KR20110011228A - The method for preparing of al-mg-mn alloy strip using twin roll cast and al-mg-mn alloy strip - Google Patents

Abstract

PURPOSE: An Al-Mg-Mn alloy strip, and a method for manufacturing the Al-Mg-Mn alloy strip using a twin-roll casting technique are provided to enhance yield strength, maximum tension strength and elongation to form a finer structure than an existing ingot casting strip. CONSTITUTION: A method for manufacturing the Al-Mg-Mn alloy strip using a twin-roll casting technique comprises next steps. Al-Mn master alloy is manufactured by the mixing of Al ingot with Mn element. The manufactured Al-Mn master alloy is mixed with molten Mg. The mixed material is filled in a metal mold to manufacture Mg-Al-Mn alloy ingot. The manufactured Mg-Al-Mn alloy molten-metal is changed to the Mg-Al-Mn alloy strip using a twin-roll casting technique. After the molten Mg is added to the master alloy, it is maintained at a temperature of 700~800°C for 20~40 minutes.

Description

The method for preparing of Al-Mg-Mn alloy strip using twin roll cast and Al-Mg-Mn alloy strip}

The present invention relates to a method for producing a magnesium-aluminum-manganese alloy cast using a twin roll casting method and a magnesium-aluminum-manganese alloy cast prepared accordingly.

Magnesium alloy is excellent in low density, high strength and rigidity, and castability and machinability, and can be usefully used for light weight structure. Therefore, the use of magnesium alloys as a lightweight structural component is rapidly increasing, and high pressure die casting parts are mainly cast using near net-shape die-casting technology. However, process magnesium alloys are often expensive and difficult to cast at room temperature as compared to those cast by traditional methods. In addition, workable magnesium alloys generally have better mechanical properties than cast alloys, but still lack competition in the workmanship of magnesium, particularly plates, required to produce a variety of lightweight metals. Therefore, processing cost and moldability improvement are calculated | required.

In recent years, the twin roll casting method has the advantage of manufacturing a rolled product of thin sheet in one step process, and it is possible to economically manufacture a magnesium alloy sheet for processing from the melt by consisting of continuous cast steel casting and direct hot rolling. In addition, the twin roll casting method has an even distribution in the particle size of the formed non-metallic inclusions and the like, and maintains uniformity in the microstructure. In order to improve the strength and formability of the working magnesium alloy, the working magnesium alloy should have a uniform microstructure (crystals and particles) and a low anisotropy structure. High cooling rates facilitate dispersion strengthening upon solidification by alloying components with limited solubility in Mg alloys and facilitate solid solution strengthening, which is commonly used in ingot casting because it forms large intermetallic particles at low cooling rates. I never do that. Therefore, dispersion strengthening and solid solution strengthening is given - can be used for ssangrol casting with a relatively high cooling rate of 10 ³ k / s-speed solid for 10 ^second. Korean Patent Laid-Open Publication No. 10-2007-0087137 discloses a method for producing an Al-Mg-based aluminum alloy plate having a plate thickness of 0.5 to 3 mm cast and cold rolled by a twin roll continuous casting method. In addition, the Republic of Korea Patent No. 0711793 describes a casting roll of a twin-roll thin plate casting machine and a method for manufacturing a cast piece manufactured using the same. U.S. Patent Publication No. 2003/0196733 contains Fe 0.15-1.5%, Mn 0.35-1.9% and additionally Si <0.8%, Mg <0.2%, Cu <0.2%, Cr <0.2%, Zn <0.2% A method for producing an aluminum alloy slab is described, and U.S. Patent No. 6193818 contains Si 0.5-13%, Mg 0-2%, Cu 0-2%, Mn 0-1%, Fe 0-2% And casting an aluminum alloy having a thickness of 1.5-5 mm.

Therefore, the inventors of the present invention while studying a magnesium alloy plate produced by twin roll casting method, by adding Al to strengthen the solid solution and Mn to cause the dispersion of the Al-Mn mixture to exhibit a uniform microstructure mechanical properties This improved magnesium alloy plate was developed and the present invention was completed.

An object of the present invention is to provide a method for producing a magnesium-aluminum-manganese alloy cast using a twin roll casting method.

Still another object of the present invention is to provide a magnesium-aluminum-manganese alloy cast having improved microstructure, yield strength, maximum tensile strength and elongation.

In order to achieve the above object, the present invention comprises the steps of preparing an aluminum-manganese master alloy by mixing the aluminum ingot and manganese element (step 1); Adding the aluminum-manganese mother alloy prepared in step 1 to molten magnesium, mixing the mixture, and then pouring the aluminum-manganese master alloy into a metal mold to prepare a magnesium-aluminum-manganese alloy ingot (step 2); And manufacturing a magnesium-aluminum-manganese alloy slab from the magnesium-aluminum-manganese alloy molten metal prepared in step 2 by a twin roll casting method (step 3). To provide.

In addition, the present invention provides a magnesium-aluminum-manganese alloy slab with improved microstructure, yield strength, maximum tensile strength and elongation.

Magnesium-aluminum-manganese alloy cast using the twin roll casting method according to the present invention, aluminum is added to strengthen the solid solution, manganese is added to promote dispersion strengthening, and has an improved microstructure than the ingot cast slab manufactured by the conventional method , Yield strength, maximum tensile strength and elongation also have improved values, so it can be used as a lightweight structural material.

The present invention comprises the steps of preparing an aluminum-manganese master alloy by mixing the aluminum ingot and manganese element (step 1); Adding the aluminum-manganese mother alloy prepared in step 1 to molten magnesium, mixing the mixture, and then pouring the aluminum-manganese master alloy into a metal mold to prepare a magnesium-aluminum-manganese alloy ingot (step 2); And manufacturing a magnesium-aluminum-manganese alloy slab from the magnesium-aluminum-manganese alloy molten metal prepared in step 2 by a twin roll casting method (step 3). To provide.

Hereinafter, the present invention will be described in detail step by step.

First, step 1 according to the present invention is a step of preparing an aluminum-manganese master alloy by mixing the aluminum ingot and manganese elements.

The content of aluminum and manganese in the step 1 is preferably 2.5 to 3.5% by weight, 0.5 to 1.5% by weight, respectively. If the aluminum content is less than 2.5% by weight, there is a problem that the strength is lowered. If the content of aluminum is more than 3.5% by weight, precipitation phases such as Mg ₁₇ Al ₁₂ and Mg ₈ Al ₅ , which are not good for corrosiveness and weaken _solid solution strengthening, have a problem. There is a problem formed. In addition, when the content of manganese is less than 0.5% by weight, there is a problem in that the dispersed precipitated phase is less, and when it exceeds 1.5% by weight, the dispersed precipitated phase is excessively coarse to reduce the ductility.

Next, the step 2 according to the present invention is a step of preparing a magnesium-aluminum-manganese ingot by adding the aluminum-manganese mother alloy prepared in step 1 to the molten magnesium, mixed and then poured into a metal mold.

After the molten magnesium is added in step 2 according to the present invention, it is preferable to maintain the alloying elements at 700-800 ° C for 20-40 minutes so that the alloying elements are completely dissolved and dispersed. If the temperature is less than 700 ℃, there is a problem of low fluidity of the molten metal, if the temperature exceeds 800 ℃ there is a problem that the gas content due to overheating increases. In addition, if the time is less than 20 minutes, there is a problem that the dispersion is reduced by the complete solid solution of the alloying elements, if more than 40 minutes there is a problem that excessive energy is consumed in terms of energy efficiency.

Next, step 3 according to the present invention is a step of producing a magnesium-aluminum-manganese alloy cast piece by the twin roll casting method of the magnesium-aluminum-manganese alloy molten metal prepared in step 2.

It is preferable that the twin roll casting of the said step 3 has a roll speed of 3-3.5 rpm, and the interval between rolls is 3.0-4.0 mm. If the roll speed is less than 3 rpm, there is a problem that the liquid-liquid interface is located in front of the roll, if the roll speed exceeds 3.5 rpm, there is a problem that the solid-liquid interface is located behind the roll. Moreover, when the space | interval between rolls is less than 3.0 mm, there exists a problem that productivity falls, and when it exceeds 4.0 mm, there exists a problem that a solidification rate becomes slow and a structure becomes coarse.

In addition, the magnesium-aluminum-manganese alloy cast slab cast in step 3 may be further heated for 20 to 40 minutes at 300-400 ℃ and rolling with a warm rolling mill.

The roll of the warm rolling mill is preferably heated to 200-300 ℃. If the heating temperature of the twin roll is less than 200 ℃, there is a problem that the rolling bonds due to crack generation is increased, and if it exceeds 300 ℃, there is a problem that sintering of the roll surface and management of the roll equipment is difficult.

In addition, although the roll speed of the warm rolling mill is variable according to the rolling mill function, it is preferable to carry out at 3.0-4.0 rpm in the present invention.

Further, the warm rolling is preferably performed at a temperature range of 300-350 ° C. If the warm rolling temperature is less than 300 ℃, there is a problem that the rolling bond is increased by the occurrence of cracks, if the temperature exceeds 350 ℃ there is a problem that the surface state of the plate is not good.

In addition, the warm rolling is preferably performed 1-7 times. If the warm rolling is performed more than seven times, work hardening occurs, so that there is a problem that sufficient intermediate annealing treatment should be performed to soften it.

Furthermore, it is preferable that the magnesium-aluminum-manganese alloy slab is heated for 3 to 7 minutes at 300-400 ° C. for each warm rolling step. If the heating temperature is less than 300 ℃, there is a problem that the rolling bonds due to crack generation increases, and if the heating temperature exceeds 400 ℃, there is a problem that the surface state of the plate material is not good. In addition, when the heating time is less than 3 minutes, there is a problem that the internal and external temperature is uneven, and when it exceeds 7 minutes, there is a problem in that excessive energy is consumed in terms of energy efficiency.

Method for producing a magnesium-aluminum-manganese alloy cast according to the present invention may further comprise the step of heat treatment.

The heat treatment is preferably carried out at 300-400 ℃ for 50-70 minutes. If the heat treatment temperature is less than 300 ° C., there is a problem that the internal stress cannot be sufficiently removed, and if the heat treatment temperature is higher than 400 ° C., there is a problem of increasing the surface oxidation. In addition, when the heat treatment time is less than 50 minutes, there is a problem that the internal stress is not sufficiently removed, if more than 70 minutes there is a problem that excessive energy is consumed in terms of energy efficiency.

The magnesium-aluminum-manganese alloy slab according to the present invention has an improved microstructure, and has improved values in yield strength, maximum tensile strength and elongation, and thus can be usefully used as a lightweight structural material.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are merely to illustrate the invention, the content of the present invention is not limited by the following examples.

Example 1 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using Twin Roll Casting Method 1

A horizontal twin roll casting machine with a water cooling system was used to produce magnesium alloy slabs. Copper alloy twin rollers with a diameter of 300 nm were used in horizontal twin roll casting machines. Pure magnesium and aluminum ingots were used to produce the alloy. Manganese element was added to the Al-Mn mother alloy (Al 10 wt%). SF ₆ as protective gas to protect the molten alloy And CO ₂ were used. Alloying elements of Al and Al-Mn mother alloys were added to the molten magnesium at 750 ° C., and the melt was held at 750 ° C. for 30 minutes to completely dissolve and disperse the alloy elements. For ingot casting, the molten alloy was injected into a metal mold of 180 mm × 160 mm × 25 mm size at 720 ° C. For twin roll casting, the molten metal flows from the melting furnace into the tundish, and after entering the inlet of the tundish, the molten metal is moved to the rotating roller surface. The molten metal solidifies rapidly in contact with the cooled roller and passes between the rollers. The rolling speed is 3-3.25 rpm and the roller spacing is 3 mm. A twin roll cast strip having a thickness of 4 mm, a width of 180 mm, and a length of 10 m was produced.

Example 2 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using Two Roll Casting Method 2

Magnesium-aluminum-manganese alloy slabs were prepared in the same manner as in Example 1, except that warm rolling and heat treatment were performed to produce an equiaxed and fine grained magnesium alloy plate. Prior to warm rolling, the magnesium-aluminum-manganese alloy slabs prepared by twin roll casting were reheated at 350 ° C. for 30 minutes and passed through a roller mill having a roller diameter of 200 mm. The roller was heated to 250 ° C. and operated at 3.5 rpm. Between each passing point the alloy was reheated at 350 ° C. for 5 minutes. Warm rolling was performed once to prepare a magnesium-aluminum-manganese alloy cast.

Example 3 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using Two Roll Casting Method 3

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Example 2 except that the warm rolling was performed three times.

Example 4 Fabrication of Magnesium-Aluminum-Manganese Alloy Cast Using Two Roll Casting Method 4

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Example 2 except that the warm rolling was performed five times.

Example 5 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using Two Roll Casting Method 5

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Example 2 except that the warm rolling was performed seven times.

Example 6 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using Twin Roll Casting Method 6

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Example 5 except that the heat treatment was performed at 350 ° C. for 60 minutes.

<Comparative Example 1> Preparation of magnesium-aluminum-manganese alloy cast using a conventional ingot casting method 1

Magnesium-manganese molten metal was injected into the metal mold to prepare an ingot having a thickness of 25 mm, and an aluminum-manganese billet having a thickness of 4 mm from the casting ingot was used in the same manner as in Example 1 above. Casting ingots were prepared.

Comparative Example 2 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using 2 Conventional Ingot Casting Method 2

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Example 2 except that the warm rolling was performed once.

Comparative Example 3 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using a Conventional Ingot Casting Method 3

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Example 2 except that the warm rolling was performed three times.

Comparative Example 4 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using the Ingot Casting Method 4

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Example 2 except that the warm rolling was performed five times.

Comparative Example 5 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using the Ingot Casting Method 5

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Example 2 except that the warm rolling was performed seven times.

Comparative Example 6 Preparation of Magnesium-Aluminum-Manganese Alloy Cast Using the Ingot Casting Method 6

A magnesium-aluminum-manganese alloy cast was prepared in the same manner as in Comparative Example 5 except that the heat treatment was performed at 350 ° C. for 60 minutes.

The chemical composition, the number of warm rolling and the heat treatment conditions of Examples 1 to 6 and Comparative Examples 1 to 6 are shown in Table 1 above.

alloy Al (% by weight) Mn (% by weight) Mg Warm rolling count Heat treatment Example 1 3.26 0.75 Remainder - - Example 2 3.26 0.75 Remainder One - Example 3 3.26 0.75 Remainder 3 - Example 4 3.26 0.75 Remainder 5 - Example 5 3.26 0.75 Remainder 7 - Example 6 3.26 0.75 Remainder 7 350 ° C., 60 minutes Comparative Example 1 3.26 0.75 Remainder - - Comparative Example 2 3.26 0.75 Remainder One - Comparative Example 3 3.26 0.75 Remainder 3 - Comparative Example 4 3.26 0.75 Remainder 5 - Comparative Example 5 3.26 0.75 Remainder 7 - Comparative Example 6 3.26 0.75 Remainder 7 350 ° C., 60 minutes

Experimental Example 1 Analysis of Microstructure of Cast Steel Made by Twin Roll Casting Method and Conventional Ingot Casting Method

In order to analyze the microstructure of the cast steel produced by the twin roll casting method and the cast produced by the conventional method by optical microscopy (optical microscopy) and the results are shown in Figures 1 and 2.

Specimens were prepared for optical microscopy, cold-mounted, polished and polished for 5-10 seconds with aqueous picric acid and acetic acid (5 g of acid, 10 ml of acetic acid, 100 ml of distilled water, and 100 ml of ethanol). During etching.

As shown in Figure 1, it can be seen that the microstructure of the twin roll cast slab is different from the surface and the central portion. Dendritic crystals associated with directional solidification and hot deformation during twin roll casting were observed on the surface (see FIG. 1 (a)) and were inclined at 45-80 ° along the casting rolling direction. The transition from columnar to equiaxed occurred in the mid-thickness section and no macro segregation through the slab thickness was found (see FIG. 1 (b)).

The microstructural difference between the surface and the center of the cast is due to the different solidification rate depending on the thickness of the cast when casting the horizontal twin roll. The molten alloy is in direct contact with a copper roller which is cooled with water, so that the cooling rate is higher at the surface than at the center. The dendritic structure is formed in the central portion of the slab on the surface according to the temperature gradient.

As shown in (a) of FIG. 2, it can be seen that small primary particles dispersed at the interface between the dendritic crystals of the twin roll cast slab exist. A few intermetallic compound phases are found in cast alloys. The average size of the dispersed particles is about 1 μm. 2 (b) shows that large primary particles and a few intermetallic compound phases exist along or within the grain boundaries. The average size of the dispersed particles is about 8 μm. The volume of primary particles in twin roll cast and ingot cast alloys is about 3.2% and about 4.6%, respectively.

Experimental Example 2 Particle Analysis of Cast Steel Made by Twin Roll Casting Method and Conventional Ingot Casting Method

In order to analyze the particles of the cast steel produced by the twin roll casting method and the conventional ingot casting method, it was analyzed by transmission electron microscope (TEM, JEOL, JEM-2100F), and the results are shown in FIG.

As shown in FIG. 3, the second crystallized particles having nano size in the cast steel of Example 1 were much smaller than the ingot cast slabs because the solidification rate of the cast steel of Example 1 was faster. Al and Mn exhibit high solid solubility in twin roll cast slabs, and Al and Mn alloy elements form Al and Mn-rich intermetallic phases, so that the amount of Al and Mn dissolved in α-Mg is reduced to small size. It can be seen that the particles of exist in the microstructure.

Experimental Example 3 Analysis of Microstructure after Warm Rolling of Cast Steel Made by Twin Roll Casting Method and Conventional Ingot Casting Method

After performing the warm rolling of the cast steel produced by the twin roll casting method and the conventional ingot casting method was observed with an optical microscope (OM) to analyze the microstructure of the cast steel, the results are shown in Figures 4, 5 and 6.

4 is a photograph showing the microstructure of a twin roll cast magnesium-aluminum-manganese slab rolled at different reduction ratios at 350 ° C. Figure 4 (a) is a photograph of Example 2, Figure 4 (b) is a photograph of Example 3, Figure 4 (c) is a photograph of Example 4, Figure 4 (d) is implemented Example 5 is a photo.

The modified dendritic structure of Example 2 having a thickness reduction of 30% can be seen from FIG. 4A. Many dendritic crystals were deformed into elongated shapes and in a direction parallel to the rolling direction. No twins were found, and in Example 3, where the thickness was reduced by 67%, strain bands or shear bands appeared extensively, and the distance between strain bands and shear bands became narrower. Uniform strain microstructures were found in Example 4, in particular by Example 86, which was reduced by 80% in thickness. Twin and micro recrystallized crystals did not appear in modified microstructure shapes including modified dendritic structures, modified bands or shear bands.

5 shows a typical optical microstructure of the magnesium-aluminum-manganese alloy prepared by the conventional method during the warm rolling, (a) is a photograph of Comparative Example 2 (30% reduction), (b) A photo of Comparative Example 3 (67% reduction), (c) is a photo of Comparative Example 4 (80% reduction), and (d) is a photo of Comparative Example 5 (86% reduction). Twins occur extensively during warm rolling, and as shown in Fig. 5A, most of the rolling deformations are generated by twins. Most of the twins in FIG. 5A are {10-12} twins most easily occurring in Mg. In Comparative Example 3 (FIG. 5B) in which the thickness was reduced to 67%, more crystals with dynamic recrystallization were observed in the twinned region. The size of the dynamic recrystallized crystal can be estimated by the width of the twin, and the formation of the dynamic recrystallized crystal is closely related to the specific mechanism associated with the twin. When the thickness reduction is 80% (Fig. 5 (c)), small crystals recrystallized appear at the grain boundaries, forming a typical necklace structure, it can be seen that the overall microstructure is nonuniform. Some crystals are sensitive to dynamic recrystallization and quickly turn into dynamic recrystallized microcrystals. On the other hand, some crystals are not sensitive to dynamic recrystallization and therefore exist in large crystal size in the microstructure. The heterogeneous microstructure is due to the heterogeneous recrystallization rate in the determination of different trends. In addition, microcrystals, such as shear bands, are deeply related to agglomerated dynamic recrystallized crystals in the twin range. As shown in (d) of FIG. 5, when the reduction ratio was 80%, particularly at 86%, dynamic recrystallization and crystal growth reached a uniform state.

6 (a) and 6 (b) show the microstructures of the alloy plate of Example 5 manufactured by twin roll casting and warm rolling (rolled at a reduction ratio of 86%) and Comparative Example 5 manufactured by a conventional casting method. Fine, uniformly distributed particles with a main diameter of 0.8 μm are clearly observed through the twin roll cast plate, as shown in FIG. In contrast, large, non-uniformly dispersed particles having an average diameter of about 6.8 μm are shown in FIG. 6 (b). It can be seen that relatively small particles having a diameter of 1 to 3 μm tend to be arranged in the same strain zone, and decompose into larger particles from smaller particles during the warm rolling process. Therefore, the fine and homogeneously distributed particles observed in the twin roll cast plate shown in FIG. 6 (a) are due to the fine and uniformly distributed particles in the twin roll cast slab shown in FIG.

From the above experimental results mentioned above, the warm rolling deformation behavior is significantly different from that of Example 2-5 and Comparative Example 2-5. The deformation behavior of Example 2-5 is due to the slip dislocation mechanism during warm rolling, and the alloy of Comparative Example 2-5 is the deformation behavior during warm rolling due to dynamic recrystallization. Thus, the difference in deformation behavior is due to the difference in microstructure of the two alloys.

Experimental Example 4 Phase Analysis After Warm Rolling of Cast Steel Made by Twin Roll Casting Method and Conventional Ingot Casting Method

The phase after the warm rolling of the cast steel produced by the twin roll casting method and the conventional ingot casting method was analyzed through the above figure.

The microstructure of the twin roll cast slab is determined by the solubility of Al and Mn atoms. In the alloy of Mg-Al, Al is added to the Mg-base to increase solid solution strength, and Mn is added to cause dispersion of the Al-Mn intermetallic compound. In conventional ingot casting, Mn at α-Mg matrix based on Mg-Mn binary phase diagram shows low solubility. However, in the present invention, Al, in particular Mn, exhibits high solubility due to fast solubility during twin roll casting as compared to conventional ingot casting. The difference in composition at the α-Mg matrix is due to the very different deformation modes of the α-Mg matrix. The microstructure change of the conventional ingot cast alloy during hot rolling at 350 ° C. is due to the twin and the continuous and discontinuous dynamic recrystallization by dynamic recrystallization (see FIG. 5). However, in twin roll cast alloys, the microstructure change during the warm rolling process is due to strain bands or shear bands. As shown in FIG. 4, no significant twins and dynamic recrystallized microcrystals were observed. Warm rolling microstructure was analyzed using transmission electron microscope (TEM, JEOL, JEM-2100F), and Example 5 and Comparative Example 5 are shown in FIG. In a twin roll cast alloy plate after warm rolling, aligned subgrains with high density dislocations appear, and dislocation propagation slip (dislocation) is <c + a> slip in the pyramid slip system as shown in FIG. multiplication slip occurs extensively. However, in the ingot cast alloy sheet after warm rolling, aligned high-angle grain boundaries can be observed, and it can be seen from FIG. 7B that sufficient dynamic recrystallization has occurred.

{10-12} tensile twins or {10-11}-{10-12} double-twins easily occur in Mg and are extensively used during compression experiments or during hot rolling in Mg-Al-Zn (Mn) alloys. (See FIG. 4A). However, as shown in Fig. 4A, twins were not found during warm rolling in a twin roll cast slab. Therefore, twins and dynamic recrystallization are suppressed by the high solubility of Mn at the α-Mg matrix or fine particles dispersed in the twin roll cast slabs.

At Mg, not only {0002} <11-20> basal slip but also {10-12} <10-11> twins occur selectively and critical resolved shear stree is critical decomposition of non-basal slip at room temperature. It is much lower than the shear stress. However, the base slip has only two independent slip systems, and the {10-12} twins show only limited plastic deformation (0.13). Five independent slip systems allow isotropic deformation of polycrystalline materials without cracking, resulting in low ductility and deformation of Mg and Mg alloys at room temperature. The critical decomposition shear stress of the non-base slip decreases with increasing temperature and the tensile twin is independent of temperature. As shown in FIG. 5, the warm rolling is performed four times or less, and is represented by a combination of twin-dynamic recrystallization and continuous-dynamic recrystallization. However, twinning does not occur in twin roll cast steel. Therefore, inhibition of twins is manifested as the activity of non-base slip, and the critical breakdown shear stress of the non-base slip is reduced.

Since the width of the increased potential is inversely proportional to the stacking defect energy, the re-slip is further activated by the increased stacking defect energy. In the Mg and Mg alloys, the activity of the <a> slip coincides with the cross slip of the spiral potential from the base to the square face. Lamination defect energy of Mg decreases and dynamic recrystallization occurs with the addition of Al. The addition of Zn to the Mg-Y alloy is effective in reducing stacking defect energy and suppressing non-base slip. Non-base slip plays an important role in the deformation of Mg and Mg alloys. The reaction rate control process is the cross-slip of spiral potentials by the Fridel-Escaig mechanism. Therefore, the lamination defect energy increases due to the high solubility of Mn in the twin roll cast alloy, so that the cross slip increases, and twins are suppressed and non-base slip occurs during warm rolling. Thus, the twine does not occur during warm rolling in twin roll cast slabs due to an increase in stacking fault energy, which appears to be independent of particle / twine interaction, but is manifested by the high solubility of Mn in α-Mg.

Figure 4 (a) shows the microstructure change of the twin roll cast slab with rolling at 350 ℃. Unlike alloys made by conventional ingot casting methods rolled at these temperatures, dynamic recrystallized crystals are associated with grain boundaries and deformation characteristics. Because of the thermally activated process, dynamic recrystallization occurs during deformation of the magnesium alloy. On the other hand, particles of intermetallic compounds have the effect of delaying the movement of grain boundaries during crystal growth. In the alloy of the present invention, due to the fast solidification rate as shown in Figure 2, the twin roll cast slab has a large number of fine dispersed particles, it can effectively form grain boundaries and delay the recrystallization characteristics of the microstructure not recrystallized Indicates.

Experimental Example 5 Analysis of Microstructure after Warm Rolling and Heat Treatment of Cast Steel Made by Twin Roll Casting Method and Conventional Ingot Casting Method

Observed by optical microscope (OM) in order to analyze the microstructure after the warm rolling and heat treatment of the cast slab produced by the twin roll casting method and the conventional ingot casting method, the results are shown in Figure 8 and Table 2.

After performing warm rolling (86% reduction rate, seven passes of the roll), Example 5 and Comparative Example 5 were heat-treated at 350 ° C. for 1 hour.

alloy Average Crystal Size (㎛) Average particle size (㎛) Example 6 8.6 1.0 Comparative Example 6 12.8 6.8

Referring to FIG. 8 and Table 2, it can be seen that the heat treatment of the twin roll cast slab shows a micro-crystallized and equiaxed structure, and that uniform agglomeration and crystal growth occurs in the warm rolled plate of the twin roll cast slab during static recrystallization. . The main crystal size was measured to be about 8.6 μm. 8B illustrates an optical microstructure of Comparative Example 6. FIG. Crystal growth occurs during heat treatment. Non-uniform microstructures including microcrystals, such as plastic bands with a size of 3-5 μm and relatively coarse crystals with a size of 15-20 μm, were closely associated with warm rolling twin roll casting microstructures. The measured crystal size is about 12.8 μm, and it can be seen that it has a larger size than the twin roll cast microstructure. In addition, some large particles with a diameter of 3-10 μm were observed in FIG. 8 (b). On the other hand, although there was no apparent tendency for the particles to selectively exist at the grain boundaries, some of the microcrystals present at the grain boundaries interfere with the movement of the grain boundaries and a uniform micro-crystal structure can be obtained in the twin roll cast plate.

Experimental Example 6 Analysis of Mechanical Properties after Warm Rolling and Heat Treatment of Cast Steel Made by Twin Roll Casting Method and Conventional Ingot Casting Method

Yield strength, maximum tensile strength and elongation were measured in order to analyze the mechanical properties after the warm rolling and heat treatment of cast steel produced by the twin roll casting method and the conventional ingot casting method, and the results are shown in FIGS. 9 and 3.

alloy Yield strength (YS, MPa) Tensile strength (UTS, MPa) Elongation (%) Example 6 201 256 20.2 Comparative Example 6 172 235 18.3

Referring to Table 3, it can be seen that the yield strength, the maximum tensile strength, and the elongation of Example 6 manufactured by the twin roll casting method increased compared with Comparative Example 6 manufactured by the conventional ingot casting method.

1 is an optical microscope photograph of Example 1 prepared by a twin roll casting method according to the present invention;

2 is an optical microscope photograph of Example 1 prepared by a twin roll casting method and Comparative Example 1 manufactured by a conventional casting method according to the present invention;

3 is a transmission electron microscope photograph of Example 1 prepared by a twin roll casting method and Comparative Example 1 manufactured by a conventional casting method according to the present invention;

4 is an optical micrograph of Examples 2, 3, 4 and 5 prepared by the twin roll casting method according to the present invention;

5 is an optical micrograph of Comparative Examples 2, 3, 4 and 5 prepared by a conventional casting method;

6 is an optical microscope photograph of Example 5 prepared by a twin roll casting method and Comparative Example 5 manufactured by a conventional casting method;

7 is a transmission electron microscope photograph of Example 6 prepared by a twin roll casting method and Comparative Example 6 manufactured by a conventional casting method according to the present invention;

8 is an optical microscope picture of Example 6 prepared by a twin roll casting method and Comparative Example 6 manufactured by a conventional casting method; And

9 is a graph measuring the tensile strength of Example 6 prepared by a twin roll casting method according to the present invention and Comparative Example 6 manufactured by a conventional casting method.

Claims (13)

Mixing the aluminum ingot and manganese element to produce an aluminum-manganese master alloy (step 1); Adding the aluminum-manganese mother alloy prepared in step 1 to molten magnesium, mixing the mixture, and then pouring the aluminum-manganese master alloy into a metal mold to prepare a magnesium-aluminum-manganese alloy ingot (step 2); And Method for producing a magnesium-aluminum-manganese alloy cast using a twin-roll casting method comprising the step (step 3) of manufacturing a magnesium-aluminum-manganese alloy molten metal prepared in step 2 by a twin roll casting method. The method of claim 1, wherein the content of aluminum and manganese of the step 1 is 2.5 to 3.5% by weight and 0.5 to 1.5% by weight, respectively. The method of manufacturing a magnesium-aluminum-manganese alloy cast according to claim 1, wherein after the molten magnesium is added in Step 2, the molten magnesium is maintained at 700 to 800 ° C. for 20 to 40 minutes. The method of claim 1, wherein the twin roll casting of step 3 has a roll speed of 3 to 3.5 rpm and an interval between rolls of 3.0 to 4.0 mm. The magnesium-aluminum aluminum according to claim 1, further comprising the step of heating the twin-rolled magnesium-aluminum-manganese alloy slab at 300 to 400 ° C. for 20 to 40 minutes and rolling with a warm rolling mill. -Manganese alloy cast method. The method of claim 5, wherein the roll of the warm rolling mill is heated to 200-300 ℃, the roll speed is 3.0-4.0 rpm. The method of claim 5, wherein the warm rolling is performed in the temperature range of 300 to 350 ℃ magnesium-aluminum-manganese alloy cast. The method of claim 5, wherein the warm rolling is performed 1-7 times. The method of claim 8, wherein the magnesium-aluminum-manganese alloy slab is heated for 3 to 7 minutes at 300-400 ° C for each warm rolling step. The method of claim 5, further comprising the step of heat treatment. 12. The method of claim 10, wherein the heat treatment is performed at 300-400 ° C for 50-70 minutes. 12. A magnesium-aluminum-manganese alloy slab having an improved microstructure produced by the process of claims 1-11. 13. The magnesium-aluminum-manganese alloy slab of claim 12, wherein the cast steel has improved mechanical properties including yield strength, maximum tensile strength, and elongation.

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