JPH0635624B2 - Manufacturing method of high strength aluminum alloy extruded material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-strength aluminum alloy extruded material used for, for example, vehicle parts, machine parts, baseball bats, etc., particularly Al-high Zn-Mg-Cu system. The present invention relates to a method for manufacturing an aluminum alloy extruded material.

Definition In this specification, "%" means "% by weight".

2. Description of the Related Art Conventionally, as a high strength aluminum alloy wrought material, representative ones are A7075 alloy, A7178 alloy and A70.
50 alloy and the like are known.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Recently, even with these alloys, the number of applications in which the strength is unsatisfactory has increased, and it has been strongly demanded to further increase the strength. For this reason, recently, with respect to the Al-Zn-Mg-Cu based alloys as described above, attempts have been made to further increase the addition amounts of Zn, Mg and Cu which are the main hardening elements, but these hardening If the element is contained in a large amount exceeding the range of conventional alloys, casting cracks will occur during continuous casting, making its production difficult.

On the other hand, as a measure for preventing the casting crack, it is generally considered to lower the casting temperature. In this case, Mn and Cr which are usually added to prevent stress corrosion cracking and grain refinement are used. , Zr, etc. cause a new problem that coarse or huge crystallized substances are formed during casting. For this reason,
There is a limit to lowering the casting temperature, and Zn, Mg, Cu exceeds the permissible range of the conventionally known 7000 series alloy.
The fact is that the industrial production of high-strength aluminum alloy materials with an increased content of was extremely difficult. However, although it is known that such an alloy can be manufactured by powder metallurgy, it is not suitable for industrial production because it becomes expensive and there is a problem of reduced ductility due to the inclusion of oxides. It was something.

As a result of various experiments and studies, the present inventor has found that Zn, Mg, Cu
By solidifying a molten aluminum alloy containing a large amount of hardening elements such as, for example, under a predetermined high pressure, solidification cracking does not occur, and the formation of coarse crystallized substances by additive elements such as Mn, Cr, and Zr is also prevented. As a result, they have found that a defect-free billet suitable for extrusion processing can be produced, and completed the present invention.

That is, the present invention contains Zn; 7 to 12%, Mg; 2 to 7%, Cu; 0.5 to 3%, or further Mn; 0.2 to 1.0%, Cr; .About.0.4%, Zr; 0.05 to 0.3%, and one or more of them are dissolved, the balance aluminum alloy consisting of aluminum and impurities is melted, and the molten metal is heated to 300 to 350.degree. A high-strength aluminum alloy extruded material characterized by being prepared by forming a billet by pouring it into a preheated mold for pressure solidification and solidifying it under high pressure of 300 kgf / cm ² or more, and then extruding the billet. The manufacturing method is as a gist.

First, the reason for limiting the alloy components is as follows.

As is known, Zn, Mg and Cu as essential components mainly contribute to improving the strength of the alloy, and if all are less than the lower limit value, that is, Zn; less than 7%, Mg; less than 2%, C
If u is less than 0.5%, it is not possible to achieve a high strength, which exceeds the desired range of the conventional alloy, which is expected by the present invention. Therefore, when the content is less than the above lower limit value, the continuous casting of the billet by the conventional ordinary method is possible, and it is meaningless to adopt the manufacturing method of the present invention. Further, the upper limit values are Zn; 12%, Mg; 7%, Cu; 3
%, The coarse crystallized substances of the above elements are still generated even when the billet is produced by the high-pressure solidification method according to the present invention, which rather hinders achievement of high strength of the alloy material. In particular, even if Zn is contained in an amount of more than 12%, a comparative strength improving effect is not expected and it is substantially meaningless.
The most preferable contents are generally Zn; 8-10%, Mg; 3-5
%, Cu; 1-2%.

Mn added as necessary as an optional component,
Both Cr and Zr can be evaluated as equivalent since they are effective in refining crystal grains and improving stress corrosion cracking resistance. Mn: less than 0.2%, Cr: 0.1% Less than Z
If r is less than 0.05%, the above effect is poor, and Mn is 1.0%.
When the content of Cr exceeds 0.4%, the content of Cr exceeds 0.4%, or the content of Zr exceeds 0.3%, coarse crystallized substances are generated in the alloy to achieve the desired high strength of the alloy. Can not.

Next, the manufacturing process will be described. The above-mentioned Al-Zn-Mg-Cu-based alloy having a high Zn content is difficult to manufacture by the continuous casting method which is conventionally performed as a conventional method due to the occurrence of remarkable casting cracks. However, the present invention overcomes this problem by adopting the pressure coagulation method. That is, by melting the above aluminum alloy and pouring the molten metal into a mold for pressure solidification to solidify under pressure, a fine billet having crystal grains without defects can be produced. The mold for pressure solidification may use a container of an extruder for this. That is, the molten aluminum alloy may be poured directly into the container and solidified while being pressurized by the stem. Of course, in this case, it is necessary that a blind die is attached to the front surface of the container so as to close the front surface of the container so as to prevent the molten metal from spouting during pressure solidification.

In addition, when pouring the above, the mold is preliminarily 300
It shall be heated to about 350 ° C. This makes it possible to obtain a finer structure in the billet. That is, when the temperature is lower than about 300 ° C., solidification of the aluminum immediately starts after pouring, and it is difficult to sufficiently achieve the effect of pressure solidification. On the other hand, when heated to a high temperature of more than 350 ° C., the cooling rate becomes slow, and crystallized substances tend to grow to make it difficult to sufficiently achieve the above-mentioned refinement effect.

Immediately after pouring, the molten metal in the mold is pressurized by a pressure piston to allow solidification to form a billet. That is, the billet is produced by the pressure solidification method. Pressure at this time is necessary to set at least 300 kgf / cm ² or more in order to obtain sufficient effect of pressurized solidification, and it is preferably a 500~1000kgf / cm ² approximately. As described above, by solidifying the aluminum alloy under a predetermined pressure condition, a billet having small crystallized substances can be produced without causing casting cracks. Therefore, when the billet is produced by the conventional casting method, it becomes possible to omit the subsequent heating homogenization treatment required for homogenizing and refining the structure, which saves heat energy and processing time. Can be achieved. The magnitude of the pressing force does not greatly affect the quality of the billet. However, 300
If it is less than kgf / cm ^2, it is insufficient in the effect of preventing casting cracks and refining of crystal grains by the pressure solidification method.
Even if a high pressure exceeding 0 kgf / cm ² is applied, it is rather useless because it is not possible to see a proportional improvement in the effect commensurate with the increase in energy required. The reason why the crystallized product can be made finer by the pressure solidification is that the cooling speed increases because the voids between the mold and the melt and in the melt disappear due to the pressure. Presumed to be present.

The billet produced by the above-mentioned pressure solidification method is then extruded into a desired high-strength aluminum alloy extruded material. Here, the billet may be in a solid state that is once cooled, but preferably the temperature of the billet is a temperature suitable for extrusion, for example, about 1/2 of the liquidus temperature due to the progress of the pressure solidification. It is recommended that the pressure solidification step be terminated when the temperature is reduced to a certain degree and the state becomes a semi-molten state, and the container is immediately loaded as it is to start extrusion. By adopting such a procedure, it becomes possible to omit the billet heating step at the time of extrusion processing, save the energy and time required for the heating, improve the production efficiency of the alloy extruded material and reduce the production cost. You can enjoy the benefits.

EFFECTS OF THE INVENTION As described above, the present invention is composed of an Al-Zn-Mg-Cu-based alloy that contains Zn in a very high content ratio in terms of composition and has a relatively high Mg and Cu content. It is possible to obtain an excellent high-strength aluminum alloy that has superior strength to conventional alloys and can be used for various machine parts etc. to achieve further thinning and weight reduction.

In terms of manufacturing process, a molten aluminum alloy having the above composition is poured into a pressure solidification mold preheated to 300 to 350 ° C., and a billet is manufactured by a high pressure solidification method of 300 kgf / cm ² or more. The billet is to be extruded. Therefore, despite being a high-strength alloy as described above, a high-strength aluminum alloy material excellent in fine ductility of crystal grains is produced as a extruded material at high efficiency and at a low price without causing casting cracks in the production of billets. can do.

Examples Next, examples of the present invention will be shown together with comparative examples.

Alloys of various chemical structures shown in Table 1 above were used for liquidus temperature +10
Melt at 0 ℃, pour the melt into a mold for pressure coagulation heated to about 320 ℃, and immediately add 100kgf /
It was pressurized to cm ² and solidified under the pressure. Then, when cooled to about ½ of the liquidus temperature, the pressure solidification process is completed, and the resulting semi-molten billet (diameter 75 mm, length 100 mm) is immediately put into the container of the extruder. And extruded into a 12 mm diameter round bar. In the above process, the billet was obtained in a state without casting cracks, and its extrusion could be performed without any trouble.

Then, this extruded material is then subjected to solution treatment at 460 ° C.,
After further aging treatment at 120 ° C. for 24 hours, the mechanical properties of each obtained sample were examined. The results are shown in Table 2. The comparative alloys shown in Table 1 are those having a composition range in which the contents of Zn, Mg, and Cu are considered to be almost the limit values in the production by the conventional production method.

As shown in the results in Table 2 above, the alloys of the present invention are slightly higher than those of the comparative alloys, which are considered to have a limit of Zn content in the conventional production method mainly due to the high content of Zn. It can be seen that although the elongation decreases, the tensile strength and proof stress are much better.

Claims (2)

[Claims] 1. An aluminum alloy containing Zn; 7 to 12%, Mg; 2 to 7%, Cu; 0.5 to 3%, the balance being aluminum and impurities, and melting the molten metal to 300 to 350. After being poured into a mold for pressure solidification preheated to ℃ and solidified under high pressure of 300 kgf / cm ² or more, a billet is prepared.
A method for producing a high-strength aluminum alloy extruded material, which comprises extruding the billet. 2. Zn; 7-12% Mg; 2-7% Cu; 0.5-3%, and Mn; 0.2-1.0% Cr; 0.1-0.4 % Zr; One or more of 0.05 to 0.3%, aluminum alloy consisting of balance aluminum and impurities is melted, and the molten metal is preheated to 300 to 350 ° C under pressure solidification. A method for producing a high-strength aluminum alloy extruded material, which comprises forming a billet by pouring it into a casting mold and solidifying it under a high pressure of 300 kgf / cm ² or more, and then extruding the billet.