RU2019335C1 - Method of making bent sections from hard-to-deform aluminium alloys - Google Patents

Abstract

FIELD: metal pressure forming. SUBSTANCE: method of making bent sections from hard-to-deform aluminium alloys by cold profiling over two-four stages in roller-type apparatus by restricted bending and by applying at a final stage a sizing-expanding effort along the whole cross section of the blank comprises steps of using aluminium-copper- lithium alloys as hard-to-deform alloys, performing quenching of the blank before its profiling; applying the sizing-expanding effort in a zone of maximum plastic deformations with a degree of residual deformation, equal to 2-4; subjecting the ready section to artificial aging according to double-stage mode with temperature 120-130 C and 145-160 and with curing over 2-4 hours and 20-30 hours respectively. The method may be used in all machine engineering plants, dealing with bent sections of respective aluminium-lithium alloys. EFFECT: enlarged using range. 1 cl

Description

 The invention relates to the processing of metals by pressure, in particular to the manufacture of profiles from sheet blanks by profiling in rolls, and can be used in mechanical engineering.

 A known method for the manufacture of bent profiles from difficultly deformed alloys by constrained cold bending for two to four transitions with continuous profiling of a flat workpiece in roller devices with the application of a calibrating tensile force at the final transition (see, for example, "Production of bent sheet profiles of increased stiffness from difficult to deform materials) .

When using this method, high mechanical properties of the manufactured profile are not guaranteed with uncertainty in the magnitude and degree of strain of the dressing by stretching; the production of a profile from caked material obtained by cold rolling is not ensured;
thermomechanical processing of workpieces and profiles is not provided, which allows for the majority of hardly deformed aluminum alloys to significantly improve the mechanical properties and performance characteristics of the profiles.

A known method of low-temperature thermomechanical processing (NTMO) of an alloy of an aluminum-magnesium-lithium system (alloy 1420), in which, before forming, the material is quenched with cooling in water, sheet metal parts are stamped, followed by artificial aging at different temperatures (t = 120 ... 250 ^о С0 and holding time τ = 5 ... 15 h, with the application of tensile force during dressing with the degree of deformation ε = 5 ... 15%.

Disadvantages of the process of aging in the temperature range 120-190 ^{° C,} are considered most suitable for aluminum-lithium alloys with increased aging time is gradually reduced elongation in the absence of practically increase _in the tensile strength σ and the yield strength σ _0.2, which complicates technology and increases the manufacturing cycle; when conducting NTMO, σ _in increases no more than 10-15%, and the relative elongation δ is significantly reduced, which does not satisfy the requirements for structural aviation materials; an increase of σ _0.2 due to editing by stretching with a significant decrease in elongation worsens the performance characteristics of product designs.

 There is also a known method of manufacturing bent profiles from hardly deformed sheet materials in two transitions, in which the forming of the profiles is carried out in the cold state by continuous pulling in a roller device with simultaneous support of its side edges, while the axial support force is applied to the profile at the first transition, and at the second transition - axial tensile force. The method adopted as a prototype.

However, when using the method, it is impossible to produce a profile, for example, of cured roll tape, preliminary heat treatment is required; it is impossible to conduct a process with extreme degrees of deformation in order to produce a profile of a complex section shape for the least number of transitions; the presence of a developed calibrating tension does not provide definiteness of the quality and mechanical properties of the profiles;
it is impossible to provide high strength properties of profiles while maintaining ductility.

 This technical solution allows to improve the quality of the profiles due to thermomechanical processing of the material.

 The essence of this technical solution is as follows.

In the method of manufacturing bent profiles from hard-deformed aluminum alloys in the cold state by profiling in two to four transitions in roller devices with a constrained bending or applying a calibrating tensile force over the entire cross section of the workpiece at the final transition, the alloys of the aluminum-copper-lithium system are taken as hard-deformed, immediately before profiling harden the workpiece, and calibrating tensile forces are applied in the focus of the greatest plastic deformations s having a degree of residual strain of 2 ... 4%, the finished profile is artificially aged by a two-step mode with the temperature and exposure respectively 120 ... 130 ^{° C for} 2 ... 4 h; 145 ... 160 ^о С, 20 ... 30 h.

 The method is as follows.

A flat blank of a sheet or strip of aluminum-lithium alloy with a thickness of S _o having a margin of material in width compared to a recess along the midline of the profile of the final dimensions and in the inlet of the bevel “to the whisker” to create initial tangential compression along the ends is subjected to quenching in water with a temperature of 510 ... 530 ^C and a profiled svezhezakalennom state in roller rotating tool for the transition from two to four, depending on the predetermined profile geometries. At the transition of the final shaping under conditions of tight bending (bending with small radii) in the center of the greatest plastic deformations, a tensile force with a degree of residual deformation of 2 ... 4% is applied simultaneously over the entire cross section, ensuring the straightness of the obtained profile. The finished product is subjected to artificial aging to increase its mechanical properties in a two-stage mode at temperatures t ₁ = 120 ... 130 ^o C, exposure 2 ... 4 hours and t ₂ = 145.. . 160 ^о С, holding time 20 ... 30 hours depending on the chemical composition of the alloy.

PRI me R. A number of flat blanks cut from a roll tape of indefinite length, system alloy of aluminum-copper-lithium, for example, marks 1451 rolled on the reel, subjected to quenching in water from a temperature of 525 ± ^{5 °} C, holding 20 min and svezhezakalennom state profiled on volochilno - rolling installation of model VPU-120 / 7.5 in a roller tool, providing plastic flow of metal in the bend zone during cold deformation. Due to the calibrating roller pair, rotating at an increased speed and providing straightening of the profiles at the exit of VPU-120 / 7.5, tensile force with a degree of residual deformation ε = 1.5 was applied in the focus of constrained bending. . . 3.2%. At ε> 4.5% under constrained bending, a decrease in the strength characteristics and ductility of the profile was observed. At high stiffness of the corner part of the profiles due to local thickening of the material, it was not always possible to equalize the residual stresses over the cross section if ε≅ 1.5%. Prepared profiles held at artificial aging temperatures t ₁ = 125 ± ^{5 °} C, holding for 3 hours, t = ₂ 150 ± ^{5 °} C, holding for 20 hours. With the initial mechanical properties _{in the} coiled ribbon σ = 215-245 MPa, σ _{0, 2} = 200-215 MPa, δ ≈2%, profiles had mean values of the mechanical properties of σ _in = 480-500 MPa, σ _0,2 = 450 MPa, δ = 7,2-8,0%.

Claims (1)

The METHOD of MANUFACTURING BENT PROFILES FROM DIFFICULTY DEFORMABLE ALUMINUM ALLOYS in the cold state by profiling for two or four transitions in roller devices by constrained bending and applying the final transition of calibrating tensile force over the entire cross-section of the billet, which is more difficult to alloy, is more difficult to alloy lithium, immediately before profiling, the workpiece is quenched, and calibrating tensile forces are applied in the focus of the greatest elastic deformations with a degree of residual deformation equal to 2 - 4%, while the finished profile is subjected to artificial aging according to a two-stage regime with temperature and exposure, respectively, 120 - 130 ^o С, 2 - 4 h, 145 - 160 ^o С, 20 - 30 h.