RU2451105C1 - Manufacturing method of plates from alloy of aluminium-magnesium-manganese system - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: possibility of complication of geometrical shape of items due to improvement of relative elongation at high-temperature deformation with increased speeds is provided due to the fact that molten metal at temperature of 800°C is poured into water-cooled casting mould; crystallisation is carried out at cooling rate of not less than 15 K/s; after that, homogenisation annealing is performed at temperature of 480°C during 6 h, subjected to hot rolling at temperature of 430°C with total crimping of 50%, and cold rolling is performed as per the following scheme: rolling with crimping of 70%, intermediate recrystallisation annealing at temperature of 510°C during 30 min, and rolling with 70% crimping. Obtained plate has δ_t=320%, σ=17 MPa at temperature of 500°C and deformation rate of 10^-2 s^-1.

EFFECT: optimisation of technology used for obtaining plates from Al-Mg-Mn alloy, which are intended for superplastic moulding.

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Description

The invention relates to the field of metallurgy, mainly to heat treatment and metal forming, and is intended for the manufacture of superplastic sheets of aluminum alloy.

One of the main methods of the superplastic state in aluminum alloys is to achieve a fine-grained structure (I. I. Novikov, V. K. Portnoy “Superplasticity of alloys with ultrafine grain”, 1981).

A number of methods are known in the industry for the manufacture of aluminum alloys with a fine-grained structure (Japan Patent No. 3100146 from 09/13/89, US Patent No. 4,284,437 from 08/18/81), in which the alloy is poured continuously into a strip with a thickness of 5-10 mm, annealed and rolled to cold final size, then conduct recrystallization annealing. But due to the complexity of the process (strip casting) and insufficient degree of deformation during cold rolling, the structure in the substrates turns out to be heterogeneous with inclusions of large intermetallic compounds (up to 9 μm) and a sufficiently large grain size (20 μm), which is unacceptable for superplastic molding.

The closest technical solution to the claimed method is RF patent No. 2042736 dated 08/27/1995, according to which, as a result of hot pressing, hot rolling, cold rolling and recrystallization annealing, aluminum alloy sheets with intermetallic particle size of not more than 2 microns and grain size of not more than 20 microns. However, such a technological process does not allow to obtain the values of the structural characteristics necessary for superplastic molding (grain size less than 10 microns).

The technical task of this invention is to obtain a sheet of aluminum alloy with a homogeneous fine-grained structure and a uniform distribution of dispersed particles of intermetallic compounds, the details of which can be obtained by superplastic molding. To solve this problem, the following technology is proposed: a melt from a temperature of 800 ° C is poured into a water-cooled mold (cooling rate of at least 15 K / s), then homogenization annealing is carried out at a temperature of 480 ° C for 6 hours, subjected to hot rolling at a temperature of 430 ° C with a total compression of 50%. Next, cold rolling is carried out according to the following scheme: rolling with compression of 70%, intermediate recrystallization annealing at a temperature of 510 ° C for 30 minutes, rolling with compression of 70%. As a result of subsequent heating under a superplastic molding, a homogeneous ultrafine-grained structure (grain size less than 5 microns) is formed due to the uniform distribution of intermetallic particles containing together chromium and manganese. The uniform distribution of particles is achieved due to the relatively fast crystallization of the melt, as well as the careful study of the structure during hot and cold plastic deformation.

Example

Alloy of the composition Al - 6.0-6.5 Mg - 0.2-0.6 Mn - 0.08-0.2 0Cr - 0.05-0.30 Fe was processed as follows.

1. For the preparation of the alloy, aluminum of grade A7 or more pure, magnesium Mg90, alloys, for example, “Al - 10 wt.% Mn”, “Al - 5 wt.% Ti” and “Al - 10 wt.% Cr” were used. Melting was carried out in graphite-chamotte crucibles with the sequential introduction of Al - 10% Cr alloys into molten aluminum; "Al - 10% Mn"; "Al - 5% Ti" and pure magnesium. Before the introduction of magnesium, the melt was brought to a temperature of 780 ° C for faster dissolution and less waste losses during subsequent heating to 800 ° C. For more complete homogenization of the melt, it was kept for 15 min at 800 ° С before casting. The temperature of the casting is explained by the fact that primary chromium aluminides are released from the melt below 700 ° C, which subsequently reduces the superplastic properties of the material.

The melt was cast in a semi-continuous casting unit with cooling rates of at least 15 K / s. Slower cooling rates can lead to depletion of the aluminum solid solution due to the release of primary crystals.

The next step in the process is homogenizing annealing of the ingots. Homogenization was carried out at 480 ° C for 6 hours. In this mode, the homogenization of the ingots and the formation of dispersoids are completely completed. After homogenization, the ingots should be processed to remove surface defects and cut off the shrink shell.

Hot rolling was carried out at 430 ± 5 ° C with a total compression of 50%.

Cold rolling was carried out with a total compression of 70%.

Recrystallization annealing at 510 ° С was carried out for 30 min.

The final cold rolling was carried out with a total compression of 70%.

The hardness of the finished sheets was evaluated according to the Vickers method on an IT 5010 hardness tester (GOST 23677-79). The sheet hardness turned out to be 168 ± 5 HV, which subsequently guaranteed the formation of a micrograin structure when the sheets were heated for 20 min to the superplastic deformation temperature.

This mode provided a structure with a grain size of 5 μm, which, in contrast to the most similar technology, allows superplastic forming of sheets, which confirms the fact that the maximum elongation to break obtained during tests with a constant maximum strain rate (1 · 10 ^-2 s ^-1 ) at a temperature of 500 ° C, amounted to 320%.

Claims (1)

A method of manufacturing sheets from an alloy of an aluminum-magnesium-manganese system suitable for superplastic forming of parts of complex shape, including crystallization of ingots at a speed of at least 15 K / s with a casting temperature of at least 800 ° C, homogenization combined with heterogeneous annealing at a temperature of 480 ° C for 6 hours, hot rolling at a temperature of 430 ° C with a total compression of 50%, preliminary cold rolling with a compression of 70%, intermediate annealing at a temperature of 510 ° C for 30 minutes and final cold rolling with a compression of 70% .