JPS604897B2 - Al alloy with excellent stress corrosion cracking resistance and hot workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to an AZ alloy with excellent stress corrosion cracking resistance and hot workability.

Conventionally, Zn has been used as the A-alloy with the highest strength among the A-alloys.
:5.1-6.1%, Mg:2.1-2.9%, Cu:
A〆 alloy (hereinafter referred to as ``A〆 alloy (hereinafter referred to as ``A〆 alloy) having a composition (weight %) containing 1.2 to 2.0% and the remainder consisting of A〆 and unavoidable impurities.
Conventionally, high-strength A-alloys) are known. However, this conventional high strength A-alloy has the drawback of being highly susceptible to stress corrosion cracking. Therefore, in order to improve the susceptibility of the high strength A-alloy to stress corrosion cracking,
Attempts have been made to add a third component such as Cr, Mn, or Zr, or to perform heat treatment or surface treatment, but at present no satisfactory improvement has been achieved by these means. be. Furthermore, the conventional high strength A alloys have poor hot workability. Therefore, from the above-mentioned viewpoints, the present inventors conducted research to find alloys such as A that have excellent stress corrosion cracking resistance and hot workability as well as strength, and found that, in weight percent, Zn: 4
．． 5-6.5%, Mg: 1.05-1.45%, Cu:
Contains 1.8 to 2.5%, and further contains Cr:
0.08-0.40%, Mn: 0.15-0.70%,
and Zr: 0.10 to 0.20%, the remainder consists of A and unavoidable impurities, and the ratio of Mg content to Zn content (Mg/Z
It was found that an A-alloy having a composition satisfying n): 0.185 to 0.255 has excellent stress corrosion cracking resistance and hot workability, and also has sufficiently satisfactory strength. It is. This invention was made based on the above knowledge, and the reason why the component composition range was limited as described above will be explained below. (a) Zn The Zn component has the effect of improving the strength of the alloy, but
If the content is less than 4.5%, the desired and fully satisfactory strength cannot be ensured, while if the content exceeds 6.5%, the susceptibility to stress corrosion cracking increases significantly, and Since processability also deteriorates, its content was set at 4.5 to 6.5%.

'b} Mg The Mg component improves hot workability and significantly improves stress corrosion resistance in coexistence with Zn and Cu.
Furthermore, it has the effect of improving strength, but its content is 1
．． If the ratio of Mg content to Zn content (Mg-Zn) is less than 0.185, the desired excellent stress corrosion cracking resistance and strength cannot be secured; Exceeds 1.45% and Mg/
If the Zn ratio exceeds 0.255, the stress corrosion cracking resistance will rapidly deteriorate and the hot workability will also deteriorate, so the Mg content should be adjusted to 1.05 to 1.
45% and the Mg/Zn ratio is 0.185~
It was set at 0.255.

Furthermore, in detail, Zn: 5.7%, Cu: 2.0%
In the A-alloy containing Mg, 0.75 to 2.3
Added stress: 30k9/stress corrosion on side 2 for A-alloys with various compositions containing various contents within the range of 0% and varying the Mg/Zn ratio within the range of 0.13 to 0.41. In addition to measuring the cracking life, 0.2% proof stress was also measured. The measurement results are shown in FIG. As shown in Figure 1, Mg: content 1.25%, Mg/Zn:
When the Mg content is less than 1.05% and more than 1.45%, it is possible to ensure the desired excellent stress corrosion cracking resistance. Furthermore, it is clear that stable and high stress corrosion cracking life cannot be obtained even if the Mg/Zn ratio is less than 0.185 or more than 0.255.

The reason for this excellent stress corrosion cracking resistance is that when subjected to age precipitation hardening treatment as described below, MgZn
This is thought to be due to the fact that fine particles of two compositions are uniformly dispersed and precipitated in the matrix. Also, in Figure 1, 0.2
Looking at the % yield strength, the strength increases as the Mg content increases up to 1.6%;
．． It has been shown that when the stress corrosion cracking life exceeds 45%, the stress corrosion cracking life rapidly decreases. Also, the Mg content is 1.05 to 1.45.
%, and the ratio of Mg and Zn is 0.185 to 0.25
It is necessary to set it to 5.

'c} Cu The Cu component has the effect of improving stress corrosion cracking resistance and strength.

In general, the A alloy of the present invention is treated with a solution that is maintained at a high temperature for a considerable period of time in order to substantially and sufficiently solidify the alloy components in the alloy, namely Zn, Mg, and Cu, into the A alloy. This is followed by a quenching treatment in which the alloy components are cooled as quickly as possible to bring the dissolved state of the alloy to room temperature, and then held at room temperature or a certain predetermined temperature for a considerable period of time to bring it to a supersaturated solid state. A heat treatment consisting of an aging precipitation hardening treatment is performed to precipitate the alloy components as fine particles.

In this case, when the content of the alloy components, that is, Zn, Mg, and C↓, especially Cu, increases in the solution treatment, the temperature to substantially fully dissolve these alloy components in the A base material becomes high. On the other hand, the melting start temperature of the alloy decreases, but it is usually an essential condition that the solution treatment temperature is lower than the melting start temperature. It is necessary to lower Cu by more than 2.5%, and if Cu is contained in excess of 2.5%, the above-mentioned temperature difference becomes small and the solution treatment temperature becomes too close to the melting start temperature, which is not desirable. For this reason, the Cu content must be 2.5% or less, but if the Cu content is less than 1.8%, the strength and stress corrosion cracking resistance will decrease, making it difficult to achieve the desired high strength and high stress corrosion cracking resistance. Therefore, it is necessary to contain 1.8% or more. 'd
} Cr, Mn, and Zr These components have the effect of further improving stress corrosion cracking resistance by refining crystal grains, so they are necessary when particularly excellent stress corrosion cracking resistance is required. Cr: less than 0.08, Mn: less than 0.15,
and Zr: less than 0.10, the desired effect of improving the above action cannot be obtained; on the other hand, Cr: 0.4%, Mn: 0.7%,
and Zr: When contained in excess of 0.2%,
Since the alloy strength will drop significantly, the contents should be changed to Cr: 0.08 to 0.4% and Mn: 0.
．． 15 to 0.7%, and Zr: 0.10 to 0.2%.

In addition, when two or more of these components are contained, it is desirable that the total amount does not exceed 0.8%. Furthermore, rolled materials, forged materials, and even extruded materials of the A-alloy of the present invention containing Cr, Mn, and Zr are subjected to stress in the direction perpendicular to the fibrous structure, that is, in the thickness direction. When used under such conditions, there is almost no effect of improving stress corrosion cracking resistance due to the above-mentioned ingredients, and sometimes the stress corrosion cracking resistance decreases due to the strengthened fibrous structure. .

However, the present invention A containing Cr, Mn, and Zr
The susceptibility of the final alloy to stress corrosion cracking is highest in the thickness direction, and stress corrosion cracking resistance in the thickness direction is often a problem in practical applications as well. Therefore, when manufacturing thick structural materials, it is desirable to apply the alloy of the present invention A which does not contain Cr, Mn, and Zr. Furthermore, in the A-alloy of the present invention containing Cr, Mn, and Zr, if the dawning speed cannot be increased during solution treatment, the dawning effect will be weakened, resulting in a decrease in alloy strength. Therefore, Cr, Mn, and Zr are also used in the manufacture of structural materials that require a slow quenching rate, such as those that dislike thermal strain caused by rapid quenching or those that are designed to prevent air cooling. It is desirable to apply the present invention A〆 alloy which does not contain .

Next, the A〆 alloy of the present invention will be specifically established through examples.

Example Alloys 1 to 13 of the present invention and Comparative Alloys 1 to 5 having the compositions shown in Table 1 were melted using a conventional melting method, and cast into a mold with a width of 12 mm. Sail x length:
After forming into an ingot with dimensions of 15 mounds x 4 mounds in thickness, it was homogenized at a temperature of 45,000 for 20 hours, and then the ingot was hot rolled under normal conditions. After making a hot-rolled plate with thickness: 3 side, it is cold rolled to make a cooling plate with thickness: 1 side, and from this cooling plate width: 2
Cut out a test piece for stress corrosion cracking test with dimensions of rib x length: 95 ribs, and a test piece for tensile test with parallel part dimensions of width 6 willow x length: 35. , temperature: 4
After holding at 80q0 for 1 hour, water quenching melting treatment, holding at temperature: 110°C for 2 hours, and temperature: 170oo for 10
A two-stage aging precipitation treatment held for 0 minutes was performed, and the samples were subjected to each test.

In the stress corrosion cracking test, a stress of 30k9/fence 2 was applied to a specimen with the above dimensions using the three-point support bending method, and this was
:36/Z, K2Cr207:30/T, NaC So:3 It was done by immersion in an aqueous solution containing Tanok at room temperature, and cracks occurred in half of the specimens of 6 or more under one condition. The time point was defined as the stress corrosion cracking life.

In addition, in the tensile test, a specimen of the above dimensions was pulled at a speed of 0.5
This was done by pulling at 1/min.

Table 1 The results of the above stress corrosion cracking test and tensile test are shown in Table 1. In addition, comparison A〆alloys 1 to 5
is the component content of any of the constituent components (
Those marked with * in Table 1) have compositions that are outside the scope of the present invention, and in particular, comparative A-alloy 1 has a composition that corresponds to the conventional high-strength A-alloy mentioned above. .

From the results shown in Table 1, Invention A and Alloys 1 to 13 all exhibit excellent stress corrosion cracking resistance and sufficiently satisfactory strength, while Comparative A and Alloy 1 ~
5, it is clear that if the content of any of the constituent components falls outside the range of the present invention, at least one of the stress corrosion cracking resistance and strength will be inferior. .

In addition, regarding the present invention A〆alloy 1 having the composition shown in Table 1 and the comparative A〆alloy 1 having a composition corresponding to the conventional high strength A〆alloy mentioned above, from the above-mentioned material in the middle of hot rolling. , Diameter: IQ looking up x height: 12 A willow test piece was taken, and a high-temperature, high-speed compression test was conducted using the test piece under the conditions of temperature: 470 oo and strain rate: 2 sides/sec. Ta.

The test results are shown in FIG. 2 in terms of the relationship between strain amount and deformation resistance. As shown in FIG. 2, the deformation resistance of Invention A Alloy 1 is extremely small compared to that of Comparative A Alloy 1, and there are no small cracks in the test specimens of Comparative A Alloy 1. On the other hand, no defects were observed in the test piece of Invention A Alloy 1, and these results show that Invention A Alloy 1 is superior to Comparative A Alloy 1. It is clear that the material has excellent deformability and therefore excellent hot workability.

As mentioned above, the A-alloy of the present invention has excellent stress corrosion cracking resistance and hot workability, both of which are significantly superior to conventional high-strength A-alloys. Furthermore, it has useful properties such as being comparable in strength to conventional high-strength A-type alloys.

[Brief explanation of the drawing]

Figure 1 shows the M in the A alloy containing Zn and Cu.
Figure 2 shows the relationship between g content and Mg/Zn ratio, stress corrosion cracking life, and 0.2% yield strength. Figure 2 is a high-temperature high-speed compression test of Invention A So Alloy 1 and Comparative A〆 Alloy 1. It is a figure showing the relationship between strain amount and deformation resistance in . 2 illustrations

Claims (1)

[Claims] 1 Zn: 4.5-6.5%, Mg: 1.05-1.4
5%, Cu: 1.8 to 2.5%, the remainder consists of Al and inevitable impurities, and the ratio of Mg content to Zn content (Mg/Zn): 0.185 to 0.255. An Al alloy with excellent stress corrosion cracking resistance and hot workability, characterized by having a satisfactory composition (the above weight %). 2 Zn: 4.5-6.5%. Mg: 1.05-1.4
5%, Cu: 1.8 to 2.5%, and further contains Cr:
0.08-0.40%, Mn: 0.15-0.70%,
and Zr: 0.10 to 0.20%, the remainder consists of Al and unavoidable impurities, and the ratio of Mg content to Zn content (Mg/Z
n): An Al alloy with excellent stress corrosion cracking resistance and hot workability, characterized by having a composition (weight %) satisfying 0.185 to 0.255.