JPH0713275B2 - High-strength stress corrosion cracking resistant aluminum-based powder metallurgy alloy - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum-based alloy material produced by a powder metallurgy method. More specifically, the present invention relates to an aluminum-based powder metallurgy excellent in tensile strength and stress corrosion cracking resistance. Regarding alloy materials.

(Prior Art) Conventional high-strength aluminum alloys include Al-Cu-Mg (20
00 series) and Al-Zn-Mg-Cu series (7000 series) alloys are well known. It is known that Cu, Mg, and Zn contained in these alloys are effective as a precipitation hardening element because they have a relatively large solid solubility in Al at high temperature and a small solid solubility at low temperature. To obtain a material having specific properties. Another method for increasing the strength of aluminum alloys is to add elements (Zr, Cr, Mn, etc.) that form compounds that have low solid solubility at high temperatures and are difficult to diffuse, and strengthen the dispersion or recrystallize with these compounds. There is a method for preventing coarsening of grains.

On the other hand, structural materials used in equipment in the fields of aviation and space are required not only to have high strength but also to be resistant to cracking when stressed in a corrosive environment.

Therefore, as a material having the above-mentioned two characteristics, that is, high strength and excellent stress corrosion cracking resistance,
-Zn-Mg-Cu based 7075, 7475, 7050, 7150 alloys have been used.

By the way, the production of such an aluminum alloy uses a method of forming a cast ingot from a molten aluminum alloy which has been conventionally performed, and then processing this into a raw material. Since the speed is low, relatively large crystal grains and intermetallic compounds are formed, and the effect remains until the subsequent processing and heat treatment steps, so there is a limit to improving the properties of the finally obtained material. For example, 7000 series alloys are prone to exfoliation corrosion or stress corrosion cracking under heat treatment conditions that give the highest strength, so it was necessary to use a material that had been overaged at the expense of strength.

On the other hand, to improve strength and stress corrosion cracking resistance,
Atomizing the molten metal of Al-Zn-Mg-Cu alloy, hot working,
Methods for solutionizing, quenching and two-step artificial aging have been proposed. (U.S. Pat. No. 3,563,814).

(Problems to be Solved by the Invention) However, in recent years, as the weight of structural members has been reduced, further improvement in material properties is desired, and materials having strength and stress corrosion cracking resistance higher than those of conventional products are required. .

Therefore, it is an object of the present invention to provide a novel high-strength stress-corrosion-cracking-resistant aluminum-based powder metallurgy alloy material having a composition excellent in strength and stress-corrosion cracking resistance.

(Means for Solving the Problems) As a result of intensive studies to overcome the drawbacks of the conventional aluminum alloy materials, the present inventors have found that Zr in the Al-Zn-Mg-Cu-based powder metallurgy alloy material is 0.3- Add 1% and make the average grain size 3
It was found that the strength and the stress corrosion cracking resistance can be improved by restricting the intermetallic compound particle size to 0 μm or less and 5 μm or less, respectively, and the present invention has been made based on this finding.

That is, the present invention is Zn5-10%, Mg2-5%, Cu0.5-3
%, Zr 0.3-1% (above wt%, the same below),
The balance has an alloy composition consisting of Al and inevitable impurities, and
An aluminum-based powder metallurgy alloy material having an average crystal grain size of 30 μm or less and an intermetallic compound grain size of 5 μm or less.

The meaning of limiting the composition of each component in the aluminum alloy material in the present invention is as follows.

Zn is 5-10%. Zn in the alloy composition enhances the strength of the alloy by forming a solid solution or aged precipitation in aluminum, but if less than 5%, its effect is small, and if it exceeds 10%, the intermetallic compound becomes coarse and the ductility of the material decreases. .

Mg is 2 to 5%. Mg also improves the strength of the alloy by forming a solid solution or aged precipitation in aluminum.
If it is less than 5%, the effect is small, and if it exceeds 5%, the intermetallic compound becomes coarse and the ductility of the material decreases.

Cu is 0.5 to 3%. Cu also improves the strength of the alloy by forming a solid solution or aged precipitation in aluminum,
If it is less than 0.5%, its effect is small, and if it exceeds 3%, the corrosion resistance of the material decreases.

Zr is 0.3-1%. Since Zr has a small solid solubility in aluminum and precipitates as a compound, its strength is improved as a dispersion strengthening effect by finely and uniformly dispersing it, and further, it is resistant as a crystal grain coarsening preventing effect by recrystallization. Improved stress corrosion cracking resistance can be obtained. If it is 0.3% or less, these effects are small, and if it is 1% or more, coarse crystals are crystallized as primary crystals and the ductility of the material is lowered.

Incidentally, the aluminum-based alloy material of the present invention, Mn, Cr, Co,
It is not necessary to add Fe, Ni, V, Mo, W, etc., but the addition of one or more small amounts (0.5% or less) does not impair the characteristics.

Next, in the aluminum-based alloy material of the present invention, the average crystal grain size is 30 μm or less and the intermetallic compound diameter is 5 μm or less. If the average crystal grain size exceeds 30 μm, the stress corrosion cracking resistance is not sufficiently improved, and if the intermetallic compound grain size exceeds 5 μm, the ductility deteriorates.

During the production of the aluminum-based alloy material of the present invention, a powder alloy having a target average crystal grain size and intermetallic compound diameter is a molten aluminum alloy, preferably a cooling rate of 500 ° C / se.
It can be produced by subjecting to a treatment of c or more by a gas atomizing method or other method and rapidly solidifying.

In the present invention, the particle size of the aluminum alloy powder obtained by the atomizing method is 150 μm or less.

Usually, this powder is preformed to a density of 70 to 90% of the true density, vacuum degassed at 300 to 450 ° C., and then compression molded to the true density at the same temperature to obtain a billet. Further, this billet is subjected to hot working (extrusion, forging or rolling) to obtain a target material. And solution treatment by the conventional method,
Quenching and aging heat treatment are sequentially performed to obtain a material having desired material properties.

(Example) Next, the present invention will be described in detail with reference to examples.

Examples 1 to 8 Alloys having compositions Nos. 1 to 8 shown in Table 1 were processed by the steps shown below to prepare rod-shaped raw materials, which were Samples 1 to 8 of Examples.

[Sample preparation process]

 1) Alloy preparation and melting 2) Atomizing under argon gas Cooling rate 1000 ℃ / sec or more Average particle size of powder 100μm 3) Preforming 80% of true density 4) Degassing at 400 ℃ vacuum degassing 5) Hot press 400 A billet is formed by compression molding to true density at ℃.

6) Extrude at 400 ° C and extrude ratio of 14 to make a rod with a diameter of 30 mm.

7) Heat treatment After solution treatment at 488 ° C for 1 hour, water cooling is performed.

Then, it is aged at 120 ° C for 24 hours and further at 163 ° C for 24 hours.

For each of the obtained samples, the crystal grain size (measured on the ST plane), the compound grain size, the tensile test, and the stress corrosion cracking test were performed. The results are shown in Table 2.

[Stress corrosion cracking resistance test method]

 Test conditions According to ASTN G47.

(1) Stress load; circumferential direction of extruded round bar.

(2) Cycle: Soak in NaCl solution for 10 minutes and dry for 50 minutes.

(3) NaCl solution; concentration 3.5%, pH 6.4-7.2, temperature 25 ± 3
Use at an amount of 3.2 liters or more per sample surface / dm ² at 1 ℃.
Updated weekly.

(4) Drying; Temperature 27 ± 1 ° C, Temperature 45 ± 6% (5) Test period: 20 days Comparative Example Using alloys with compositions No. 9, 10, 11, and 12 shown in Table 1 below. A rod-shaped material was prepared by the steps shown as Samples 9, 10, 11, and 12 as comparative examples, and these samples were subjected to the same measurements and tests as in the example. The results are also shown in Table 2.

[Sample preparation process]

 1) Alloy preparation, melting, casting A billet with a diameter of 80 mm is prepared.

2) Homogenization treatment The billet is homogenized at 470 ° C for 24 hours.

3) Extrusion 400 ° C, extrusion ratio 14, rod diameter 30mm.

4) Heat treatment Alloy No. 9; 466 ℃ × 1.5 hours solution heat treatment followed by water cooling. Then, an aging treatment is carried out at 107 ° C. × 7 hours and 177 ° C. × 7 hours.

Alloy No. 10; water-cooled after solution heat treatment for 477 ° C x 1.5 hours. Next, aging treatment is performed at 121 ° C. for 5 hours and 163 ° C. for 17 hours.

Alloy Nos. 11 and 12; solution-treated at 488 ° C for 1 hour and then water-cooled.
Then, aging treatment is performed at 120 ° C. for 24 hours and at 163 ° C. for 24 hours.

Tests similar to those in the example were performed on these samples. The results are shown in Table 2.

As is clear from these results, Samples 1 to 8 have mechanical properties equal to or higher than those of the conventional alloy samples 9 and 10, and the stress corrosion cracking resistance is greatly improved.

Further, although Samples 11 and 12 are alloys having components within the scope of the present invention, they are inferior in mechanical properties and stress corrosion cracking resistance due to large average crystal grain size and intermetallic compound grain size.

(Effect of the Invention) The high-strength, stress corrosion cracking-resistant aluminum-based powder metallurgy alloy material of the present invention provides a structural material excellent in strength and stress corrosion cracking resistance. Therefore, it is particularly suitable for members such as aircraft materials which require high material properties.

Claims (1)

[Claims] 1. Zn5-10%, Mg2-5%, Cu0.5-3%, Zr
It is characterized by containing 0.3 to 1% (or more by weight), the balance being an alloy composition of Al and inevitable impurities, and having an average crystal grain size of 30 μm or less and an intermetallic compound grain size of 5 μm or less. High strength stress corrosion cracking resistant aluminum base powder metallurgy alloy.