JPS6379942A - Manufacture of aluminum-alloy pipe for piping excellent in strength, workability, and corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain an Al-alloy pipe for piping having superior strength, workability, and corrosion resistance, by hot-extruding an Al-alloy ingot in which value of Mg/Si and also respective contents of Mg and Si are specified and then by applying controlled cooling and aging treatment to the above. CONSTITUTION:An alloy in which value of Mg/Si is regulated to >=1.4 and which consists of 0.3-0.7% Mg, 0.2-0.4% Si, and the balance essentially Al is cast. The resulting Al-alloy ingot is hot-extruded into tubular state, which is subjected to forced cooling at >=3 deg.C/sec cooling rate without delay, followed by aging treatment by the conventional method. If necessary, 0.05-5% Cu is further incorporated to the above alloy. The Al-alloy pipe for piping obtained by the above method hardly causes intercrystalline crack at the time of cold working and has excellent workability and, moreover, it has superior strength and corrosion resistance similar to those of conventional pipes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aluminum alloy tube for piping, and particularly to a method for manufacturing an alloy tube by hot extruding an aluminum alloy ingot.

[Prior art] Rubber has traditionally been used as a material for car cooler piping, but it has problems in that it is heavy and expensive, so aluminum alloy materials are now being used in place of rubber. be. Generally, 6063 alloy or 6061 alloy is used as an aluminum alloy material for car cooler piping.

[Problems to be Solved by the Invention] When using an aluminum alloy pipe as a car cooler piping material, the alloy pipe is required to have the following characteristics.

■ Good workability.

■ Possess a certain degree of strength.

■ Good corrosion resistance.

6063 commonly used for force-tala piping
For tubes made of alloy or 6061 alloy, refer to (2) above.

Item (3) is fully satisfied. However, regarding item (1), depending on the alloy composition, 3i or MQ2Si precipitates at the grain boundaries, which tends to cause intergranular cracks during cold working, such as bending, tube expansion, and spooling. There are sexual problems.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an aluminum alloy pipe for piping in which intergranular cracking is less likely to occur during cold working.

[Means for Solving Problems] In order to prevent intergranular cracks from occurring during cold working in aluminum alloy pipes for piping, the present invention improves the Mg/Si ratio to 1.
．． 4 or more, Mq: 0.3-0.7% and 3i
: Contains 0.2 to 0.4%, or in addition to the above, C
An aluminum alloy containing u: 0.05 to 0.5% and the remainder being substantially aluminum is used, and after hot extruding an ingot of this alloy, 3i or M (
3'C/Sec to suppress grain boundary precipitation of lsi
It is characterized in that it is cooled at the above cooling rate and subjected to aging treatment by a conventional method.

The reason for limiting the alloy composition as described above in the aluminum alloy used in the present invention is as follows.

MCI:1VtQ forms Mg2Si with 3i, contributes to aging treatment, and has the effect of increasing strength. However, if it is less than the lower limit, the strength will not be sufficient, while if it is more than the upper limit, extrudability and processability will deteriorate.

Si: Si forms MQ and MQ2Si, which contributes to age hardening and has the effect of increasing strength. However, if it is less than the lower limit, the strength will not be sufficient, and if it is more than the upper limit, the strength will further increase, and 3i/fV1g2si will precipitate at the grain boundaries, resulting in a decrease in workability.

Mg/Si ratio: Mg/Si ratio is low, 3i is Mg2S
If i is significantly in excess of the Si/Mq ratio, Si will be present at the grain boundaries.
and Mq2Si precipitate, resulting in a significant decrease in workability. Therefore, the v+crZsr ratio is set to 1.4 or more.

Cu: The addition of Cu has the effect of further increasing the strength under the above ranges of MCI and Sl.

If it is less than the lower limit, this effect will not be sufficient, and if it is more than the upper limit, workability and corrosion resistance will decrease.

In addition, if the Fe content exceeds 0.3%, the amount of Fe-based insoluble compounds increases and the processability may deteriorate, so F
It is desirable that e be less than 0.3%. Further, it is desirable to add a small amount of T r and B since they have the function of refining the casting structure and making the structure of the extruded material uniform.

This alloy is manufactured into tubes using the following steps.

(1) Homogenization process Homogenization process requires J, sij'%. in this case,
The ingot is heated to 520° C. to 590° C. and homogenized for 2 to 16 hours, thereby infiltrating the eutectic compound crystallized at the casting orifice into the matrix.

(2) Hot extrusion The ingot is heated to 480-540°C and extruded into a tube of a predetermined size. The cooling rate after extrusion needs to be 3'C/Sec or more. If the cooling rate is slower than 3°C/sec, 3i or MQ23i will precipitate at grain boundaries and workability will decrease, but if it is faster than 3°C/sec, grain boundary precipitation will decrease and workability will improve. .

As for the cooling method, forced air cooling or spray quenching is preferable to water cooling in order to avoid generation of distortion.

(3) Drawing processing If necessary, cold drawing processing is performed.

(4) Aging treatment The tube obtained in the above process is aged at 140-200°C.
Aging is performed for ~10 hours to impart a predetermined strength.

Examples of the present invention will be described below along with comparative examples.

Examples 1 to 9 The alloys listed in Table 1 were melted by alloy type and cast into round bar ingots for extrusion with a diameter of 6 inches. 56 of these ingots
After homogenization treatment at 0°C for 10 hours, each at 520°C.
extruded into a tube with an inner diameter of 14.9 x outer diameter of 18.5 x wall thickness of 1.8 mm, and immediately cooled with forced air at an average cooling rate of 6°C/se.
It was cooled at c.

Next, the main pipe is subjected to drawing processing, and then 11 Oxl
4.5 xl, 751mm rainbow? ,[,150'CX
Aging treatment was performed for 6 tir.

A tensile test and a tube expansion test were performed on the base pipe produced by the above process to evaluate the strength and workability of the base pipe. The results are shown in Table 2. The tubes according to Examples 1 to 9 have excellent strength and workability, but the tubes according to Comparative Example 1 have low strength, and the tubes according to Comparative Examples 2 to 4 have excellent strength and workability. had poor workability.

Table 1 Chemical composition of the alloy used (wt%) Table 2 Pipe strength and workability The value obtained by dividing the previous pipe outer diameter) by the pipe outer diameter before expansion.

Table 2 continued Examples 10 to 13 Mc): 0.51%, Si: 0.32%, Fe: 0.1
An aluminum alloy containing 4% aluminum alloy with the remainder being A1 after removing impurities was melted and cast into round bar ingots with a diameter of 6 inches for extrusion in the number of samples. After each ingot was homogenized at 570 °C for 12 h, it was extruded into 14.9 X 18.5 Xl, 8' mm tubes and immediately subjected to different cooling as shown in Table 3 for each sample tube. Cooled by forced air cooling. Then 1111 stretching L Te 11.0Dx 14.50Dx 1.75
tmmk: After that, aging treatment was performed at 140°C for 8 hours.

A tensile test and a tube expansion test were performed on the stand pipe manufactured by the above process to evaluate its strength and workability. The results are in Table 3
As shown in , Examples 10 to 3 were excellent in both strength and workability, but Comparative Examples 5 to 7 had poor workability.

Table 3 Strength and Workability of Pipe Examples 14 to 18 The alloys listed in Table 4 were melted by type and cast into round bar ingots for extrusion with a diameter of 6 inches. 560 of these ingots
After homogenization for 10 hours at 520°C, each was extruded into a tube of 1.11.91D cut 8.5°D x 1.8 tm... and then cooled with forced air at an average cooling rate of 6°C/s.
Cooled with EC. Next, the main pipe was subjected to drawing processing, 11.01 DXD 14.5 xl, 75 tmnH,... 150
Aging treatment of °CX 611r was performed.

A tensile test and a tube expansion test were performed on the base pipes manufactured through the above process to evaluate the strength and workability of the base pipes.

The results are shown in Table 5, and Examples 14 to 18
Comparative Example 8 had low strength, and Comparative Example 9.10 had poor workability.

Table 4 Chemical composition of alloy used Table 5 Pipe strength and workability Examples 19 to 22 Mg: 0.52%, Si: 0.35%, Cu: 0.20
% and the remainder was A1 except for impurities, and the aluminum alloy was melted and cast into 6-inch diameter round bar ingots for extrusion in the number of samples. After each ingot was homogenized at 570°C for 12 hours, it was
It was extruded into 1.0 mm tubes and immediately cooled by forced air cooling at different cooling rates as shown in Table 6 for each sample tube. Then, it is drawn to 11.0” x 14.50D x 1.75tn.
After aging for +m, 140'Cx 8Hr (i') aging treatment was performed.

A tensile test and a tube expansion test were performed on the tube manufactured through the above steps to evaluate its strength and workability. The results are in Table 6.
As shown in , Examples 19 to 22 were excellent in both strength and workability, but Comparative Examples 11 to 13 had poor workability.

= 13- Table 6 Pipe strength and workability [Effects of the invention] The aluminum alloy pipe for piping obtained by the present invention contains Si and MQ, which are found in conventional aluminum alloy pipes.
There is almost no grain boundary precipitation of 2Si. Therefore, intergranular cracks were less likely to occur during cold working, and workability was significantly improved.

Also, its strength and corrosion resistance are as good as conventional pipes.

Claims (2)

[Claims] (1) Mg:0.3 with Mg/Si ratio of 1.4 or more
After hot extrusion, an aluminum alloy ingot containing ~0.7% and Si: 0.2~0.4%, with the remainder being substantially aluminum, was cooled at a cooling rate of 3°C/sec or more, and then cooled using a conventional method. A method for manufacturing aluminum alloy pipes for piping that has good strength, workability, and corrosion resistance, and is characterized by aging treatment. (2) Mg:0.3 with Mg/Si ratio of 1.4 or more
~0.7% and Si:0.2~0.4%, and further C
After hot extrusion of an aluminum alloy ingot containing u: 0.05 to 0.5% and the remainder being substantially aluminum, the temperature is 3°C.
A method for producing an aluminum alloy pipe for piping having good strength, workability, and corrosion resistance, characterized by cooling at a cooling rate of 1/sec or more and aging treatment by a conventional method.