JPS63307239A - Al alloy having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain an Al alloy improved in corrosion resistance by specifying the compsn. and recrystallization ratio of the Al alloy contg. Li. CONSTITUTION:The titled Al alloy is obtd. by incorporating 0.5-4.0wt.% Li thereto and regulating the recrystallization ratio to 30-80%. As for Li content, the effect of the desired decrease of sp.gr. and the improvement in modulus of elasticity can not be expected in the case of <0.5% and the 8 phase is coarsely and drastically deposited to considerably deteriorate the ductility and toughness thereof in the case of >4.0% content. Said prescribed recrystallization ratio can furthermore be obtd. by controlling the working conditions and heat treatment conditions preperly. By this method, partial recrystallization is attained and the structure is made inhomogeneous to partially disperse the deltaphase of the grain boundary, and to improve the corrosion resistance of the Al alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to Li-containing An) alloys with improved corrosion resistance.

[Prior Art] A11 alloy containing Li has poor ductility and toughness, and there are many studies and inventions aimed at improving these properties.

Regarding the corrosion resistance of these alloys, although methods have been proposed to improve the corrosion resistance through surface treatments (anodic treatment, cladding with pure Al, etc.), no substantial improvements have been attempted through manufacturing methods. Although the surface treatment method is certainly an effective means for improving corrosion resistance, corrosion resistance becomes a problem.

It is known that the corrosion resistance of Aj7 alloy containing Li is greatly affected by the segregation of components and the distribution of precipitates, but at present no simple and effective method for improving corrosion resistance has been found. .

[Problems to be Solved by the Invention] The present invention attempts to solve the following problems of the prior art.

(1) The crystal grains obtained by the normal manufacturing method of Li-containing AΩ alloys are pancake-like extensions of the crystal grains of the initial material, and the grain boundaries are selectively corroded, resulting in so-called exfoliation corrosion. is likely to occur.

(2) Stress corrosion cracking also occurs in members used under stress.

That is, the present invention aims to improve the corrosion resistance of LL-containing AΩ alloys.

[Means for solving the problem] The present inventors used various Li-containing AN alloys as test materials, changed the heating temperature, processing rate (area reduction rate), and finishing temperature by rolling and extrusion, Corrosion resistance after temporary solution treatment was determined according to ASTM G34 and JIS H8711.
As a result of research and investigation using prescribed corrosion tests, it was found that Ai) alloys containing 0.5 to 4.0 weight percent Li do not peel off even after performing peel corrosion tests when the recrystallization rate is 30 to 80%. It was found that the corrosion resistance was excellent.

That is, the present invention is an A47 alloy with excellent corrosion resistance, which is characterized by containing 0.5 to 4.0% by weight of Li and having a recrystallization rate of 30 to 80%.

[Operation] The present applicant previously proposed in Japanese Patent Application No. 61-47317 that
A method for grain refinement of i-containing An) alloy was filed.

As a result of further studies on the grain refinement method of this Li-containing Aρ alloy, the present inventors found that Li-containing AI! It has been found that in order to improve the corrosion resistance of alloys, it is necessary to recrystallize fine parts of the microstructure. The technical factors are shown below.

In the case of Li-containing AΩ alloys, when the A11-Liδ phase precipitates in a chain on the grain boundaries, preferential corrosion of the grain boundaries occurs, and exfoliation corrosion occurs under static conditions or stress corrosion cracking occurs under stress.

However, when treatments such as solution treatment and aging are performed after processing in order to obtain a predetermined strength, it is impossible to completely eliminate the precipitation of the A, 17-Liδ phase.

By controlling the processing and heat treatment conditions and achieving partial recrystallization, the structure becomes finer and it is possible to locally disperse the precipitation of the δ phase mainly on the unrecrystallized stretched grain boundaries. Become.

In such materials, corrosion is localized and the degree of corrosion is slight.

The present inventors completed the present invention as a result of conducting various tests on various Li-containing AfI alloys as shown in FIG. 1 and Table 2 of Examples described later. That is, the present invention aims to control the recrystallization rate of A and Q alloys containing 0.5 to 4.0% Li to 30 to 80%, thereby significantly improving the corrosion resistance.

Note that when the recrystallization rate is higher than 80%, although δ is dispersed, localization cannot be achieved, resulting in poor corrosion resistance.

Here, the recrystallization rate was defined as the area ratio (%) of grains that were not etched white when observed with a deer optical microscope at a magnification of 400 times after etching with Keller's reagent.

In the present invention, processing and heat treatment conditions for obtaining a predetermined recrystallization rate are not particularly defined.

However, as an example of a general manufacturing process, ■ Homogenization treatment -
(1) Processing (cold to hot) - (2) Solution treatment - (2) Aging or processing (cold to warm) or a combination thereof, and control of (1) and (2) is relatively important.

In addition, in the present invention, in addition to Li, Cu: 4.0% or less, Mg
: 4.0% or less, Mn: 1.0% or less, Cr: 0.5%
Below, Zr: 0.5% or less, Ti: 0.2% or less, B:
0.015% or less, V2 0.2% or less, Si: 0.5%
Adding the following and Fe: 0.5% or less alone or in combination will not impair corrosion resistance.

Further, the same effect can be obtained with an ingot material or a powder preform material, and the hot working method may be any method such as a rolling method, a forging method, or an extrusion method, and is not limited to -4=.

Next, the reasons for the limitations of the present invention will be described.

Li content 2: 0.5 to 4.0% If it is less than 0.5%, the effects of reducing specific gravity and improving elastic modulus, which are the features of Li-containing Al1 alloys, cannot be expected.

Moreover, if it exceeds 4.0%, the δ phase will precipitate coarsely and in large quantities, resulting in a significant deterioration in ductility and toughness.

Cu and Mg are important elements that increase strength through aging precipitation, but even if they each contain more than 4.0%, not only will further strengthening not be obtained, but excessive addition will also cause Deteriorates hot workability. Therefore, the upper limit of the amount added is preferably 4.0%.

Mn, Cr, and Zr are important elements that, when added in appropriate amounts, form fine intermetallic compounds in the alloy, prevent grain coarsening during heat treatment, and form a fine grain structure. However, if Mn is added in excess of 1.0% and Cr and Zr are added in excess of 0.5% each, coarse intermetallic compounds are likely to be formed, which may deteriorate the cold and hot workability of the material. without deteriorating toughness. Therefore, Mn
, the upper limits of the amounts of Cr and Zr added are 1.0% for Mn and 1.0% for C.
Preferably, r and Zr are each 0.5%. If each element is added in an amount below its upper limit, the above-mentioned deterioration is not observed and there is no problem.

Ti, B, and V are effective additive components for obtaining a fine structure after cold and hot working in order to refine the casting structure. That is, Ti, B, and (2) are elements useful for stabilizing the structure of the material. However, even if Ti and V are contained in amounts exceeding 0.2% each and B in amounts exceeding 0.015%, the above-mentioned effects do not change. Rather, the proportion of undissolved intermetallic compounds increases, deteriorating cold and hot workability.

Therefore, the upper limit of the amount of Ti, B, and V added is 0.2 for Ti.
%, B is preferably 0.015%, Vl;lto, 2%.

Si and Fe are effective elements for increasing the strength and heat resistance of materials, but if each is added in excess of 0.5%, they cause a decrease in toughness. Therefore, it is preferable that the upper limit of the amount of Si and Fe added is 0.5% each.

Next, the recrystallization rate was set at 30 to 80% because, in order to improve corrosion resistance, it is necessary to achieve partial recrystallization to make the structure non-uniform and prevent full-scale corrosion. Recrystallization rate 30%
If it is less than that, local dispersion of the grain boundary δ phase cannot be achieved. On the other hand, 8
If it exceeds 0%, local dispersion of the grain boundary δ phase cannot be achieved, so corrosion resistance cannot be improved. Therefore, the appropriate range is 30 to 80%.

Next, examples of the present invention will be described.

[Example] [Example 1] First, an AΩ alloy (◇◆ mark) containing 2.61j-1,3Cu-0,12Zr (at least % by weight); BLi-2
, 6Cu-0,7Mg-0,15Zr-containing Aρ alloy (
The heating temperature, processing rate (section reduction rate), and finishing temperature were changed as follows by rolling and extrusion. b:400
°C heating, 70% processing (rolling) c: 400 °C heating, 50
% processing (rolling) d: 450°C heating, 30% processing (rolling)
e: 500°C heating, 60% processing (rolling), solution treatment (480-520°C), temporary aging (190°C x 24 hours)
As a result of investigating the corrosion resistance after r), the recrystallization rate was 30 to 80.
%, no peeling occurred even after conducting a peeling corrosion test specified by ASTM G34, and it was revealed that the corrosion resistance was excellent. The results of the test are shown in Figure 1.

In addition, ◇○... No exfoliation corrosion ◆... Exfoliation corrosion [Example 2] Next, using the alloys shown in Table 1, processing and solution treatment conditions shown in Table 2 were carried out, ASTM G34 and JIS
A corrosion test was conducted according to H8711.

Table 1 shows the chemical composition (% by weight) of the test gold, and Table 2 shows processing and solution treatment conditions and corrosion test results.

Before the processing in Table 2, homogenization treatment at 520-550°C, and cold working at 0-8% and 180-190°C for solution treatment.
Aging is carried out at a strength level of 45 to 60) cg f
/ +n+a 2 is shown as a result of corrosion of the obtained alloy.

No. 1 to No. 11 in Table 2 each had an appropriate recrystallization rate range, so even in the exfoliation corrosion test, they remained at most pits, and stress corrosion cracking did not occur. No
, No. 12 undergoes severe processing at low temperatures, so the recrystallization rate is too high at 83%, resulting in poor corrosion resistance. Or No, 1
On the other hand, No. 3.14 has a relatively high temperature and low workability, has a recrystallization rate of less than 30%, and has poor corrosion resistance.

[Effects of the Invention] The corrosion-resistant alloy 1 of the present invention has a lower specific gravity and a higher elastic modulus than the normal A1 alloy, so it is effective in reducing the weight of aircraft and has excellent corrosion resistance, so it can be used as a structural material. It is a very promising alloy, and its uses can be expanded not only to aircraft but also to rockets, vehicles, light structures in coastal areas, etc.

[Brief explanation of drawings]

FIG. 1 is a graph of the corrosion test results of working finish temperature and recrystallization rate in Example 1.

Claims (1)

[Claims] Contains 0.5 to 4.0% by weight of Li and has a recrystallization rate of 3
Al with excellent corrosion resistance characterized by a content of 0 to 80%
alloy.