KR850000478B1 - Heat treatment of a precipitation hardenable non-ferro material(al-mg-si alloy) - Google Patents

Abstract

A precipitation hardening Al-Mg-Si alloy is heated to 470≰C. The alloy is cooled rapidly to a semi-hot working temperature of 260-340≰C. The alloy is the cooled rapidly to the quenching temperature of 140-200≰C at a cooling rate of 50≰C/sec. In the rapid cooling process, the formation of precipitates, which are larger than 1 micron, is inhibited. The alloy is hot-worked while the temperature is in the semi-hot working temperature range.

Description

Heat Treatment Method of Precipitation Hardening A1-Mg-Si Alloy

The present invention relates to a process for the treatment of precipitation hardenable A1-Mg-Si alloys to produce wire rods suitable as starting materials for drawing into electrical conductors. Such alloys are called precipitation hardening, and when such alloys are made of alloying elements, these alloying elements can supersaturate the crystal lattice when quenched at the dissolution temperature, and as known in the art, by aging at an intermediate temperature It can be hardened by being precipitated from the grating. Representative compositions for electric conductors include A1-Mg-Si alloys, which include 0.3-0.9% magnesium, 0.25-0.75% silicon, 0-0.6% iron, and residual amounts of aluminum and impurities (i.e. elements of 0.05% or less). I make it). Although the present invention is described with respect to such an electrical conductor alloy is not limited thereto. In order to obtain fresh wire from such alloys, these alloys are generally hot worked and / or cold worked. Hot work is to process at a temperature that can be recrystallized as the structure of the alloy is processed, and cold work is to be processed below this temperature. The final product preferably has optimum properties, ie high tensile strength, with adequate ductility, but existing mechanical and heat treatment methods do not necessarily combine these properties, and the treatment to obtain these combinations is not necessarily straightforward. . Moreover, since the specifications for electrical wires are very strict with respect to the minimum tensile strength, ductility and electrical conductivity in the combination, there is not much choice in the process of how to combine them.

In general, the following several steps are used to make alloy wires for electric conductors: first, after the alloy is cast continuously on a casting wheel or in the form of a discontinuous cast bar, about 490 ° -520 It is introduced into a rolling mill at a hot working temperature of < RTI ID = 0.0 > C < / RTI > to produce a drawing material having a diameter of 5-20 mm (usually 7-12 mm) at the exit of the rolling mill. However, the alloy cooled to about 350 ° C. during rolling. This means that most of the magnesium and silicon introduced for the precipitation hardening treatment in the final stage of manufacture are lost to premature precipitation and hardening.

For this reason, the second manufacturing step is the solution treatment after rolling. In order to re-melt the precipitate in the crystal lattice, the bobbin of the wire rod is denatured in the furnace at a temperature of 500-520 ° C. for a long time, and then immediately by quenching the bobbin of the wire rod to 260 ° C. or lower at the solution treatment temperature. The alloying elements in the body remain in the supersaturated solution in the crystal lattice. This quenching temperature is usually kept at room temperature. The wire is then cold drawn to have high tensile strength, but the ductility is significantly reduced to unacceptable levels. For this reason, after drawing, the lead wire is held at a temperature of about 145 ° C. for several hours to undergo aging treatment with precipitation hardening. This increases the ductility to an acceptable level with a significant increase in tensile strength, because the loss due to softening of the displaced structure is greatly compensated by precipitation hardening. For this reason, there are as many alloying elements as possible up to the last stage to participate as much as possible in precipitation hardening. In addition, this aging step has a great advantage in improving the electrical conductivity because the internal tension is reduced by the rearrangement of dislocations and extraction of alloying elements from supersaturation. This electrical conductivity decreases with increasing internal tension during quenching and drawing.

Attempts have been made to find a simple method to obtain the proper combination of properties. In particular, since conventional methods require long-term solution treatment at high temperatures, this has been an important factor in cost, and has been attempted to eliminate such treatment. All of these attempts keep the conductors at a high temperature at the exit of the rolling mill so that no alloying elements are pre-precipitated or only a fraction of the pre-deposition, and the wire can be quenched at the exit of the direct rolling mill. It aimed to be present in the solution so that it can participate in precipitation hardening later. Thus, it has been proposed to use a high temperature inlet temperature towards the rolling mill, a high speed of passage through the rolling mill, or an intermediate heating between rolling steps. In the first proposal, the wire rod is too soft during rolling due to the liquid eutectic compound between the grains, in the second proposal the speed is too fast for use with the feed mechanism of continuous casting wheels or other rolling mills, and in the third proposal Intermediate heating has the disadvantage of complicating the rolling step.

In general, it is an object of the present invention to provide a method for treating precipitation hardenable A1-Mg-Si alloys for the production of wire rods (suitable as starting materials for drawing into electrical conductors), which is an existing treatment method. This gives you the possibility to obtain a combination of features that simply cannot be obtained. Another object of the present invention is to provide another method which does not require any solution treatment, especially when obtaining the electrical wire of the A1-Mg-Si composition, in which case the aging treatment is obtained by a method having a different aging effect. It can be omitted because it loses.

In the above prior art, no attention has been paid to the cooling after hot working, particularly to the treatment of the alloy in the half hot temperature range. Half-hot temperature refers to the temperature between the hot and the quenching temperature, the hot temperature is the temperature at which the structure is recrystallized according to the treatment, and the quenching temperature is sufficient to ensure that the atoms in the structure have an invariant metal structure apart from the aging phase. It indicates the temperature to be fixed. This half-hot temperature range will be described in more detail later, but in the above-described A1-Mg-Si composition for electric conductors, the half-hot temperature range is about 260 ° -340 ° C.

In the prior art, this half-hot temperature was carried out in a simple quenching form, so that an intermediate product having a structure containing hot-rolled and recrystallized particles and having the maximum number of alloy raw water under supersaturation was loaded. In the present invention, however, the treatment can be performed during quenching at half hot temperature. Therefore, the treatment method according to the present invention is as follows.

a) the alloy is introduced in a rapid precooling step to bring the temperature of the actual solubility of the alloying elements from the temperature of the half-heat to night;

b) the alloy is introduced into the quenching stage from a temperature within a half-heat temperature range to a quenching temperature, the quenching stage being made very short to prevent the formation of precipitates larger than 1 micron,

c) the alloy is treated while the alloy is at a temperature within the range during the quenching step.

The resulting wire rod had a special grain structure showing good structure to obtain excellent characteristics after cooling processing with electric wire and, if necessary, after aging treatment.

During processing in the half-heat temperature range, the particles deform and have a rectangular shape, while dislocations occur through the particles, subdividing them into a number of subgrains that differ from one another by the slight orientation difference of the crystal lattice. . This structure does not break down as the alloy is processed because the mixture is in a temperature range below the hot working temperature at which fracture occurs. An extremely fine precipitate, which cannot be seen with an optical microscope, is formed and fixed to the potential described above.

It is also important that the structure obtained should not be destroyed later by excessive supply of energy and temperature, i.e. for the active mobility of the atoms by excessive neglect of the cooling stage. Therefore, in order to prevent this, the cold step must proceed fast enough in the aforementioned half-hot temperature range, and in this sense, it is called "quick cooling step". In addition, this step is sufficiently rapid in a very short period of time to prevent the formation of precipitates having a size of 1 micron or more, in addition to the precipitates generated during the pre-cooling or heat treatment step and grown to a size of 1 micron or more by coalescence. Should be. Because these alloying elements and large precipitates do not form a final structure with very fine precipitates formed during processing at half-heat temperature or at the final aging step thereafter.

Prevention of excessive coalescence of precipitates is only a time It is not just a matter of temperature, it is a matter of a combination of time and temperature that provides enough energy to start small precipitates to solidify. It is also apparent that the size of 1 micron is not an absolute limit, but merely to determine the degree of size.

The range of half hot temperature is determined by the range between the lower limit temperature of hot working and the upper limit temperature of quenching. Hot working refers to a process of recrystallizing and re-fixing the structure to mitigate the deformations involved in the process as the mixture deforms and hardens. The range of useful hot working temperatures for a given alloy is not strictly limited. In order to prevent actual work hardening, the lower limit temperature of hot working is determined by the possibility of sufficient intermediate recrystallization between hot working deformations, and the lower limit temperature for each alloy is known by those skilled in the art. For example, the lower limit temperature for the A1-Mg-Si alloy for electric conductors described above is about 340 ° C. Quenching temperature, on the other hand, refers to the temperature at which atoms move slowly and the structure actually solidifies in its original state. That is, atoms that have not yet been extracted from the crystal lattice remain supersaturated in the lattice, leaving precipitates in the lattice without recrystallization and maintaining the state and shape of the dislocation. The range of useful quenching temperatures for a given alloy is also not strictly limited. The upper limit temperature of quenching is determined by sufficient instability of atoms to prevent fast and sensitive deformation of the structure apart from aging, and the upper limit temperature of quenching for each alloy is known by those skilled in the art. For example, the upper limit temperature of quenching for the above-mentioned A1-Mg-Si alloy for electric conductors is about 260 degreeC.

As mentioned above, when the structure is processed at half-heat temperature, it takes too much time to bring it to the quenching temperature and then this structure is destroyed. However, this time can be used to continuously process the alloy or to quench the alloy by passing it through a quenchig bath. In the first case, the alloy can be treated during the first half of the quenching stage described above. Once the quenching temperature is reached, the structure can be cooled to room temperature with or without aging and the product is then ready for cooling to the desired form.

The desired special structure is obtained in the cooling step at half-heat temperatures in the above range, apart from the processing in the previous step. However, the treatment in the above range is preferable because it can start with the alloy element remaining in the solution at the maximum, thereby preventing premature precipitation for precipitation in the cooling step or subsequent aging step. In general, the alloy is hot worked before rolling or extrusion, and the pre-cooling step at the hot working temperature is performed before the cooling step described above.

It is recommended that the pre-cooling step be carried out at the highest possible temperature so that the alloy element remains in the solution after the pre-cooling step. At least half of the alloying elements participating in precipitation hardening can be dissolved. It is more preferable to carry out at the temperature of actual solubility. The lower limit temperature of the preliminary cooling step for the aforementioned A1-Mg-Si composition for electric conductors is about 470 ° C. It is more apparent that this precooling step will proceed quickly enough, otherwise these alloying elements will precipitate before being treated at half-hot temperatures in the above range. The alloy is preferably heat processed during this precooling step. Generally, this precooling step is introduced immediately after the initial hot working step to ensure maximum alloying elements remain in the solution. The starting temperature is the temperature of the actual solubility of the alloying elements and maintains this temperature.

When obtaining the product in the form of wire, the initial hot working step, the preliminary cooling step, and the processing step in the cooling step to bring the quenching temperature can be achieved by extrusion molding and rolling, and rolling is more preferable. These three treatments can be carried out in one type of process in a rolling mill consisting of the same successive single pass stages, with initial hot rolling, with the intermediate constituents rolling in the precooling stage and with the final quenching temperature. Rolling in the cooling step to achieve In the initial unit for initial hot rolling, excessive cooling may not be desirable in order to keep the alloying elements in the solution to the maximum, so that intermediate heat may be supplied, whereas the intermediate and intermediate units promote rapid cooling for the reasons described above. It is desirable to. For this reason, a rolling mill consisting of several successive passes may be divided into two parts. That is, in the first part for the initial hot working step, the cooling of the rolling components is kept to a minimum (intermediate salts can be supplied) so that the temperature is maintained at the temperature of the actual solubility of the alloying elements. In the second part for the precooling step and then the cooling step to bring the subsequent quenching temperature, the cooling of the rolling unit takes place very strongly, so that the cooling step of the pressure-bearing unit proceeds fast enough (this leads to excessively large precipitates). To obtain specific metallographic structure without recrystallization). By this method, the wire rod has an excellent metal structure to be drawn out into the wire without an intermediate heat treatment step, and may be accompanied by an aging treatment if necessary. The product entering the rolling mill may be rod-shaped or block-shaped, but is preferably in the form of a continuous line passing through a continuous casting machine. In this way, the loss of thermal energy can be minimized and the alloying elements remain at the maximum in the solution. In the case where the alloy wire is too cold or in order to keep the alloying element in the solution to the maximum, the alloy wire may be heated on the way to the rolling mill but does not reach the melting temperature. This is because it softens at the melting temperature and prevents excellent rolling. The alloy wire has a circular cross section.

The present invention is particularly applicable to the production of A1-Mg-Si drawn material for electric wires having the composition described above. According to the prior art, alloys are cast continuously by passing casting wheels at a temperature where alloying elements are still present in the solution so as to produce a continuous solidified alloy wire, and then the alloy wire is continuously divided into two parts. Immediately and continuously flow into the rolling mill consisting of a passing step. In the first part where the cross section of the alloy wire is reduced, cooling is minimized to prevent excessive precipitation, which takes considerable time for the first formed precipitates to round and so that the temperature is reduced to the actual solubility temperature of the alloying element of about 470 ° C. Because it is maintained. In the second part, the cooling is so intense that the temperature immediately changes from the actual solubility temperature of these alloying elements to below the quenching temperature of 260 ° C. In this way, the temperature passes over the half-heat temperature range where the structure described above is formed. It is further cooled towards the quenching temperature while still being processed.

Although the final rolling in the half-hot temperature range described above has a function of cold working before drawing, it is important to sufficiently cool the structure to prevent the breakage of specific granular structures. In general, a drawn wire having a diameter of 7-10 mm obtained in this manner has a good metallographic structure to be drawn with appropriate characteristics without intermediate solution treatment.

If premature precipitation is considered harmless, the temperature of the hot rolling in the first part may be lower than 470 ° C, but must be at least 340 ° C and cooling to bring the half-hot temperature in the range of 260-340 ° C is to be carried out slowly. However, it is preferable to cool the quench after passing through the last part at 470 ° C. or higher and below 260 ° C., and after passing through the last part, quenching should be cooled to a temperature of 210 ° C. or higher. The average cooling rate at this time is 50 degreeC or more every second. The alloy entering the rolling mill is preferably in the form of a continuous cast line, but may be rod-shaped or otherwise, and the cast line may also undergo intermediate heating as it passes through the cast wheel to the mill.

Four samples of this alloy were processed. Four samples passed through the continuous casting machine in the form of an alloy wire having a thickness of 40 mm enters a continuous pass rolling mill of 13 stages at a temperature of about 500 ° C. and comes out in the form of a wire rod having a diameter of 9.5 mm. The outflow rate of fresh wire from the rolling mill is 3m every second. However, in the four cases, the degree of cooling is different: In the first three samples, the consumption of the coolant is at least 5 m3 per hour, at least until the first six passes of the rolling mill. The temperature of the wire rod is about 480 ℃ or less. During the remaining seven passes, the consumption of the coolant is different but about 30 m 3 is consumed every hour, and the desired outflow temperatures are 140 ° C., 180 ° C. and 250 ° C., respectively, for three samples 1,2 and 3. These wire rods are wound as starting materials for subsequent cold drawing and aging. The fourth sample was processed in the usual way: at every pass step, rolling at a temperature of about 500 ° C., consuming about 10 m 3 of the same amount of coolant every hour, to obtain an exit temperature of about 350 ° C. After cooling, the solution was rapidly cooled at room temperature immediately after solution treatment at a furnace at 530 ° C. for 10 hours to obtain Sample 4 having a diameter of 9.5 mm mm.

These four samples were drawn to obtain a conductor of about 3.05 mm mm without intermediate heat treatment and then aged at 145 ° C. for 10 hours.

The results are as shown in the following Tables I and II. The values marked with “WR” are the values measured for the wire rod before drawing, and the values marked with “AD” are aged after drawing. It is the value measured for the lead before. In addition, A1 and A3-A10 values are measured for lead wire drawn after aging for 1 hour, 3 hours to 10 hours to see the effect of aging treatment.

Table I: Tensile Strength ㎏ / ㎠ and Elongation% (R and A are abbreviations respectively)

Table II: Resistivity ohms mm2 / cm

In Table I, Sample 1 is the closest to Sample 4 prepared by conventional methods. Most important in this case, however, is that specification ESE 78 (tensile strength> 33 kg / m 2 and elongation> 4%) can be obtained without costly solution treatment. In addition, in Sample 2, the aging treatment no longer deforms the mechanical properties, and thus the aging treatment may be omitted in this case. This is due to the aging effect on the granular structure that occurs during the cooling of the spiral to air to room temperature and no longer requires aging. This has the advantage that these wires are no longer naturally ageed while waiting for the drawing process for several weeks after rolling, so the properties given are identical to those after manufacture. It also sometimes eliminates the need to introduce fresh wire into the intermediate aging process after manufacture. Finally, looking at Table II, it can be observed that the electrical conductivity is increased by 5%, and users can save 5% of the material.

In Table II, Sample 3 can be seen that the electrical conductivity is much better. If the tensile strength is less important, the process of obtaining such a product can be controlled. For Sample 3, the subgranular structure is slightly destroyed, with slightly more precipitates produced by quenching in the second part of the rolling mill less quickly, which accounts for the inferior mechanical properties and good electrical conductivity.

For sample 1, the quenching in the second part proceeded very quickly. At this time, only a fraction of the alloying elements may be precipitated in a desired manner, but the other portions remain supersaturated. This is because this sample is still sensitive to aging. Thus, some of the conventional methods, some of the advantages of the structure of the present invention, yield a good combination of mechanical and electrical properties, and require a final aging step to avoid costly solution treatment. give.

The method according to the invention comprising the treatment of Samples 1-3 provides an excellent means of controlling a product having a combination of different properties depending on the desired electrical field or other applications. It is preferable that the outflow temperature from a rolling mill is 140 degreeC-200 degreeC.

Looking at Samples 1 and 2, it can be seen that Sample 1 treated while quenched at 140 ° C. is still partially supersaturated. After cold drawing, the aging treatment at 145 ° C. for 10 hours clearly shows the effect of precipitation of alloying elements in the supersaturated state. However, the effect of the aging treatment can be achieved more quickly by replacing the cold drawing with an aging heat treatment that draws at an aging temperature of 135 ° C-155 ° C. The effect of the mechanical treatment performed during the time that the wire rod is at the aging temperature is to make the aging proceed much faster, at the end of the post-drawing cooling. This eliminates long term aging heat treatment.

However, in Sample 2 treated with quenching at 180 ° C., the alloying elements were actually all precipitated into a specific subparticulate structure during the treatment and due to the aging effect on the spiral that the sample was further cooled to room temperature. Thereafter, upon cooling drawing, the accompanying aging treatment shows no aging effect, because the precipitates remain in the structure. In order to obtain better ductility or electrical conductivity, the aging effect can be obtained by drawing at the aging temperature as in sample 1.

Deformation of Sample 2, which is also treated with quenching at 180 ° C. but rapidly cooled to 100 ° C. or less at the exit of the rolling mill instead of slowly cooling the spiral at 100 ° C., can be obtained. This results in the avoidance of any aging effects during the slow cooling of the spirals, which are less advanced. This less advanced state can also be obtained by quenching at temperatures above 180 ° C., but then aging can be achieved by cooling more rapidly because of the fluidity (or temperature) of the atoms and the time the atoms move. If the sample in less advanced age is drawn at the aging temperature, the result is more aging but less advanced than in sample 2. It can thus be concluded that drawing at an aging temperature of 140 ° C.-150 ° C. with or without prequenching below about 100 ° C. suggests the possibility of modifying the combination of alloying properties as needed.

As already mentioned, the inlet temperature of the A1-Mg-Si alloy and the temperature in the initial hot working or hot rolling step is preferably above the actual solubility temperature of the alloying element (about 470 ° C for this alloy), but this is an absolute limit. It does not depend on the exact composition. For example, the temperature of complete solution or homogenization for different compositions is as follows: for 0.6% magnesium and 0.6% silicon: 520 ° C; For 0.6% magnesium and 0.4% silicon: 500 ° C .; For 0.4% magnesium and 0.6% silicon:: 490 ° C; For 0.4% of magnesium and 0.4% of silicon:: 470 ° C. When a hot alloy at a desired temperature of 500 ° C.-530 ° C. is introduced, most of the alloying elements are present in the solution without the risk of melting the alloy. This temperature should not exceed 550 ° C because only the eutectic compounds A1-Mg-Si and A1-Si-Mg ₂ Si are condensed at 585 ° C and 550 ° C, respectively.

The wire drawn out of the rolling mill is usually in the form of a rolled alloy wire with a diameter of 7-10 mm, and has a metallic structure with elongated particles obtained by rolling and, as previously mentioned, It is subdivided into subparticles of the formed interface. When alloying elements are used for precipitation, these elements are present in the alloy in the form of fine precipitates of 20, 30, 40 or 50% smaller than 1 micron, which cannot be seen by optical microscopy, because larger precipitates are characterized. Because it is lost for improvement.

In addition, this invention is not limited to rolling as a process step. In particular, in the processing step carried out during quenching within the half-heat temperature range, it is bent in different directions, for example by twisting through a series of rolling mill dies or by twisting to form a cable, for example. It can be in the form of. The wire rod does not necessarily have to have a circular cross section.

The rolling process does not necessarily require continuous rolling after continuous casting. For example, rolling may be used to reduce wrought iron or new wire, and the alloy wires thus formed are welded together as they leave the rolling step. Then, the long alloy wire thus formed can be continuously introduced into the multi-continuous rolling mill.

Claims (1)

A method of treating a precipitation hardenable A1-Mg-Si alloy for producing a new wire material suitable as a starting material for drawing into an electric conductor, wherein the precipitation hardenable A1-Mg-Si alloy is used at an actual solubility temperature of about 470 ° C. or higher of an alloying element. The preliminary precooling stage was introduced to a temperature within the half-heat temperature range from about 260 ° C to 340 ° C, and the alloy was then 260 ° C or less (preferably 140-200 ° C) from a temperature within the half-temperature range. The quenching step is introduced into the quenching step at a cooling rate of 50 ° C. or more per second to achieve a quenching temperature, and the quenching step is performed very short to prevent the formation of precipitates having a size of 1 micron or more, and the alloy is in the semi-heating stage during the quenching step. A method of heat treatment of a precipitation hardenable A1-Mg-Si alloy characterized by treating the alloy while at a temperature within the inter-temperature range.