JPS6256942B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to lithium-containing aluminum alloys, particularly alloys suitable for use in spacecraft applications. It is known that adding lithium to an aluminum alloy reduces its density and increases its elastic modulus, resulting in a significant improvement in specific stiffness. Furthermore, 0° to 500°C
The rapid increase in the solid solubility of lithium in aluminum over a temperature range of 10 to 10% results in an alloy system that can be precipitation hardened to achieve strength levels comparable to some of the existing industrially produced aluminum alloys. . To date, the potential advantages of lithium-containing alloys have been offset by the difficulties inherent in the actual alloy compositions previously developed and the conventional methods used to manufacture these compositions. Only two lithium-containing alloys have been used for applications in the aerospace field. These are American alloys [i.e. Al-4.5 Cu-1.1
X2020] with the composition Li-0.5 Mn-0.2 Cd (all figures relating to this and future compositions are in weight percent), and the Russian alloy 01420 [i.e.
The alloy described in the specification No. 1172736, which contains Al
―4～7 Mg―1.5～2.6 Li―0.2～1.0 Mn―0.05
~0.3Zr (one or both of Mn and Zr are present)]. For X2020, the density reduction with the addition of 1.1% lithium is 3%, making the alloy extremely high in strength, but also with extremely low levels of fracture toughness, making it advantageous for use under high stresses. isn't it. Additionally, problems with ductility were also found during forming operations. Although Russian Alloy 01420 has a better specific modulus than conventional alloys, its specific strength levels are only comparable to commonly used 2000 series aluminum alloys, and weight savings are achieved only in stiffness-critical applications. can do. Both alloys mentioned above were developed in the 1950s, and a more modern alloy from the 1960s described in technical publications has the composition Al-2Mg-1.5 Cu-3Li-0.18Zr. . Although this alloy has a high degree of strength and stiffness, its fracture toughness is still too low for many spacecraft applications. Therefore, although attempts have been made to overcome the problems associated with high solute contents, e.g. cracking of the ingot during casting or subsequent rolling, many researchers in this field have His interest was in powder metallurgy technology. Although this technology solved some of the problems with the casting route, the technology itself had many inherent drawbacks, so even if one technical problem was solved, another one was created. So it was warm. Problems with the powder route include the removal of residual porosity, contamination of the powder particles with oxides, and practical constraints on the dimensions of the products that can be manufactured. Now, by adding relatively small amounts of magnesium and copper as alloying elements and optimizing the manufacturing process parameters and post-heat treatment, an aluminum alloy with sufficient properties including increasingly high fracture toughness can be produced. I figured it out. The alloy composition in this alloy provides an optimal balance between reduced density and increased stiffness with sufficient strength, ductility and fracture toughness to maximize the degree of weight reduction possible from both reduced density and increased stiffness. It was developed for the purpose of The aluminum alloy according to the present invention essentially consists of an aluminum base, 2.0 to 2.8% by weight of lithium, 0.4 to 1.0% by weight of magnesium, and 1.0 to 1.5% by weight of copper, and further contains 0.2% by weight or less of zirconium and 0.5% by weight or less of manganese. , a particle size selected from the group consisting of 0.5% by weight or less of nickel and 0.5% by weight or less of chromium, and at least one component for controlling particle growth during recrystallization. The preferred range of zirconium addition is 0.1 to 0.15% by weight. The main advantage of more dilute lithium-containing alloys is that they are extremely easy to manufacture and process.
The alloy according to the invention can be manufactured by conventional casting techniques, such as direct cooling semi-continuous casting. In contrast, known alloys have many casting problems, forcing many engineers to use manufacturing techniques based on the powder metallurgy route. The alloy of the present invention with lower solute content is
It can be homogenized more easily and subsequently processed more easily than conventional alloys with relatively high solute contents. Because it has various favorable mechanical and physical properties such as low density and excellent corrosion resistance (excellent corrosion resistance also depends in part on the lower solute content),
The alloy is particularly suitable for use as a spacecraft fuselage material. Composition Al―2.44Li―0.56Mg―
The density of the alloy with 1.18Cu-0.13Zr is 2.54g/ml
For example, the density of 2014 alloy is 2.8g/ml
It is advantageous compared to This corresponds to a density reduction of more than 9% compared to conventional alloys with comparable properties. It will be appreciated that the alloys of the present invention also have the advantage of low amounts of heavy elements that increase density due to their low solute content. For sheet alloys, the preferred magnesium content is about 0.7%. This magnesium level was found to be critical in terms of precipitation phase and subsequent strength levels. Examples of alloys according to the invention are described below, together with their properties and corresponding heat treatment data. Example 1 Composition Al-2.32Li-0.5Mg-1.22Cu-0.12Zr This alloy ingot was homogenized, hot worked to a thickness of 3 mm, and cold rolled to 1.6 mm with an intermediate stage of tempering. The alloy sheet was then solution processed, quenched in cold water, and stretched 3%. Table 1 below shows the average test results of tests carried out at 170°C with various aging times.

[Table] Example 2 Composition Al-2.44Li-0.56Mg-1.18Cu-0.13Zr The details of processing the alloy are the same as in Example 1.
The test results are shown in Table 2 below.

[Table] Example 3 Composition Al-2.56Li-0.73Mg-1.17Cu-0.08Zr The details of alloy processing were the same as in Example 1, except that the stretching ratio was 2%. The test results are shown in Table 3 below.

[Table] Example 4 Composition Al-2.21Li-0.67Mg-1.12Cu-0.10Zr The details of the alloy treatment are the same as in Example 3. The test results are shown in Table 4 below.

[Table] Example 5 Composition Al-2.37Li-0.48Mg-1.18Cu-0.11Zr The alloy of this example was tested in the form of a plate with a thickness of 11 mm. Measured values for vertical and horizontal specimens (average values)
are shown in Table 5. This alloy did not cross-roll.

[Table] Example 6 Composition Al―2.48Li―0.54Mg―1.09Cu―0.31Ni―
0.12Zr The alloy of this example was solution treated at 530°C.
The test was conducted in the form of a 25 mm hot rolled plate that was water cooled and stretched by 2%. The test results are shown in Table 6 below.

TABLE All the alloy materials of the examples described above were produced by conventional water-cooled casting methods, but the alloy systems can also be processed by powder metallurgy techniques. However, the main advantage of the alloy of the present invention is that
Large ingot casting ability. From ingots of this kind it is possible to produce sheets and plates of dimensions comparable to those already produced from customary aluminum alloys in the space industry. The above embodiments are limited to products manufactured in the form of sheets and plates. However, the alloys of the invention are also suitable for producing materials in various forms by extrusion, molding and casting. Example 7 An alloy ingot having the following composition was prepared using, as a starting material, an aluminum ingot with a purity of 99.86% by weight, in which the iron and silicon impurity levels were adjusted to 0.1% by weight or less.

[Table] This alloy ingot was homogenized, hot worked to a thickness of 2 mm, and cold rolled to 1.6 mm with an intermediate stage of tempering. Next, this alloy sheet was further stretched by 2% and then subjected to aging treatment. The influence of age on the mechanical properties of alloy sheets was investigated. The results are shown in the table below.

[Table] We also investigated the effect of stretching ratio on the mechanical properties of the alloy sheet. The results are shown in the table below.

[Table] The mechanical properties of a sample obtained by extrusion molding the above alloy ingot are as follows.

[Table] The alloys of the present invention are not limited to use only in spacecraft. The alloys of the present invention can be used wherever light weight is required, such as in some applications in land and sea vehicles.

Claims (1)

[Claims] 1. Consisting essentially of an aluminum base, 2.0 to 2.8% by weight of lithium, 0.4 to 1.0% by weight of magnesium, and 1.0 to 1.5% by weight of copper, further comprising 0.2% by weight or less of zirconium, 0.5% by weight or less of manganese, Suitable for use in spacecraft, comprising a particle size selected from the group consisting of 0.5% by weight or less of nickel and 0.5% by weight or less of chromium, and at least one component for controlling particle growth during recrystallization. Aluminum alloy. 2. An alloy according to claim 1, consisting essentially of an aluminum base and 2.0-2.8% by weight of lithium, 0.4-1.0% by weight of magnesium, 1.0-1.5% by weight of copper and 0.08-0.2% by weight of zirconium. 3. Claims 1 or 2 consisting essentially of an aluminum base, 2.0-2.8% by weight of lithium, 0.4-1.0% by weight of magnesium, 1.0-1.5% by weight of copper, and 0.1-0.15% by weight of zirconium. alloy.