film is mainly composed of MgO, the formation of the oxide film is promoted in alloys containing Cu, and a good lubrication effect is exhibited.

That is, for 2024 aluminum alloy, 470'C
It was confirmed that extrusion with good lubricity can be achieved by depositing an oxide film under heating conditions of 4 hours.

The inventors conducted similar experiments on 7075.2011, an aluminum alloy containing Mg and Cu as alloying elements.
Good extrusion was achieved when the oxide film was deposited under heating conditions of 520° C. for 4 hours.

However, 5 does not contain Cu as an alloying element.
For 056.5183 aluminum alloy, 520°C, 4
Even if the oxide film was deposited under the above heating conditions, good extrusion was not achieved.

The inventors conducted various experiments as described above on aluminum alloys containing Mg and Cu as alloying elements.
From the obtained results, it was found that the thickness of the oxide film deposited on the billet surface is sufficient if the material is heated under conditions for homogenization treatment.

That is, the homogenization treatment conditions for 2024 aluminum alloy are 470°C for 4 hours, the homogenization treatment conditions for 7075 aluminum alloy are 450°C and 4 hours, and the homogenization treatment conditions for 2011 aluminum alloy are 520°C and 4 hours. However, it was confirmed that a sufficient oxide film could be deposited by heating under these homogenization treatment conditions.

Therefore, the inventors considered attaching an oxide film at the same time as the homogenization process without performing a new heat treatment to generate an oxide film.

However, the conventional high-temperature isostatic extrusion process involves the following steps: casting billet → homogenization → external machining/cutting, billet processing → heating → extrusion. Even if oxide is attached to the billet, it is pointless because the billet will be externally ground and cut in the subsequent process.

Therefore, the inventors devised a method in which a cast billet is externally milled and cut into a billet shape for extrusion, the material is homogenized, and then hydrostatic extrusion is performed using a high strainer.

In other words, casting billet → external machining/cutting, billet processing →
By adopting the process of homogenization → (heating) → isostatic pressure extrusion, high temperature isostatic pressure extrusion can be performed with a sufficient amount of oxide film generated on the billet surface.
Extrusion with extremely good lubrication is now possible, and extremely efficient high-temperature isostatic extrusion can be carried out with no seizure on the die, no product damage, and no additional oxide film deposition process required. It is.

In addition, after applying an oxide film treatment to the billet surface, if a lubricant made by dispersing graphite in a solvent containing a polymeric material is applied, and then heated to an extrusion vorticity and extruded, both the oxide film and the lubricant will be removed. This effect enables more stable high-temperature isostatic extrusion.

[Brief explanation of the drawing]

FIG. 1 is a front cross-sectional view showing an embodiment of the high-temperature isostatic extrusion method for an aluminum alloy containing Mg and Cu as alloying elements according to the present invention, in which 1 is a container, 2 is a die receiver, 3 is a die, and 4 is a 5 indicates a billet, and 6 indicates a pressure medium.

Claims (1)

[Claims] 1. After processing the cast billet into a billet shape for extrusion by externally machining and cutting, by heating the scraped material under homogenization treatment conditions, an oxide film is generated on the billet surface at the same time as the homogenization treatment of the extrusion billet. 1. A method for high-temperature hydrostatic extrusion of an aluminum alloy containing Mg and Cu as alloying elements, the method comprising the steps of: