JPH07115132B2 - Casting method of Al-Mg alloy with twin rolls - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention arranges a pair of rolls at an appropriate interval and supplies an Al-Mg alloy melt between the rolls to form an Al-Mg alloy plate. The present invention relates to a casting method of an Al-Mg alloy by twin rolls for casting.

[Prior Art] It is a well-known technique to cast an aluminum or aluminum alloy sheet by a twin-roll type casting machine, then roll it to a predetermined thickness and use it for the intended purpose. The casting roll of this twin roll type casting machine has a core part through which cooling water flows, and a shell part with which molten aluminum or aluminum alloy directly contacts. The pair of casting rolls are arranged so as to face each other with an appropriate length interval,
The molten metal is injected between the two water-cooled rolls through a nozzle, and is cooled and solidified. Then, the slab obtained by solidifying the molten metal is further slightly rolled by a roll to form a so-called cast plate.

When casting a thick ingot with a continuous casting machine, a mold release agent (lubricant) such as rapeseed oil is usually applied to the wall surface of the mold in order to improve the peelability between the mold and the solidified aluminum and to perform the casting smoothly. Apply. Even when casting with a twin roll type casting machine, conventionally, a lubricant is used as in a continuous casting machine, but as this lubricant, a suspension of graphite powder or magnesia powder dissolved in water is used. The lubricant was applied to the peripheral surface of the roll by spraying this suspension on the roll.

[Problems to be Solved by the Invention] However, in this prior art, since the lubricant is a suspension, it tends to settle in a place where the flow velocity is slow, so the concentration at the time of spray injection to the roll is not constant. However, it has a drawback that the lubricant concentration changes with time.

Further, the amount of the spray spray applied is not constant depending on the part of the roll, and there is local variation.

Further, the lubricant on the peripheral surface of the roll is removed by the contact with the cast plate, but the amount of the removed lubricant varies depending on the part of the roll.

Due to these factors, the amount of lubricant becomes non-uniform on the peripheral surface of the roll, and as a result, uneven cooling occurs locally and surface defects (solidification defects) of the cast plate tend to occur.

Further, such surface defects occur remarkably in an alloy having a wide solidification temperature range, such as an Al-Mg alloy having a high Mg content.

The present invention has been made in view of such problems,
To provide a method for casting an Al-Mg alloy by twin rolls capable of reliably preventing surface defects caused by non-uniform lubrication even in a high Mg content Al-Mg alloy where surface defects are likely to occur. To aim.

[Means for Solving the Problem] The method for casting an Al-Mg alloy by twin rolls according to the present invention is
A pair of rolls with a shell thickness of 35 to 60 mm are arranged at an appropriate interval, and A with a Mg content of 3.5 wt% or more is placed between the rolls.
l-Mg alloy melt is supplied, and the melt is cooled by a roll without applying a lubricant to the peripheral surface of the roll to cool the Al-Mg alloy.
It is characterized by casting an alloy plate.

[Operation] In the present invention, an Al-Mg alloy is cast based on the completely new idea of casting a molten metal without applying a lubricant to the roll peripheral surface. Therefore, since there is no lubrication, the surface defects of the cast plate due to uneven cooling caused by applying the conventional suspension of the lubricant can be eliminated.

On the other hand, the mold releasability between the cast plate and the roll shell is that the Mg content of the molten metal is 3.5% by weight or more and an oxide film is formed on the surface of the cast body regardless of the conventional lubricant. It is secured by. Further, since the shell thickness is set to 35 to 60 mm to increase the cooling rate of the molten metal, instantaneous volume shrinkage also contributes to the improvement of the mold releasability.

[Examples] Hereinafter, examples of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a molten metal injection part of a twin roll type casting apparatus showing a method of an embodiment of the present invention.

The pair of rolls 1 and 2 are arranged so that their axial directions are parallel to each other and are vertically opposed to each other with an appropriate length interval. The rolls 1 and 2 have a cylindrical shape with a constant shell thickness t,
A cooling member 3 through which cooling water flows is fixed to its inner peripheral surface. By flowing the cooling water through the cooling member 3, the shells of the rolls 1 and 2 are cooled.

The rolls 1 and 2 are driven to rotate in the direction of the arrow.
A cylindrical nozzle 4 is arranged at a position upstream of the rotational direction of 1 and 2. The nozzle 4 is connected to a molten metal supply source such as a molten metal ladle, and a molten aluminum alloy 5 is injected into the gap between the rolls 1 and 2 through the nozzle 4.

The molten metal 5 is cooled by the rolls 1 and 2 and solidified to obtain a cast plate 7. A solid-liquid coexisting phase 6 exists between the molten metal 5 and the rolls 1, 2 or the cast plate 7.

Conventionally, in such a twin roll type casting machine,
In order to secure the mold releasability between the shells 1 and 2 and the cast plate 7, the lubricant of the suspension was spray-coated on the outer peripheral surfaces of the shells of the rolls 1 and 2.

However, in the method of the present invention, Al-
It is characterized by casting a molten Mg alloy.

Since unevenness of cooling (heat transfer) occurs due to uneven application of lubricant, in order to prevent the surface defects of the cast plate by making cooling uniform, naturally, a method for even application is considered. It is common sense that the inventors of the present application initially conducted experimental research in that direction. However, when the Mg content is high, it was not possible to prevent coating unevenness and eliminate surface defects due to this coating unevenness by any method.

Therefore, the inventors of the present application omitted the step of applying the lubricant itself, that is, aiming at a method of casting without lubrication, which has not been studied at all in the past, and as a result of various experimental studies,
The present invention has been completed.

The purpose of lubrication is, as described above, the mold release between the cast plate and the roll shell, and if the mold releasability is poor, defects such as sticking occur. This poor sticking means
It is a defect in which the cast plate adheres to the roll and the cast body remains adhered to the peripheral surface of the roll for a while even after passing through the roll outlet. The surface gloss is completely different in the portion where the sticking failure occurs, the matte surface becomes defective, and the plate shape is disturbed.

For this reason, it is necessary to secure the releasability by another method when the lubricant is not used. As a result of conducting various experimental studies on mold releasing means other than the mold releasing using such a lubricant, the inventors of the present application, if the cooling rate of the molten metal is sufficiently high, in the case of an alloy having a sufficiently high Mg content, It was clarified that it can be cast without lubrication. This is because when the Mg content is high, an oxide film is easily formed on the surface of the cast plate 7, and the oxide film has some releasability. Also,
This is because if the cooling rate is sufficiently high, the mold releasability is enhanced together with the formation of the oxide film due to the instantaneous volume contraction when the molten metal is cooled and solidified.

As described above, in order to sufficiently bring out the effect of improving the releasability by the oxide film, it is necessary to contain 3.5% by weight or more of Mg in the molten metal, and when this Mg content is less than 3.5% by weight. Has a poor releasability and causes significant sticking failure without a lubricant. In order to achieve the object of the present invention, it is not necessary to set an upper limit on the Mg content, but it is desirable that the Mg content be 5.5% by weight or less from the viewpoint of the flow of molten metal.

Further, in order to increase the cooling rate and improve the mold releasability by volume contraction, it is necessary to make the shell thickness of the casting roll 35 mm or more. When the thickness of the shell is less than 35 mm, when the molten metal comes into contact with the shell of the roll to start solidification, the steam between the shell and the cooling water becomes an adiabatic state, and the cooling capacity of the shell is significantly reduced. . Further, if the shell thickness exceeds 60 mm, the cooling effect of the cooling water in the roll on the surface of the roll becomes small, and the shell surface cannot be cooled in just one rotation of the roll. Therefore, the shell thickness is set to 60 mm or less. That is, the cooling capacity of the molten aluminum alloy due to the heat capacity of the roll shell is
Very high in the 60 mm range, it is necessary to make the roll shell a thickness within this range. In order to further enhance the cooling ability of the roll shell, it is desirable to set the shell thickness to a narrow range of 40 to 55 mm.

Thus, the composition of the molten metal 5 of the Al-Mg alloy contains 3.5% by weight or more of Mg, whereby an oxide film is formed on the surface of the Al alloy cast plate 7 and Despite not applying a lubricant to the outer peripheral surface of the shell, the casting plate 7
Is released without adhering to the outer peripheral surfaces of the shells of rolls 1 and 2. Further, since the shell thickness is 35 to 60 mm, the heat capacity of the roll shell is optimized in terms of cooling efficiency, and the molten metal is cooled at a high cooling rate. Therefore, the cast plate 7 quickly contracts in volume and separates from the roll shell.

Due to these effects, in the method of the present embodiment, excellent releasability is secured in spite of no lubrication. Also,
Since no lubricant is used, the uneven cooling caused by the uneven coating is eliminated, and the surface defects of the cast plate are prevented.

Next, the result of producing an Al-Mg alloy by the method of the embodiment of the present invention will be described together with a comparative example.

Example 1 A heat-resistant steel casting roll having a roll diameter of about 900 mm and a shell thickness of 55 mm was used. The thickness was 7 mm, and the Mg content was 2.5% by weight, 4% by weight, and 5% by weight. An Al-Mg alloy plate was cast. The casting conditions are a roll peripheral speed of 100 cm / min, a casting temperature of 700 ° C., a roll cooling water temperature of 30 ° C., and a roll cooling water flow rate of 300 l / min. As a result, the relationship between the surface quality of the manufactured cast plate, the Mg content, and the presence or absence of lubrication was as shown in Table 1 below.

Also, the lubrication condition with lubrication is 1% of graphite.
The suspension was spray-injected onto the roll surface at a flow rate of 0.3 l / min per roll.

Further, the stain defect is a segregation of 1 to 5 cm length extending in the casting direction, and in the case of being remarkable, it becomes a crack. Blemish defects are formed because the solidification of this part is slower than the surroundings.

As is clear from Table 1, in the case of the present example in which the Mg content was 4% by weight or 5% by weight and no lubrication was performed,
Excellent surface quality without defects was obtained.

Example 2 Roll diameter is about 900 mm, shell thickness is 25 mm, 45 mm, 55 mm and 7
An AA5182 alloy plate (containing 4.8% Mg) was cast to a thickness of 7 mm by using four types of casting rolls of 0 mm. The casting conditions are a roll peripheral speed of 120 cm / min, a casting temperature of 700 ° C., a roll cooling water temperature of 30 ° C., and a cooling water flow rate of 300 l / min. No lubricant was used.

Table 2 below shows the relationship between the surface quality and the shell thickness of the cast plate manufactured as described above.

As is clear from Table 2, the shell thickness is 45mm or 55mm.
In the case of this example of mm, excellent surface quality without defects was obtained.

[Effects of the Invention] As described above, according to the present invention, the shell thickness is 35 to
Since the molten aluminum alloy containing 60% of Mg and 3.5% by weight or more of Mg is cast, it is possible to perform unlubricated twin-roll casting, which has never been considered before, and to produce a cast plate with excellent surface quality. can do.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an injection part of a twin roll type casting apparatus showing a method of an embodiment of the present invention. 1,2; roll, 4; nozzle, 5; molten metal, 7; casting plate

Claims (1)

[Claims] 1. A pair of rolls having a shell thickness of 35 to 60 mm are arranged at appropriate intervals, and the Mg content is 3.5 between the rolls.
An Al-Mg alloy melt is supplied at a weight% or more, and the molten metal is cooled by a roll without applying a lubricant to the peripheral surface of the roll to cast an Al-Mg alloy plate. -Mg alloy casting method.