RU2817097C1 - Method of linear friction welding of parts from aluminium alloy - Google Patents

Abstract

FIELD: various technological processes.

SUBSTANCE: invention can be used in production or repair of monoblocks of turbomachines from aluminium alloys using linear friction welding. Prior to friction welding, contact surfaces of elements of parts 1 and 3 are prepared. Vacuum is created in the vacuum chamber, then argon is fed into it, at pressure in range of 0.8·10^-1 to 1.0·10^-1 Pa, induction high-frequency discharge plasma is ignited, negative bias voltage from 400 to 600 V is supplied and parts contact surfaces are cleaned to remove oxides therefrom. Then, heating and forging are performed in the same vacuum chamber. Elements of part 1 and 3 are heated, pressed to each other along contact surfaces with a force providing pressure at the specified amplitude and frequency of their relative movement. After displacement is stopped, forging is performed with application of forging pressure.

EFFECT: method ensures high operational reliability of parts made of aluminium alloys produced by linear friction welding by increasing their endurance limit.

5 cl, 2 dwg, 1 ex

Description

The invention relates to friction welding and can be used in various branches of mechanical engineering, for example, in the production or repair of turbomachinery monoblocks made of aluminum alloys.

Heating of the surfaces of parts connected by friction welding can be carried out either due to rotation of one of the parts relative to the other, or due to linear oscillatory motion [European patent No. 0719614, IPC B23K 20/12], or due to angular oscillatory motion [European patent No. 0624420, IPC B23K 20/12, and RF patent No. 2043891, IPC B23K 20/12]. At the same time, the most common and developed methods of friction welding are rotational welding and stir friction welding [Friction welding: Handbook / V.K. Lebedev, I.A. Chernenko, R. Michalski and others; Under general ed. VC. Lebedeva, I.A. Chernenko, V.I. Bill. - L.: Mechanical engineering. Leningr. department, 1987. - 236 p. ].

There is also a known method of friction welding [AC USSR No. 1512740, publ. 07.10.89, BI No. 37], including a heating stage, at which the parts are brought into relative rotation with constant application of contact pressure, and a forging stage, which is carried out after the rotation has stopped.

The disadvantages of the known friction welding methods are either their unsuitability [AS USSR No. 1512740] or low stability of the quality of welded joints [European patent No. 0624420, IPC B23K 20/12, and RF patent No. 2043891, IPC B23K 20/12] for such parts , like the blades of turbomachines, due to the high probability of lack of fusion and undercuts caused by the snatching of the surface layers of the metal adjacent to the joint by flash. These disadvantages are caused by the uneven heating of the joint over the entire cross section.

Linear friction welding processes are becoming key technologies for forming welded joints from difficult-to-weld materials and can be widely used in repair production. The advantage of linear friction welding is the minimal preparation of surfaces for welding. Linear friction welding is quite actively used in aircraft engine construction for connecting blades to disks [Corzo M., Torres Y., Anglada M., Mateo A. Fracture behavior of linear friction welds in titanium alloys // Anales de la Mecanica de Fractura. - V.1, 2007. - Pp.75-80].

There is a known method for manufacturing or repairing a monoblock bladed disk, including the formation of a welded joint surface on a protruding protrusion belonging to the disk and passing from the front end to the rear end along the chord of the protruding protrusion, intended for the subsequent stage of installing the blade by linear friction welding on the protrusion of the disk [US patent No. 7125227, IPC B23K 20/12, Process for manufacturing or repairing a monobloc bladed disc, 2006]. This method makes it possible to produce monoblocks of turbomachinery blade disks or to repair them.

However, the known method cannot be used for welding aluminum parts, since an oxide film appears on the contact surfaces of the welded parts made of aluminum alloys, which prevents the high-quality formation of the weld.

The closest technical solution, chosen as a prototype, is a method of linear friction welding of parts made of aluminum alloys, including the stage of preparing the contact surfaces of the parts, the heating stage, in which the parts are pressed against each other along the contact surfaces with a force that ensures the pressure of the joint welding process at a given amplitude and frequency of relative movement of parts along their contact surfaces, and the forging stage, carried out after the cessation of reciprocating movements of parts by applying forging pressure [S.A. Tokorenko, S.R. Shekhtman, I.V. Kandarov. Some features of the microstructure and properties of the aluminum alloy of the Al-Cu-Mg system in the blade-disk joint area obtained by linear friction welding. //Bulletin of UGATU, vol. 22, no. 4 (82), 2018, pp. 41-47]. This method is intended for the production of monoblock blade disks of turbomachines.

However, the prototype method is not capable of providing a sufficiently high reliability of the welded joint, since there is a fairly high probability of contamination in the form of elements of an oxide film entering the welding joint area. This largely applies to the manufacture of such turbomachinery parts as a unicycle with blades, where it is necessary to weld a fairly large number of blades to the disk and the likelihood of a defect in the welded joint of even one blade can lead to the failure of the entire unicycle.

In this regard, the prototype method under consideration does not allow obtaining high-quality welded joints that ensure high performance properties of parts and their reliability.

The objective of the present invention is to create high-quality welded joints of parts made of aluminum alloys, obtained by linear friction welding, by removing contaminants and oxide film from the contact surfaces of the parts being welded.

The technical result of the claimed invention is to increase the operational reliability of parts made of aluminum alloys produced by linear friction welding by increasing their endurance limit.

The technical result is achieved due to the fact that in the method of linear friction welding of parts made of aluminum alloy, including the stage of preparing the contact surfaces of the parts, the heating stage, in which the parts are pressed against each other along the contact surfaces with a force ensuring the pressure of the joint welding process at a given amplitude and the frequency of relative movement of parts along their contact surfaces, and the forging stage, carried out after the reciprocating movements of parts have ceased by applying forging pressure, unlike the prototype, the stage of preparing the contact surfaces of parts is carried out in a vacuum chamber, in which a vacuum is first created, then let into argon and at a gas pressure in the vacuum chamber in the range from 0.8×10 ^-1 Pa to 1.0×10 ^-1 Pa, the high-frequency induction discharge plasma is ignited, applying a negative bias voltage to the parts being welded in the range from 400 to 600 V and The contact surfaces of the parts are cleaned to remove oxides from them, and then the heating stage and the forging stage are carried out in the same vacuum chamber.

In addition, it is possible to use the following additional techniques in the method: the pressure value of the welding process is taken in the range from 30 to 180 MPa, time from 0.3 to 6 s, amplitude from 1 to 3 mm and frequency from 40 to 80 Hz, at the forging stage the pressure value on the contact surfaces of the parts being welded is set from 160 to 320 MPa, and the time of the forging stage is taken from 0.1 to 2.0 s; reciprocating movement of the workpieces is carried out with a stop time interval of 0.05 to 0.3 s; the blade blade and turbomachine disk are used as welded parts made of aluminum alloys; The coefficient of specific power input when welding turbomachine parts is selected from 2.2 to 3.2 kW.

During the reciprocating movement of the parts, the surfaces to be welded are pressed to form tight contact. The heat generated in the welding plane promotes plastic deformation of the near-surface volumes of the parts being welded. During the welding process, ductile-plastic layers of metal move towards the boundaries of the welded surface. In this case, partial removal of oxides and contaminants that may be present in the welding zone occurs. To reliably remove oxides and contaminants present on the contact surfaces of welded parts made of aluminum alloys, they are cleaned by placing the parts in a vacuum chamber, in which a vacuum is first created, then argon is introduced into it and at a pressure in the range of 0.8⋅10 ^{- 1} Pa to 1.0⋅10 ^-1 Pa ignite the plasma of an induction high-frequency discharge, applying a negative bias voltage in the range from 400 to 600 V to the parts being welded. Thus, ensuring clean contact surfaces of parts is achieved due to two factors: a protective environment (vacuum and argon) and high-frequency plasma sputtering of the oxide film.

The short duration of the welding process (a few seconds) provides a small heat affected zone. To ensure welding accuracy, it is necessary to take measures to eliminate distortions and errors in the location of the surfaces being welded. The process of weld formation is quite complex and is determined by the tribological properties of the contact, the peculiarities of the processes of internal friction and plastic deformation, as well as physicochemical and metallurgical aspects.

To carry out intensive heating of the joint surfaces of the joined workpieces, as well as to additionally remove residual contaminants and oxides from the contact zone, it is necessary to supply significant energy, which is determined, ceteris paribus, by the frequency and amplitude of the reciprocating movement of the workpieces, as well as the force of their pressing. In this case, the same amount of supplied energy can be obtained with different combinations of the specified parameters of the welding process, and the properties of the welded joint will differ in all these cases.

The figures show photographs of welded seams of aluminum parts. Figure 1 shows the appearance of the welded joint (Fig. 1a - side view, Fig. 1b - front view). Figure 2 shows fragments of welds of parts made of aluminum alloy obtained using the compared options (Fig. 2a - weld seam obtained by the prototype method, Fig. 2b - weld seam obtained by the proposed method). Figures 1 and 2 contain: 1 - basic element of the part, 2 - weld, 3 - welded element of the part, 4 - oxide inclusion (the hollow red arrow shows the location of the weld joint defect in the form of an oxide inclusion, the red rectangle indicates the location of the weld).

The method is carried out as follows. On the assembled end-to-end and fixed joined elements, parts 1 and 3 are installed in one of the known devices for linear friction welding [for example, RF patent No. 2280546, IPC B23K 20/12. Blade clamping tool and its use for friction welding of blades. Publ. July 27, 2006 Bulletin. No. 21]. Then the welded elements of the part 1 and 3 are placed in the vacuum chamber of the welding installation, a vacuum is created in it (about 1.0⋅10 ^-2 Pa), argon is introduced into the vacuum chamber and at a gas pressure in the chamber of the order of 0.8⋅10 ^{- 1} Pa to 1.0⋅10 ^-1 Pa ignite the plasma of the induction high-frequency discharge, applying a negative bias voltage in the range from 400 to 600 V to the welded elements of parts 1 and 3 and clean the contact surfaces of the elements of parts 1 and 3 and remove oxides from them , and then in the same vacuum chamber the heating stage and the forging stage of part elements 1 and 3 are carried out. To do this, set the required pressing force, ensuring the value of the welding process pressure in the range from 30 to 180 MPa, time from 0.3 to 6 s, set required heating values and forging force. Moreover, at the heating stage, the amplitude value is set from the range from 1 to 3 mm and the frequency from the range from 40 to 80 Hz. The forging pressure value is selected from the range of values from 160 to 320 MPa, and the forging time is taken from the range from 0.1 to 2.0 s. Then turn on the welding device, programmed according to the selected process parameters, and perform the entire welding cycle.

Example. In order to evaluate the performance properties of aluminum alloy parts (AA2139) obtained using the proposed method and the prototype method, the following studies were carried out. Two batches of samples were produced. The first batch of blades was manufactured according to the prototype method, and the second - in accordance with the proposed technical solution.

Linear friction welding of parts according to the prototype method was carried out in the following modes: amplitude 3 mm, frequency 45 Hz, welding process pressure 40 MPa, forging pressure 160 MPa.

Linear friction welding of parts according to the proposed method was carried out under the following conditions and modes.

The preparation of the contact surfaces of the parts was carried out in a vacuum chamber, in which a vacuum was first created (1.0⋅10 ^-3 Pa), then argon was introduced into it and at a gas pressure in the vacuum chamber in the range from 0.8⋅10 ^-1 Pa to 1 ,0⋅10 ^-1 Pa, the plasma of an induction high-frequency discharge was ignited, applying a negative bias voltage in the range from 400 to 600 V to the parts being welded and the contact surfaces of the parts were cleaned, removing oxides from them, and then the heating stage was carried out in the same vacuum chamber and forging stage.

Moreover, when assessing the welding results, a satisfactory result (S.R.) for the proposed method was considered to be a result that exceeded the fatigue strength obtained by the prototype method by at least 1.1 times, otherwise the result was considered unsatisfactory (N.R.).

Modes:

- gas pressure (argon) in the vacuum chamber: 0.6⋅10 ^-1 Pa (N.R.), 0.8⋅10 ^-1 Pa (U.R.), 0.9⋅10 ^-1 Pa (U .R.), 1.0⋅10 ^-1 Pa (U.R.), 1.2⋅10 ^-1 Pa (N.R.);

- induction high-frequency (HF) discharge (power - 800 W): negative bias voltage: 300 V (NR), 400 V (UR), 500 V (UR), 600 V (U .R.), 700 V (N.R.). At a voltage of 300 V - incomplete removal of oxides, at 700 V - etching of the base material. In the range from 400 V to 600 V - removal of the oxide film;

- pressure value of the welding process: 20 MPa (N.R.), 30 MPa (U.R.), 90 MPa (U.R.), 180 MPa (U.R.), 200 MPa (N.R.) ;

- time from 0.3 to 6 s: 0.2 s (N.R.), 0.3 s (U.R.), 1 s (U.R.), 4 s (U.R.), 6 s (U.R.), 8 s (N.R.);

- amplitude: 0.5 mm (N.R.), 1 mm (U.R.), 3 mm (U.R.), 5 mm (U.R.);

- frequency: from 40 to 80 Hz, 30 Hz (N.R.), 40 Hz (U.R.), 50 Hz (U.R.), 80 Hz (U.R.), 100 Hz (N.R.) R.);

- pressure value on the contact surfaces of the welded parts at the forging stage: 140 MPa (N.R.), 160 MPa (U.R.), 220 MPa (U.R.), 320 MPa (U.R.), 360 MPa (N.R.);

- forging stage time: 0.05 s (N.R.), 0.1 s (U.R.), 1 s (U.R.), 2 s (U.R.), 3 s (N. R.).

The endurance limit (based on N=20⋅10 ⁶ cycles, 10 samples) of flat samples (Fig. 1) made from AA2139 alloy after linear friction welding (LWW) according to the prototype method is 14 kgf/mm ² , and the resulting LST according to the proposed method is at the level of 18 kgf/mm ² . The decrease in the endurance limit of samples obtained using the prototype method is associated with the presence of oxide inclusions (Fig. 2a) that enter the welded joint due to the lack of removal of the oxide film from the contact surfaces before the LST.

Thus, comparative tests have shown that the proposed method of LSW of parts made of aluminum alloy makes it possible to achieve the stated technical result of the invention - increasing the operational reliability of parts made of aluminum alloys produced by linear friction welding by increasing their endurance limit.

Claims (5)

1. A method of linear friction welding of parts made of aluminum alloy, including the stage of preparing the contact surfaces of the parts, the heating stage, in which the parts are pressed against each other along the contact surfaces with a force that ensures the pressure of the joint welding process at a given amplitude and frequency of the relative movement of the parts along their contact surfaces surfaces, and a forging stage, carried out after stopping the reciprocating movements of parts by applying forging pressure, characterized in that the stage of preparing the contact surfaces of the parts is carried out in a vacuum chamber, in which a vacuum is first created, then argon is released into it and under argon pressure in the vacuum chamber in the range from 0.8·10 ^-1 Pa to 1.0·10 ^-1 Pa, the plasma of an induction high-frequency discharge is ignited, applying a negative bias voltage to the parts being welded in the range from 400 to 600 V and the contact surfaces of the parts are cleaned and removed from them oxides, and then in the same vacuum chamber a heating stage and a forging stage are carried out. 2. The method according to claim 1, characterized in that the pressure value of the welding process is taken in the range from 30 to 180 MPa, time from 0.3 to 6 s, amplitude from 1 to 3 mm and frequency from 40 to 80 Hz, at the stage During forging, the pressure on the contact surfaces of the welded parts is set from 160 to 320 MPa, and the time of the forging stage is taken from 0.1 to 2.0 s. 3. The method according to claim 2, characterized in that the reciprocating movement of the workpieces is carried out with a stopping time interval of 0.05 to 0.3 s. 4. The method according to any one of claims 1-3, characterized in that the blade feather and the turbomachine disk are used as welded parts made of aluminum alloys. 5. The method according to claim 4, characterized in that the coefficient of specific power input when welding turbomachine parts is selected from 2.2 to 3.2 kW.