RU2489217C1 - Method of sheets production from heat-hardened aluminium alloys alloyed with scandium and zirconium - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy and may be used in production of sheets from high-strength heat-hardened aluminium alloys alloyed by scandium and zirconium. Proposed method comprises smelting, overheating of aluminium melt containing scandium and zirconium to 750-780°C. Melt is cast at 715-730°C in semi-continuous process to flat ingots to be homogenized at 420-440°C for 4 - 10 h, hot-rolled at 360 - 420°C and cold-rolled with total reduction over 70%. Cold-rolled sheets are quenched and aged.

EFFECT: high strength, ductility and residual strength and lo rate of fatigue crack development.

4 tbl, 1 ex

Description

The present invention relates to the field of metallurgy and, in particular, to methods for the production of sheets of high-strength thermally hardened aluminum alloys doped with scandium and zirconium, which are used in aircraft, including aircraft as casing materials. Sheets of aluminum alloys alloyed with scandium and zirconium have a high level of service properties, which is unattainable for sheets of ordinary, traditional aluminum alloys. To obtain sheets with such high properties, it is necessary to strictly adhere to all technological parameters in the production of sheets along the entire technological chain, starting from melting and casting ingots and ends with heat treatment of finished sheets. Only in this case, the unique effect of the combined addition of scandium and zirconium is manifested.

A known method of manufacturing sheets of thermally hardened aluminum alloys, used in world practice, which consists in melting, casting flat ingots at a temperature of 690-700 ° C by semi-continuous casting, homogenization of ingots at 460-520 ° C for 12-24 hours, hot rolling at 380-460 ° C, subsequent cold rolling to the required thickness, hardening and artificial aging (Smelting and casting of aluminum alloys. Reference book. M., Metallurgy, 1983, p.159-177. Production of semi-finished products from aluminum alloys. Reference Owner. M., Metallurgy, 1971, pp 49-75, the patent №2394113 C1 cells. S22S 21/08, 10.07.2010).

Using this method for the production of sheets and: high-strength thermally hardened aluminum alloys doped with scandium and zirconium leads to a complete loss of the positive effect of the aforementioned joint additive. Sheets made of high-strength aluminum alloys alloyed with scandium and zirconium completely lose all their advantages with respect to sheets made of ordinary aluminum alloys.

A known method for the production of sheets of high-strength aluminum alloys containing zirconium additive, which consists in smelting, overheating of an aluminum melt with zirconium to 720-730 ° C and casting flat ingots by a semi-continuous method at elevated temperatures up to 700-710 ° C, homogenizing the ingots at 460 -520 ° C for 12-24 hours, hot rolling at 380-460 ° C, and subsequent cold rolling to the required thickness, hardening and artificial aging (Napalkov V.I., Makhov S.V. Alloying and modification of aluminum and magnesium . M., MISiS, 2002.p.358- 359. Napalkov V.I., Cherepok G.V., Makhov S.V., Chernovol Yu.M. Continuous casting of aluminum alloys (Moscow, Intermet Engineering, 2005, p. 152-178). Prototype.

This method provides the assimilation of zirconium by aluminum melt during melting and casting of ingots and creates the prerequisites for a positive effect of zirconium on the properties of the finished sheets. However, when using this method in the production of sheets containing a joint additive of scandium and zirconium, the positive effect of the joint additive is only partially manifested. The potential of scandium and zirconium is only partially used. Sheets obtained by this method do not achieve the required set of properties.

The proposed method for the production of sheets of high-strength thermally hardened aluminum alloys containing scandium and zirconium includes melting, overheating of an aluminum melt containing scandium and zirconium to 750-780 ° C with a holding time of up to 1 h, casting of flat ingots at a melt temperature of 715-730 ° C, homogenization of ingots at a temperature lowered to 420-440 ° C for 4-10 hours, hot rolling at 360-420 ° C, cold rolling with a total compression of more than 70%, quenching and subsequent artificial aging.

The proposed method for the production of sheets of high-strength thermally hardened aluminum alloys containing scandium and zirconium differs from the known one in that when melting, the aluminum melt containing scandium and zirconium is overheated to 750-780 ° C, maintained at this temperature for up to 1 hour, casting ingots are carried out at a temperature of 715-730 ° C, ingots are homogenized at 420-440 ° C for 4-10 hours, hot rolling is carried out at a temperature of 360-420 ° C, and cold rolling is carried out with a total compression of more than 70%.

The technical effect achieved in this case consists in obtaining sheets with a high complex of service properties not achievable for ordinary traditional aluminum alloys that do not contain the joint addition of scandium and zirconium. The production of sheets according to the proposed method with a unique set of properties is determined by two circumstances: ensuring the optimal degree of decomposition of the solid solution (prior to the coagulation stage) of scandium and zirconium in aluminum formed during the used temperature-time regimes of melting and casting of ingots and, as a result, storing them in the sheets after quenching unrecrystallized polygonized structure with a well-developed fine subgrain structure.

Example

An alloy was prepared based on the Al-Zn-Mg-Cu system with the addition of scandium and zirconium with the following chemical composition (Table 1).

Table 1 Actual chemical composition of Al-Zn-Mg-Cu alloy with scandium and zirconium additives,% by weight Al Zn Mg Cu Sc Zr Mo Be Ti Fe Si The basis 4.66 3.61 0.85 0.21 0.12 0.02 0,0007 0,03 0.09 0.05

Two flat ingots with a section of 165x550 mm and a length of about 1300 mm weighing 340 kg were cast from the above alloy by semi-continuous casting. In the preparation of the melting and casting of ingot No. 1, the usual traditional modes were used: melting was prepared in the temperature range of 700-720 ° C, casting was carried out at a temperature of 700 ° C. In the preparation of the melting and casting of ingot No. 2, the proposed technological regimes were used: the aluminum melt, after introducing Al-Sc and Al-Zr alloys and other transition metals into it, was overheated to 770 ° C, held for about 40 minutes, the required amount of zinc and copper was introduced and after lowering the temperature to 730 ° C, magnesium was added. Molding was conducted at a temperature of 720-725 ° C.

Ingot No. 1 was homogenized at 460 ° C for 24 hours, and ingot No. 2 at 430 ° C for 8 hours. Then, the ingots were mechanically processed into billets for rolling measuring 150 × 530 × 900 mm. After that, the ingots were hot rolled. Ingot No. 1 was heated to 440 ° C and rolled to 6 mm. Ingot No. 2 was heated to 390 ° C and rolled to 9 mm. Then the hot rolled tackle was annealed at 350 ° С for 1 hour, air cooling and cold rolled up to 2 mm. The sheets rolled by the known method received a total compression during cold rolling of 66%, and the sheets by the proposed method 78%.

The 2 mm thick cold-rolled sheets obtained by two methods were water-quenched from a temperature of 470 ° С, straightened by a roller-straightening machine and artificially aged in a two-stage mode of 100 ° С, 10 hours + 150 ° С, 8 hours.

The study of the structure of hardened sheets using a light microscope and x-ray diffraction analysis showed that the sheets obtained by the known method have a completely recrystallized structure, and the sheets obtained by the proposed method had an unrecrystallized polygonized structure. In addition, in the structure of the sheets obtained by the known method, inclusions of primary intermetallic compounds (Al ₃ (Sc, Zr) up to 10 μm in size were observed, which were absent in the sheets according to the proposed method.

The study of thin foils in a transmission electron microscope showed that in the sheets obtained by the known method, the secondary particles (Al ₃ (Sc, Zr) are coagulated, have a diameter of about 50-60 nm and their number in the aluminum matrix is small. the proposed method, the secondary particles (Al ₃ (Sc, Zr) have a spherical shape, a diameter of 10-15 nm, and their number per unit volume of the aluminum matrix is an order of magnitude greater.

The non-crystallized polygonized structure and the presence of a large number of small spherical particles (Al ₃ (Sc, Zr) in the sheets obtained by the proposed method, led to a unique set of service properties of the obtained sheets.

Table 2 presents the results of mechanical tensile sheet tests.

table 2 The mechanical properties of the sheets of the alloy Al-Zn-Mg-Cu-Sc-Zr obtained by the known and proposed method.
Condition: hardening and artificial aging Production method Longitudinal direction Cross direction σ _V , MPa σ ₀₂ , MPa δ,% σ _V , MPa σ ₀₂ , MPa δ,% Famous 504 440 12.0 491 432 IL Proposed 602 526 11.2 582 518 11.8

The sheets obtained by the proposed method have significantly higher strength characteristics at close values with respect to elongation.

и на скорость развития усталостной трещины da/dN (табл.3 и 4).160 × 320 mm specimens were cut from sheets in the longitudinal and transverse directions and tested for fracture toughness $${\text{TO}}_{\text{from}}^{\text{at}}$$

and the rate of fatigue crack development da / dN (Tables 3 and 4).

Table 3

и остаточная прочность $${\text{σ}}_{\text{тр}}^{\text{нетто}}.$$

Состояние: закалка и искусственное старениеCharacteristics of the static crack resistance of Al-Zn-Mg-Cu-Sc-Zr alloy sheets: fracture toughness $${\text{TO}}_{\text{from}}^{\text{at}}$$

and residual strength $${\text{σ}}_{\text{tr}}^{\text{net}}.$$

Condition: hardening and artificial aging The method of obtaining sheets Longitudinal direction Transverse direction $${\text{TO}}_{\text{from}}^{\text{at}}$$

, MPa√m $${\text{σ}}_{\text{tr}}^{\text{net}},$$

MPa $${\text{TO}}_{\text{from}}^{\text{at}}$$

, MPa√m $${\text{σ}}_{\text{tr}}^{\text{net}},$$

MPa Famous 79.0 380 78.0 381 Proposed 85.3 415 89.8 436

и остаточной прочности $${\text{σ}}_{\text{тр}}^{\text{нетто}}.$$

The sheets obtained by the proposed method have higher values of fracture toughness $${\text{TO}}_{\text{from}}^{\text{at}}$$

and residual strength $${\text{σ}}_{\text{tr}}^{\text{net}}.$$

Table 4 Fatigue crack growth rate of Al-Zn-Mg-Cu-Sc-Zr dA / dN alloy sheets, mm / ktsikl. Condition: hardening and artificial aging The method of obtaining sheets Sample cutting direction da / dN at ΔK, equal, MPa√m 10 fifteen twenty 25 thirty Famous Longitudinal 0.24 0.44 1.05 2.47 5.5 Transverse 0.25 0.51 1,07 2,53 5,6 Proposed Longitudinal 0.23 0.40 0.69 1.33 2.61 Transverse 0.23 0.45 0.71 1.12 2.22

The consideration of table 4 shows that the rate of development of a fatigue crack in sheets obtained by the proposed method, at large values of the amplitude of the stress intensity factor ΔK is noticeably lower than that of sheets obtained by the known method, and when ΔK is 30 MPa√m lower by two times.

Tests for low-cycle fatigue were carried out at a loading frequency f = 30 Hz, asymmetry of the cycle R = 0.1, maximum cycle stress σ _max = 160 MPa on samples with stress concentrator α _σ = 2.5. Samples taken from sheets obtained by the known method, stood before the destruction of 180-247 kilocycles, and samples taken from sheets obtained by the proposed method - 380-500 kilocycles.

Sheets were tested for superplasticity at 450 ° C at strain rates of 2 ÷ 8 × 10 ^-3 sec ^-1 . The relative elongation of samples taken from sheets made by the known method was 70-100%, and samples of sheets made by the proposed method was 400-425%.

и остаточная прочность $${\text{σ}}_{\text{тр}}^{\text{нетто}}$$

выше на 7-14%, скорость распространения усталостной трещины при больших значениях размаха коэффициента интенсивности напряжений ΔK значительно меньше (при ΔK=30 МПа√м меньше в два раза), число циклов до разрушения при испытаниях на малоцикловую усталость в два раза больше, кроме того листы, полученные по предлагаемому способу, обладают способностью к сверхпластической деформации.Thus, sheets of alloy Al-Zn-Mg-Cu-Sc-Zr made by the proposed method are 18-20% stronger than sheets made by the known method with the same level of ductility, fracture toughness $${\text{TO}}_{\text{from}}^{\text{at}}$$

and residual strength $${\text{σ}}_{\text{tr}}^{\text{net}}$$

7-14% higher, the propagation speed of a fatigue crack at large values of the amplitude of the stress intensity factor ΔK is much lower (at ΔK = 30 MPa√m less than half), the number of cycles to failure in low-cycle fatigue tests is twice as large, except Moreover, the sheets obtained by the proposed method have the ability to superplastic deformation.

Claims (1)

A method for the production of sheets of high-strength thermally hardened aluminum alloys containing scandium and zirconium, comprising melting and casting flat ingots in a semi-continuous way, homogenization, hot and cold rolling, quenching and artificial aging, characterized in that during melting the aluminum melt containing scandium and zirconium , overheat to 750-780 ° C, incubated at this temperature for up to 1 h, while casting the ingots in a semi-continuous way is carried out at a temperature of 715-730 ° C, the ingots are homogenized at a rate 420-440 ° C for 4-10 hours, hot rolling is carried out at a temperature of 360-420 ° C, and cold rolling is carried out with a total compression of more than 70%.