RU2699423C1 - Brass for superplastic molding of parts with low residual porosity - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to non-ferrous metallurgy, particularly, to brass compositions, and is intended for production of superplastic sheets from Cu-Zn-Al system alloy. Two-phase brass sheet for superplastic molding of articles with reduced residual porosity not exceeding 1.5 % contains the following, wt. %: zinc - 38–42, aluminum - 0.5–2.5, copper is the rest, wherein the brass sheet has a fine-grained structure and relative elongation before the beginning of superplastic deformation of not less than 500 % at the rate of superplastic deformation of 1 × 10cand temperature of 550 °C.EFFECT: technical result is high quality of sheets by increasing relative elongation and significant reduction in porosity during high-temperature deformation.1 cl, 4 ex

Description

The invention relates to the field of non-ferrous metallurgy, in particular to brass compositions and is intended for the manufacture of superplastic sheets from an alloy of the Cu-Zn-Al system.

The main factors determining the realization of the superplasticity effect in brass are the presence of a fine-grained structure in the sheet and the minimization of residual porosity during superplastic deformation. Both factors depend both on the composition of the alloy and on the technological parameters of the sheets. At the moment, the use of brass sheets for the manufacture of parts by the superplastic molding method is limited by the development of post-molding porosity, and, consequently, a decrease in the operational characteristics of the products.

The method of thermomechanical processing of brass L63, which provides a material with increased ductility, is described in patent No. 1643629, published 04/23/1991. The invention can be used in mechanical engineering in the production of semi-finished products and complex products by the method of superplastic molding. At a strain rate of 0.008-0.15 s ^-1 , dynamic recrystallization occurs in the material, which leads to a decrease in stress and an increase in elongation during deformation.

The proposed method can be used for stamping and deep drawing to obtain products of complex shape, however, the technology provides a maximum elongation of 230%, which is not enough for superplastic forming of complex shape parts.

In the patent of the Russian Federation No. 2393265 dated 01/09/2008, a method for producing semi-finished products from lead alpha + beta brass is described, characterized in that the hot pressing of the preforms is performed above the transition temperature of the alpha + beta structure to the beta phase, but 100 ° C lower than the solidus temperature. The alloy LS59-1 (57 ... 60% Cu) is considered.

The disadvantage of this method is the heterogeneity of the structure along the length of the semi-finished product, resulting in instability of properties, which reduces the consumer characteristics of the product.

The closest technical solution to the claimed method is a method for processing two-phase brass copyright certificate No. 503938, registered 10/29/1975. The method describes the processing of two-phase brass containing 58-62% copper, the rest is zinc, including quenching from the single-phase region, deformation with compression 80-90% with exposure at a quenching temperature of 8-12 hours, then deformation to a predetermined sheet thickness at a temperature of 350 -450 ° C.

As a result of processing, a superplastic sheet is obtained, in which a maximum elongation after deformation of about 630% is possible. However, the brass product obtained by superplastic molding in the structure has a strongly developed residual porosity (more than 5%), which greatly reduces the mechanical properties of the product. Mechanical properties yield strength and strength are reduced by 25-35%. High residual porosity is the main disadvantage of a sheet of this composition obtained in this way.

The technical result of the invention is the production of brass for producing parts by the method of superplastic molding with a uniform micrograin structure and low residual porosity.

Brass containing the following components (wt.%):

Zinc-38-42,

Aluminum - 0.5-2.5,

Copper - the rest

was obtained by technology including casting, homogenization annealing, hot and cold rolling. As a result of subsequent heating before superplastic deformation, a homogeneous micrograin structure is formed consisting of two phases α and β (the average grain size of both phases is less than 5 μm). In the process of superplastic deformation of this alloy, the parameters of the grains of the α phase change slightly, and the grains of the β phase undergo dynamic recrystallization, as a result of which their average size decreases to 200 nm. After superplastic deformation, the volume fraction of pores does not exceed 1.5%, which makes it possible to obtain high-quality products with a high level of operational properties. After processing, the alloy has a yield strength of 200 ± 30 MPa, a tensile strength of 500 ± 30 MPa, which do not decrease after deformation.

The concentration of zinc should provide a two-phase structure during high-temperature annealing, and the aluminum content should allow slowing down the diffusion process and form an oxide film on the surface on air. Going beyond the upper and lower limits of the concentration range for zinc does not make it possible to obtain a fine-grained two-phase structure in the temperature region of superplastic deformation. Going beyond the lower boundary of the concentration range for aluminum does not provide the possibility of the formation of an oxide film on the surface, while going beyond the upper limit negatively affects the superplasticity of the alloy.

The optimal strain rate was determined by the results of a series of tests with a jump change in the strain rate. The sheets show the best superplasticity at a temperature of 550 ° C and a strain rate of 10 ^-3 s ^-1 , under these conditions, the elongation to failure is at least 500% and the residual porosity does not exceed 1.5%.

The use of the composition of the brass sheets within the proposed limits ensures the production of products using superplastic molding with high mechanical properties and low residual porosity.

A superplastic sheet under optimal deformation conditions has a relative elongation of more than 450% and a residual porosity of not more than 1.5%, whereas in the prototype and example 4, the residual porosity reached about 5% with similar elongations.

Example 1

An alloy of the following composition Cu-40.5% Zn - 0.5% Al was obtained.

To prepare the alloy, copper of the M00 grade, zinc Ts1 and aluminum of the A7 grade were used. Melting was carried out in graphite-chamotte crucibles with successive introduction of components into molten copper. The melt temperature is 1100 ° C. For a more complete homogenization of the melt, it was kept before casting for 15 minutes. The casting was carried out in a water-cooled mold with cooling rates of at least 3 K / s. This was followed by homogenization annealing of the ingots, after homogenization, the ingots were processed to remove surface defects and the shrink shell was cut off. Hot rolling was carried out at 750 ± 10 ° С, then cold rolling followed by intermediate annealing. The final sheet thickness is 1.2 mm.

This mode provided a structure with a grain size of less than 6 microns, which allows for superplastic forming of sheets. Maximum elongation to break, which may be obtained by uniaxial trials with a constant strain rate 1⋅10 ^-3 s ^-1 at a temperature of 550 ° C was 470%. The residual porosity did not exceed 1.5%.

Example 2

Alloy composition Cu-37.8% Zn-1% Al. A sheet was obtained according to the technology described in example 1. The difference in the percentage of aluminum.

The alloy shows the best properties, as in example 1, at a superplastic deformation temperature of 550 ° C (with an accuracy of maintaining the temperature of 5 ° C) at the same strain rate. This alloy has provided the maximum elongation at break of 500% while maintaining a constant strain rate 1⋅10 ^-3 s ^-1 in the deformation process and up to 1,000% at an initial strain rate 1⋅10 ^-3 s ^-1, and the residual porosity is not exceeded 1 %

Example 3

The alloy composition is Cu-33.3% Zn-2.2% Al. The alloy obtained is the same as in example 1. The difference in the percentage of aluminum.

The alloy shows the best properties, as in example 1, at a superplastic deformation temperature of 550 ° C and 1⋅10 ^-3 s ^-1 strain rate. This alloy provided a maximum elongation to failure of 470% while maintaining a constant strain rate, while the residual porosity was 1.2%.

Example 4

Alloy composition Cu-40.8% Zn. The alloy obtained is the same as in example 1. The difference is in the absence of aluminum additives (the composition is similar to the prototype).

The alloy shows the best properties, as in example 1, at a superplastic deformation temperature of 550 ° C and a strain rate of 1⋅10 ^-3 s ^-1 . This alloy provided a maximum elongation to failure of 620% (300% while maintaining a constant strain rate during deformation), and the residual porosity in this case was more than 5%.

Claims (5)

A sheet of two-phase brass for superplastic forming of products with a reduced residual porosity not exceeding 1.5%, containing copper, zinc and aluminum in the following ratio, wt. %: zinc - 38-42, aluminum - 0.5-2.5, copper - the rest Moreover, it has a fine-grained structure before superplastic deformation and a relative elongation of at least 500% at a superplastic deformation rate of 1 × 10 ⁻³ s ⁻¹ and a temperature of 550 ° C.