RU2623557C1 - METHOD OF THERMOMECHANICAL PROCESSING OF THERMALLY-SIMPLIFIED ALUMINIUM ALLOYS OF Al-Cu-Mg-Mn-Ag SYSTEM - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used in the aerospace, transport and other industries to manufacture semi-finished products from thermally strengthened aluminium alloys of the Al-Cu-Mg-Mn-Ag system. The method includes preliminary homogenization annealing in the temperature range 500-520°C for at least 20 hours, subsequent quenching into water and intensive plastic deformation of the billet at room or cryogenic temperature with the accumulated true degree of deformation e≥4.

EFFECT: set of proposed operations makes it possible to increase the yield strength of alloys to 760 MPa, the ultimate strength to 850 MPa while maintaining a high level of plastic properties.

2 cl, 1 ex, 1 tbl, 3 dwg

Description

The invention relates to the field of thermomechanical processing of thermomechanical materials with a change in their mechanical properties and can be used in aerospace, transport and other industries for the manufacture of semi-finished products from thermally hardened aluminum alloys of the Al-Cu-Mg-Mn system, additionally alloyed with Ag.

The development of the aerospace industry is inextricably linked with improving the operational characteristics of aircraft, improving fuel efficiency and reducing costs associated with their manufacture and maintenance. Improving performance and fuel efficiency can be achieved by reducing the mass of individual structural elements through the use of materials with an improved set of mechanical properties. There are several approaches leading to an increase in the mechanical characteristics of aluminum alloys of the Al-Cu-Mg-Mn system: 1) varying the chemical composition of the alloys, 2) optimizing the heat treatment conditions, 3) applying thermomechanical treatment. The first two approaches in relation to alloys of the Al – Cu – Mg – Mn system have limited possibilities in the direction of a noticeable quantitative improvement in the mechanical properties. Practice shows that thermomechanical processing contributes more effectively to the increase of mechanical properties.

Known alloy containing, wt.%: Cu - 4.97; Mg 0.84; Mn 0.61; Ag - 0.53; V is 0.02; Fe - 0.06; Si - 0.05, the rest is aluminum (US patent No. 5652063, IPC C22C 21/00, publ. July 29, 1997). Alloy processing includes obtaining high-quality castings, homogenizing the workpiece in the temperature range 513 ... 527 ° C, quenching from the homogenization temperature, 8% cold deformation, and artificial aging at 163 ° C for 10 days (state T8). After this treatment, the alloy has the following mechanical characteristics: tensile strength 565 MPa, elongation of 9%.

Known alloy containing, wt.%: Cu - 6.0; Mg - 0.5; Mn - 0.5; Ag - 0.4; V is 0.1; Zr 0.15; Si - 0.04, the rest is aluminum (US patent No. 4772342, IPC C22C 21/16, publ. September 20, 1988). The alloy processing method involves obtaining a melt of a given chemical composition in a crucible of an induction furnace from high-purity powders of chemical elements with a dispersion of not more than 50 μm, crystallization of castings with a diameter of 36 mm, subsequent homogenization for 5 hours at a temperature of 450 ° C, hot extrusion to a diameter of 9 mm at a temperature 420 ° C, annealing for 3 hours at 530 ° C, quenching in water from this temperature, followed by artificial aging at 195 ° C for 7 hours. After processing, the alloy has a tensile strength of 620 MPa and an elongation of 8.5%.

Known methods for thermomechanical processing of aluminum alloys of the Al-Cu-Mg-Mn-Ag system, as a result of which they reach a tensile strength of 480 ... 540 MPa and a relative elongation of 8 ... 15% (US patents No. 7704333, IPC C22C 21/12, published April 27, 2010 G., No. 5376192, IPC C22C 21/00, published December 27, 1994). These methods are based on hot deformation by forging, rolling or extrusion of homogenized ingots, quenching after hot deformation, cold stretching or compression with degrees of deformation of 1.5 ... 15% and subsequent artificial aging.

However, the known methods do not provide a sufficient increase in strength characteristics.

A known method of thermomechanical processing (RF patent No. 2425165, IPC C22C 21/16, published July 27, 2011) of a complex-alloyed aluminum alloy of the Al-Cu-Mg-Mn-Ag system, which includes equal channel angular pressing at a temperature of 300 ° C in three the passage, rolling the billets obtained at room temperature to a thickness of 2 mm., quenching from a temperature of 525 ° C and artificial aging for 6 hours at a temperature of 190 ° C. As a result of this treatment, an improved set of strength properties is achieved: yield strength 490 MPa, tensile strength 550 MPa, elongation of 10%.

However, the achieved set of properties is not high enough for use in critical structures.

The technical result of the invention is to increase the level and uniformity of the strength characteristics of thermally hardened aluminum alloys of the Al-Cu-Mg-Mn-Ag system by creating a fragmented ultrafine-grained structure with strengthening phases that is homogeneous in the longitudinal and transverse sections.

The specified technical result is achieved by the method of producing ultrafine-grained preforms, including preliminary homogenization annealing in the temperature range 500 ... 520 ° C for at least 20 hours, subsequent quenching in water and intense plastic deformation of the preform at room or cryogenic temperature with the accumulated true degree of deformation e≥4 .

According to the invention, intense plastic deformation is carried out by equal-channel angular pressing, or rolling, or torsion

It is known that the necessary conditions for the formation of an ultrafine-grained (UFG) structure, which contains predominantly high-angle boundaries, which makes it possible to achieve an unusually high strength in metallic materials, is the realization of intense plastic deformation at relatively low temperatures (below the recrystallization temperature) with a true accumulated degree of deformation e≥4 [R.Z. Valiev, I.V. Alexandrov. Volumetric nanostructured metallic materials. - M.: IKC "Akademkniga", 2007 - 308 p. (p. 322-328)].

In this case, grain boundary hardening makes the greatest contribution to increasing the strength of the alloy by reducing the grain size of less than 0.5 μm in accordance with the well-known Hall-Petch relation for yield strength [Yu.V. Koks Physics of strength and ductility. Per. from English., collection. M .: Metallurgy, 1972. 304 pp.], As well as due to the formation of high-angle grain boundaries with a total fraction of at least 60%, which, combined with small-angle and special borders, make the largest contribution to hardening. The large-angle grain boundaries contribute to an increase in plasticity due to the involvement of grain-boundary processes in the deformation, in particular, due to the accumulation of dislocation at the grain boundaries. An additional contribution to plasticity is also made by the relatively low dislocation density (less than 10 ¹⁴ m ^-2 ) inside ultrafine grains, their equiaxial shape, and relatively equilibrium boundaries, which increases the uniformity of the plastic flow and reduces the likelihood of early localization of deformation [E. Ma Eight routes to improve the tensile ductility of bulk nanostructured metals and alloys, JOM (2006) P. 49].

The technical result of the invention is achieved due to the proposed set of operations, providing the above properties, which includes:

- homogenization of castings at temperatures of 500 ... 520 ° C for 20 ... 30 hours. Provides dissolution of coarse nonequilibrium eutectic inclusions and uniform distribution of alloying elements over the volume of the ingot;

- quenching in water with a temperature of homogenization;

- фазы (MgAg) и U- фазы (AlMgAg) равноосной формы, выделение которых невозможно при условиях стандартной упрочняющей термической обработки. Последовательность выделения фаз принимает следующий вид: α твердый раствор,

фаза -

фаза,

фаза. Описанные структурные изменения, вызванные интенсивной пластической деформацией, наряду с повышенной плотностью дефектов обеспечивают достижение высоких прочностных свойств.- intense plastic deformation at room or cryogenic temperature with a true degree of deformation e≥4, which results in a refinement of the structure and formation of a fragmented nanostructure of the alloy matrix, decomposition of a supersaturated solid solution with the formation of thermodynamically stable hardening phases that heterogeneously nucleate during deformation at subgrain boundaries and dislocation clusters. Moreover, an increase in the degree of deformation to e≥4 promotes the formation of the θ phase (Al2Cu), S phase (Al2CuMg), and

- phases (MgAg) and U-phases (AlMgAg) of equiaxial form, the isolation of which is impossible under the conditions of standard hardening heat treatment. The sequence of phase separation takes the following form: α solid solution,

phase -

phase,

phase. The described structural changes caused by intense plastic deformation, along with an increased density of defects, ensure the achievement of high strength properties.

The invention is illustrated by drawings, where in FIG. 1 shows the dependence of flow stresses on the degree of deformation for various types of processing: 1 - for the deformed state by the proposed method, 2 - after hardening heat treatment for maximum hardness (quenching from a temperature of 510 ° C and subsequent artificial aging for 10 hours at a temperature of 165 ° C), 3 - after homogenizing annealing for 24 hours at a temperature of 510 ° C, 4 - in the delivery state. In FIG. 2 presents the microstructure of the alloy obtained by transmission electron microscopy after processing by the proposed method (e≈6). In FIG. 3 shows the dependence of microhardness on the temperature of exposure (annealing) for 1 hour on samples processed by the proposed method.

An example embodiment of the invention

From cast aluminum alloy of the following chemical composition, wt.%: Cu 4,4; Mg 0.5; Mn 0.4; Ag 0.5; Ti 0.1; the rest is aluminum, by machining, they prepared billets for subsequent thermomechanical processing.

Homogenization annealing was carried out at a temperature of 510 ± 5 ° C for 24 hours, followed by quenching in water. Then, intense plastic deformation by torsion method (IPDK) was carried out under high hydrostatic pressure: one preform at room temperature to a true degree of deformation e≈6, another preform at a temperature t = -50 ° С to a true degree of deformation e≈4.

To assess the effect of thermomechanical processing on the mechanical properties of the alloy, comparative tensile tests were carried out at room temperature of a series of samples made from semi-finished products in various states (Fig. 1). The results are shown in the table.

As can be seen from the data obtained, the proposed method of thermomechanical treatment allows to increase the strength characteristics of the alloy compared to standard hardening heat treatment by about 60% with an increase in ductility to 55%.

The results of transmission electron microscopy (TEM) showed that a uniform fragmented structure consisting of a mixture of high-angle and small-angle grain boundaries is formed during IPDC, the ring-shaped electron diffraction pattern indicates a high density of dislocations (Fig. 2).

The study of the effect of subsequent exposures for 1 hour in the temperature range 100 ... 300 ° C on microhardness and mechanical properties (Fig. 3) showed that up to 180 ° C after thermomechanical processing according to the proposed invention, the alloy retains its high strength characteristics, which opens up large the possibility of using the alloy as a structural material with an operating temperature of up to 165 ° C. The proposed method can be used as the main method of forming high-strength properties in aluminum alloys of the Al-Cu-Mg-Mn-Ag system.

Thus, the proposed invention improves the level and uniformity of the strength characteristics of thermally hardened aluminum alloys Al-Cu-Mg-Mn-Ag.

Claims (2)

1. The method of thermomechanical treatment of thermally hardened aluminum alloys of the Al-Cu-Mg-Mn-Ag system, including preliminary homogenization annealing in the temperature range of 500-520 ° C for at least 20 hours, subsequent quenching in water and intense plastic deformation of the workpiece at room or cryogenic temperature with the accumulated true degree of deformation e≥4. 2. The method according to p. 1, characterized in that the intense plastic deformation is carried out by equal-channel angular pressing, or rolling, or torsion.

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