RU2724209C1 - Method of plastic deformation of aluminum and its alloys - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to plastic processing of metals, in particular to method of plastic deformation of aluminum and its alloys, consisting in simultaneous thermomechanical and ultrasonic action. Ultrasound action on metal or alloy is carried out during the whole process of thermomechanical action and is formed by application to ultrasonic piezoelectric transducer of low-voltage alternating voltage with amplitude of 50 mV at frequency of main resonance determined by geometry of deformed volume of sample.EFFECT: method provides increased service life of plasticity of alloy at simultaneous action of mechanical stress, temperature, standing waves formed by acoustic emission and low-amplitude ultrasonic oscillations of external source at plastic deformation of aluminum and its alloys.1 cl, 3 tbl, 5 dwg, 5 ex

Description

The invention relates to the field of plastic processing of metals can be used in various fields of industry and science for deep molding of metallic materials.

Known acoustoplastic effect [Blaha, B. Langeneckei // Naturwiss. Rundsch. - 1955. - 42. - N. 20. - S. 556.], which consists in increasing the plasticity of materials under the action of ultrasound, experimentally detected at ultrasonic frequencies by Blach and Langezenecker [1] and representing a stepwise decrease in the stress of unidirectional deformation of the crystal when applied to alternating deformations.

The acoustoplastic effect is observed in a wide range of frequencies from units of hertz to megahertz, but he found the most widespread application in the range of 15-40 kHz. The acoustoplastic effect, which is realized under the simultaneous action of ultrasound and static loading, is the result of the summation of static stresses and dynamic stresses of an ultrasonic wave. In technological processes, for example, during rolling, the amplitude of dynamic stresses lies in the range 10 ⁷ -10 ⁸ Pa. The ultrasound is introduced into the sample to form a standing wave through a waveguide in the form of an ultrasound concentrator combined with an ultrasonic magnetostrictive transducer. With the simultaneous action of ultrasonic vibrations with a frequency of 20 kHz and static loads, for example, in a copper sample, the density of vacancies increases significantly (10 ²⁰ vacancies / s with an oscillation amplitude of 1 μm). With prolonged exposure to ultrasound, destruction of the samples is observed due to intense pore formation along the grain boundaries.

Disadvantages: the effect of embrittlement and fracture as a negative manifestation of prolonged ultrasonic action on the deformable material, which actually limits the use of ultrasound in practice.

It is known that when a sample is placed in a node of a standing wave, the creep rate in copper [2] and aluminum [3] increases under the action of a longitudinal standing wave with a frequency of 20 kHz. The effect is observed under the combined action of static stresses up to 10 ⁷ Pa and dynamic stresses up to 10 ⁸ Pa. Disadvantages, as in the previous case, the destruction of the material during prolonged ultrasonic exposure during creep.

A known method of plastic deformation of aluminum and its alloys [4] under mechanical loading, temperature and ultrasound. According to this method, ultrasonic action is carried out at a frequency of ultrasonic vibrations from the low frequency range of 20-90 kHz, which corresponds to the main resonances determined by the geometry of the resonator sample, i.e., the geometry of the deformable volume of the metal or alloy, when critical parameters are reached corresponding to the deformation structural transition in the deformable material.

Ultrasonic action is carried out only after the deformation structural transition, the deformation structural transition is fixed at the time instant of a significant (4-5 times) increase in the rate of accumulation of deformation in the deformable material, which corresponds to the mechanical stress and the temperature reached.

The choice of this moment of ultrasonic exposure and determines the disadvantages of the method and complicates its implementation.

The objective of the invention is to simplify the implementation of the method; an increase in the plasticity resource of a metal (alloy) under conditions of simultaneous action of mechanical stress, temperature, standing waves formed by acoustic emission and low-amplitude ultrasonic vibrations of an external source during plastic deformation of aluminum and its alloys.

The problem is achieved in that the ultrasonic effect on the metal or alloy is carried out during the entire process of thermomechanical exposure.

Ultrasonic exposure is carried out by low-amplitude ultrasonic vibrations at a frequency selected from the low-frequency range of 20-100 kHz, which corresponds to the main resonances of acoustic emission, determined by the geometry of the resonator sample, i.e., the geometry of the deformable volume of the metal or alloy. To exclude the negative effect of generating an excessive concentration of point defects in an ultrasonic field, the oscillation amplitude is about 50 mV. In this regard, the excitation of ultrasound is carried out through the waveguide using a piezoelectric sensor based on the TsTS-19 piezoceramics connected to a low-power oscillation generator.

Upon reaching the critical parameters of the temperature-force thermomechanical effect and the critical value of the vibrational energy of acoustic emission corresponding to the deformation structural transition in wrought aluminum and its alloys, acoustic emission and external ultrasound form a common acoustic field of standing waves, including on resonators associated with the deformable volume, whose vibrational energy exceeds the critical value of the vibrational energy of only acoustic emission, which provides a significant increase in the ductility of the material.

The method is implemented as follows

1. Prepared samples of aluminum or aluminum-magnesium alloys are placed in the installation for high-temperature mechanical and ultrasonic exposure.

2. Samples are loaded with mechanical stress near the yield strength: aluminum - 15 MPa, aluminum-magnesium alloys 90-200 MPa.

3. The loaded samples are heated:

aluminum to a temperature in the range of 480-640 ° C;

aluminum-magnesium alloys - for a voltage of 90 MPa, the temperature is not lower than 450 ° С, for a voltage of 200 MPa, the temperature is not lower than 250 ° С,

registering strain growth and acoustic emission.

4. Low-intensity ultrasonic vibrations are excited using a piezoceramic transducer based on the TsTS-19 piezoceramics and introduced into the deformable sample using a waveguide simultaneously with the onset of thermomechanical action.

5. The frequency of the generator of ultrasonic vibrations corresponds to the main resonances of the acoustic field of standing waves, formed both by converting the primary signals of acoustic emission on natural resonators, one of which is a deformable volume, and by converting ultrasonic waves on the same resonators.

6. The excitation of low-intensity ultrasonic waves in the sample-waveguide system is provided by a piezoceramic transducer that converts the electric oscillations of a generator with an amplitude of 50 mV into mechanical ones.

The main increase in deformation is carried out during the deformation structural transition, when the vibrational energy of acoustic emission is not lower than 15 * 10 ^-12 V ² s, and the external flow of ultrasonic vibrations, converted to natural resonators, forms a joint acoustic field of standing waves in the low frequency range from 20 to 100 kHz., the vibrational energy of which is significantly higher than the vibrational energy of acoustic emission, which increases the plasticity resource and ensures the accumulation of large plastic deformations.

The combination of ultrasonic and thermomechanical effects simplifies the implementation of the method.

The invention is illustrated by graphic materials:

FIG. 1. A sample in the form of two waveguides A and B, combined with a strain localization section with a length of 40 mm and a diameter of 4 mm.

FIG. 2. Installation diagram for high-temperature deformation of metals: 1 - a sample in the form of a rod; 2 - motionless capture of installation; 3 - movable gripper installation with a device for loading and measuring strain; 4 - heater; 5 - analog-digital converter and computer. Symbols I, II, III, IV, V denote respectively the acoustic emission channel, the temperature measurement channel, the strain measurement channel, the stress measurement channel, the ultrasound input channel as part of the piezoelectric transducer and generator.

FIG. 3. The spectral density of the acoustic field of standing waves excited in the sample-waveguide system by an external generator at a frequency of about 80 kHz and a signal amplitude of 50 mV. 7 - resonance frequency of 35.4 kHz (35400 Hz), 8 - resonance frequency of 80 kHz (79900 Hz).

FIG. 4. The spectral density of acoustic emission signals during the accumulation of deformation in the absence of external ultrasonic exposure.

FIG. 5. The spectral density of acoustic emission signals during the accumulation of deformation under the action of an external source of ultrasonic vibrations.

Examples of specific performance

Example 1

A metal sample of aluminum or aluminum alloy AMgb in the form of a rod (Fig. 1) consists of two waveguides A and B, between which there is a section of the rod 40 mm long and 4 mm in diameter in the form of a stress concentrator in which the deformation process is localized. The waveguide “A” provides the transmission of acoustic vibrations from an external source of ultrasonic vibrations to the deformable volume, and the waveguide “B” provides the transmission of the acoustic stream of acoustic emission signals to the receiver. The sample is placed in the installation for thermal and mechanical impact, shown in Fig 2.

Sample 1 is fixed in a fixed grip 2, loaded with a mechanical load of about 15 MPa using a movable grip 3, heated by an element 4 to 620 ° C. The strain gain is measured on channel III by the computer program of computer 5. On channel IV, information about the mechanical load also enters computer 5. At the same time as loading and heating, the emitting piezoelectric transducer of channel V connected to the electric oscillation generator forms a longitudinal acoustic wave in waveguide A, which propagates along the waveguides and the deformation localization region, reaching the receiving piezoelectric transducer of channel I. Acoustic emission signals generated during the deformation of the localization region of sample 1 and the acoustic waves generated by the radiating piezoelectric transducer of channel V are recorded and processed by computer 5.

Example 2

Let us analyze the spectrum of the acoustic field of standing waves generated in the sample-waveguide system using an external signal generator at a frequency of 80 kHz and a signal amplitude of 50 mV. Spectrum analysis is carried out by the fast Fourier transform method. In FIG. Figure 3 shows the distribution of the spectral density of the acoustic field in the range from 10 kHz to 140 kHz, recorded using the acoustic emission sensor of channel I during the excitation of ultrasound in the sample-waveguide system by channel V.

As follows from FIG. 3 data there are two resonant peaks: one at a frequency of 35.4 kHz, (35400 Hz), the second at a frequency of 80 kHz (79900 Hz). The resonance at a frequency of 80 kHz is obviously associated with a longitudinal standing wave, since the generator frequency was chosen from the condition of a standing longitudinal wave

L = kλ / 2, where

L is the size of the acoustic resonator equal to the size of the deformable volume, i.e., the size of the concentrator is 40 mm long, λ is the length of the longitudinal wave, k is the resonance number, at k = 1 the wavelength corresponds to the first (main) resonance, and the piezoelectric transducer excited exactly the longitudinal the wave. It should be noted that the frequency of 80 kHz corresponds to resonance at the resonator (stress concentrator) under conditions when there is no deformation process. That is, 80 kHz is the resonance response of the original sample volume. During the accumulation of deformation, the geometry of the deformation volume changes within small limits; in this connection, the resonant frequencies will also change, remaining close to the selected values of 80 and 35, 4 kHz ..

The resonance at a frequency of 35.4 kHz is associated with the acoustic field of the transverse waves. It is well known [5] that when a longitudinal wave is excited in a cylindrical waveguide, when it interacts with the waveguide wall at a critical angle, the longitudinal wave transforms into a transverse wave, that is, a longitudinal front and trains (wave packets) of transverse waves propagate in the waveguide. Thus, a complex acoustic field of standing longitudinal and transverse waves is formed in the sample waveguide system.

Example 3

Multiple cycles were carried out to accumulate strain in aluminum when heated to 620 ° C and a load of 15 MPa without external ultrasound (odd cycles) and external ultrasound (even cycles). In the table. Figures 1 and 2 show the results of strain accumulation in odd and even cycles.

As follows from the data table. 1 and 2, the magnitude of the accumulated strain in a cycle with ultrasonic action (even cycles) is many times greater than the strain in cycles (odd cycles) without ultrasonic treatment. This confirms the increase in plasticity in the acoustic field, which is the result of the resonance addition of the field of standing waves of acoustic emission and the field of standing waves of external ultrasound at the frequency of the main resonance.

Example 4

Let us analyze the spectral density of the acoustic field generated by the primary acoustic emission signals (Fig. 4) and together with an external ultrasound source (Fig. 5) with an amplitude of 50 mV at a primary signal frequency of 80 kHz during deformation of the aluminum sample.

The data of FIG. 4 and 5 indicate that in the absence of an external oscillation source, the spectral density of the field of acoustic standing waves is significantly lower than the spectral density of the main resonances under external ultrasonic action, which are the result of the resonance addition of the acoustic field of standing waves generated by the primary signals of acoustic emission and the acoustic field of standing waves generated ultrasonic waves of an external source of oscillations. It should be noted that an increase in the amplitude of the main resonances at frequencies of 35 and 80 kHz with the participation of external ultrasound is accompanied by additional resonances in the frequency range 60-80 kHz, indicating the transformation of the deformable volume of the sample. Thus, when exposed to an external ultrasound source, an increase in the vibrational energy of the field of standing longitudinal and transverse waves generated by the primary acoustic emission signals is observed due to resonant summation with the acoustic field of standing waves generated by an external source of ultrasonic vibrations, which significantly increases the ductility of the deformed metal.

Example 5

Let us analyze the geometry of the deformable volume (resonator) using the spectral density data obtained in Example 4 (Table 3). The size of the resonator is determined according to the formula given in example 2

L = kλ / 2, where

L is the size of the acoustic resonator equal to the size of the deformable volume, that is, the size of the concentrator is 40 mm, λ is the longitudinal wavelength, k is the resonance number, and for k = 1 the wavelength corresponds to the first (main) resonance. The wavelength is defined as λ = C / f, where C is the velocity of the longitudinal or transverse wave in aluminum, f is the resonance frequency. The longitudinal wave velocity in aluminum is 6420 m / s, the shear wave velocity is 3040 m / s.

From the above table. From the data 3 it follows that both in the longitudinal and in the transverse waves, the two main resonances at frequencies of about 35 and 80 kHz are connected with the resonator, which is a deformable volume of about 40 mm long. Resonances are observed both in odd and even cycles on longitudinal and transverse waves.

As already mentioned [1] in technological processes, the amplitude of dynamic stresses lies in the range 10 ⁷ -10 ⁸ Pa. In comparison with the above examples 2-5, such values of dynamic stresses are beyond. It is no coincidence that prolonged ultrasonic exposure with such amplitudes leads to the destruction of the deformed sample. Obviously, such ultrasound parameters are used in practice due to the fact that the resonance properties of the deformable volume of the sample (part) are not taken into account. Moreover, the resonances of acoustic emission signals are not taken into account, which, when converted to standing acoustic waves on natural resonators of a deformable volume, provide activation and correlation of elementary deformation shifts on a macroscopic scale. This scale (correlation scale) is determined by the length of the standing acoustic wave, which in our case is equal to the geometric dimensions of the strain localization region. Resonant addition, more precisely, a resonant superposition of the spectral components of acoustic emission and external ultrasound, is accompanied by a significant increase in the amplitudes of the main spectral components, which leads to the accumulation of a considerable amount of vibrational energy of standing acoustic waves in the deformable volume. This vibrational energy, together with the static voltage applied to the sample, and thermal fluctuations of the thermal field, determine the abnormally high ductility of the deformed metal.

According to examples 2-5, high-temperature deformation of the sample under the conditions of external low-amplitude ultrasound with an amplitude of 50 mV is accompanied by a significant increase in the vibrational energy of the field of standing longitudinal and transverse waves generated by both primary acoustic emission signals (Fig. 4) and with the participation of an external ultrasound source ( Fig. 5). This field (as a result of resonance superposition) creates the effect of an abnormally high plasticity of the deformable volume of the sample (resonator), which allows one to accumulate significant plastic deformations (examples 3-5).

Literature

1. Blaha, B. Langeneckei // Naturwiss. Rundsch. - 1955. - 42. - H.20. - S. 556.

2. Millstone C.A., Omelyanenko I.F., Sirenko A.F. High-temperature creep and destruction of copper in the field of ultrasound // FMM. 1984. T. 58. No. 3. S. 589-595.

3. Ushakov V.I., Omelyanenko I.F., Sirenko A.F. Creep of aluminum and its alloys in the field of ultrasound // FMM. 1985.V. 59. No. 5. S. 584-592.

4. Makarov S.V., Plotnikov V.A. The method of plastic deformation of aluminum and its alloys. RF patent No. 2661980 dated 07/23/2018.

5. Bergman. Ultrasound and its application in science and technology. - M.: Publishing House of Foreign Literature, 1957. - 726 p.

Claims (1)

A method of plastic deformation of aluminum and its alloys, including simultaneous thermomechanical and ultrasonic treatment, characterized in that the ultrasonic treatment is formed by applying to the ultrasonic piezoelectric transducer a low-voltage alternating voltage with an amplitude of 50 mV at a fundamental resonance frequency determined by the geometry of the deformable volume of the sample.

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