RU2255135C1 - Method of strain-thermal treatment of aluminum alloys - Google Patents

Abstract

FIELD: methods of reinforcing treatment of aluminum alloys.

SUBSTANCE: the invention is pertaining to the methods of reinforcing treatment of aluminum alloys, in particular, to the methods of is strain-thermal treatment. The offered method provides for processes of a hot straining and aging of an aluminum alloy of Al-Zn-Mg system containing the following alloying additives: manganese, titanium, chrome, zirconium introduced either separately or in a complex in any combinations. At that after a thermal straining conduct either a straining at the temperature of 20-200°C with an extent of 25-50 % and a recrystallization annealing - at the temperature of 500-550°C within 4-8 hours with the following quenching, or a straining at the temperature of 480-520°C with a preliminary seasoning at this temperature for 30-90 minutes with an extent of straining of 20-50 % and the following chilling in water. Before the thermal straining they conduct homogenization. The thermal straining is realized at the temperature of 400-450 °C, and the seasoning process is conducted in one - or two stages. The technical result of the invention is development of a method of the combined strain-thermal treatment ensuring improvement of the plastic performances and resistance to destruction of mainly high-strength aluminum alloys at preservation of the level of their mechanical properties.

EFFECT: the invention presents a developed method of the combined strain-thermal treatment ensuring improvement of the plastic performances and resistance to destruction of mainly high-strength aluminum alloys at preservation of the level of their mechanical properties.

Description

The invention relates to the field of technology for hardening processing of aluminum alloys and, in particular, to methods of deformation-heat treatment.

The basis of existing methods for hardening aluminum alloys are, as a rule, alloying and heat treatment. Using these methods, it was possible to create a wide range of engineering materials based on aluminum, including high strength (σ _in ≥ 686 MPa), the use of which became the basis for the development of modern art specimens, especially aerospace.

Alloy deformation processes for a long time were considered simply as forming, providing the necessary sizes and shapes of the product, although they also took into account the strengthening effect of deformation. In recent years, in connection with the exhaustion of the possibilities of further improving the properties of alloys due to alloying and heat treatment in their classical sense, researchers turned to studying the possibilities of more efficient use of deformation processes as the leading (most powerful) factor in the formation of the structure of metal materials, especially in combination with heat treatment . Such combined deformation-heat treatment today represents a combination of plastic deformation and heat treatment operations combined in one technological process.

A known method of thermomechanical processing of aluminum alloys containing manganese, including deformation and hardening, carried out from one nyagrev, carried out at a speed of 10-15 ° C / min, preliminary aging at temperatures of 5-30 ° C for 0.5-16 hours, plastic deformation with a degree of 5-19% and final aging (patent 2176284, IPC 7 C 22 F 1/04). This technical solution is primarily aimed at increasing strength by increasing the alloying of the solid solution, the completeness and speed of the processes of dispersion hardening, which is ensured by the application at the final stage (between two aging) of the cold deformation process. Indeed, with some restructuring of the structure, this leads to an increase in the strength characteristics, primarily the relative yield strength, and reduces the plastic characteristics and fracture resistance.

Deformation-heat treatment processes, including at the final stage (before aging) low-temperature or even warm deformation, are known as low-temperature thermomechanical processing (NTMO). There is a fairly large number of works devoted to studies of NTMO processes aimed specifically at increasing the strength properties, as a rule, of alloys of small and medium strength. For high-strength alloys (σ ≥ 500 MPa _in) the most urgent problem today is the increasing ductility stock which determines the resistance to brittle fracture and thus provides increased efficiency and operational reliability of highly responsible constructions which use such alloys.

Today, the possibilities of increasing the plastic characteristics of these high-strength alloys by traditional alloying methods, heat treatment, or deformation methods taken separately, which are used today, as a rule, to obtain the necessary shapes and sizes of semi-finished products, are practically exhausted.

The objective of the invention is the creation of a method of combined deformation-heat treatment, providing an increase in plastic characteristics and resistance to destruction of high-strength aluminum alloys, while maintaining the same level of their strength properties.

The proposed method is carried out on high-strength alloys of the Al-Zn-Mg system containing alloying additives Mn, Cr, Ti, Zr, having high processability for all types of plastic deformation, a wide range of quenching temperatures and resistance to grain growth. The conditions for the reconstruction of the structure in such alloys from textured to fine equiaxed grain with a developed substructure and uniform distribution of dispersed precipitates of hardener phases, the combination of which provides increased ductility and fracture work, are determined by the fact that after the usual processes of homogenization and hot deformation at 400-450 ° C, either “warm” deformation is carried out at low temperatures, followed by high-temperature recrystallization annealing and quenching in water, or hot deformation is carried out at elevated temperatures, followed by quenching in water from one heating.

It is also possible that, after standard hot rolling for these alloys at 400-450 ° C, further heating to temperatures of 480-520 ° C, deformation at these temperatures, and immediately after that quenching in water.

Practically the proposed method is as follows:

1. Actually carried out process in the production of thin sheets.

In the production of sheet products (up to 5-6 mm thick), the standard technology includes, after the usual hot deformation at temperatures of 440-400 ° C, which ensures the production of blanks 6-8 mm thick, the so-called warm rolling, which is carried out in the temperature range 200-100 ° C and provides the final sheet thickness. At this stage, the proposed DTO method involves regulating the temperature and the degree of deformation, as well as the exposure time at a given temperature before rolling. After rolling and obtaining the final sheet thickness according to the proposed method, high-temperature recrystallization annealing is carried out followed by quenching in water instead of standard annealing at 400 ° C for 1 hour, intended only to relieve stresses after deformation. Further, the standard technology involves quenching from a temperature of 420-450 ° C in water and aging at a temperature of 100 ° C for 24 hours. For sheets subjected to ATT according to the proposed regime, only aging is naturally carried out.

2. The process for the production of hot rolled plates.

The standard technology for the production of alloy plates of the Al-Zn-Mg system provides for hot rolling in the temperature range 440-400 ° C until the final thickness is obtained, then cooling in air. The hardening of the plates is performed as a separate operation - heating to a temperature of 470 ° C, holding for 1.5 hours with cooling in water, aging 100 ° C, 24 hours. When using the proposed DTO method at the end of the standard rolling mode, the billets are additionally heated to 480-520 ° C and deform at this temperature with predetermined compression ratios (20-50%) and immediately quenched with rolling heating.

These processes were carried out in practice in a production environment, did not cause difficulties and did not require the installation of additional equipment.

The technical result of the invention is achieved by the fact that the proposed method of heat-treatment of high-strength aluminum alloys of the Al-Zn-Mg system containing manganese, chromium, titanium and zirconium, including hot homogenization, hot deformation at a temperature of 400-450 ° C and one-two-stage aging , after the specified hot deformation, provides either deformation at a temperature of 20-200 ° C with a degree of 25-50% and recrystallization annealing at a temperature of 500-550 ° C for 4-8 hours, followed by hardening, or deformation at at a temperature of 480-520 ° C with preliminary exposure at this temperature for 30-90 min, with a degree of deformation of 20-50% and subsequent cooling in water. Moreover, the alloy contains alloying additives of manganese, chromium, titanium, zirconium, either individually or in combination in any combination.

In all cases, the final properties of the semi-finished products after the final operation (one- or two-stage aging) showed that the proposed method of deformation-heat treatment provides optimization of the structural state of the alloys and increase such characteristics as elongation (δ), relative transverse narrowing (ψ), impact viscosity (KCU) 1.3-1.5 times in comparison with serial technology while maintaining the level of strength.

Claims (1)

Method of heat-treatment of semi-finished products from high-strength aluminum alloys of the Al-Zn-Mg system, including hot deformation and aging, characterized in that the alloy contains the following alloying additives: manganese, titanium, chromium, zirconium, either individually or in combination in any combination after hot deformation, either deformation at a temperature of 20-200 ° C with a degree of 25-50% is carried out and recrystallization annealing at 500-550 ° C for 4-8 hours, followed by hardening, or deformation at 480-520 ° C with preliminary exposure at that perature for 30-90 minutes with the strain of 20-50%, followed by cooling in water, wherein before hot deformation is carried out homogenization, hot deformation is carried out at 400-450 ° C, and the aging is carried out single- or two-stage.