RU2277992C2 - Fine-grain structure blank producing method - Google Patents

Abstract

FIELD: plastic working of metals and alloys, possibly making blanks and semi-finished products with normalized physical and mechanical properties.

SUBSTANCE: method comprises steps of subjecting blank to plastic deforming at preset thermal and mechanical conditions by extruding with use of apparatus having container, punches and shaping tool with cavity arranged in duct of container. Shaping tool provides directed flow of blank metal for creating zone of intensified plastic deformation. Before feeding blank to said zone, volume-stress condition of all-round compression is provided in it. Such compression is created due to punch action and end pushing through bulk of powder material that fills cavity of shaping tool. At creating intensified plastic deformation tool or its part is driven to rotation.

EFFECT: enhanced quality of blanks, enlarged assortment of blanks due to lowered friction and efforts acting upon tool.

9 cl, 5 dwg, 1 ex

Description

The invention relates to the field of processing of metals and alloys by pressure and can be used to obtain blanks and semi-finished products with regulated physical and mechanical properties, including due to the formation of a fine-grained structure in them. The method is intended for processing lengthy workpieces and semi-finished products in the form of rods, rods, etc.

It is known that many physical and mechanical properties, for example, strength and ductility, depend on the structure of materials. Therefore, with a change in the structural state occurring as a result of plastic deformation of the material, they also change. In particular, the formation of a cellular or subgrain structure in it usually leads to hardening of the material. Most significantly, the physicomechanical properties of materials change as a result of grinding the grains to a fine-grained state (to microcrystalline sizes of 10 microns or less). Such materials at low temperatures have significantly higher strength characteristics than conventional coarse-grained materials, and at elevated temperatures they have a low flow stress and high ductility or superplasticity (SP). However, for the formation of a microcrystalline structure of less than 1 μm, a more radical deformation processing of the material (pumping of large degrees of deformation) is required than for any other fragmented structure, for example, subgrain.

Various methods are used to achieve large deformations of the material: torsion under quasi-hydrostatic pressure (Bridgman anvils), equal channel angular pressing (ECC pressing), rolling, all-round forging, fractional deformation, etc. Their essence lies in repeated intensive plastic deformation (IPD) of the shear of the processed materials, while the true logarithmic degree of deformation is e≥4-7. The use of SPD allows, along with a decrease in the average grain size, to produce massive samples with an almost pore-free material structure, which cannot be achieved by compaction of highly dispersed powders. The main laws of the formation of the microstructure during SPD are determined by a combination of the parameters of the initial structural state of the material and the specific conditions of deformation, as well as the mechanics of the deformation process. Other things being equal, the main role in the formation of the structure and properties of the material belongs to the mechanics of the deformation process: if it ensures uniformity of the stressed and deformed state over the entire volume of the material, then deformation is most effective [Gusev AI Nanocrystalline materials: production methods and properties. Yekaterinburg: Ural Branch of the Russian Academy of Sciences, 1998].

Experimental studies indicate that for metals and alloys, a gradual decrease in the deformation temperature contributes to a decrease in grain size. To obtain a submicrocrystalline (SMC) and nanocrystalline (NC) structure in technically pure metals, the deformation temperature should not exceed (0.25-0.3) the melting temperature. For alloys, the required temperature depends on its chemical and phase composition and is usually (0.5-0.6) the melting temperature. In addition, it is noted that with decreasing grain size, as well as increasing the degree of deformation, the temperature leading to their growth decreases . Therefore, taking these factors into account, in general, for all materials, deformation at a temperature below the temperature of collective recrystallization means conditions under which there is no growth of small grains formed as a result of the previous deformation. Compression and torsion deformation, carried out at a temperature below the temperature of collective recrystallization, provides SMC and NC structures after large plastic deformations (e≥4-7) of the workpiece material.

Known methods of deformation processing of workpiece materials, such as equal-channel angular pressing (ECG-pressing) [RF Patent No. 2146571, IPC B 21 C 25/00, 03/20/2000], where when passing the material through the second channel carry out its additional deformation with changing the cross section of the workpiece, and the removal of the latter is carried out when releasing its ends. Also known is a method of processing axisymmetric blanks by torsion [RF Patent No. 2021064, IPC B 21 J 5/00, 10/15/1994], where the processing of blanks is carried out in a composite container. During processing, the workpiece is moved in the axial direction until each section crosses in height at least once through the junction plane of the container parts to obtain regulated physical and mechanical properties in the workpieces, including by obtaining a microcrystalline structure in them. These methods make it possible to obtain only small-sized fine-grained semi-finished products with a homogeneous structure and are characterized by high complexity, energy intensity and duration of the process.

A known method of producing preforms with a fine-grained structure and specified physical and mechanical properties [RF Patent No. 2116155, IPC B 21 J 5/00, 07/27/1998], where the workpiece is deformed by repeated reduction and subsequent increase in its cross section, respectively, by extrusion and sediment container. This method allows to obtain small in size rods from materials with enhanced physical and mechanical properties and is characterized by high labor intensity, low quality.

Closest to the proposed invention is a method for producing blanks with a fine-grained structure [RF Patent No. 2191652, IPC B 21 J 5/00, 04/04/2001]. This method involves the plastic deformation of billets of metals and alloys under predetermined thermomechanical conditions, where the plastic deformation of the billet is carried out by pressing in a pressing container through a profiling tool installed in its pressing channel, which guides the metal flow and creates a combined scheme of intense plastic torsion-upset-shear without violation of the integrity of the workpiece.

The processing of workpieces according to this prototype method provides a relatively better study of the structure, but requires a sufficiently large energy consumption to overcome the friction forces in the container and on the contact surfaces of the tool with the workpiece. Therefore, this method is practically difficult to use to obtain large-sized fine-grained semi-finished products, in particular, long meters of several meters long rods with a diameter of ≥150-200 mm from hardly deformed alloys. In this case, presses of enormous power, developing efforts of several tens of thousands of tons, as well as the corresponding expensive tool from superhigh-strength materials will be required.

The objective of the invention is to improve the quality and expand the range of workpieces both in size and in materials by reducing friction and efforts on the tool in the process of forming a homogeneous microcrystalline structure in them.

The problem is solved by the method of producing workpieces with a fine-grained structure, including plastic deformation of the workpiece under specified thermomechanical conditions by pressing in a tool having a container, punches and a profiling tool located in the channel of the container with a cavity that provides the direction of flow of the workpiece metal and forms an area of intense plastic deformation. In contrast to the prototype, before entering the workpiece into the zone of intense plastic deformation, it creates a volume-stress state of comprehensive compression by acting on the side of the tool and the supporting volume of the powder material filling the complex cavity of the profiling tool, and intensive plastic deformation is additionally provided by rotating a part or complex of the tool.

When implementing the method used techniques that expand its technological capabilities:

- the volume-stress state of the comprehensive compression of the workpiece is created by the reciprocal movement of two punches with simultaneous rotation with the possibility of reversing at least one of them;

- the rotation of the tool is carried out with reversal;

- upon receipt of preforms from low-plastic hardly deformed alloys before creating intense plastic deformation, asymmetric flow of the preform material through the profiling tool is provided;

- after deformation of the workpiece by pressing, it is formed using an additional matrix that creates back pressure when the workpiece is deformed and has the possibility of rotation;

- deformation of the workpiece by pressing is carried out in conditions of superplasticity;

- deformation of the workpiece by pressing is carried out in isothermal conditions;

- the process of deformation of the workpiece by pressing is carried out with decreasing temperature after each technological transition;

- graphite, or aluminum powder, or titanium nitride is used as the powder material.

The main significant difference of the proposed method is the creation before the IPD in the workpiece material of the body-stress state of comprehensive compression for the realization and accumulation of large deformations in the material, providing gradual grinding of the microstructure to the SMC and NK states without breaking continuity, which in known methods is possible only with the use of high-energy plants and long technological processes with a large number of transitions. In addition, the combinations of various processing schemes proposed in the method also make it possible to increase the efficiency of the process due to a significant reduction in friction and uniform study of the structure over the cross section of the workpiece. The fine-grained structure thus formed makes it possible to further reduce the processing temperature, making it possible to further refine the material structure. Moreover, the proposed method allows you to choose various optimal combinations of processing depending on the type of workpiece material.

Thus, the proposed combination of essential features provides a new non-obvious effect and determines the compliance of the invention with the criterion of "inventive step".

The method is illustrated by the following illustrations:

figure 1 - diagram of the processing of the workpiece by pressing using various combinations of deformation: heating and / or cooling, with rotation or reversal of the part or complex of the tool;

figure 2 - scheme of processing a workpiece with an asymmetric flow of material;

figure 3 - diagram of the processing of the workpiece by pressing using various combinations of deformation: heating and / or cooling with rotation or reversal of the part or complex of the tool using an additional matrix;

figure 4 - appearance of the workpiece from aluminum alloy:

a) processed in a non-optimal mode,

b) processed according to the optimal mode,

c) processed using an additional matrix;

5 is a microstructure of samples before and after processing by the proposed method.

The device for implementing the method (Fig. 1) consists of an upper container 1 with a blank 2 placed in it, which is supported on top by a punch 3, and on the bottom by a profiling tool 4 through the volume of powder material filling the cavity 5 of the profiling tool to the lower punch 6, which is placed into the lower container 7. The upper and lower containers, as well as the profiling tool, can rotate relative to each other in different directions, heat and / or cool, in various combinations.

A device for implementing a method with an asymmetric flow of material for the initial processing of low-plastic materials (Fig. 2) using various combinations of deformation and heating and / or cooling consists of an upper container 1 with a blank 2 placed in it, which is propped up by a punch 3 and from below - asymmetric profiling tool 4 through the volume of powder material filling the cavity 5 of the profiling tool to the lower punch 6, which is placed in the lower container 7. Asymmetry to the profile In this case, the tool 4 is provided by the presence of an insert 8. The upper and lower containers, as well as the profiling tool, can be rotated relative to each other in different directions, heated and cooled in various combinations.

A device for implementing the method using at the last stage of the processing of additional shaping (figure 3) contains an additional matrix 9, providing the workpiece counter-pressure with the possibility of rotation.

Examples of specific performance.

To verify the reliability of the proposed method for producing billets with a fine-grained structure and optimize the modes, a model installation of 5XHM alloy was made. A blank 2 in the form of a rod of aluminum alloy D16 or Al-Mg-Zr or a copper alloy M1 with a diameter of 20 mm and L = 100 mm was installed in the upper container (Fig. 1), and the lower punch 6 was pre-installed in the lower container 7. 5 profiling tools were filled with a powder material (flake graphite), which at the same time served as a lubricant, a support between the lower punch and the workpiece. The filling volume was selected so that when creating a preliminary volume-stress state in the workpiece material by compressing it, the lower end of the workpiece would not fall into the area of the profiling tool. Compression of the preform to a stress close to the yield stress σ _t was provided by the movement of the upper punch 3, the lower punch 6 was supported by the ejector hydraulic cylinder, and subsequently, by relieving the pressure, they provided the necessary support. The container with the billet was heated at a temperature of 50-100 ° С below the recrystallization temperature of the D16 alloy (for Al – Mg – Zr, respectively). When most of the workpiece was in the upper container, the upper punch 3 and the container 1 were rotated in opposite directions. In this case, a decrease in the deformation force by 20-30% was observed. The assembled tool design was turned over 180 ° each time during processing on a hydraulic press table to repeat the experiment. A decrease in temperature at each transition by 20-50 ° C ensured the most efficient grinding of the microstructure over the entire cross section of the workpiece to obtain the necessary structure.

Pressing experiments were carried out on aluminum and copper samples at various speeds and temperatures. Relatively optimal speeds were selected for aluminum and copper alloys from the point of view of ensuring the continuity of the workpiece and maximum grinding of the microstructure. Also, experiments were conducted where, at the last stage of processing, an additional matrix was used as a backpressure (while changing only the diameter of the additional matrix). For relatively low-plastic materials (type D20), the pressing scheme according to Fig. 2 was used, with an asymmetric material flow at the first processing stage, which is similar to ECG pressing with back pressure.

After each pressing option, a quantitative and qualitative analysis of the structure of the deformed material over the entire cross section of the preform was performed (Fig. 5a, b, c, d). Position a) shows the structure of the material (copper Ml) before deformation - the grain size d _z is 130 microns; b) the structure of the same material after locally shear deformation - d _z is 0.5 microns; c) the structure of the workpiece material (Al-Mg-Zr) in the initial state - d _s is 3 mm; g) the structure of the same material after deformation - d _s is 0.3 microns.

In general, using the proposed method under optimal conditions for each alloy, we achieved uniform microcrystal grinding over the entire cross section of the workpiece in aluminum alloys of type D16, D20 in 1 pass of locally shear deformation from 3 mm to 0.3 μm, and for copper alloys of type M1 for 2 transitions from 150 microns to 0.5 microns, and here there was a decrease in effort by 15-20% compared with the level of efforts at the first transition.

Experimental data, carried out using snap-in equipment made of heat-resistant alloy ZhS6U, show that treatment by the proposed method of titanium alloys, including low-plastic titanium intermetallic compound, at 700-900 ° С also shows similar results, i.e. significant refinement of the initial coarse-grained (200-300 microns) structure in 2 transitions up to 0.5 microns, i.e. to the QMS state over the entire cross section of the preform, and at the second transition, it was possible to decrease the deformation temperature by 50-100 ° C and pressing efforts by 10-20% due to the significant refinement of the microstructure at the first processing stage.

Thus, the proposed method for producing blanks with a fine-grained structure allows:

- reduce the pressing force and process large (long) workpieces to form QMS and NC structures in them;

- to achieve the accumulation of large degrees of deformation without violating the integrity of the workpiece with high uniformity of the microstructure over the entire cross section of the workpiece, thereby ensuring high stable physical and mechanical properties.

Claims (9)

1. A method of producing preforms with a fine-grained structure, including plastic deformation of the preform under specified thermomechanical conditions by pressing in a tool having a container, punches and a profiling tool located in the channel of the container with a cavity that provides the direction of flow of the workpiece metal and forms an intensive plastic deformation zone, characterized in that before the introduction of the workpiece into the zone of intense plastic deformation in it create a volume-stress state comprehensively compression by the action of the punch and backwater volume through the powder material that fills the cavity of the die tool, and when creating severe plastic deformation is performed rotation of the tool or part thereof. 2. The method according to claim 1, characterized in that the volume-stress state of the comprehensive compression of the workpiece is created by the reciprocal movement of two punches with simultaneous rotation with the possibility of reversing at least one of them. 3. The method according to claim 1, characterized in that the rotation of the tool part is carried out with reversal. 4. The method according to claim 1, characterized in that upon receipt of the workpieces from low-plastic hardly deformed alloys before creating intense plastic deformation, an asymmetric flow of the workpiece material through the profiling tool is provided. 5. The method according to claim 1, characterized in that after deformation of the workpiece by pressing, it is formed using an additional matrix that creates back pressure during deformation of the workpiece and has the possibility of rotation. 6. The method according to claim 1, characterized in that the deformation of the workpiece by pressing is carried out under superplastic conditions. 7. The method according to claim 1, characterized in that the deformation of the workpiece by pressing is carried out in isothermal conditions. 8. The method according to claim 7, characterized in that the deformation is carried out with decreasing temperature after each technological transition. 9. The method according to claim 1, characterized in that graphite or titanium nitride is used as the powder material.

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