JPS61259828A - Production of high-strength aluminum alloy extrudate - Google Patents

Abstract

PURPOSE:To produce a defectless billet suitable for extrusion by solidifying a molten Al alloy contg. a specific ratio each of hardening elements such as Zn, Mg and Cu under a high pressure. CONSTITUTION:The Al alloy contg., by weight %, 7-12% Zn, 2-7% Mg and 0.5-3% Cu, contg. 1 or >=2 kinds among 0.2-1.0% Mn, 0.1-0.4% Cr and 0.05%-3% Zr, if necessary and consisting of the balance Al and inevitable impurities is melted. Such molten metal is poured into a metallic mold for high-pressure solidification and is solidified under the prescribed high pressure (<=50kgf/cm<2>) to produce the billet. Such billet is subjected to extrusion. The defectless billet consisting of the fine crystal grains is thus produced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to high-strength aluminum alloy extrusions used, for example, in vehicle parts, machine parts, baseball bats, etc., particularly in A1-high ZN-XG-CU series. This invention relates to a method for producing aluminum alloy extrusions.

Definitions In this specification, all "%" refers to % by weight.

Conventional technology Conventionally, typical high-strength aluminum alloy wrought materials include A7075 alloy, A7178 alloy, and A70 alloy.
50 alloy etc. are known.

Problems to be Solved by the Invention Recently, however, even these alloys have been increasingly used in applications where their strength is unsatisfactory, and there is a strong demand for further increases in their strength. For this reason, attempts have recently been made to further increase the amounts of Zn, Mg, and Cu, which are the main hardening elements, in AI-Zn-Mq-cu alloys such as those mentioned above. If the alloy contains a large amount of elements beyond the range of conventional alloys, casting cracks will occur during continuous casting, making production difficult.

On the other hand, as a measure to prevent casting cracks, lowering the casting temperature is generally considered, but in this case, Mn and Cr, which are usually added to prevent stress corrosion cracking and refine grains, etc. , Zr.

A new problem arises in that coarse or large crystallized substances are generated during casting. For this reason, there is a natural limit to lowering the casting temperature, and it is difficult to industrially produce high-strength aluminum alloy materials with increased Zn, Ma, and Cu contents beyond the allowable range of conventional 7000 series alloys. The reality is that it was extremely difficult. Although it is known that such alloys can be produced by powder metallurgy, they are expensive and suffer from reduced ductility due to the inclusion of oxides, making them unsuitable for industrial production. It was something.

Means for Solving the Problems As a result of various experiments and research, the present inventor has developed 7-n, MCI
By solidifying a molten aluminum alloy containing large amounts of hardening elements such as CI and CI under high pressure, solidification cracking does not occur, and the formation of coarse crystals due to additive elements such as Mn, Or, and Zr is also prevented. As a result, they discovered that it is possible to produce a defect-free billet suitable for extrusion processing, leading to the completion of this invention.

Therefore, the gist of this invention is that Zn;
2%, M(]; 22-7% Cu; 0.5-3%, and if necessary Mn; 0.2-1°0%, Cr; 0
．． 1 to 0.4%, Zr; 0.05 to 13% of O, and the balance consists of aluminum and unavoidable impurities. This is a method for producing a high-strength aluminum alloy extruded material, which is characterized in that a billet is produced by pouring molten metal into the aluminum alloy and solidifying it under a predetermined high pressure, and then extruding the billet.

First, the reasons for limiting the above alloy components are as follows.

As is known, Zn, Mg, and CU as essential components mainly contribute to improving the strength of the alloy, and when they are all below the lower limit values, that is, Zn: less than 7%, MU: less than 2%, C1: 0. If it is less than 5%, it is impossible to achieve the desired high strength of the present invention that exceeds the range achieved by conventional alloys. Therefore, when the content is less than the above lower limit, it is possible to continuously cast a billet by the conventional conventional method, and there is little significance in adopting the manufacturing method of the present invention. In addition, the upper limit of Zn; 12%, M! II
7% and CO; 3% respectively, even when producing billets by the high-pressure solidification method according to the present invention, coarse crystallized substances of the above elements will occur, which will actually reduce the strength of the alloy material. impede the achievement of In particular, Zn is 12%
Even if the content exceeds 100%, no proportional strength improvement effect can be expected and it is essentially meaningless. The most suitable content is approximately Zn;8
-10%, Mg: 13-5%, Cu: about 1-2%.

Mn added as necessary as an optional component
SCr and Zr are both effective in refining crystal grains and improving stress corrosion cracking resistance, so they can be evaluated as equivalent substances.Mn: less than 0.2%, Cr: 0.1%
Less than %, Zr;O,.

If it is less than 5%, the above effects will be poor, and if Mn exceeds 1.0%,
If Cr' exceeds 0.4% or Zr exceeds 0.3%, coarse crystallized substances will occur in the alloy, making it impossible to achieve the desired high strength of the alloy. .

Next, the manufacturing process will be explained. The above-mentioned Al-Zn-Mg-Cu alloy with a high Zn content cannot be manufactured using the conventional continuous casting method due to the occurrence of significant casting cracks. Although it is difficult, the present invention overcomes this problem by employing a pressure coagulation method. That is, by melting the above aluminum alloy, pouring the molten metal into a pressure solidification mold, and solidifying it under pressure, a billet with fine grains and no defects can be produced. The pressurized solidification mold may utilize a container of an extruder. That is, the molten aluminum alloy may be directly poured into a container and solidified while being pressurized by a stem. Of course, in this case,
It is necessary to close the front surface of the container with a blind die to prevent the molten metal from spouting out during pressurized solidification.

In addition, when pouring the metal, prepare the mold in advance to a temperature of 300~
It is desirable to heat it to about 350°C. This makes it possible to obtain a finer texture in the billet. That is, if the temperature is less than about 300°C, solidification of the aluminum starts immediately after pouring, making it difficult to fully achieve the effect of pressure solidification. On the other hand, if it is heated to a high temperature exceeding 350° C., the cooling rate slows down, and crystallized substances tend to grow, making it difficult to sufficiently achieve the above-mentioned refinement effect.

Immediately after pouring, the molten metal in the mold is pressurized.

A billet is produced by applying pressure with a stone and advancing the i-detour. That is, a billet is produced by a pressure coagulation method. The pressing force at this time is 50KIf/crA
If it is above, the effect of pressure coagulation can be obtained, but preferably it is about 500 to 1000'Jf/crA. In this manner, by solidifying the aluminum alloy under a predetermined pressurized condition, a small billet of crystallized material can be produced without causing casting cracks. Therefore, when producing a billet using the conventional casting method, it is possible to omit the subsequent heating homogenization treatment required to homogenize and refine the structure.
Savings in thermal energy and processing time can therefore be achieved. The magnitude of the above-mentioned pressing force does not significantly affect the quality of the billet. However, 3f in 50
/c less than 17 iL is insufficient for preventing casting cracks and refining crystal grains by the pressure solidification method;
Even if a high pressure exceeding 500 K'Jt/cra is applied, it is rather useless because the effect cannot be proportionally improved to compensate for the increase in energy required.

One of the reasons why the crystallized material can be made finer by pressure solidification is that - Pressure eliminates the voids between the mold and the molten metal and within the molten metal, increasing the cooling rate. It is assumed that

The billet produced by the above pressure solidification method is then extruded to form the desired high-strength aluminum alloy material. Here, the billet may be once cooled and in the same phase state, but preferably, as the pressure solidification progresses, the temperature of the billet is a temperature suitable for extrusion processing, for example, about 1/2 of the liquidus temperature. It is recommended that the pressurized solidification step be completed when the temperature has decreased to a semi-molten state, and that the extruder be immediately loaded into the container of the extruder and extrusion be started. By adopting such a procedure,
It becomes possible to omit the step of heating the billet during extrusion processing, saving the energy and time required for heating, and enjoying the benefits of improved manufacturing efficiency and reduced manufacturing costs of alloy extruded materials.

Effects of the Invention As described above, the present invention is composed of an Al-Zn-Mg-Cl alloy containing extremely high Zn content and relatively high content of Mg and CU. , which has superior strength compared to conventional alloys, can be used in various mechanical parts to make them even thinner and lighter. By performing post-extrusion processing, we were able to create a high-strength aluminum alloy material with fine crystal grains and excellent ductility, without causing casting cracks during billet production, even though it is a high-strength alloy as described above. It can be manufactured with high efficiency and at low cost.

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

Table 1 Alloys with various chemical compositions shown in Table 1 above have liquidus temperature +10
The molten metal was melted at 0℃, poured into a pressurized solidification mold heated to about 280℃, and then immediately heated to 1000K.
It was pressurized to lf/cri and solidified under the pressure. When the billet is cooled to about 1/2 of the liquidus temperature, the pressure solidification process is completed and the resulting billet (diameter 7
5, length 100 mm) was immediately inserted into the container of an extruder and extruded into a round bar with a diameter of 12 m.

In the above process, a billet with no casting cracks was obtained, and the billet could be extruded without any problems.

Therefore, this extruded material was then solution treated at 460'C and further aged at 120'C for 24 hours.
The mechanical properties of each sample obtained were investigated. The results are shown in Table 2. The comparative alloys shown in Table 1 are Zn, Mg,
The composition range of the Cu content and Cu content is approximately at the manufacturing limit when using conventional manufacturing methods.

[Margins below] Table 2 As shown in the results in Table 2 above, the alloys of the present invention exceeded those of the comparative alloys, which are considered to be the limits of conventional manufacturing methods, mainly due to the high content of Zn. In comparison, it can be seen that although the elongation is slightly lower, the tensile strength and yield strength are much better.

that's all

Claims (3)

[Claims] (1) Zn; 7-12%, Mg; 2-7%, Cu; 0.
5 to 3%, and optionally Mn; 0.2 to 1
．． 0%, Cr; 0.1-0.4%, Zr; 0.05-0
．． An aluminum alloy containing one or more of 3% aluminum and the remainder aluminum and unavoidable impurities is melted, and the molten metal is poured into a pressure solidification mold and solidified under a predetermined high pressure. 1. A method for producing a high-strength aluminum alloy extruded material, the method comprising producing a billet by extruding the billet. (2) Pressure coagulation for billet production at 50Kgf
2. The method for producing a high-strength aluminum alloy extruded material according to claim 1, which is carried out under pressurized conditions of /cm^2 or more. (3) The pressure solidification process for billet production ends when the billet is cooled to a temperature suitable for extrusion processing, and the billet is immediately charged into the extruder container and extrusion processing is performed as is. A method for producing a high-strength aluminum alloy extruded material according to claim 1 or 2, characterized in that: