JPS6360820B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a high strength, high toughness aluminum alloy. Age-hardening Al-Zn-Mg-Cu alloys, which have the highest strength and toughness among aluminum alloys, are used as materials for aircraft because of their excellent specific strength (strength/specific gravity). . Traditionally used as a high-strength alloy
When 7075 alloy is aged to its maximum strength (T6 treatment), there are problems such as deterioration of fracture toughness and stress corrosion cracking resistance, so over-aging treatment is performed to increase toughness at the expense of strength. T73 treated wood is used. 7050 alloy, which is an improved version of this alloy, has recently been developed.
T736 material or 7175 alloy - T736 material was developed, but these alloy treated materials reduce the content of impurities Fe and Si to reduce the volume fraction of second phase particles for the purpose of improving toughness. is regulated. Incidentally, when casting Al-Zn-Mg-Cu alloy,
Al-Cu-Mg system, Al-Fe-Si system, Al-
Fe-based or Al-Fe-Cu based intermetallic compounds are generated, and most of these intermetallic compounds re-dissolve in the solid solution by soaking treatment, but some remain undissolved and are distributed in the product to improve toughness. It is the cause of the decline. The 7175 alloy, which is said to be a new material, has improved toughness by controlling the content of Fe and Si, which tend to remain as unsolid dissolved crystals. The present inventor focused on the second phase particles, which is a fundamental problem in high-strength, high-toughness aluminum alloy materials, and how to refine or redissolve crystallized substances produced during aluminum alloy casting. The present invention was completed as a result of examining whether the volume fraction could be reduced by
This was done as a result of research based on various problems in the conventional technology of Al-Zn-Mg-Cu alloys and the knowledge of the present inventor.
By dividing and refining the above-mentioned various crystallized substances in the system alloy through preliminary hot working and promoting re-solid solution formation during the soaking treatment in the subsequent process, high strength can be achieved that can reduce the volume fraction. A method for manufacturing a high toughness aluminum alloy is provided. The feature of the manufacturing method of high strength and high toughness aluminum alloy according to the present invention is that Zn5.0 to 7.0wt
%, Mg1.5~3.0wt%, Cu1.0~3.0wt%, Ti0.001
~0.1wt% is an essential component, Cr0.05~0.25wt%,
Contains any one of Zr0.05 to 0.20wt%,
After casting an aluminum alloy with Fe 0.5wt% or less and Si 0.4wt% or less and the remainder essentially consisting of Al, it is subjected to strain relief and precipitation treatment at a temperature of 250 to 360℃ for 2 hours or more. After performing heat treatment, hot working is performed at a temperature of 300 to 480°C with a processing rate of 40% or more, and after performing soaking treatment at a temperature of 450 to 525°C for 4 hours or more, further 420
The method is to carry out hot working at a working rate of 20% or more at a temperature of 450 to 525 degrees Celsius, and then to perform a solution treatment for 2 to 8 hours at a temperature of 450 to 525 degrees Celsius. The method for producing a high-strength, high-toughness aluminum alloy according to the present invention will be described in detail below. That is, Zn5-7wt%, Mg1.5-3.0wt%, Cu1.0
Contains ~3.0wt%, Ti0.001~0.1wt% as essential components, contains any one of Cr0.05~0.25wt%, Zr0.05~0.20wt%, Fe0.5wt% or less, Si0 .4wt
% or less, and heat-treating an aluminum alloy ingot with the remainder essentially consisting of Al at a temperature of 250 to 360°C for 2 hours or more to relieve strain and precipitate an equilibrium phase, and at a heating rate of 40°C/hour or more. By heating the product to a temperature of 300 to 480°C and immediately hot working at that temperature at a processing rate of 40% or more, the crystallized material during casting is broken and made fine. Therefore, the coarse equilibrium phase before hot working increases the amount of dislocations introduced during working, and is effective in breaking and dispersing crystallized materials. This means that in the case of the same hot working, if a coarse equilibrium phase exists, the amount of dislocations introduced during working will be greater than if it does not exist.
This is because the deformation resistance increases and the crystallized material becomes more likely to break. In this way, the divided and finely divided crystallized material has an increased specific surface area (surface area/volume) in the subsequent soaking treatment, so that it becomes easy to be solid-dissolved again. Therefore, normal soaking treatment (approximately 460℃)
The crystallized material becomes finer than that in the case where the crystallized substance is formed, and the amount of solid solution increases. Furthermore, by increasing the amount of dislocations introduced during processing through precipitation treatment before preliminary processing, there is an effect of making recrystallized grains finer during soaking. This is effective in refining recrystallized grains (sub-crystal grains) generated by the solution treatment after reheat processing, and can improve the toughness of the product. After this precipitation treatment, the hot-worked material is further subjected to soaking treatment at a temperature of 450 to 525° C. for 4 hours or more to make the component distribution in the material uniform and to re-dissolve the crystallized substances. After that, hot processing is performed at a temperature of 300 to 420℃ with a processing rate of 20% or more to obtain the desired product dimensions.
Solution treatment is carried out at a temperature of 450 to 525°C for 2 to 8 hours, water quenching is carried out, pre-aging is carried out at a temperature of 100 to 125°C, and overaging treatment is carried out at a temperature of 150 to 180°C. The size and distribution of precipitates obtained by this final aging vary depending on the aging temperature and time, as well as depending on the soaking conditions. In other words, if the Al-Cu-Mg crystals are not completely dissolved during soaking, the Cu and Mg contents in the matrix will decrease, the density of the aged precipitates will become coarser, and the aging time will increase. Strength decreases. Therefore, if the final aging time is shortened to increase the strength, the problem arises that the precipitates become fine, the toughness decreases, and stress corrosion cracking becomes more likely to occur. Therefore, Al―Cu
-Complete re-dissolution of Mg-based crystallized substances is an important condition for obtaining high-strength, high-toughness aluminum alloy materials. From this point of view, it is extremely important to pre-process the aluminum alloy ingot after precipitation treatment and to perform soaking treatment. The components, component ratios, and heat treatment conditions of the aluminum alloy used in the method for producing a high-strength, high-toughness aluminum alloy according to the present invention will be explained. If the Zn content is less than 5.0 wt%, sufficient strength cannot be obtained, and if the Zn content exceeds 7.0 wt%, the toughness decreases and stress corrosion cracking is likely to occur.
Therefore, the Zn content is set to 5.0 to 7.0 wt%. If the Mg content is less than 1.5 wt%, strength cannot be obtained, and if the Mg content exceeds 3.0 wt%, hot workability decreases and processing cracks are likely to occur. Therefore, the Mg content is set to 1.5 to 3.0 wt%. If the Cu content is less than 1.0 wt%, strength cannot be obtained, and if the content exceeds 3.0 wt%, toughness decreases. Therefore, the Cu content is 1.0~3.0wt%
shall be. If the Ti content is less than 0.001wt%, refinement of the casting structure will not occur, and if it is 0.1wt%, giant compounds will be generated during casting, resulting in a decrease in the toughness of the product. Therefore, the Ti content is set to 0.001 to 0.1 wt%. When the content of Cr is less than 0.05 wt%, it has no effect on grain refinement, and when the content exceeds 0.25 wt%, it tends to generate giant compounds during casting. Therefore, the Cr content is set to 0.05 to 0.25 wt%. If the content of Zr is less than 0.05 wt%, it has no effect on grain refinement, and if the content exceeds 0.20 wt%, giant compounds are generated during casting, reducing toughness. Therefore, the Zr content is set to 0.05 to 0.20. When the content of Fe and Si exceeds 0.5wt%, Al-Fe-Cu crystals are generated during casting, which lowers the Cu content of the matrix and deteriorates age hardenability. If it exceeds 0.4wt%, coarse Mg--Si precipitates will form during soaking, resulting in a decrease in product strength. Therefore, Fe content is less than 0.5wt% and Si
The content is regulated to 0.4wt% or less. Aluminum alloy ingots with the above-mentioned components and ratios are subjected to strain relief and precipitation treatment at a temperature of 250 to 360°C, but at temperatures below 250°C, the precipitates become fine and may cause processing cracks during hot working. In addition, at temperatures exceeding 360℃, the equilibrium phase re-dissolves into solid solution.
The effect of precipitation treatment is no longer observed. The treatment time must be 2 hours or more; if it is less than 2 hours, the amount of coarse precipitates will be small and the crystallized substances will not be refined during preliminary processing. Next, hot working is performed at a working rate of 40% or more at a temperature of 300 to 480°C, but at temperatures below 300°C, processing cracks occur;
At temperatures exceeding this temperature, the precipitation treatment effect disappears. If the processing rate is less than 40%, the crystallized substances will not be made finer, and the recrystallized grains will not be made finer during soaking. After this preliminary processing, a soaking treatment is performed at a temperature of 450 to 525℃ for 4 hours or more, but in this case, the temperature
At temperatures below 450°C, Al--Cu--Mg crystallized substances do not re-dissolve, and at temperatures above 525°C, eutectic melting occurs. It is necessary to perform the soaking treatment for 4 hours or more; if it is less than 4 hours, the Al-Cu-Mg crystallized material will not be completely re-dissolved and some undissolved crystallized material will remain. remain. Furthermore, desired product dimensions are obtained by hot working at a temperature of 300 to 420°C and a processing rate of 20% or more. Next, solution treatment is carried out for 2 to 8 hours at a temperature of 450 to 525°C.
If the temperature is lower than 525°C, Al--Cr--Mg compounds tend to precipitate during solution treatment, lowering the Mg content in the matrix and deteriorating age hardenability, and melting occurs at temperatures exceeding 525°C. The time for this solution treatment is 2 to 8 hours; if it is less than 2 hours, the age-hardening elements will not be completely dissolved, and if it exceeds 8 hours, fine crystal grains will grow abnormally, reducing the toughness. An example of the method for manufacturing a high-strength, high-toughness aluminum alloy according to the present invention will be described. Example 1 Three types of aluminum alloy ingots (300φ) shown in Table 1 were cast by a semi-continuous casting method, and cast products (100φ) were produced by the manufacturing process shown in Table 2.

【table】

[Table] After solution treatment of each forged material at 500℃ x 3 hours,
It was quenched in water at 18°C, pre-aged at 110°C for 6 hours, and then over-aged at 175°C for 7 hours. Table 3 shows the strength and toughness of each material at that time. The toughness was tested according to ASTME-399 (L-T). Tensile property is L-
Indicates the value in the T direction. ○ indicates a material produced by the method for producing a high-strength, high-toughness aluminum alloy according to the present invention, and no mark indicates a comparative material.

【table】

[Table] It is clear from this Table 3 that when the Fe content increases, high strength and high toughness cannot be obtained. It can be seen that a high toughness material can be obtained by hot working at a high working rate of . Example 2 Fe0.09wt%, Si0.05wt%, Cu2.15wt%,
Mg1.93wt%, Zn6.24wt%, Zr0.15wt%,
Aluminum alloy ingot (210φ) containing Ti0.04wt%
is extruded according to the manufacturing process shown in Table 4,
After solution treatment at a temperature of 480°C for 4 hours, quenching in water at 60°C was performed, pre-aging at a temperature of 120°C for 24 hours, and then aging treatment by holding at a temperature of 175°C for 10 hours. The strength and toughness values at this time are shown in Table 5.

【table】

【table】

[Table] The tensile properties show the values in the LT direction, and the fracture toughness values show the measured values in the LT direction. As is clear from this example, even if the aluminum alloy contains Zr, high strength and high toughness can be obtained by performing precipitation treatment. As explained above, since the method for producing a high-strength, high-toughness aluminum alloy according to the present invention has the above structure, Al-Zn-Mg-Cu
This has the effect of making the aluminum alloy superior in terms of high strength and toughness.

Claims (1)

[Claims] 1 Zn5.0~7.0wt%, Mg1.5~3.0wt%, Cu1.0~
3.0wt%, Ti0.001~0.1wt% are essential components,
Any one of Cr0.05~0.25wt%, Zr0.05~0.20wt%
An aluminum alloy containing seeds, regulated to 0.5wt% or less of Fe, 0.4wt% or less of Si, and the remainder consisting essentially of Al is cast by a conventional method and then heated at a temperature of 250 to 360℃.
After heat treatment that also serves as strain relief and precipitation treatment for more than an hour, the
Hot processing is carried out at a processing rate of 450 to 525℃.
After soaking for 4 hours or more at a temperature of A method for producing a high-strength, high-toughness aluminum alloy, which comprises performing solution treatment.