JPS59166658A - Preparation of high tensile aluminum alloy plate for forming - Google Patents

Abstract

PURPOSE:To obtain a high tensile aluminum alloy plate of which the crystal grain is made fine and the forming processability is improved, by applying rapid heat treatment to a cold rolled plate comprising an Al-Cu-Mn-Mg alloy having a specific composition of which the Si and Fe amounts are limited while subjecting thus, heat treated alloy plate to perfect annealing treatment. CONSTITUTION:A cold rolled plate is fabricated from an Al-alloy having a composition consisting of, on a wt. basis, 3.5-5.0% Cu, 0.2-1.3% Mn, 1.2-1.8% Mg, 0.12% or less Si, 0.15% or less Fe and the remainder of Al and inevitable impurities. This cold rolled plate is rapidly heated at a speed of 2X10<4> deg.C/hr or more and heat treated at 350-450 deg.C for 5sec-30min. Subsequently, usual perfect annealing treatment is applied to the heat treated plate. By this method, a crystal grain is made fine and formability is improved and a high tensile aluminum alloy plate suitable for an airplane is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a high-strength aluminum alloy plate for forming, and in particular, improves formability by refining the crystal grains of a fully annealed high-strength aluminum alloy plate for forming. This is what I did.

Generally, high-strength aluminum alloy sheets for forming are used to manufacture interior and exterior panels for aircraft and other aircraft, instrument panels, equipment exteriors, etc., and are usually cold-rolled sheets that have been completely annealed, after being formed into the desired shape. Solution treatment and aging treatment are applied. As shown in Table 1, 2×XX series alloys, represented by 2024 alloy, have been used for conventional high-strength aluminum alloy plates for forming.
After finishing the plate to the desired thickness by casting, soaking, face rolling, hot rolling, and cold rolling, the plate is heated in the atmosphere to a temperature of 400° C. or higher for several hours, and then slowly cooled to complete annealing. Such high-strength aluminum sheets for forming are not only inferior in toughness, but also contain Fe, an impurity, like the 2324 alloy shown in Table 1.
A high-strength aluminum alloy plate for forming with improved toughness by controlling the amount of Si has also been produced in the same manner.

However, in all of these high-strength aluminum alloy plates for forming, the crystal grains become coarse during the complete annealing process, and as a result, they overhang during the forming process. Formability 1 There are disadvantages such as poor bending formability and rough skin, especially when Fe and 81 are impurities.
This tendency is noticeable in high-strength aluminum alloy sheets for forming made from the 2324 alloy, which has a regulated

In view of this, as a result of various studies, the present invention has decided to rapidly heat a cold rolled plate to a temperature of 350 to 450°C before complete annealing. We discovered that coarsening can be prevented, and as a result of further inspection, we developed a method for manufacturing high-strength aluminum alloy sheets with excellent formability.
t% is simply abbreviated as %).

MnO, 2-1.3%, Mg1.2-1.8%,
In a high-strength aluminum alloy plate that has been completely annealed, a cold-rolled aluminum alloy plate consisting of 3i0.12% or less, FeO, 15% or less, and the balance A°C and unavoidable impurities is heated at 2X104°C/hour or more. 350-450° at a speed of
After raising the temperature to C and heat-treating at that temperature for 5 seconds to 30 minutes,
It is characterized by complete annealing treatment.

That is, in order to improve the toughness of the present invention, an alloy having the above composition range in which the impurities Fe and 5iffi are controlled is cast, soaked, and face-sided by a conventional method.

Finish the plate to the desired thickness by hot rolling and cold rolling, and roll it to 350-450°C at a speed of 2 x 104°C/hour or more.
The temperature is raised to °C, and heat treatment is performed at this temperature for 5 seconds to 30 minutes. By heating this again and performing a complete annealing treatment, the crystal grains of the fully annealed high-strength aluminum alloy sheet for forming are refined, and the formability is significantly improved.

However, in the present invention, the alloy composition is limited as described above for the following reasons.

The reason why the CU content was limited to 3.5 to 5.0% was 3.5%.
If it is less than 5.0%, sufficient strength will not be obtained even if solution treatment and aging treatment are performed after forming, and if it exceeds 5.0%, C1
This is because intermetallic compounds precipitate, which not only lowers toughness but also lowers cold rollability and formability. The Mn content was limited to 0.2 to 1.3% because if it is less than 0.2%, crystal grains will not be refined and moldability will not be improved; if it exceeds 1.3%, cooling This is because the inter-rollability and moldability deteriorate. Moreover, the Mg content is 1.2 to 1.
The reason why we limited it to 8% is that it should be less than 1.2% [after molding].
This is because even if solution treatment and aging treatment are performed, sufficient strength cannot be obtained, and if the content exceeds 1.8%, cold rollability and formability deteriorate.

The impurity Fe content was limited to 0.15% or less and the Si content was limited to 0.12% or less.
This is because if Fe is contained, the toughness is reduced and the molding processability is also reduced. Even if other impurities are contained within the normal range, the properties of the high-strength aluminum alloy sheet for forming may not be impaired in any way.

In the present invention, before completely annealing a cold-rolled plate of a high-strength aluminum alloy having the above-mentioned composition range, an appropriate method such as a salt bath furnace or an electric heating furnace is used to heat the cold-rolled plate of a high-strength aluminum alloy having the above-mentioned composition range to 350° C. at a rate of not less than 2
The temperature is raised to ~450°C, and heat treatment is performed at this temperature for 5 seconds to 30 minutes. However, the reason for limiting the heat treatment conditions in this way is that grain refinement can be achieved even if the heating rate is less than 2 x 104°C/hour, the heating temperature is less than 350°C, and the holding time is less than 5 seconds. The heating temperature was 450℃.
If the temperature exceeds 30 minutes, the crystal grains tend to become coarser, and if the heat treatment is held for more than 30 minutes, the grain refining effect of the heat treatment will be saturated, and further heating will not only be economically disadvantageous but also require a salt bath furnace. This is because the heat treatment caused by the above causes surface roughening.

For complete annealing, 50'C/
The temperature may be raised to about 400°C at a rate of 1 hour, held at this temperature for about 2.5 hours, then lowered to 260°C at a rate of 28°C/hour or less, and then cooled with N1 in air.

The present invention will be described in detail below with reference to examples.

An alloy having the composition shown in Table 2 was melted, water-cooled and cast to form an ingot with a thickness of 100 m, and after soaking at a temperature of 490° C. for 12 hours, the ingot had a thickness of 9 mm on each side.

The edge was heated to a temperature of 430°C and hot rolled into a plate with a thickness of 5 mm, followed by cold rolling into a plate with a thickness of 1 mm.
Finished on a board. This was subjected to heat treatment and complete annealing treatment under the conditions shown in Table 3, and then the crystal grain size and moldability were examined. Further, after forming the completely annealed specimen into a U-shape, it was subjected to solution treatment (water quenching from a temperature of 495°C) and natural aging treatment (left at room temperature for 4 days or more), and its tensile strength was measured. These results are shown in Table 3 (M).

For the complete annealing treatment, the temperature was raised to 400°C at a rate of 50°C/hour, held at this temperature for 2.5 hours, and then slowly cooled to a temperature of 2GO°C at a rate of 25°C/hour, and then air cooled.

In addition, the crystal grain size was measured from micrographs, and the moldability was determined by the Erichsen value using the Erichsen test.

Minimum bending radius (1) Find the rough skin limit radius by bending.

As is clear from Tables 2 and 3, the high-strength aluminum alloy sheets for forming formed by the method of the present invention have finer grains and are easier to form than the high-strength aluminum alloy sheets formed by the conventional method No. 16. It is clear that the properties are excellent.

On the other hand, comparative method No. 5 has a slow temperature increase rate during heat treatment.
．． It can be seen that in Comparative Method No. 016 where the heating temperature is low, Comparative Method No. 7 where the heating time is short, and Comparative Method No. 008 where the heating temperature is high, the crystal grains are not refined and the moldability is not improved.

Furthermore, if the alloy composition is outside the range specified by the present invention, even if heat treatment is performed before complete annealing, the crystal grains will not become finer and the formability will be poor, especially if a comparative alloy with a low Cu content is used. It can be seen that with Comparative Method No. 009, which was used, and Comparative Method No. 13, which used Comparative Alloy H with a low Mg content, sufficient strength could not be obtained even if solution treatment and aging treatment were performed after forming.

As described above, according to the method of the present invention, a high-strength aluminum alloy plate with excellent formability can be obtained, which facilitates the manufacture of aircraft and other interior and exterior panels, instrument panels, equipment exteriors, etc., and improves manufacturing yield. It has remarkable effects such as an improvement of 1q.

Claims (1)

[Claims] Cu 3.5-5.0wt%, MnO, 2-1.3
wt%. M (11,2-1.8wt%, S i O, 12vt
% or less, FeO, 15 wt% or less, the balance (and unavoidable impurities) In a high-strength aluminum alloy sheet for forming that is completely annealed, the cold rolled sheet is heated at 2X104℃/hour or more. A method for producing a high-strength aluminum alloy plate for forming, which comprises raising the temperature at a speed of 350 to 450°C, heat-treating at that temperature for 5 seconds to 30 minutes, and then completely annealing.