JPH0641704A - Manufacture of age hardening type aluminum alloy - Google Patents

Abstract

PURPOSE:To manufacture an age hardening type Al alloy excellent in ductility, toughness and stress corrosion cracking resistance by improving soaking treatment therefor. CONSTITUTION:At the time of subjecting the ingot of the Al-Cu-Mg or Al-Zn- Mg-Cu age hardening type Al alloy contg. specified amounts of Mn, Cr, Zr or the like to soaking treatment, hot working, cold working and quench aging treatment, at first, it is heated to 200 to 400 deg.C at <=100 deg.C/min temp. raising rate and is held to the same temp. for <=48hr. After that, its temp. is raised to a soaking temp. at <=100 deg.C/min temp. raising rate, and soaking treatment is executed. Next, hot working, cold working and quench hardening are executed, by which the Al alloy member excellent in ductility and stress corrosion cracking resistance while the strength of the alloy is maintained can be manufactured.

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 an age hardening type aluminum alloy, and in particular, by improving the soaking treatment, the ductility, toughness and SCC resistance of the alloy are improved.

[0002]

2. Description of the Prior Art Age-hardening type aluminum alloys, for example, JIS 2014 and 221 having the compositions shown in Table 1.
4, 2219, 2319, 2419, 2020, 202
4, 2124, 2025, 2036, 2048 (Al-
Cu-Mg type) alloy and JIS 7049, 7050, 70
75, 7175, 7475 (Al-Zn-Mg-Cu
The (type) alloys are used for structural members such as aircrafts, but in the case of particularly large and thick members, there is a problem that sufficient strength cannot be obtained even after a predetermined quenching aging treatment. That is, even after natural aging or artificial aging after solution treatment or quenching, if the cooling rate after solution treatment is low, the phenomenon that the strength after aging decreases may occur. When the strength is sensitively affected by the cooling rate after the solution treatment as described above, it is said that the quenching sensitivity is high, which is a serious problem in practical use of the heat-treatable alloy.

[0003]

[Table 1]

In the age-hardening type aluminum alloy, transition elements such as Mn, Cr, and Zr are added to suppress recrystallization, but it is known that addition of these transition elements increases the quenching sensitivity of the alloy. Has been. Therefore, when a Cr-added alloy such as JIS7075 is used as a practical material, it has a high quenching susceptibility, and the size of the material is limited. On the other hand, high strength aluminum alloys used for structural materials such as aircraft require considerable strength,
At present, ductility and stress corrosion cracking resistance (SCC resistance) are inferior.

[0005]

When an age-hardened aluminum alloy is used as a practical material, it has a high quenching susceptibility after solution treatment, so that the plate thickness must be kept small in order to maintain high strength. In addition, at present, strength is sacrificed in order to improve ductility and SCC resistance. Therefore, a manufacturing method for obtaining an aluminum alloy having excellent strength, ductility, and SCC resistance is desired.

[0006]

As a result of various studies in view of this, the present invention has developed a method for producing an age-hardening aluminum alloy excellent in ductility and SCC resistance while maintaining high strength.

That is, the present invention relates to Al--Cu--Mg system, Al
In a manufacturing process in which a -Zn-Mg-Cu age-hardening aluminum alloy is melt-cast, and then subjected to soaking treatment, hot working, cold working, and quenching aging treatment, first, 200 to 40
The temperature is raised to 0 ° C at a heating rate of 100 ° C / min or less,
The method is characterized in that the temperature is maintained at 200 to 400 ° C for 48 hours and then the temperature is raised to the soaking temperature at a heating rate of 100 ° C / min or less.

[0008]

In the high-strength aluminum alloy, transition elements such as Mn, Cr, and Zr are added to suppress recrystallization, and the ductility and SCC resistance of the alloy are improved. These transition elements are usually called insoluble compounds because they precipitate as a dispersed phase during the soaking treatment of the ingot of the alloy and do not dissolve even at the temperature of the subsequent solution treatment. In the case of an alloy treated by the conventional soaking method, solidification segregation occurs during casting of the alloy, so that the distribution of the insoluble compound becomes nonuniform even after the soaking treatment, and the effect of suppressing recrystallization is limited.

In addition, in the case of an aluminum alloy containing Mn or Cr, if the quenching rate is slow after the solution treatment of the alloy, the Mn-based insoluble compound or C which has already segregated during quenching is added.
Since a coarse precipitation phase preferentially precipitates nonuniformly on the r-type insoluble compound, the distribution of the precipitation phase finally becomes nonuniform and high strength of the alloy cannot be obtained. That is, the quenching sensitivity of these alloys is high and there is a practical problem.

Based on the above findings, an industrial manufacturing method was applied to an age hardening type aluminum alloy, and a manufacturing method capable of improving ductility and SCC resistance while maintaining the strength of the alloy was examined. That is, regarding the manufacturing process of soaking treatment, hot working, cold working, quenching aging treatment after melt casting,
As a result of each examination, after melting and casting the alloy by a usual method, as shown in FIG. 1, first, (A) the temperature is raised at a heating rate of 100 ° C./min or less, and (B) the temperature is from 200 ° C. to 400 ° C. When the temperature reaches the range, the temperature is maintained within 48 hours, preferably several hours or more, and then the temperature is raised to the soaking temperature (C) again at a heating rate of 100 ° C./min or less,
(D) After soaking for a long time, followed by quenching and aging treatment, hot working, cold working and quenching aging treatment are carried out in the same manner as in the conventional method, whereby ductility, while maintaining the strength of the alloy,
It is possible to improve the SCC resistance.

However, the heating rate is set to 100 ° C./min or less in order to more uniformly precipitate the insoluble compound while diffusing the atoms. When the heating rate exceeds 100 ° C./min, the precipitation of the insoluble compound is not uniform. And the effect of suppressing recrystallization is reduced.

The holding temperature during the temperature rise is set to 200-40
The temperature was set to 0 ° C. in order to ensure sufficient nucleation of the insoluble compound and finally obtain a uniform distribution of the insoluble compound.
Nucleation of the insoluble compound is less likely to occur at a temperature lower than 400 ° C., and if the temperature exceeds 400 ° C., the insoluble compound is likely to coarsen, which adversely affects the properties of the alloy. Furthermore, the reason why the temperature is kept within 48 hours is to obtain a highly dense and uniform distribution of the insoluble compound. If it exceeds 48 hours, the insoluble compound becomes coarse before the alloy is sufficiently homogenized.
It adversely affects the properties of the alloy.

[0013]

EXAMPLES The present invention will be described below with reference to examples. Table 2
After melting and casting three kinds of aluminum alloys having the chemical composition (wt%) shown in Fig. 1 by the usual method, the temperature is raised at a heating rate of 50 ° C / min, and after reaching the temperature range of 200 ° C to 400 ° C. Hold at that temperature for 24 hours. Then 50 ° C
The temperature is raised to 465 ° C at a heating rate of / min and the temperature is raised to 24
I soaked time. Next, after hot rolling at 400 ° C., cold rolling was performed to a plate material having a thickness of 1 mm, which was subjected to quenching aging treatment. The solution treatment was performed at 465 ° C. for 1 hour, followed by quenching and T73 treatment (121 ° C. × 6 hr + 177 ° C. × 9 hr). For comparison, an ingot of the same alloy as the above was heated to 465 ° C. by a conventional soaking method at a temperature rising rate of 50 ° C./min without being held midway, and was soaked at that temperature for 24 hours. After that, processing and heat treatment were performed under the same conditions as above.

The strength of these plate materials was measured and the SCC test was conducted. The results are shown in Table 3. SCC
The test is a static immersion test in a 3.5% NaCl aqueous solution at 30 ° C., and a uniaxial tensile load of 0.2% proof stress of 95%, 1
It was carried out with an accelerated anode current load of mA / cm ² .

[0015]

[Table 2]

[0016]

[Table 3]

As is clear from Table 3, the alloys produced in the examples of the present invention are superior not only in strength but also in ductility, toughness and SCC resistance as compared with the conventional alloys subjected to conventional soaking. I understand.

[0018]

As described above, according to the present invention, the ductility, the toughness, and the SCC resistance are particularly excellent as compared with the alloy treated by the conventional soaking method, and the strength is not inferior, and the member for aircraft or the like. It is most suitable as, and has remarkable effects such as large contribution to the improvement of material safety.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a soaking process step in the present invention.

Claims (1)

[Claims] 1. Al-Cu-Mg system, Al-Zn-Mg
-In the manufacturing process of performing soaking treatment, hot working, cold working, and quenching aging treatment after melt-casting a Cu-based age hardening type aluminum alloy, first, a heating rate of 100 ° C / min or less up to a temperature of 200 to 400 ° C. Temperature rises at 200-40
A method for producing an age-hardening aluminum alloy, which is characterized by holding at a temperature of 0 ° C for 48 hours or less and then raising the temperature to a soaking temperature at a heating rate of 100 ° C / min or less.