JPS60125354A - Manufacture of superplastic high strength aluminum alloy - Google Patents

Abstract

PURPOSE:To manufacture the titled Al alloy having fine grains by adding a specified amount of Cr or Zr to a precipitation hardening Al alloy, hot and cold working the resulting alloy, heating it to the soln. heat treatment temp., and carrying out cooling, working and heating under specified conditions. CONSTITUTION:0.05-0.35% Cr and/or 0.05-0.25% Zr is added to a precipitation hardening Al alloy contg. about 5.1-8.1% Zn, about 1.8-3.4% Mg, about 1.2- 2.6% Cu and <=about 0.2% Ti. The resulting alloy is hot-worked, cold-worked, and heated to the soln. heat treatment temp. It is cooled at 0.2-0.001 deg.C/sec cooling rate, cold worked at >=60%, and heated to 400-530 deg.C at 1 deg.C/sec heating rate to form grains of <=25mum grain size by recrystallization. Thus, a superplastic high strength Al alloy is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing superplastic high strength aluminum alloys with fine grains of 25 μm or less.

The rolled material made from precipitation hardening aluminum alloy through the usual manufacturing process of filling → homogenization heat treatment → hot rolling → cold rolling → solution treatment has a crystal grain size of 30 mm on the plate surface. ~
100 .mu.m, and in order to obtain crystal grains of 25 .mu.m or less, it is necessary to apply cold working of more than 90%.

However, when cold rolling is applied to a higher degree of working than 90%, edge cracks occur at the end face of the plate, or the tentacles break at right angles to the rolling direction.

Therefore, a method of obtaining fine crystal grains even with a low working degree has been proposed, as seen in, for example, Japanese Patent Application Laid-Open No. 53-132420. However, this method requires overaging treatment.

In view of the above-mentioned prior art, the present invention aims to obtain a superplastic high-strength aluminum alloy that does not require over-aging treatment and does not suffer from defects such as edge cracking and breakage even under high working conditions. The gist of it is Oro, 0
A precipitation hardening aluminum alloy containing at least one of 5% to 0.35% or 0.05% to 0.25% of Zr is hot worked and cold worked according to a conventional method, heated to a solution treatment temperature, and then Cooled at a cooling rate of .2 to o, ooi°C/SeC and subjected to cold processing of 60% or more to 400
This is a method for producing an ultra-short t1 high-strength aluminum alloy, which is characterized by increasing the temperature to ~530°C at a heating rate of 1°C/sec or more and recrystallizing it to 25μ or less.

First, the precipitation hardening aluminum alloy used in the present invention is 7n
s, i ~8.1%, M(+1.8~3.4%, C
U 1.2-2.6%, TiO, 2% or less, and at least one of the above-mentioned <Oro, 05-0.35% or ZrO, 05-0.25%. . The reasons for limiting the composition of each component are as follows.

7n: If it is less than 5.1%, high strength cannot be obtained by tempering, but if it exceeds 8.1%, stress corrosion cracking is likely to occur.

Mg: If it is less than 1.8%, high strength cannot be obtained by tempering, and if it exceeds 3.4%, rolling workability is poor and stress corrosion cracking is likely to occur.

CO: If it is less than 1.2%, strong color will be produced by tempering.
If it exceeds 2.6%, rolling workability will be poor and toughness will deteriorate.

1"i: Addition of 0.20% or less is effective in refining the casting structure and preventing cracking of the ingot during casting, but if it exceeds 0.20%, huge intermetallic compounds will crystallize.

C; r: Addition of 0.05 to 0.35% has the effect of grain refinement and is effective in preventing stress corrosion cracking. If it is less than 0.605%, these effects will not be achieved, and if it exceeds 35%, a huge intermetallic compound will crystallize, which is not preferable.

Zr: Addition of 0.05 to 0.25% has the effect of grain refinement and is effective in preventing stress corrosion cracking. If it is less than 0.05%, there will be no effect, and if it exceeds 0.25%, it will be a huge gold mine.
This is not preferred because the compound crystallizes.

In the present invention, the fine precipitated phases formed during hot rolling or cold rolling of an alloy having such a composition are subjected to solution treatment.
l! Heating to a temperature of 0.2-0.
By cooling at a rate of 001°C/5e (i,
Age hardening at room temperature is small because supersaturated solute atoms precipitate during cooling. For this reason, in the case of rolling, it is possible to perform rolling with a cold rolling rate of over 90% with fewer edge cracks and fewer breaks. The material that has been strongly processed in this way is
If the temperature is raised at a heating rate higher than sea and recrystallized, 2
A material with crystal grains of 5 μm or less can be obtained.

The reason for the limitation of the condition from the solution treatment temperature to room temperature in the present invention is that when the cooling rate is slower than 0.2°C/Sec, plate-like, rod-like,
Precipitation of bulky coarse compounds (M phase [M (l Zn 1, etc.) In this way, the amount of solute elements precipitated differs depending on the cooling rate.If the cooling rate is fast, the supersaturated solute R atoms tend to form a GP zone or a precipitated phase after quenching.On the other hand, if the cooling rate is slow, Supersaturated wJ atoms precipitate in the grains and grain boundaries as M phase or other compounds during cooling. Also, GP zones and precipitated phases are less likely to occur after quenching.

The ease of cold working differs depending on the difference in precipitation state as described above. Slow cooling below 0.2°C/513C produces coarse precipitates and reduces the deformation resistance of the matrix. Therefore, it is easy to deform. On the other hand, 0.2℃/
If it is cooled more quickly than SeC, the deformation resistance is large due to the GP zone and fine precipitates, and it is easy to cause edge cracks and pressure cracks. Furthermore, if the cooling rate is slower than 0.001°C/sec, the cooling rate is very slow and there is little merit in terms of economics.

Cold working facilitates recrystallization by imparting processing strain. If the degree of cold working is less than 60%, the grain size will be larger than 25μ. In the case of water-based alloys, the size of recrystallized grains becomes finer as the degree of cold working increases. This is because the higher the degree of cold working, the more regions undergo strong working, and at the same time the dislocation density also increases, so solute atoms tend to precipitate on more dislocations, hindering the movement of dislocations, and thus crystal growth. The recrystallized grains become smaller.

After cold working, it is heated at 400 to 530°C for recrystallization. It is difficult to recrystallize below 300℃,
When the temperature is lower than 0°C, solute atoms precipitated on dislocations tend to aggregate and form compounds. This is thought to be because the fixing effect of dislocations by the molten metal decreases, making it easier for dislocations to move and recrystallized grains to become larger.

When the heating rate is high at 400° C. or higher, it is thought that recrystallization proceeds before solute atoms aggregate. Of course, if the temperature exceeds the solution treatment temperature, the solute atoms become solid solution. Furthermore, since the alloy melts when the temperature exceeds 530°C, it is necessary to carry out recrystallization at a temperature of 400 to 530°C.

If the heating rate is slower than 1°C/See,
Because the crystal grains slowly pass through the grain coarsening region of 300 to 400°C, the grain size becomes 25μ or more, but the heating rate is 1
The faster the speed is above °C/See, the finer the crystal grains will be.

Next, examples will be described.

Example 1 [Cooling conditions from solution treatment temperature] zn 5.
7%, Mg2.4%, cut, e%, Cr0.20%
An aluminum alloy containing 0.05% of FeO, and 0.04% of Si was ingot-formed by a continuous casting method to form a 300-element slab. After homogenization heat treatment at 470°C for 30 hours, the surface segregation layer was removed, and a 6 mm thick plate was hot rolled at 400 to 450°C. This is 482℃
The sample was heated to a solution treatment temperature of , and held for about 60 minutes, and then quenched to room temperature by changing the cooling rate. This heat-treated plate was subjected to 65% and 80% cold working to a final temperature of 482°C.
It was rapidly heated to a temperature of . Heating rate is 50℃/S
It is eC. After being held for 10 minutes, it was water quenched and the crystal grain size on the plate surface was examined.

The results are shown in Table 1.

Table 1 Example 2 [Cold working degree] The alloy shown in Example 1 was hot rolled to a thickness of 8-1, further cold rolled to a thickness of 411°C, and after solution treatment at 500°C for 1 hour. , at a cooling rate of 0.2.0.005°C/See. This sample was cold rolled to 1,811 (
1,411J iml, O,,6111゜0.4m-
The sheets were rolled to various thicknesses. The rolling reduction ratio is 55.65.
It is 15.85.90%. The processed materials were heated to 482°C at a heating rate of 50°C/SeC, held for 10 minutes, and then water quenched. Table 2 shows the grain size of the plate surface after water quenching.
Shown below.

Table 2 Example 3 [Recrystallization temperature and heating rate] The alloy shown in Example @1 was continuous rolled to a thickness of Amm.
After solution treatment at 60°C for 1 hour, it was furnace-heated at 0.005°C/SeC. This sample was subjected to 85% cold working to yield 0.61
The thickness was 11. This board is 330.380.420.45
The temperature was increased to 0.480°C at a heating rate of 50°C/Sec. After being held at each temperature for 30 minutes, it was water quenched and tempered at a final temperature of 120° C. for 24 hours. Table 3 shows the relationship between crystal grain size and tensile strength at this time. Furthermore, the furnace-cooled I was subjected to 65.85% cold working, and the temperature was 1.4-month, 0.
61 thickness plate up to 480℃, 0.1.0.5.1.10
．． 50. Raise the temperature at each heating rate of 100 ° C / SeC, 3
After holding for 0 minutes, water quenching was performed. Table 4 shows the crystal grain size on the plate surface at this time.

Table 3 Table 4 Example 4 [6. Application to pipes] Zn 5.6%, M (12.5%, Cu 1.5%, Q
An aluminum alloy billet with a diameter of o and am containing ro, 22%, Feo, 12%, and Sin, 06% was formed into an ingot, and after homogenization heat treatment at 470°C for 24 hours, the segregation layer was removed to form a 440 Hot extruded at °C. Extrusion is 80m
m diameter round bar, part of the round bar has an outer diameter of 80IIIl11
It was molded into a tube with an inner diameter of 60IIIl11 and a wall thickness of 10IlO1.

Each piece was made into a length of 200 mm, subjected to solution treatment at 480°C for 2 hours, and then cooled in a furnace at a rate of 0.01°C/Sec. These samples were cut into diameters of 2 mm using a cold isostatic extruder.
5mm round bar, outer diameter 52.5mm, inner diameter 501IllI
11 was extruded into a tube with a wall thickness of 1.25 mo+. In both cases, the degree of cold working is approximately 90%. These were heated to a temperature of 480°C at a heating rate of 5°C/sec for rods and 50°C/sec for tubes. After being held at 480° C. for about 30 minutes, it was water quenched and the crystal grain size on the surface was measured. The result is 14 μm in the bar.

In the tube, the particle size was 8 μm.

Example 5

Claims (1)

[Claims] Cr 0.05-0.35% or Z r O, 05-
Precipitation hardening aluminum alloy containing at least one of
It was cooled at the cooling rate of SeC, subjected to cold working of 60% or more, and heated to a temperature of 400 to 530°C at a heating rate of 1°C or more for 7 seconds or more. A method for producing a superplastic high-strength aluminum alloy characterized by recrystallization to a size of 25 μm or less.