JP2746520B2 - Method for producing Al-Zn-Mg based alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a wrought Al-Zn-Mg alloy used for aircraft, vehicles and the like.

[0002]

2. Description of the Related Art Among aluminum alloys for spreading, Al-Zn-Mg alloys are widely used as welding structural materials for railway vehicles and the like because of their excellent properties such as strength and weldability. Al-Zn-
For Mg-based alloys, in addition to the main alloying elements Zn and Mg, Mn, in order to improve strength, stress corrosion cracking resistance, weldability, etc.
Usually, alloying elements such as Cr, Ti, and Zr are added,
At present, it is put into practical use as an alloy containing these elements.

[0003] Thus, in an Al-Zn-Mg alloy,
Alloying elements such as Mn, Cr, Ti, and Zr are added, and these elements are added in appropriate amounts so that various properties such as strength, stress corrosion cracking resistance, weldability, etc. become the best. . For example, in the case of JIS 7N01 alloy, which is a typical Al-Zn-Mg alloy,
The standard values of Mn, Cr, Zr and Ti are as follows: Mn is 0.2-0.7%, Cr is 0.
3% or less, Zr is 0.25% or less, and Ti is 0.2% or less.

[0004] However, when these elements are added within such a specification range, there are the following problems. When an alloy melt containing a large amount of these elements is smelted and cast by a normal method such as semi-continuous casting to produce an ingot, a large intermetallic compound (hereinafter referred to as a huge Compound).

[0005] Such giant compounds usually reach tens of microns to hundreds of microns, and in extreme cases, even a few millimeters. When they are formed in an ingot, these giant compounds can be subsequently rolled. It does not disappear during processing steps such as extrusion, forging, etc., but remains in a processing material such as a plate material or extruded material of the final product. These giant compounds remaining in the final product, as well as inclusions in metallic materials such as iron and steel, may degrade the properties, such as strength, ductility, toughness, and fatigue strength, of the final product, or reduce its reliability. Is already well known.

For example, when a large amount of a large compound is generated and occurs in the entire ingot, a product or a part manufactured from the ingot through a processing step such as extrusion contains the large compound. , And promotes crack propagation, which causes a decrease in fatigue strength. In addition, the generation of giant compounds is relatively small,
If there is a giant compound scattered locally in the ingot,
Products or parts manufactured from the ingot of the portion containing the macro-compound have lower fatigue strength characteristics than those not containing it.

Thus, when a huge compound is generated,
Depending on the degree of occurrence, the yield of products and parts exhibiting sound characteristics changes, and it becomes difficult to supply stable and reliable products and parts. In addition, the giant compound may cause cracks or the like at the time of processing such as rolling, extrusion, forging, or the like, and may cause processing to be hindered.

[0008] Regarding the above-mentioned harmful giant compounds, some alloy systems have been investigated comparatively in detail, and are reported as follows. First, JIS 7075 alloy, which is a high-strength Al-Zn-Mg-Cu alloy, and Al
In JIS 5083 alloy, which is a -Mg alloy, the giant compound is crystallized as a primary crystal before α-Al crystallizes during solidification, and its composition is a CrAl ₇ intermetallic compound containing Mn, Fe, etc. It is said that there is. (References, (1) MKBDay: JIM
85 (1956-57), 263, (2) LESteele, et al: JIM 88
(1959-60), 260, (3) Donald J. Beerntsen: Metallurgical
Transactions B 8B (1977) 687, (4) Yoshikawa et al .: Light metal
29 (1979) 4, 144). To prevent this, it is necessary to reduce and control the Mn and Cr concentrations below the primary crystal line of the CrAl ₇ phase, and various equations for the primary crystal line have been proposed.

In the JIS 3004 alloy, which is an Al-Mn alloy, the giant compound is a primary crystal compound like the 7075 and 5083 alloys, and its composition is reported to be (Fe, Mn) Al ₆ . (References, Yoshikawa et al .: Light Metal 33 (1983) 10, 602). Further, in the Al-Zn-Mg-based alloy, the giant compound is a Ti-containing ZrAl ₃ -based primary crystal compound similarly to the above-mentioned alloys, and the primary crystal region thereof has been reported. In addition, it has been considered that the suppression and control of the Ti and Zr amounts are effective in preventing the above. (Reference, 19th Symposium of the Japan Institute of Light Metals, "Continuous casting technology and ingot structure of aluminum", October 1981, p.65).

However, as for the target value of the control, although a quantitative value has been proposed for Zr,
No clear quantitative values have been reported for Ti so far.

As described above, according to the previous research,
Giant compounds are intermetallic compounds that crystallize as primary crystals,
Although the composition varies depending on the alloy system, one kind of giant compound is generated for each alloy system, and a primary crystal line for preventing such a giant compound has been proposed.

[0012]

As described above, a primary crystal line for preventing a giant compound in each alloy system has been proposed, and the Al-Zn-Mg based alloy is also applicable to the Al-Zr based giant compound. The primary crystal line has been proposed.

However, as a result of the inventor's intense research on the giant compound of the Al-Zn-Mg alloy, the present inventors have found that the Zr content of this alloy system is based on the primary crystal line for only one kind of giant compound. It has been clarified that the conventional method for reducing the odor cannot completely prevent the generation of a giant compound. The cause is that in the present alloy system, a CrAl _7- based giant compound is newly generated in addition to the conventional ZrAl _3- based giant compound.Therefore, it is necessary to establish a new method to prevent both of them at the same time. Faced with new problems.

The present invention has been made in order to solve the above-mentioned problems. By controlling the amounts of Mn, Cr, Ti, and Zr at the time of melting the present alloy system, it is possible to prevent the generation of a primary crystal giant compound. It is an object of the present invention to provide a method for producing an Al-Zn-Mg-based alloy.

[0015]

The gist of the present invention is that Zn: 4 to
5%, Mg: 1-2%, Mn: 0.2-0.7%, Cr: 0.3% or less, T
i: In an Al-Zn-Mg alloy containing 0.2% or less and Zr: 0.25% or less, and other elements such as Cu, Si, and Fe each being 0.2% or less, Mn, Cr content is% Mn + 3.25
Al-Z which controls the composition such that% Cr <0.905 and the content of Ti and Zr is% Zr + 0.909% Ti <0.127 to prevent the generation of primary crystals.
This is a method for producing an n-Mg alloy.

[0016]

The present inventors have conducted further studies on the formation behavior of both ZrAl ₃ -based and CrAl ₇ -based giant compounds. As a result, the results shown in Table 1 and FIG. 1 were obtained. Table 1 shows Mn,
The temperature at which JIS 7N01 alloys with various Cr, Ti, and Zr contents are melted in a crucible and α-Al crystallizes (the liquidus temperature of this alloy,
This is the result of an equilibrium experiment in which isothermal holding was performed at a temperature of 654 ° C directly above the temperature of 654 ° C, and the formation of giant compounds precipitated at the bottom of the crucible was investigated.

[0017]

[Table 1]

The explanatory diagram of the giant compound observed with a microscope shown in FIG. 1 is the giant compound observed in the sample No. 1 in Table 1. The compounds indicated by A and B in the figure clearly show the color tone under the microscope. It is clear that two types of giant compounds were formed. As a result of further investigation and study of these compounds, Compound A was found to be a primary Ti-containing ZrAl ₃ containing the same Ti as that reported in the Al-Zn-Mg alloy described above.
A compound (hereinafter, referred to as (Ti, Zr) Al ₃ ). On the other hand, compound B is a compound that has not been recognized in the aforementioned report,
As a result of the investigation, a primary CrAl ₇ compound containing Mn (hereinafter, referred to as
(Mn, Cr) Al ₇ ).

As can be seen from the results of Table 1, Nos. 1 to 7,
When Mn, Cr, Ti, Zr are high, (Mn, Cr) Al ₇ , (Ti, Zr) A
l ₃ giant compounds are formed simultaneously. On the other hand, in the compositions of Nos. 8 to 20 in which the Mn and Cr concentrations were reduced, the formation of the (Mn, Cr) Al ₇ giant compound was not recognized, but the other (Ti, Zr) Al ₃ giant compound Formation is observed. In addition, Mn, Cr, Ti,
In the samples of Nos. 21 to 27 in which the concentration of Zr was suppressed, generation of both giant compounds was not observed at all. In other words, it became clear that, in addition to the previously reported (Ti, Zr) Al ₃ primary crystal compound, a new (Mn, Cr) Al ₇ primary crystal compound is generated in this alloy.

Taking the results of Table 1 above and the temperature dependence of the primary crystal line into consideration, the primary crystal line of (Mn, Cr) Al ₇ of the JIS 7N01 alloy is obtained at an equilibrium state of 648.8 ° C., as shown in FIG. % Shown
It became clear that Mn + 3.25% Cr = 0.905. Therefore, by controlling the Mn and Cr concentrations to be% Mn + 3.25% Cr <0.905, it was possible to completely prevent the (Mn, Cr) Al ₇ giant compound.

Further, Mn that satisfies% Mn + 3.25% Cr <0.905,
In the Cr concentration range, the primary crystal line of (Ti, Zr) Al ₃ is shown in Table 1, No. 8
~ 27, the primary crystal line is% Zr + 0.
It became clear that 909% Ti = 0.127. Therefore, by controlling the concentration of Ti and Zr to be% Zr + 0.909% Ti <0.127, it was possible to prevent (Ti, Zr) Al ₃ giant compound at the same time.

As described above, since two types of giant compounds are generated in the present alloy system, it has been difficult to prevent the generation by the conventional method for preventing one type of giant compound. According to the invention, the Mn and Cr concentrations are set to% Mn + 3.
25% Cr <0.905 and Ti and Zr concentrations as% Zr + 0.909% Ti <0.
Since it is controlled to 127, two types of giant compounds can be prevented at the same time.

[0023]

Embodiments of the present invention will be described below.
Mn, Cr, Ti, Zr concentrations are changed in various ways, and other elements such as Mg, Zn, etc. other than these elements are melted in various molten metals equivalent to JIS 7N01 alloy and cast by a usual continuous casting method. After the ingot was formed, the inside of the ingot was observed under a microscope to check for the occurrence of a giant compound. The results of the investigation are shown in Table 2 together with the composition of the molten metal. The dimensions of the ingot were 500 mm thick and 1500 m wide.
m, 5000 mm long. Investigation of giant compounds was performed by cutting out a 500 × 1500 × 20 mm sample at the center of the ingot in the length direction, and observing the center of the sample in the width direction from the surface of the ingot to the center. Was.

As is clear from Table 2, Comparative Examples Nos. 1 to 3
Since the concentration of Mn, Cr, Ti, and Zr exceeds the primary crystal line of the present invention, giant compounds of (Mn, Cr) Al ₇ and (Ti, Zr) Al ₃ are simultaneously generated.

In Comparative Examples Nos. 4 to 6, since the concentrations of Mn and Cr were below the primary crystal line of the present invention and the concentrations of Ti and Zr exceeded the primary crystal line of the present invention, (Mn, Cr) No generation of a giant compound of Al ₇ is observed, but generation of another giant compound of (Ti, Zr) Al ₃ is observed.

In methods 7 to 10 of the present invention, since all of Mn, Cr, Ti and Zr are suppressed to a concentration below the primary crystal line of the present invention, generation of both giant compounds is not recognized at all.

[0027]

[Table 2]

As described above, according to the present invention, it is possible to simultaneously prevent both giant compounds generated in the present alloy system.

[0029]

According to the present invention, Zn: 4-5%, Mg: 1-2%, M
n: 0.2-0.7%, Cr: 0.3% or less, Ti: 0.2% or less, Zr: 0.25
%, Other elements such as Cu, Si, Fe etc.
In an Al-Zn-Mg alloy having a content of 0.2% or less, when the alloy is melted, the amount of Mn and Cr is% Mn + 3.25% Cr <0.905, Ti, Zr
The amount is controlled to a composition of% Zr + 0.909% Ti <0.127 to prevent the generation of a primary crystal giant compound.
It is possible to simultaneously prevent the generation of two types of primary crystal giant compounds, (Mn, Cr) Al ₇ and (Ti, Zr) Al ₃ , generated in the present alloy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a giant compound.

FIG. 2 is a view showing a primary crystal line of (Mn, Cr) Al ₇ of a JIS 7N01 alloy.

FIG. 3 is a diagram showing a primary crystal line of (Ti, Zr) Al ₃ of JIS 7N01 alloy.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenzo Iizuka 15 Kinuigaoka, Moka City, Tochigi Prefecture Kobe Steel, Ltd. Inside Moka Works (58) Field surveyed (Int.Cl. ⁶ , DB name) C22C 1 / 02 503 C22C 21/10

Claims (1)

(57) [Claims] [Claim 1] Zn: 4 to 5%, Mg: 1 to 2%, Mn: 0.2 to 0.7
%, Cr: 0.3% or less, Ti: 0.2% or less, Zr: 0.25% or less, and the content of other elements such as Cu, Si and Fe is 0.2% or less, respectively. When melting the alloy, M
n, Cr content is% Mn + 3.25% Cr <0.905, Ti, Zr content is% Zr +
A method for producing an Al-Zn-Mg-based alloy, wherein the composition is controlled to be 0.909% Ti <0.127 to prevent generation of a giant primary crystal compound.