JPH0586464B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention is applicable to JIS2000 series, 6000 series or
This invention relates to a method for manufacturing heat-treated aluminum alloy rolled plates, such as No. 7000 series. Conventional technology As is well known, JIS standard 2014 alloy, 2017 alloy,
2000 series alloys such as 2219 alloy, 6000 series alloys such as 6061 alloy, or 7000 series alloys such as 7075 alloy and 7NO1 alloy
The manufacturing method for heat-treated aluminum alloy rolled sheets, which is represented by number series alloys, involves hot rolling, cold rolling if necessary, solution treatment, and room temperature aging. Or 100-200℃
Artificial aging is generally performed by heat treatment. The purpose of the solution treatment is to sufficiently dissolve the elements that contribute to strengthening into a supersaturated solid solution by rapidly cooling them to room temperature. The supersaturated solid solution is then decomposed and toughening is achieved by precipitating fine GP zones or precipitates. In order to achieve toughening by precipitation after solution treatment, the precipitates or crystallized substances of elements that contribute to strengthening, which are coarsely precipitated during casting or during preheating of the ingot, are removed by solution treatment. It is necessary to form a sufficient solid solution in the solid solution. The heating temperature for this solution treatment is a temperature between the solidus temperature and the solubility line in the α phase region of the target alloy,
Although the specific optimum temperature range varies depending on the alloy composition, the liquefaction treatment temperature of typical alloys is typically indicated in the MILL standard or the JIS standard. for example
493-505℃ for 2014 alloy, 495℃ for 2017 alloy
~510℃, 2024 alloy plate 490~500℃, 6061 alloy 515~550℃, 7075 alloy plate 460~500℃,
The optimum temperature for 7NO1 alloy is approximately 450℃. By the way, solution treatment has traditionally been carried out using salt bath furnaces,
Usually, the process is carried out in a batch furnace such as an air furnace. Although it varies depending on the thickness,
For example, if the plate thickness is 1.0 mm, it is desirable to hold the plate for at least 20 minutes in a salt bath furnace and for at least 30 minutes in an air furnace. On the other hand, recently, in the case of thin plates with a thickness of 3 mm or less, a method of continuously solution-hardening the coil while continuously unwinding the coil has been practiced.
Continuous furnaces for this purpose generally consist of a heating zone, a holding zone, and a cooling zone, and the sheet material is solution-treated while passing through the holding zone. When such a continuous furnace is used, the solution treatment time is considerably shortened compared to the case of a batch furnace system, but a holding time of at least 4 to 5 minutes is still required. Problems to be Solved by the Invention As mentioned above, even in continuous furnace solution treatment and quenching, the holding time for solution treatment is at least 4 to 30 minutes.
5 minutes is required, and in order to ensure such a holding time, the line speed of the continuous furnace cannot be increased beyond a certain level, and this has been a bottleneck for improving productivity. Furthermore, in order to secure the above-mentioned holding time, the length of the holding zone of the continuous furnace cannot be reduced beyond a certain level, and this is also a bottleneck for reducing equipment costs. Furthermore, some general continuous annealing furnaces do not have a holding zone, but if such a continuous furnace is to be used for solution treatment, it is necessary to heat the furnace for more than 4 to 5 minutes in the temperature range mentioned above. In this case, the line speed had to be significantly slowed down, resulting in a problem that significantly reduced economic efficiency. This invention was made against the background of the above-mentioned circumstances, and is intended to improve productivity by significantly increasing the line speed of the continuous furnace compared to conventional methods when performing solution heat treatment and hardening using a continuous furnace. In addition, to provide a method that reduces equipment costs by shortening the length of a holding zone in a continuous furnace, and also allows solution treatment to be carried out at an economical line speed even in a continuous furnace that does not have a holding zone. The purpose is to That is, the present invention attempts to achieve the above-mentioned object by completing solution treatment by maintaining the solution treatment temperature range for a very short time. Means to solve the problem In order to shorten the holding time in the solution treatment temperature range during post-rolling solution treatment and to sufficiently dissolve crystallized substances and precipitates of elements that contribute to strengthening, it is necessary to It is necessary to suppress the precipitation of these elements as much as possible during the process up to solution treatment, and even if they do precipitate, it is necessary to make the size of the precipitation as small as possible. Therefore, in this invention, first, the intermetallic compounds that contribute to the strengthening of the ingot are sufficiently dissolved in solid solution during the heating of the ingot before hot rolling, and then the Precipitation during the cooling process after medium and hot rolling is suppressed as much as possible, and even if precipitation occurs, the size of the precipitation is reduced, thereby achieving sufficient solution treatment in a short period of time during post-rolling solution treatment. I made it possible to do so. Specifically, the present invention hot-rolls a heat-treated aluminum alloy ingot, further cold-rolls it if necessary, and then solution-treats the coil while continuously unwinding it to form a heat-treated aluminum alloy ingot. In manufacturing the plate, the ingot is heated immediately before the hot rolling at a temperature of 90% or more of the solution treatment temperature.
After holding the solution for 0.5 hours or more, hot rolling is immediately started without cooling to a temperature lower than 90% of the solution treatment temperature, hot rolling is finished at a temperature of 300°C or less, and the solution treatment temperature is It is characterized in that the holding time of the oxidation treatment is 180 seconds or less. Effect When heating the ingot before hot rolling, the ingot is strengthened by heating and holding at a temperature of 90% or more of the solution treatment temperature (here, 90% or more in degrees Celsius) for 0.5 hours or more. Most of the intermetallic compounds that should contribute to this are dissolved in the α-Al base. At the same time, heating the ingot at that temperature prevents the formation of coarse precipitates during heating of the ingot, and immediately heats the ingot at that temperature (90% or more of the solution treatment temperature). By starting inter-rolling, coarse precipitates are prevented from being generated between the heating of the ingot and the start of hot rolling. In other words, conventionally, the heating temperature immediately before hot rolling was, for example,
In the case of 7075 alloy, the temperature is around 400℃, which is considerably lower than the solution treatment temperature (usually 460 to 500℃ as mentioned above), and in this case, the crystallized substances in the ingot are sufficiently solidified by heating the ingot. Not only is it difficult to melt, but it also tends to produce coarse precipitates, and apart from heating the ingot immediately before hot rolling,
Before that, heating may be performed at a higher temperature to homogenize the ingot, but in this case, although it is not necessarily impossible to dissolve the crystallized substances in the ingot during the homogenization heat treatment, Coarse precipitates are formed during the cooling process after chemical heat treatment.In contrast, the method of this invention involves heating the ingot at a temperature of 90% or more of the solution heat treatment temperature, followed by hot heating at that temperature. By starting rolling, it is possible to simultaneously achieve solid solution of intermetallic compounds in the ingot and prevention of coarse precipitation until the start of hot rolling. Here, if the ingot heating temperature immediately before hot rolling is less than 90% of the solution treatment temperature, it is difficult to sufficiently dissolve the intermetallic compounds in the ingot,
Furthermore, since there is a possibility that coarse precipitates may be formed, the heating temperature of the ingot needs to be 90% or more of the solution treatment temperature. However, in reality, it is most desirable to heat the ingot within the optimal solution treatment temperature range for each alloy as described above. The upper limit of the ingot heating temperature is not particularly specified, but if it is too high, eutectic melting and high temperature oxidation will occur, so it is preferably set to below the upper limit of the solution treatment temperature range for each alloy. On the other hand, if the holding time for heating the ingot at the above temperature is less than 0.5 hours, it is difficult to sufficiently dissolve the crystallized substances during the heating of the ingot, so the holding time was set to 0.5 hours or more. There is no particular upper limit to the retention time; however,
Normally, from the point of view of economy, it is preferable to set the time period to about 24 hours or less. Furthermore, as mentioned above, hot rolling started at 90% or more of the solution treatment temperature is finished at a low temperature of 300°C or less before winding. The formation of coarse precipitates is almost no longer observed, and even if they do precipitate, their size will be fine. In addition, starting hot rolling at the above temperature and finishing hot rolling at a low temperature of 300°C or less means hot rolling in a temperature range where coarse precipitates are relatively likely to be generated. The time required for inter-rolling is much shorter than the time required for cooling the hot-rolled coil when hot rolling is finished at a high temperature, so the total time required for the cooling process during and after hot rolling is The degree of precipitation of coarse precipitates is
The amount is much smaller than when hot rolling is finished at a high temperature, and even if it precipitates, its size is finer. However, in reality, it is desirable to strengthen cooling during hot rolling in order to finish hot rolling in the above temperature range as quickly as possible. Here, since the above effect cannot be obtained at a high temperature where the hot rolling end temperature exceeds 300°C, the hot rolling end temperature was limited to 300°C or less. As mentioned above, the ingot is heated for 0.5 hours or more at a temperature of 90% or more of the solution treatment temperature, then hot rolling is started at that temperature, and hot rolling is finished at a temperature of 300°C or more. This suppresses the precipitation of coarse precipitates in the process before solution treatment, and even if they do precipitate, their size becomes fine. Therefore, even with a short holding time of 180 seconds or less during solution treatment in a continuous furnace, it is possible to sufficiently dissolve precipitates and crystallized substances into solid solution, and eventually the material becomes sufficiently strong through room temperature aging or artificial aging. It becomes possible to achieve this goal. If the holding time of solution treatment exceeds 180 seconds, the effect of increasing the line speed and improving productivity cannot be obtained sufficiently, so the holding time is
It was specified as 180 seconds or less. However, in reality, it is preferable to hold for 60 seconds or less, and even with such a short-term holding of 60 seconds or less, the method of this invention allows the precipitates to become a solid solution to a considerable extent, and the subsequent room temperature aging or artificial aging A considerable degree of toughening can be achieved. Note that the heating rate in the solution treatment is preferably 5° C./sec or more in order to prevent coarsening of crystal grains. In addition, the cooling rate during cooling (quenching) after heating and holding in solution treatment is at least 5
C/sec or more is preferred, but since the quenching sensitivity differs depending on the type of alloy, it is desirable to select an appropriate cooling method depending on the type of alloy. for example
Although 6061 alloy and 7NO1 alloy can be hardened by forced air cooling, 2024 alloy and 7075 alloy require hardening by spray water cooling. Further, the solution treatment temperature, that is, the holding temperature in the solution treatment, may be set within the optimum range according to the type of alloy as described above. After being solution-hardened in this way, the strain is usually corrected by skin pass rolls, leveling, stretching, etc. as necessary, or residual stress is removed, and the material is aged at room temperature to become a so-called T4 tempered material. Alternatively, it is subjected to artificial aging treatment to become so-called T6 tempered material and used as a product board. Here, the artificial aging treatment can be carried out according to a conventional method depending on the type of alloy. It goes without saying that cold rolling may be performed as necessary after the hot rolling is completed and before the solution treatment. In addition, in the manufacturing process of thin sheets, intermediate annealing may be performed during cold rolling, and hot rolled coils may be annealed after hot rolling, but in the case of the method of this invention, solution treatment is performed. From the perspective of suppressing the precipitation of the previous coarse precipitates, it is desirable to avoid these annealings, and even if these annealings are unavoidable, they should be performed at as low a temperature as possible (e.g.
It is desirable to hold the temperature at 300°C or less for a short time and to increase the cooling rate after annealing. Example For the five types of alloys shown in Table 1, slab ingots of 500 mm x 1000 mm x 4000 mm were cast by DC casting, and then the ingots were soaked under the conditions shown in Table 2.
It was hot-rolled to obtain a hot-rolled plate with a thickness of 3 mm. However, in the comparison method for 6061 alloy and the comparison method for 7075 alloy in Table 2, after soaking the ingot, it is heated and held as shown in the maximum heating and holding column in the table before hot rolling is started. However, in all other cases, hot rolling was started immediately after soaking. Thereafter, the hot-rolled sheets according to the present invention method and the hot-rolled sheets according to the comparative method shown in Table 2 were cold rolled to a thickness of 1.5 mm without intermediate annealing, and the coils were continuously unwound using a continuous furnace. Solution treatment and quenching were performed under the conditions shown in Table 3, and further 7NO1 alloy and 6061
For the 2017 alloy, it was made into T4 tempered material by aging at room temperature for one month, and for the 2219 alloy and 7075 alloy, it was aged at 177℃ x 18 hours and 120℃ x 24 hours, respectively.
It was made into T6 tempered material by artificial aging treatment. On the other hand, each alloy in Table 1 was made into a hot-rolled material with a thickness of 3.0 mm under the same conditions as the conditions of the present invention method in Table 2.
Furthermore, after cold rolling the plate to a thickness of 1.5 mm without intermediate annealing in the same manner as above, batch solution quenching was performed under the conditions shown in Table 4 as a "conventional method", and then T4 tempered material or T6 tempered material was applied in the same manner as above. And so. Table 5 shows the results of examining the mechanical properties and intergranular corrosion resistance of the T4 tempered material or T6 tempered material of each alloy obtained by the present invention method, comparative method, and conventional method.

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[Table] As is clear from Table 5, in the case of the method of the present invention, the solution treatment is not maintained in a continuous furnace.
Despite the short time of 10 to 30 seconds,
In the T4 tempered material and the T6 tempered material, strength comparable to that of the conventional batch solution-quenching method was obtained, and the intergranular corrosion resistance was also good. On the other hand, the heating immediately before the start of hot rolling is the solution treatment temperature of 9.
Comparative examples (6061 alloy comparative example and 7075 alloy comparative example) in which hot rolling was started at a temperature below
In all comparative examples (comparative examples of 2017 alloy), sufficient strength was not obtained. Effects of the Invention As is clear from the above embodiments, according to the method of the present invention, when solution treatment is performed on a heat-treated aluminum alloy rolled plate in a continuous furnace, the holding time at the solution treatment temperature is It has become possible to significantly shorten the time and obtain the same strength (strength after aging) as in the case of solution treatment using a conventional batch furnace. Therefore, by applying the method of the present invention, it is possible to increase the line speed of a continuous solution treatment-quenching line and significantly improve productivity, as well as shorten the length of the retaining zone of a continuous furnace and improve equipment efficiency. Various effects can be obtained, such as a significant reduction in cost and the ability to perform solution treatment at an economical line speed even in a continuous annealing furnace without a retaining zone.

Claims (1)

[Claims] 1. A heat-treated aluminum alloy ingot is hot-rolled, further cold-rolled if necessary, and then solution-treated while continuously unwinding the coil to produce a heat-treated aluminum alloy rolled plate. In manufacturing, the ingot is heated immediately before hot rolling for at least 0.5 hours at a temperature of 90% or more of the solution treatment temperature, and then cooled to a temperature lower than 90% of the solution treatment temperature. Production of a heat-treated aluminum alloy rolled sheet, characterized in that hot rolling is started immediately without any heating, hot rolling is finished at a temperature of 300°C or less, and the holding time of the solution treatment is 180 seconds or less. Method.