RU2487776C1 - Method of producing large-size annular semis from wrought aluminium alloys - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention may be used in machine building for producing all-rolled large-size annular semis from wrought aluminium alloys. Casting of produced by spun casting in medium of inert gas. Melt is fed into mould at maximum possible throughput weight of 1-4% a second at casting start and 0.02-0.08% of total casting weight at casting termination. Said throughput weight is gradually decreased inversely as carting time while mould rotation speed is smoothly increased of 0.4-6.0% a minute of initial speed. Casting is subjected to two-stage flattening. At first stage, reduction by 5-10% in every pass at total deformation of 25-30% is performed. At second stage, reduction is increased by 15-20% in every pass at total deformation of 65-70%.

EFFECT: semis with better mechanical low-anisotropy properties.

2 ex, 2 tbl

Description

The invention relates to the processing of metals by pressure and metallurgy of aluminum-based alloys, in particular to methods for the manufacture of ring semi-finished products, and can be used in mechanical engineering to produce solid semi-finished products in the form of large-sized bushings (bandages), i.e. without welds [B21H 1/06].

Currently, ring semi-finished products, for example, with a size of D × d × H = 2500 × 2300 × 160, are obtained from a pressed strip of a certain size, which is rolled into a ring, welded and adjusted. The disadvantages of this method are, first of all, the low strength of the weld, as well as the high complexity, especially in small-scale production.

Also known is the technology for producing ring semi-finished products (bandages) by the ring rolling method from a previously stitched cast ingot. In this case, the ingot is subjected to the following processing: after casting and removal of surface defects, the ingots are cut into billets, which are then heated in an oven. Hot workpieces are upset on the press and a hole is stitched in the center. In the subsequent processing, the hole is opened and the rim is precisely sized in height [VB Bakhtinov, Rolling production, Moscow: Metallurgy, 1987, 416 pp.]. An example of the implementation of this process for producing a ring product from an aluminum alloy ingot is presented in FIG. 2.

The presented technological process for producing a ring product predetermines, in addition to receiving an ingot, its precipitation and flashing, multiple intermediate heating and replanting of a workpiece. These operations contribute to stress relieving and obtaining a fine-grained isotropic structure necessary for subsequent rolling. Based on the foregoing, the process has a high complexity of manufacturing the product, low CMM (material utilization rate), and accordingly, significant cost, as well as repeated heating lead to a decrease in the level of mechanical and structural parameters of the product.

The general principles of centrifugal casting of aluminum alloys are described in the literature [NN Rubtsov. Special types of casting. M .: MASHGIZ, 1955, 331 pp.]. In this way, castings with a diameter of less than 400 mm are made, moreover, thin-walled (wall 10-20 mm), the mass of the alloy does not exceed ≈150 kg. In our case, we are talking about castings weighing 500-1000 kg and an outer diameter of more than 1000 mm, which requires special casting techniques.

Closest to the proposed invention in technical essence is a method of producing a structural material from aluminum-based alloys with a magnesium content of 10-15 wt.% [RU No. 2380453, 2011] consisting in the fact that crystallization occurs in a rotating mold with a gravity coefficient Kg = 180 -250, the melt lifetime is 12-15 sec / kg at a melt cooling rate of ≤5 ° C / sec, then the resulting ingot is heated for 2-4 hours at 340-380 ° C and rolled to 4-8 mm with a degree of deformation of each cycle up to 30%, make a tackle at 310- 330 ° C and cold rolling of the rolled product with a degree of deformation in each cycle of up to 50% with intermediate annealing for 0.5-2.0 hours at 310-390 ° C to a thickness of 0.5-2.0 mm and the final annealing of rolled products at 410-450 ° C for 5-40 minutes. The common between the prototype and our proposal is only in the very principle of using a rotating mold (i.e. centrifugal casting). The prototype is about rolling the sheet, and in our case, about a completely different process - about rolling the ring blank with its own parameters.

The term "melt lifetime" does not exist in the theory and practice of casting. But one can guess that this refers to the time the melt was in the liquid state before crystallization began. The inventors of the prototype mistakenly assume that their casting modes allow volumetric crystallization of the alloy, hence the low cooling rate of ≤5 ° C / s. The low cooling rate leads to a coarse-grained structure of the casting - this is a common position, and the pressure arising in the melt, as a result of centrifugal forces, compacts the casting, but does not affect the grain. Simple calculations show that bulk crystallization (i.e., without diffusion) can take place at enormous pressures in the melt — more than 50 atm., Which exceeds the tensile strength of the mold material. But the main thing is that with an increase in pressure (i.e., with an increase in the mold rotation speed), segregation processes develop rapidly, when a more dense than aluminum, alloying metal or crystallizing intermetallic phase moves radially on the outer surface, the phenomenon of reverse segregation occurs, when fusible eutectic along the channels between the solidified crystals of α solid solution moves from the center to the periphery.

An object of the invention is to provide a method for producing large-sized ring semi-finished products from wrought aluminum alloys with improved mechanical characteristics, low anisotropy of properties and minimal gas saturation.

The invention is illustrated by drawings.

Figure 1 shows an example of an installation for implementing the method, where 1 is a resistance furnace, 2 is an airtight melter, 3 is a loading hatch, 4 is a metal pipe inlet pipe, 5 is a sealing seal, 6 is a liquid shutter made of metal, 7 is a sealing electrical insulating seal 8 - sealed chamber, 9 - removable cover, 13 - round table, 10 - ribbed flange, 11 - cylindrical casting mold with cover - 12, 14 - metering cup, 15 - attached shaft, 16 - electric motor, 17 - V-belt drive .

Figure 2 shows the scheme of precipitation, running, replanting with firmware, where a) sediment, b) running to the fingerprint, c) replanting, d) firmware, where 18 is the outer diameter of the casting, 19 is the height of the casting, 20 is the inner diameter of the casting .

Figure 3 shows the acceleration circuit.

To achieve this goal, a method for producing large-sized ring semi-finished products (bandage) from wrought aluminum alloys is proposed, including casting, deformation processing and annealing operations, characterized in that the casting is obtained by centrifugal casting in an inert gas medium, and the melt is fed into the mold with the maximum possible second flow rate equal to 1-4% per second at the beginning of casting and 0.02-0.08% per second at the end of casting of the total mass of the casting with a gradual decrease in flow rate is inversely proportional to the time l ita, and the mold rotation speed is gradually increased by 0.4-6.0% per minute from the initial speed; moreover, the casting is subjected to a two-stage rolling during compression of 5-10% at each revolution (passage) and a total deformation of 25-30% at the first stage and during compression 15-20% at each revolution (passage) and a total deformation of 65-70% at the second stage .

The method can be implemented, for example, based on the following device.

The device (see Figure 1) contains the following equipment: a melting furnace 1 with a hermetic fuse 2, in the lid of which there is a loading hatch 3 and a metal conduit entry pipe 4 (titanium alloy pipe). An electrically heated metal conduit made in the form of a siphon, one end of which is immersed in a liquid seal from a molten metal 6 through a sealing seal 5, and the other end is inserted into a sealed chamber 8 of a centrifugal injection machine through a removable cover 9 through a sealing electrically insulating seal 7. a table 13 on which a casting cylindrical mold 11 with a lid 12 is mounted. At the bottom of the mold, coaxially with the dispenser glass, a distribution finned flange 10 is attached, Niemann cast metal shot stream. A metering cup 14 is rigidly attached to the mold cover on top or on the cover of the sealed chamber from below coaxially with the mold and the metal wire.

The dispenser glass is a heated crucible, designed for a volume of 25-50 kg of melt, having a sock for draining the metal and an adjusting locking device with a slide type shutter. The stopper has three positions: “closed”, “open” (start of casting), “partially open” (during casting).

The round table with the help of a rigidly attached shaft 15 is driven into rotation by an electric motor 16 through a V-belt drive 17.

The heating of the metal wire 4 and the dispenser cup 14 is carried out from an external source of electrical power.

Installation works as follows.

In the cooler 2, after loading the initial product, the manhole cover 3 closes and an inert atmosphere is created in the installation by successive evacuation to a residual pressure of 0.5 mm Hg. and filling with inert gas to an overpressure of 0.05 atm.

When the temperature of the metal in the furnace reaches the melting temperature, an inert gas is supplied to the melting furnace, which through a siphon barbs through the melt, thereby mixing it.

The metal wire and the metering cup are preheated to a temperature that is 10-50 ° C higher than the melting temperature of the metal.

Then, when the temperature of the metal in the furnace is 5-20 ° C higher than the melting temperature of the metal, by creating a pressure of 0.3-0.7 atm in the smelter, the melt is fed through a metal wire 4 to the sealed chamber of a centrifugal injection machine.

The molten metal through a metal wire enters the dispenser glass and fills its volume to a fixed level, while the stopper of the dispenser glass is in the “Closed” position and accordingly the slide gate is closed. After filling the dispenser glass with metal, the stopper position is set to the “Open” position as a result of which the slide gate opens and the melt through the nose of the dispenser glass enters the rotating mold on the ribbed flange, thereby starting the centrifugal casting process. The melt falling onto the rotating ribbed flange by centrifugal forces is pressed onto the side wall of the mold, gradually filling its volume to the center. Then, after 1-3 seconds, the stopper is moved to the “Partially open” position, the slide gate partially overlaps the toe of the dispenser glass, providing a further uniform flow of the melt into the rotating mold. The rotational speed of the mold during centrifugal casting is 500-2500 rpm. After casting is complete, the process is stopped by venting the inert gas overpressure in the smelter.

The mold rotates until the melt solidifies completely, which is carried out by cooling the heat transfer to the mold wall, occurring on the outer surface and along the ends of the casting (after the formation of the shrinkage gap between the casting and the mold, the contact transfer from these surfaces is partially replaced by heat radiation), as well as by neutral convection gas from the side of the free surface of the casting. After cooling the annular blank, the rotation of the mold stops, the lid of the sealed chamber with the dispenser glass opens, then the mold cover opens. Further, using a special grip on the inner surface, the annular workpiece is removed.

The melting furnace is cooled until the liquid shutter crystallizes, the hatch opens, a new loading of the source metal is performed, and after the inert atmosphere is created in the smelter and the metal is heated, a repeated casting cycle of the ring blanks is performed.

In the present invention, examples are given in relation to alloys of the industrial group AMg (4-7% Mg). To obtain a finely dispersed structure (grain), it is proposed to increase the cooling rate of the alloy by feeding it directly to the cold internal metal (steel, cast iron, copper) surface of the mold and creating still vortex movement of the neutral gas in the mold.

But when a small amount of melt is fed onto the cold surface of the mold, it can “smear” and instant crystallization occurs. Subsequent layers are not welded to the previous ones - neslitins appear, as a result, it is necessary to significantly increase machining allowances. Therefore, at the first moment, it is necessary to apply the melt to the mold with the maximum possible speed in the amount of 1-4% of the weight of the casting, which will make it possible to form an alloy layer of 6-12 mm without neslitins and which can be reliably welded to the previous melt layers. To maintain the stability of the conditions of formation of the structure of the layers, we gradually reduce the casting speed, because the radius of the solidified casting is reduced, and a smaller melt volume is required to form a constant layer thickness. This technique allows you to reduce the level of variegation of the casting. Since the pressure in the liquid part of the casting continuously decreases (from maximum on the outer radius to minimum on the inner), accordingly, the speed of rotation of the mold (mold) is proportionally increased.

Example 1. For casting from an aluminum wrought alloy AMg6 with a size of D × d × H = 1000 × 500 × 200 mm and a mass of 300 kg, from the graphs known in the literature, we find the initial rotation speed n = 400 rpm.

- initial metal consumption (2% / s): $$\frac{2\cdot 350}{\mathrm{one\; hundred}}=7\frac{\mathrm{to}g}{\mathrm{from}}$$

- by the end of casting (0.2% / s)

$$\frac{0.2\cdot 350}{\mathrm{one\; hundred}}=0.7\frac{\mathrm{to}g}{\mathrm{from}}$$

- determine the solidification time of the casting 10.3 minutes

- smoothly increase the rotation speed by 5% of the initial $$\frac{5\cdot 400}{\mathrm{one\; hundred}}=\mathrm{twenty}\frac{\mathrm{about}b}{m\mathrm{and}n}$$

- by the end of casting, the speed is: 400 + 20 · 10.3 = 606 rpm

It is not recommended to increase the speed above 12% due to the noticeable development of segregation processes. With a kind of “acceleration” of 12% / min at the end of casting, we have $$n=400+\frac{12\cdot 400}{\mathrm{one\; hundred}}\cdot 10.3=894\frac{\mathrm{about}b}{m\mathrm{and}n}$$

The ring casting obtained by centrifugal casting is homogenized, grinded and subjected to distillation and replanting at a temperature based on the optimal ductility of the alloy. This operation is due to the need for additional grinding of the grain and obtain a homogeneous structure. In the next step, if necessary, depending on the alloy, annealing is performed to remove hardening. Then, the workpiece is subjected to two-stage rolling at the RPM (rolling mill) at a temperature of optimal ductility and compression of 5-10% at each revolution (pass) and a total deformation of 15-25% at the first stage and during compression 15-20% at each revolution (pass ) and a total strain of 65-70% in the second stage. Cast, homogenized, and even more so deformed structure of most aluminum alloys allows high compression. Large reductions reduce the unevenness of deformation, contribute to the production of hot-rolled strips with a uniform structure and stable properties, provide high performance. However, in the first passes, due to the possibility of cracks on the lateral edges due to intensive broadening, it is recommended to prescribe small reductions - within 5-10%. In the future, the reduction is uniformly increased, bringing to 15-20% with a total degree of deformation of 50-60% or more.

Example 2. The rolling route of the ring semi-finished product from a casting obtained by centrifugal casting of an AMg6 alloy, dimensions D × d × H = 1000 × 500 × 200 mm, Table 1. The condition of the casting is homogenized, turned.

Table 1. Amg6 aluminum alloy ring prefabricated rolling route №№ The list of technological operations The wall thickness of the ring in the aisles, mm one Acceleration, replanting at 250-200 temperature 360-380 ° C. Total strain 20% 2 Heating to a temperature of 420-440 ° C, holding time for at least 4 hours. - 3 Roll-out 1 on the RPS at a temperature of 380-420 ° C in step mode 200.0-184.0-165.6-149.0
Passages 8-10-10%
Total strain 25.5% four Rolling 2 on the RPS with 149.0-128.5-102.0 temperature 380-420 ° C in Passages 14-20% stepped mode Total deformation 68% 5 Annealing at a temperature of 310-335 ° C, holding for 30 minutes. -

The results of structural studies and mechanical properties are presented in Table 2

Table 2. Mechanical properties of specimens from rolled rings of an aluminum alloy AMg6 (after annealing) Sample No. Sample cut point Tensile strength, MPa Yield Strength, MPa Relative extension, % one shared 371 213 10.7 2 shared 378 202 10.7 3 transverse 354 201 11.7 four transverse 352 194 11.0

Analysis of the gas saturation of the rolling rings showed a minimum gas content in the structure. An analysis of the microstructure of the rings revealed a uniform distribution of intermetallic phases in the structure of the solid solution, as well as the absence of oxidized crystallization centers.

Thus, the present invention allows to reduce the number of operations during rolling due to the production of castings with a finely dispersed structure (grain) and to increase the CMM due to the production of ring billets by centrifugal casting according to specified modes. The proposed rolling modes make it possible to obtain ring products from aluminum alloys with improved mechanical properties and low anisotropy of properties. The process does not require constructive changes to traditional equipment, and also allows you to reduce power parameters.

Claims (1)

A method for producing large-sized ring semi-finished products from wrought aluminum alloys, including casting, deformation processing and annealing operations, characterized in that the casting is produced by centrifugal casting in an inert gas medium, and the melt is fed into the mold with a maximum possible second flow rate of 1-4% in second at the beginning of casting and 0.02-0.08% per second at the end of casting of the total mass of the casting with a gradual decrease in consumption is inversely proportional to the casting time, and the mold rotation speed is gradually increasing t at 0.4-6.0% per minute from the initial speed, and the deformation processing is carried out by two-stage rolling of the casting during compression of 5-10% at each pass and the total deformation of 25-30% in the first stage and during compression of 15-20% at each pass and the total deformation of 65-70% in the second stage.

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