HU177294B - Method for extruding high-strength aluminium alloys - Google Patents

Description

The present invention relates to a process for extruding high-strength aluminum alloys. for the production of mandrels, tubes and various profiles.

Generally, high-strength aluminum alloys are those alloys which have a strength of at least 35 kg / mm after welding and heat treatment. High-strength aluminum alloys include Al-Cu-Mg Alloys containing at least 3% copper and at least 0.5% magnesium. High-strength alloys also include Al-Zn-Mg-Cu alloys.

Extrusion of high-strength aluminum alloys in the insert generally occurs at relatively low speeds. The extrusion speed is between 2 and 8 m / min. and the extrusion rate generally does not exceed 40 liters. When using high speed and / or high extrusion rates with this extrusion technology, the temperature of the product leaving the extrusion die will be so high that surface defects or burns appear on the surface due to cracks or overheating. 2

Certain high-strength aluminum alloys should be cooled immediately after extrusion. This means that the product leaving the extruder is directly into the refrigerant. In this case, the pressing speed is generally lower than in technologies where no immediate cooling is applied after extrusion.

If the extruded alloy forms a solid solution, the temperature at which the material exits the die should be precisely controlled. This temperature should be between the temperature at which the solid solution is formed and the temperature of superheat. The temperature at which the solid solution is formed must obviously be higher than the exit temperature so that the solid solution can be completely unhindered. however, it should be lower than the superheat temperature to avoid the formation of cracks and surface defects. Therefore, the initial extrusion temperature is usually quite close to the solid solution formation temperature. so that the logging process does not occur. 0 which would prevent the formation of a solid solution. On the one hand, the extrusion rate must also be reduced, on the one hand, in order to avoid frostbite and consequent cracks or burns, and, on the other hand, because the temperature exiting the tool at lower speeds approximates the solid solution formation temperature. preventing partial association of metastable or non-metastable eutectics.

Compliance with the above temperature range is now quite difficult even with a stretch ratio of 10 to 25 s / s, and this difficulty is exacerbated by increasing the stretch ratio.

The heat-producing effect of frictional forces in the extrusion tool further increases compliance with the exact temperature range.

In view of the above facts, several methods have been developed to increase the extrusion rate. It is known to increase the compression rate by reducing friction between the material in the recipient and the tool. Friction reduction can be accomplished with different lubricants.

Conventional lubricants such as grease containing molybdenum bisulfide and / or graphite may be used in the extrusion. Of course, great care must be taken when using the lubricant. so that it is always between the outgoing alloy and the tool material.

In some cases, glass or glass-like materials are used as lubricants. These materials have a viscosity in the range of 400 to 650 ° C in the range of 10 ^{3 to} 10 ⁴ poise. These lubricants are generally P, O ₅ , BO ,. Mixtures containing K, O, Na.O and capable of producing extrusion rates equal to or greater than 10 µm / min. However, this solution has not yet been widely used in industry.

The object of the present invention is to overcome the drawbacks described and to provide a process for extruding high-strength aluminum alloy articles with good physical and mechanical properties and excellent surface quality.

SUMMARY OF THE INVENTION The object of the present invention is to extrude extruded high-strength aluminum alloys at a lubrication speed of at least 15 m / min, preferably at least 30 m / min, at 50 to 180 ° C under solid alloy temperature. such that the temperature of the material leaving the mold is between the minimum solid formation temperature (Tm) and the solid temperature (Ts) and is cooled in a known manner according to the specifications for the particular alloy.

The temperature of the material leaving the tool is preferably between Tm and (Ts-30) C.

The process of the present invention enables high-strength aluminum alloys to be extruded at speeds greater than 30 m / min at 20 and 200 extrusion rates.

The present invention is based on the discovery that, under certain conditions, extrusion can be carried out at relatively high speeds and at high stretch ratios, even if cooling is performed directly after extrusion. Relatively high extrusion rates, above certain values, favorably achieve the desired temperature range.

In the process according to the invention, cooling can be carried out immediately after leaving the tool, so that it is not necessary to reheat the material to a suitable temperature before cooling. The cooling rate may be the same as the cooling rate generally used for the extrusion of a given alloy. Even after a certain time, the temperature of the extruded material does not fall below the critical temperature, i. E. where precipitates appear and interfere with solid solution formation. This temperature is approximately 450 ° C for 2017 A and 2030 alloys.

The table below gives the solid temperature T _s and the minimum solid formation temperature T _{m of} certain high-strength aluminum alloys.

Alloy T, C i "c 2014 535 490 2017 A 535 490 2024 515 480 2030 530 490 7075 535 450

The temperatures indicated depend, of course, on the exact composition of the particular alloy. The alloys of the 2000 series are generally composed as follows:

Cu 3.5-5 s /

Mg 0.4 1 s ¹ ',,

Si is a maximum of 1.2 s; optionally Pb is 0.3-1.4 s%, the remaining aluminum and common impurities. The alloys may also contain secondary additives. such as iron, chromium, titanium or manganese in conventional amounts. High-strength aluminum alloys of this composition generally have an extrusion temperature of 350 to 480 ° C. and the material leaves the tool at temperatures between 480 and 530 C, preferably between 480 and 500 C.

The temperature at which the material leaves the tool is suitably controlled by the process of the present invention, since the unusually high extrusion rate and / or reduced friction provides quasi-adiabatic conditions. In this way, the change in temperature of the material throughout the entire length of the extruded product, except for the very short front, does not exceed 10 ° C. The small front portion of the extruded material may be removed after extrusion.

Another fundamental advantage of the process is that the extrusion time is extremely short, generally less than 30 seconds, and even more often than 20 seconds, at conventional extrusion lengths.

Extremely short extrusion time allows lubrication to be smoother than usual from start to finish of the extruded product. As a result, the surface quality of the product is extremely good.

In general, it is preferable that the extruded material is not introduced into the refrigerant immediately after it leaves the die. By providing a pause between extrusion and cooling, solid solution formation is allowed to occur completely. The desired pause is usually 15 to 90 seconds, the exact size being determined by two basic factors. One is the need for the material to remain as long as possible within the temperature range of solid solution formation and thus to have the best metallurgical properties. The other is not to live within the temperature range of the precipitation, since the onset of precipitation degrades the mechanical properties of the material and makes the alloy susceptible to intergranular corrosion.

According to a preferred embodiment of the process according to the invention, the press ingot is homogenized before extrusion. This improves the surface quality and makes shaping easier. The temperature of the homogenization is preferably 480-520 C 'for 1-24 hours.

In general, it is preferred that the mandrel is heated to near the solid solution formation temperature prior to extrusion, even if it is slightly above the extrusion temperature. This temperature difference can be about 2θ C or slightly more. In this case, the billet should be cooled rapidly, in less than 3 minutes, and preferably less than 1 minute. Cooling can be effected, for example, by means of refrigerant nozzles, so that cracks are avoided. This technological step facilitates dissolution and prevents the formation of precipitates during extrusion. The heat generated during extrusion promotes dissolution in a very short period of time after leaving the tool.

Any lubricant and lubrication technology may be used in the process of the invention, regardless of extrusion rate and stretch ratio. Hydrostatic extrusion is also classified as lubricant extrusion.

It is highly advantageous to use a lubricant which is soluble in the refrigerant during the process. This allows cooling and lubricant removal in one step, even during extrusion.

For example, when used as a lubricant, a medium containing P ₂ O _S + P-.O ₃ + K ₂ O + Na ₂ O is well soluble in water or in a medium containing at least 80% water. Thus, when cooling with water or a medium containing at least 80 water and various cooling additives, the lubricant can be removed from the product during cooling.

The cooling itself may be carried out in any manner, for example by spraying refrigerant nozzles or immersion in refrigerant.

Further details of the invention will be described by way of exemplary embodiments.

Example 1

We produced press ingots from high-strength aluminum alloys 2017 A and 2030. The logs were 100 mm in diameter. The press ingots were homogenized at 500 ° C for 6 hours and then cooled in air without any separate treatment.

The appropriate cut logs were heated to 400 ° C before extrusion and held at this temperature for 5 minutes. Extrusion was performed using a lubricant and rods 22 mm in diameter were extruded from the mandrels at a speed of 70 m min. The stretch ratio was 22. The extrusion took 15 seconds.

The material was removed from the tool at temperatures between 490 and 500 ° C for both alloys. This temperature range was valid for the entire length of the extruded rod.

Post-extrusion cooling was carried out in several variants.

In the first variant, cooling was performed immediately after extrusion, in the second variant, there was a 45 second interval between extrusion and cooling, and in the third variant, 90 seconds elapsed between extrusion and cooling.

After cooling, the rods were stretched with 3% more needles. Thus, they had a diameter of 21.7 mm and a solid state of T3 grade.

In accordance with the present invention, samples of extruded materials were prepared and compared with materials made from the same alloys using conventional technology. The traditional technology was done as follows:

homogenization at 500 ° C - extrusion in a cartridge at 350 ° C and 4 5 m / min

stretching at about 30, solid solution setting heat treatment at 490 C for 30 pemg

- cooling in water and straightening.

The results of the comparative studies are summarized in the following table.

Alloy extrusion Between extrusion and cooling elapsed time flow limit RO.2-MPa Mechanical Tensile strength Rm-MPa Properties Strain A5 - lubricant 0 286 393 12 2017 A lubricant 45 sec 307 416 16 lubricant 00s 287 392 13.2 deposit ? 69 lubricant 0 348 445 12 2030 lubricant 45 sec 338 440 14.5 lubricant There S 341 443 13.6 deposit 374 448 16.7

From the table it can be seen that the quality of the extruded materials according to the invention is essentially the same as that of the conventionally produced materials, irrespective of whether they were lubricated with graphite or molybdenum sulphide or glass-like lubricants and that the straightening was only done at 3 ".

The specimens were also subjected to corrosion testing. Of the test specimens, only those exhibiting some corrosion were 90 seconds between extrusion and cooling. This is because the material is in the AlCu-Mo alloy's precipitation temperature range (about 400 ° C).

Fatigue tests were also performed in a rotary bending machine. In this respect, no difference was found between conventional technology and the material according to the invention.

The mechanical properties of the products produced by the process of the invention have always been within the limits prescribed by the standard. However, the mechanical properties of the 2017 A alloy are slightly lower than those produced by solid-solution heat treatment, especially when the tensile strength was in the range of tensile strength.

It can be seen that the highest stretching values were achieved with the technology in which 45 seconds elapsed between extrusion and cooling. During this time, the material is approx. 450

It cools to C, which is just below the cut-off temperature range. Thus, it is the time that most allows the solid solution to develop completely.

without separation.

Example 2

800 mm diameter billets were made from 2017 A and 2030 alloys. The stumps are 500 C ^l! The mixture was homogenized for 6 hours and then cooled in air without special treatment.

The appropriate sized press ingots were heated to 490 ° C prior to extrusion and maintained at this temperature for half an hour. Before starting the extrusion, the press ingots were cooled to 400 ° C for 1 minute and then extruded at 70 m / min under the conditions described in the first example. The resulting product was 22 mm in diameter and extruded using a lubricant. The material exited the die at temperatures between 490 and 500 ° C. Cooling was performed with water immediately after extrusion. The bars were finally trimmed with a stretch of 3%.

The bars obtained in this way had the same standard dispersion as the bars manufactured in the conventional manner and had the following mechanical properties.

Alloy R 0.2 - MPa Rm - MPa A 2017 407 536 15.5

2030 396 500 16

Comparison of the results shows that the bars produced in this way have significantly better mechanical properties. as in the first example. This is obviously the result of pretreatment prior to extrusion.

Example 3 x 20mm square rods are extruded from 145mm diameter die castings made of 2030 alloy with the following technological parameters:

stretch ratio

- extrusion using lubricant

- heat treatment at 410 ° C

extrusion speed 50 m / min

extrusion time 20 sec

- cooling in water 30 seconds after extrusion.

The size and surface quality of the product were such that straightening at 3 ^< RTIgt; _ll ^< /RTI> was sufficient to comply with standard values. The mechanical properties of the finished product were as follows:

R 0.2 == 404 MPa Rm = 491 MPa A, = 14.8% ·

It is clear from the example that not only circular products, but also other profiles can be produced in good quality by the process according to the invention.

Example 4

145 mm diameter press ingots made of 2030 alloy were homogenized and then air-cooled. Cutting presses of suitable size were heat treated at 370 C 'and extruded at this temperature using graphite-containing lubricant. The extrusion rate was 100 m / min and the extruded bar was 12 mm in diameter. The material came out of the die at 510 C and this temperature remained constant during the 30 seconds of extrusion. Cooling was performed 20 seconds after extrusion. The product

We stretched it to a diameter of 11.8 mm with a stretch of 3 µm. The rod has the same standard dispersion as the conventional product.

The mechanical properties of the rod were as follows:

R 0.2 = 339 MPa

Rm = 444 MPa A. = 14.,

These mechanical properties are also of the same order of magnitude as those shown in the other examples.

Patent claims

Claims (8)

Patent claims A process for extruding high-strength aluminum alloys at an elongation ratio of 20 to 200, characterized in that - extruding is carried out using a lubricant at a speed of at least 15 m / min, preferably at least 30 m / min, between 180 ° C and 180 ° C so that the temperature of the material leaving the tool is between the minimum solid formation temperature (Tm) and the solid temperature (Ts), preferably between Tm and (Ts - 30) C °, and in accordance with the specifications for the particular alloy. A method according to claim 1, characterized in that the extrusion is carried out for less than 30 seconds, preferably less than 20 seconds. Method of carrying out the process according to claim 1 or 2, characterized in that the cooling is started 15 to 90 seconds after the extrusion, at a temperature above the precipitation temperature range, preferably at least 440 ° C. 4. A process according to any one of claims 1 to 6, wherein the extrudate is heated to a temperature of at least 20 ° C above the extrusion temperature before extrusion and cooled to an extrusion temperature such that less than 3 minutes elapse between extraction from the furnace and start of extrusion. a. 5. A process according to any one of claims 1 to 4, wherein the refrigerant-soluble lubricant is used. 6. The process according to claim 5, wherein the water-soluble glass-like lubricant containing P, O ₅ , Β, Ο, KO and Na, O is used. 7. The process according to any one of claims 1 to 4, comprising 3.5 to 5% by weight of copper, 0.4 to 1% by weight of magnesium, up to 1.2% by weight of silicon and optionally 0.3 to 1.4% by weight of lead, and common impurities and / or in the case of extrusion of aluminum alloy containing iron, manganese, titanium or chromium, characterized in that the extrusion is carried out at a temperature of 350-480 ° C and a temperature of 480-530 ° C, preferably 480-500 ° C, is obtained. 8. The process of claim 7, wherein the extrudate is homogenized at 480-520 ° C for up to 1 day prior to extrusion.