RU2661980C1 - Method of plastic deformation of aluminum and aluminum alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to plastic processing of metals and can be used in various fields of industry and science for the plastic deformation of aluminum and aluminum alloys. Method of plastic deformation of aluminum and its alloys includes mechanical loading of the deformable volume of the resonator sample under temperature and ultrasonic influence, and mechanical loading is carried out at a voltage of 90–200 MPa in the temperature range 450–250 °C, while in the process of loading, the vibrational energy of the acoustic emission and when it reaches values no lower than 15⋅10^-12 V²s, corresponding to the deformation structural transition, ultrasonic action is performed with a frequency selected from the low-frequency range of 20–90 kHz and determined by the geometry of the deformable volume of the resonator sample.

EFFECT: invention is aimed at increasing the plasticity resource of aluminum and its alloys under conditions of simultaneous exposure to mechanical stress, temperature and ultrasonic vibrations.

1 cl, 5 ex, 1 tbl, 7 dwg

Description

The invention relates to the field of plastic processing of metals can be used in various fields of industry and science for the plastic forming of aluminum and its alloys.

Known acoustoplastic effect [Blaha, B. Langeneckei // Naturwiss. Rundsch - 1955. - 42 - H.20- S. 556.], which consists in increasing the ductility of materials under the action of ultrasound, experimentally detected at ultrasonic frequencies by Blach and Langezenecker [1] and representing an abrupt decrease in the stress of unidirectional deformation of a crystal when superimposed on it 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.

When a sample is placed in a node of a standing wave, the creep rate in copper increases when exposed to a longitudinal standing wave with a frequency of 20 kHz. The effect is observed at an antinode formed in a standing wave sample. In rolling technological processes, the amplitude of dynamic stresses lies in the range of 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 transducer. With the simultaneous action of ultrasonic vibrations with a frequency of 20 kHz and static loads 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 destruction as a negative manifestation of prolonged ultrasonic exposure to the deformable material and actually limits the use of ultrasound in practice.

A known method of plastic deformation of metals and a device for its implementation [Delusto Lev Georgievich. RF patent No. 2310526 from 11/20/2007] - a prototype. The method includes processing a deformable metal during rolling by ultrasound with a frequency of up to 5 MHz and a magnetic field with an induction of 70 T. An increase in the ductility of a deformable metal occurs due to a decrease in the number of defects in the metal during continuous ultrasonic and magnetic exposure, and electromagnets or permanent magnets can be used as a source of magnetic field. In accordance with the prototype, an increase in ductility is the result of a decrease in structural defects of the metal being deformed by rolling, which contradicts the physics of plasticity of materials, according to which the plastic behavior of metals is carried out precisely due to the slip of dislocations — linear defects of the crystal lattice.

Disadvantages: the method of plastic deformation does not increase the ductility of the wrought metal.

The objective of the invention is to increase the resource of plasticity of the metal under conditions of simultaneous exposure to mechanical stress, temperature and ultrasonic vibrations during plastic deformation of aluminum and its alloys.

SUMMARY OF THE INVENTION

The method of plastic deformation of aluminum and its alloys under mechanical loading, temperature and ultrasonic irradiation consists in the fact that ultrasonic irradiation 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 deformable volume of a metal or alloy, upon reaching critical parameters of the temperature-force impact, characterized by mechanical stress 90-200 MPa, with a temperature in the range of 450-250 ° C, vibrational energy of acoustic emission of at least 15 * 10 ^-12 V ² s, corresponding to a deformation structural transition in a deformable material.

The task is achieved by the fact that in the course of a joint action on a metal or alloy of mechanical loading and temperature, ultrasonic treatment is carried out only after a 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. At this point, a critical level of vibrational energy of the internal acoustic field of standing acoustic waves of at least 15 * 10 ^-12 V ² s generated from the primary acoustic emission signals is stored in the deformable volume. This moment of time corresponds to the beginning of external ultrasonic exposure at the frequency of ultrasonic vibrations corresponding to the main low-frequency resonances in the frequency range 20-90 kHz, determined by the geometry of the resonator sample.

The method is implemented as follows

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

2. Samples are loaded with mechanical stress in the range of 90-200 MPa and heated to a temperature in the range of 450-250 ° C (for a voltage of 90 MPa, the temperature is not lower than 450 ° C, for a voltage of 200 MPa, the temperature is not lower than 250 ° C), registering a strain increase and acoustic emissions.

3. At the moment of the deformation structural transition, when the vibrational energy of acoustic emission is not lower than 15 * 10 ^-12 V ² s, ultrasonic vibrations are introduced into the deformable sample at the frequency of the main resonances from the low-frequency range from 20 to 90 kHz.

4. Ultrasonic vibrations are introduced into the deformable sample using a waveguide combined with an ultrasound concentrator of a magnetostrictive transducer.

и колебательной энергией акустической эмиссии не ниже 15*10^-12 В²с, увеличивает ресурс аномальной пластичности деформируемого металла.Ultrasonic exposure at the frequency of the main resonances of the deformable volume in the low frequency range of 20-90 kHz at the time of the natural high-plastic structural state of the deformable material, prepared jointly by mechanical stress in the range of 90-200 MPa, temperature in the range

and vibrational energy of acoustic emission not lower than 15 * 10 ^-12 V ² s, increases the resource of abnormal plasticity of the deformed metal.

Examples of specific performance

Example 1

A metal sample of aluminum or AMg6 aluminum-magnesium alloy, in the form of a rod 1, connected to an acoustic emission waveguide is placed in a device for thermal and mechanical action, FIG. 1. Sample 1 is fixed in a fixed grip 2, loaded with a mechanical load in the range of 40-200 MPa using a movable grip 3, heated by an element 4 to 550 ° C and the strain growth is measured using a strain gauge combined with a movable grip 3. With simultaneous exposure mechanical loading and heating of sample 1, plastic deformation of the metal occurs, accompanied by acoustic emission. Data on acoustic emission in the form of electrical signals obtained using a piezoelectric transducer 5 is transmitted via channel I to an analog-to-digital converter 6 and computer 7. Via channels II and III, respectively, data on temperature and strain are also transmitted to an analog-digital converter 6 and computer 7 for processing and data analysis.

Using the installation (Fig. 1), the samples of aluminum-magnesium alloy were deformed in the load range of 40-200 MPa and heated from room temperature to 550 ° C. As shown in FIG. 2, at a load of 120 MPa, the character of deformation accumulation is monotonic (region I) and quasi-jumble (region II), the monotonous nature of deformation accumulation corresponds to a monotonous increase in the rms voltage of acoustic emission, and the quasi-jump nature corresponds to a sharp increase in the rms voltage of acoustic emission. A sharp increase in the rms stress indicates a significant increase in the vibrational energy of acoustic emission in the deformable volume of the sample.

It was established that the transition from region I to region II, characterized by a significant (4-5 times) increase in the rate of accumulation of deformation, is a deformation structural transition. The deformation structural transition corresponds to the critical values of the thermomechanical impact parameters: mechanical stress in the range of 90 - 200 MPa, temperature in the range of 450-250 ° C, vibrational energy of acoustic emission of at least 15 * 10 ^-12 V ² s.

Example 2

Let us analyze the spectrum of acoustic signals obtained in Example 1 in the form of time dependences of the rms voltage of acoustic emission. Spectrum analysis is carried out by the fast Fourier transform method. In FIG. Figure 3 shows the distribution of the spectral density of acoustic emission signals in the range from 10 kHz to 700 kHz, recorded during the deformation of an aluminum sample.

From the above data it follows that the energy of acoustic emission signals is distributed in two frequency ranges: in the high-frequency range from 100 kHz to 700 kHz, the spectral density is small and distributed around frequencies of 600, 350 and 150 kHz; in the low-frequency range from 10 kHz to 100 kHz, the vibrational energy is significantly higher than in the high-frequency range. The frequency range 100-700 kHz characterizes the spectrum of primary acoustic emission signals. The low-frequency range of frequencies of 10-100 kHz is a set of sharp (actually resonant) peaks formed due to the redistribution of the vibrational energy of the primary signals of acoustic emission.

Thus, the vibrational energy of acoustic emission is concentrated in the low-frequency region. The resonance nature of the distribution of the spectral density of acoustic emission in the low-frequency region indicates the formation of the acoustic field of standing waves in the deformable volume of the material.

Example 3

Let us analyze the low-frequency acoustic spectrum in the range from 10 to 100 kHz obtained by heating a loaded aluminum sample. In FIG. Figures 4a and 4b show the process of strain accumulation in the sample and the accompanying acoustic emission when the sample is heated to 650 ° C under shear load of 25 MPa. The process of strain accumulation upon heating to 560 ° C (region I) is monotonic. After 560 ° C, the accumulation of deformation is spasmodic events alternating with monotonic sections (region II). The monotonic character of strain accumulation in region I corresponds to acoustic emission, the rms stress of which monotonically increases with increasing temperature. The abrupt nature of the accumulation of deformation in region II corresponds to discrete acoustic emission.

Let us analyze the low-frequency region of the spectral density of acoustic emission signals characteristic of region I of strain accumulation. In FIG. Figure 5 shows the spectral density distribution characteristic of monotonic strain accumulation. A characteristic feature of the spectrum is its discrete form, which is a combination of low-frequency peaks of the spectral density of acoustic emission signals located in the frequency range of about 20-50 kHz. In the frequency range 60-100 kHz, the spectral density of the signals is close to the spectral density of the noise.

Let us analyze the low-frequency spectral density of acoustic emission signals, which is characteristic for the accumulation of deformation in region II (Fig. 6). As follows from the data of FIG. 6, a significant complication of the spectrum is observed; spectral components appeared in it in the range 60–90 kHz, which are weakly expressed during monotonic accumulation of deformation.

The complication of the spectrum, due to the appearance of new spectral components of the acoustic field of acoustic emission and a significant increase in spectral density in the frequency range 60-90 kHz, indicates the accumulation of vibrational energy in small-scale resonators.

Example 4

Consider the set of resonators in the sample-waveguide system in example 3 (Fig. 7).

The waveguide and the sample are a rod of cylindrical shape with a total length of about 300 mm, part of which is 30 mm long and 4 mm in diameter is a strain localization section that divides the waveguide into two parts 220 and 100 mm long. According to the geometry of the waveguide-sample system, a section of the waveguide in the form of a rod with a length of about 200 mm is selected as resonators, which transmits acoustic energy to the piezoelectric transducer, a section of the waveguide in the form of a rod with a length of about 100 mm, with which our sample is mounted in a loading device, a section of the waveguide is 30 mm and a diameter of 4 mm, located between these two sections of the waveguide, which is the area of localization of shear strain.

Let us analyze the set of possible resonators in our sample-waveguide system (Table 1). The calculation of the geometric parameters of the resonators is carried out on the basis of the standing wave condition

L = kλ / 2, where

L is the size of the acoustic resonator,

λ is the wavelength, k is the resonance number,

at k = 1, the wavelength corresponds to the first (main) resonance.

The wavelength is determined according to the expression λ = VT, where

V is the propagation velocity of acoustic vibrations,

T is the oscillation period associated with the resonance frequency f by the expression T = 1 / f.

In the calculation, it was taken into account that wave packets of acoustic emission propagate in both the longitudinal and transverse waves in the deformable volume. In addition, it must be taken into account that with increasing temperature the propagation velocity of ultrasonic vibrations decreases. For aluminum and alloys, the reduction reaches 17%.

In our case, the resonator associated with the deformable part with a length of 30 mm is important. From the table. 1, it follows that in a deformable volume with a diameter of 4.0 mm and a length of 30 mm, standing transverse (shear) waves are mainly formed, that is, shear vibrational energy of acoustic emission is accumulated.

Example 5

From the totality of the data of examples 1-4 it follows that the accumulation of deformation in aluminum alloys at high temperatures is carried out in two ways: in region I, the monotonic nature of the accumulation of deformation corresponds to monotonous acoustic emission with a low value of vibrational energy; in region II, high-speed (spasmodic) accumulation corresponds to acoustic emission with a high value of vibrational energy. The transition from region I to region II is a deformational structural transition. The deformation structural transition corresponds to the critical values of the thermomechanical effects: mechanical stress in the range of 90-200 MPa, temperature in the range of 450-250 ° C, vibrational energy of acoustic emission of not less than 15 * 10 ^-12 V ² s.

Thus, plasticity is activated during the accumulation of deformation in region II not only due to the action of mechanical stresses and temperature, but also due to the formation of an ultrasonic field of standing acoustic emission waves in the deformable volume of the material, i.e., the plastic behavior of the deformed material is determined by the combined action of thermal fluctuations thermal field, static displacements of the stress field and dynamic displacements of the acoustic field of standing waves of acoustic emission.

A typical manifestation of the acoustic-plastic effect is the state of abnormal plasticity during ultrasonic irradiation of a deformed sample. Consequently, the plasticity induced by external ultrasound is added to the natural plasticity induced by the temperature effect, the action of mechanical stresses and the field of dynamic displacements of standing acoustic waves of acoustic emission. However, during prolonged irradiation with ultrasound at a frequency of 20 kHz, excess vacancies appear in polycrystalline aluminum. The high density of vacancies (10 ²⁰ vacancies / s with an oscillation amplitude of 1 μm) leads to the destruction of the material due to intense pore formation along the grain boundaries.

Thus, the effect of external ultrasonic irradiation must be limited only by the duration of the accumulation of deformation in region II, where the natural plasticity is summed up with the plasticity induced by external ultrasonic action. The onset of the strain accumulation process in region II is determined by the achievement of the critical values given above by the temperature, mechanical stress, and vibrational energy of the field of standing waves of acoustic emission. The frequency of ultrasonic vibrations in our case is selected in the range of 60-90 kHz and is determined by the resonance properties of the deformable volume. Of course, when the geometry of the deformable volume is changed, the resonant properties of the resonator change. This circumstance requires adjustment of the frequency range of external ultrasonic exposure in the range of 20-90 kHz. Correction of the internal acoustic field of standing waves of acoustic emission is not required, since the process of formation of acoustic standing waves of acoustic emission, determined by the geometry of the resonator, is set automatically.

Parameters of acoustic resonators of the sample-waveguide system.

Claims (1)

The method of plastic deformation of aluminum and its alloys, including mechanical loading of the deformable volume of the resonator sample under temperature and ultrasound exposure, characterized in that the mechanical loading is carried out at a voltage of 90-200 MPa in the temperature range 450-250 ° C, while in the process of loading measure vibrational energy, and the acoustic emission generated at the values not lower 15⋅10 ^-12 V ² with corresponding deformation structural transition, sonication is performed at a frequency sps haven from the low frequency range of 20-90 kHz and defined by the geometry of the deformable volume of the sample cavity.

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