JPH04337044A - High strength al-li alloy excellent in scc resistance - Google Patents

Abstract

PURPOSE:To obtain an Al-Li alloy having high specific-strength and high specific-elasticity and combining superior SCC resistance with high strength. CONSTITUTION:This alloy has a composition containing, by weight, 0.5-3.5% Li, 0.5-6.0% Cu, and 0.05-1.5% Zn and further containing at least one element selected from the group consisting of 0.05-3.0% Mg, 0.05-0.3% Zr, 0.05-0.3% Cr, 0.05-1.5% Mn, 0.05-0.3% V, and 0.005-0.1% Ti.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength Al--Li alloy having both excellent SCC resistance and high strength.

0002

[Prior Art] Al-Li alloys have high specific strength and high specific elasticity, so they have been put to practical use as high-strength Al alloys that meet the characteristics required for next-generation products in the aircraft, automobile, and electrical industries. is being considered. In order to use it for these purposes, it is essential that the material properties such as strength, ductility, toughness, fatigue properties, and corrosion resistance are equivalent to or better than those of conventional Al alloys. Conventionally,
Various studies have been conducted on Al-Li alloys, but
In particular, Al-Li-Cu system and Al-Li-Cu-Mg
alloys have been developed with the aim of putting them into practical use.

0003

However, when used in applications requiring good corrosion resistance (SCC resistance), conventional Al-Li alloys do not necessarily have satisfactory properties. That is, the conventional Al-Li alloy is AA70, which was previously used as a high-strength Al alloy.
SCC resistance equivalent to that of 75 alloy and AA2024 alloy has not been obtained.

The present invention has been made in view of the above problems, and is a high-strength Al having high specific strength and high specific elasticity, as well as excellent SCC resistance and high strength. -An object of the present invention is to provide a Li-based alloy.

[0005]

[Means for Solving the Problems] The high-strength Al-Li alloy with excellent SCC resistance according to the present invention has Li;
0.5-3.5%, Cu; 0.5-6.0% and Zn; 0.05-1.5%, further Mg; 0
．． 05-3.0%, Zr; 0.05-0.3%, C
r; 0.05-0.3%, Mn; 0.05-1.5
%, V; 0.05-0.3% and Ti; 0.005
It is characterized by containing at least one element selected from the group consisting of ~0.1%, with the remainder being Al and inevitable impurities.

[0006]

[Operation] The inventors of the present application have conducted various experimental studies to improve SCC resistance while maintaining the features of Al-Li alloys having high specific strength and high specific elasticity. It has been found that the intended purpose can be achieved by containing it in the predetermined content shown below.

[0007] The reasons for adding the ingredients and the reasons for limiting the composition of the Al-Li alloy according to the present invention will be explained below.

Li Li is an essential element for lowering the density and increasing the elasticity of the alloy, and is also an element that contributes to improving the strength. In the aging treatment process of the final heat treatment in manufacturing, Li is
and Cu to precipitate as δ' phase or T1 phase,
It contributes to age hardening. Li content is 0.
If it is less than 5% by weight, the effect of lowering density and increasing elasticity will be small, and if it exceeds 3.5% by weight, ductility and toughness will be significantly reduced. Therefore, the Li content is set to 0.5 to 3.5% by weight.

[0009]Cu Cu is an element that contributes to improving the strength of the alloy, and is added to Al, Li, or M during the aging process of the final heat treatment in manufacturing.
It combines with g and precipitates as a T1 phase, θ' phase, S' phase, etc., and contributes to age hardening. However, if the Cu content is less than 0.5% by weight, the desired high strength cannot be obtained, and on the other hand, if it exceeds 6.0% by weight, the ductility and toughness are significantly reduced, and the effect of lowering the density is also reduced. . Therefore,
The content of Cu is 0.5 to 6.0% by weight.

Zn Zn is an element that contributes to improving the SCC resistance of aluminum alloys, and is an added element to achieve the main purpose of the present invention. If the Zn content is less than 0.05% by weight, the effect of improving SCC resistance is small. On the other hand, when the Zn content exceeds 1.5% by weight, the ductility and toughness of the aluminum alloy decrease significantly.

[0011] Although the mechanism by which Zn improves SCC resistance has not yet been clearly clarified, according to the findings obtained through numerous experimental studies by the inventors of the present application, the effects of adding Zn are as follows. it is conceivable that. That is,
By adding Zn, the morphology of the sub-grain boundaries and intragranular precipitated structures changes, and the electrochemical properties also change. the result,
The form of corrosion becomes a general corrosion type, which improves SCC resistance. In any case, as a result of numerous experimental studies conducted by the inventors of the present application, the Zn content was determined to be between 0.05 and 1.5.
It was found that SCC resistance can be improved without deteriorating ductility and toughness by adjusting the amount by weight%.

Zr Zr is an element that contributes to improving strength and ductility by controlling the microstructure morphology after final heat treatment. When the Zr content is less than 0.05% by weight,
Recrystallization occurs and the microstructure becomes larger, and although the strength is not significantly reduced, the ductility is significantly reduced. When the Zr content exceeds 0.20% by weight, the effect is saturated and large crystallized substances containing Zr are generated, resulting in a decrease in strength, toughness, etc. Therefore, when used in applications requiring particularly excellent strength and toughness, Zr
The content is 0.05 to 0.20% by weight.

Mg Mg is an element that improves strength without reducing ductility and toughness, and precipitates as S' phase during the aging process of the final heat treatment in the manufacturing process and contributes to improving strength. Therefore, it is optionally added when particularly high strength is required. If the Mg content is less than 0.05% by weight, the effect of improving strength will be small, and if the Mg content exceeds 3.0% by weight, ductility and toughness will decrease. Therefore, when adding Mg, the content should be 0.05 to 3.0% by weight.

Cr, Mn, V Cr, Mn, and V, like Zr, are elements that contribute to improving strength and ductility by controlling the microstructure morphology after final heat treatment. For this reason, it is preferable to add each of these elements especially for applications requiring high strength and high ductility. If the content of any of these elements is less than 0.05% by weight, recrystallization occurs and the microstructure becomes larger, resulting in a decrease in ductility. on the other hand,
Cr: 0.3% by weight, Mn: 1.5% by weight, V:
Even if the content exceeds 0.3% by weight, the effect will be saturated, so adding more than that is wasteful. Therefore, when adding each of these elements, the Cr content should be between 0.05 and 0.05.
The content of Mn is 0.05 to 1.5% by weight, and the content of V is 0.05 to 0.3% by weight.

Ti Ti is an element that contributes to refining the macrostructure of the ingot. However, if the Ti content is less than 0.005% by weight, a good refining effect cannot be obtained;
If it exceeds this amount, crystallized substances will increase and ductility and toughness will decrease. Therefore, the Ti content is 0.005 to 0.1% by weight.
shall be. These Zr, Mg, Cr, Mn, V, and Ti are optionally added components.

[0016] Furthermore, F contained as an impurity in the ingot
e, Si, if the content exceeds 0.25% by weight, Al-
Fe-Si crystallized substances increase, and the ductility and toughness of the final product are significantly reduced. Therefore, the content of Fe or Si needs to be 0.25% by weight or less.

Next, an example of a method for manufacturing a high-strength Al--Li alloy according to the present invention will be explained.

The product form of the high-strength Al-Li alloy according to the present invention may be any of a wrought material, an extruded material, and a forged material.
Both forms exhibit good material properties. For this reason, as an example of the manufacturing method, taking the manufacturing method of wrought material as an example,
This will be explained below.

[0019] An Al-Li alloy ingot having the above-mentioned composition,
The grain size should be as fine as possible, i.e.
Form the agglomerates to a thickness of 3 mm or less. If the crystal grain size of the ingot exceeds 3 mm, the size and distribution of crystallized substances present at the grain boundaries will become coarse and non-uniform, respectively, resulting in a decrease in ductility and toughness in the final product.

Next, the obtained ingot was 400 to 550
A homogenization heat treatment is carried out at a temperature of °C. The purpose of this treatment is, firstly, to sufficiently dissolve elements such as Li, Cu, Mg, etc., secondly, to partially dissolve crystallized substances to reduce their size, and thirdly, to dissolve elements such as ZrAl3, Cr2Mg3Al16, Mn
This is to form precipitates of intermetallic compounds such as Al6 and VAl6. Subsequently, hot rolling is started at a temperature of 400° C. or higher to produce a hot rolled material. In addition, if the final product has a thickness of about 8 mm or less, it is further cold rolled to a predetermined thickness.

[0021] In order to impart a predetermined strength to the products manufactured by hot rolling or cold rolling, the products are subjected to solution treatment, quenching treatment, cold working as necessary, and then aging treatment. I do.

[0022]

[Examples] Next, examples of Al--Li alloys according to the present invention will be described together with comparative examples thereof.

[0023] An aluminum alloy having the ingredients shown in Table 1 below was melted and cast to produce an ingot with a thickness of 300 mm. Next, homogenization treatment was performed at 500°C, and after the temperature was lowered to 450°C, hot rolling was started to produce a rolled material with a thickness of 25 mm. This rolled material was solution-treated by heating to 520°C for 60 minutes, water quenched, then stretched by 6% as cold working, and finally aged to 160°C for 48 hours. .

[0024] The SCC resistance test was conducted using C with an outer diameter of 19.1 mm.
- After producing a ring and applying a predetermined stress, an accelerated test was conducted using an alternate immersion method (a step of immersing it in a 3.5% NaCl aqueous solution for 10 minutes and a step of drying it for 50 minutes were repeated over a period of 30 days). Ta.

Table 2 below shows the measured values of the mechanical properties, SCC resistance, fracture toughness, and density of the obtained Al--Li alloy. However, in Table 2, F/N is the ratio of the number of damaged samples/the number of tested samples, and Days indicates the number of days until breakage.

As is clear from Table 2, the Al-Li alloys according to the examples of the present invention are superior in mechanical properties, SCC resistance, and fracture toughness compared to the comparative example alloys. It can be seen that the low density balance has excellent characteristics.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Effects of the Invention] As explained above, the S resistance according to the present invention is
Since the high-strength Al-Li alloy with excellent CC properties has the above-mentioned composition, in addition to having high specific strength and high specific elasticity,
The effect is that the SCC resistance is excellent.

Claims (1)

[Claims] Claim 1: Li; 0.5 to 3.5 in weight %
%, Cu; 0.5~6.0% and Zn; 0.05~
Contains 1.5% and further contains Mg; 0.05-3.0%
, Zr; 0.05-0.3%, Cr; 0.05-0
．． 3%, Mn; 0.05-1.5%, V; 0.05-
S-resistant material containing at least one element selected from the group consisting of 0.3% and Ti; 0.005 to 0.1%, with the remainder being Al and inevitable impurities.
High strength Al-Li alloy with excellent CC properties.