KR101303585B1

KR101303585B1 - Magnesium alloy sheet having excellent room temperature formability and method of fabricating the same

Info

Publication number: KR101303585B1
Application number: KR1020100116975A
Authority: KR
Inventors: 김낙준; 김도향; 김동욱; 배준호
Original assignee: 포항공과대학교 산학협력단
Priority date: 2010-11-23
Filing date: 2010-11-23
Publication date: 2013-09-11
Also published as: WO2012070870A3; EP2644728A2; EP2644728A4; WO2012070870A2; KR20120055304A

Abstract

The present invention adds Ca to the Mg-Zn-based alloy, which is a precipitation-reinforced alloy, improves the precipitation behavior by twin roll sheet casting and subsequent processing heat treatment process to bring excellent strength and low anisotropy, in particular press formability. It is an object of the present invention to provide a highly formed magnesium alloy sheet material which is significantly improved compared to the magnesium alloy sheet material.
In order to achieve the above object, the present invention, Zn: less than 0.95 to 3% by weight, Ca: 0.1 to 5% by weight, consisting of the remaining unavoidable impurities and magnesium, characterized in that the limit dome height (LDH) is 7mm or more It provides a highly formed magnesium alloy sheet material.

Description

Magnesium Alloy Sheet with Excellent Formability and Manufacturing Method {MAGNESIUM ALLOY SHEET HAVING EXCELLENT ROOM TEMPERATURE FORMABILITY AND METHOD OF FABRICATING THE SAME}

The present invention relates to a magnesium alloy sheet having excellent room temperature formability and a method of manufacturing the same. More specifically, the present invention exhibits excellent press formability through secondary phase control, sheet casting, and subsequent processing heat treatment through an alloy component added to magnesium. The present invention relates to a method for producing a magnesium plate that can secure high strength through additional heat treatment after molding and to a magnesium plate produced by the method.

Magnesium alloy is an alloy for structural materials exhibiting the lowest specific gravity, excellent specific strength, and rigidity among practical structural materials. Recently, demand is increasing for cases of mobile devices and materials for automobiles that require weight reduction.

However, while the research on magnesium alloys has been focused on improving the high temperature properties for application to automobile engines and gear parts, research on processing magnesium alloys that can be applied to various fields such as plates has been insufficient.

In order to use the magnesium alloy sheet in various fields, it is essential to develop a magnesium alloy sheet having excellent moldability so that it can be processed into various shaped parts. Research is ongoing.

However, in order to apply the magnesium alloy sheet to various fields, it is required to develop a magnesium alloy sheet having high formability at room temperature.

On the other hand, as a method of manufacturing a magnesium alloy sheet, a method of forming a sheet having a target thickness by hot extrusion and rolling a conventionally cast or obtained by a semi-continuous casting method such as die casting, this method is a grain size It is characterized in that the large grain size of the cast material by hot extrusion to make a material capable of pressing or forging. On the other hand, since magnesium is a highly active metal, surface blackening and combustion are likely to occur due to processing heat generated during hot extrusion. Accordingly, in the hot extrusion process of magnesium, extrusion must be performed at a speed that can be cooled to a degree that surface blackening or combustion does not occur, thereby limiting the extrusion speed. That is, the hot extrusion process, which is essential for the conventional magnesium sheet process, has been a major factor in lowering productivity and increasing manufacturing cost. Moreover, since there is a limit to making the crystal grains fine only by the hot extrusion process, there is also a problem that it is difficult to beautifully process into a complicated shape.

In order to solve this problem, the present inventors add yttrium (Y) in consideration of the content of zinc (Zn) to the Mg-Zn-based alloy, as disclosed in Korean Patent Publication No. 2010-38809, A magnesium alloy sheet with improved press formability was proposed through the refinement of the structure and the control of the dispersed phase behavior by a subsequent work heat treatment process.

However, the magnesium alloy has a problem of not only using expensive yttrium, but also having low press formability compared to commercial aluminum, which has a certain limit in the application field.

The present invention has been researched and developed to solve the problems of the conventional magnesium alloy sheet and its manufacturing method, and can be manufactured at low cost using a low-cost alloy element, and also has a press formability equivalent to commercial aluminum Therefore, to solve the problem to provide a magnesium alloy plate and a method of manufacturing the same that can be suitably used for the production of a variety of complex parts.

In order to solve the above problems, the present invention provides a magnesium alloy sheet material containing Zn and Ca as an alloying element, the limit dome height (LDH) is 7mm or more, preferably 8mm or more.

'Limit Dome Height (LDH)' is an index for evaluating the formability, in particular, the pressability of a plate, and in the present invention, as shown in FIG. After fixing the outer periphery of the test piece with a force of 5 KN, using a spherical punch having a diameter of 27 mm, deformation was performed at a speed of 0.1 mm / sec, and the distance the punch moved until the disc-shaped test piece broke (that is, the test piece was deformed). Height).

In addition, the magnesium alloy sheet according to the present invention, the content of Zn is less than 0.95 to 3% by weight, the content of Ca is characterized in that 0.1 to 5% by weight, preferably 0.5 to 3% by weight.

In addition, the magnesium alloy sheet material according to the present invention is characterized in that the grain size average grain size is 10 µm or less.

In addition, the magnesium alloy sheet according to the present invention is characterized in that the yield strength (YS) is 200MPa or more, the tensile strength (UTS) is 270MPa or more, and the elongation (EL) is 12% or more.

In addition, the magnesium alloy sheet according to the present invention is characterized in that the texture intensity of the (0002) plane is 2.5 or less.

In addition, the present invention to solve the above problems, (a) Zn: less than 0.95 to 3% by weight, Ca: 0.1 to 5% by weight to prepare a molten alloy of the alloy consisting of inevitable impurities and magnesium; (b) maintaining the molten metal in a temperature range from a temperature at which the liquid fraction is 70% to a temperature before the molten metal is ignited; (c) injecting the molten metal maintained in the temperature range between two rotating cooling rolls to form a thin sheet of magnesium alloy sheet; (d) solution treatment of the cast magnesium alloy plate at 300 to 490 ° C. for 1 to 24 hours; (e) preheating the solution-treated magnesium alloy sheet to 300 to 400 ° C. and then rolling it to a required thickness of 1 to 45% per pass with a heated rolling roll; And (f) performing a solution treatment at 300 to 490 ° C. for 0.5 to 4 hours after the rolling.

In addition, in the method for producing a magnesium alloy sheet according to the present invention, the gap between the two cooling rolls in the step (c) is 1 to 5mm and the rotational speed of the cooling roll during the injection of the molten metal is 0.2 to 20m / min, It characterized in that the cooling rate of 10 ² ~ 10 ³ K / s.

In addition, the method for producing a magnesium alloy sheet according to the present invention, the content of Zn is less than 0.95 to 3% by weight, the content of Ca is characterized in that 0.1 to 5% by weight, preferably 0.5 to 3% by weight. .

In addition, the method for producing a magnesium alloy sheet according to the present invention may further include the step of performing an aging treatment for 1 to 72 hours at 150 to 200 ℃ the solution-treated magnesium alloy sheet after the rolling.

In addition, the method for producing a magnesium alloy sheet according to the present invention is characterized in that the addition of Ca is carried out by a method of adding a Mg-Ca mother alloy. This is because, when pure Ca is used, the melting point of Ca is not so high that it is not easily added as desired in casting, and the Mg-Ca master alloy is preferably a Mg-2 to 3.5 wt% Ca master alloy.

Next, the reason for limiting the alloy composition and the manufacturing process as described above in the present invention will be described.

Zn is 6.2% by weight at 340 ° C and the maximum solid solution at Mg is Zn. When 0.95% by weight or more is added, it forms an acicular precipitate through heat treatment. The hardening phenomenon is hardly expected, and when Zn is added in excess of 10% by weight, equilibrium precipitation may be encouraged at grain boundaries, resulting in deterioration of mechanical properties. Therefore, the content of Zn is preferably in the range of 0.95 to 3% by weight, more preferably in the content of Zn is less than 0.95 to 3% by weight. On the other hand, in the Mg-Zn binary alloy, the addition of an appropriate amount of Zn leads to softening of the base and activates the base slip, but the addition of more Zn causes not only the bottom base but also a decrease in mechanical properties. In order to maximize the slip and precipitation strengthening effect of the upper limit of Zn is more preferably limited to 7% by weight.

Ca is an effective element for improving the high temperature strength of magnesium alloy. If the Ca content is less than 0.1% by weight, the effect of increasing the high temperature strength is insufficient, and if the Ca content is more than 5% by weight, the spreading decreases and the fluidity of the molten metal is reduced, resulting in poor castability and hot cracking. When solidified, the adhesion to the mold increases, resulting in a decrease in productivity. Therefore, the content of Ca is preferably in the range of 0.1 to 5% by weight, more preferably 0.5 to 3% by weight because the effect can be maximized.

In the present invention, the unavoidable impurity refers to a component that is incorporated in an unintentional state in a raw material or a manufacturing process, and the incorporated component is preferably contained at 0.5 wt% or less so as not to affect the physical properties of the magnesium alloy according to the present invention. More preferably 0.01% by weight or less. In particular, elements such as Fe, Ni, Cr, Cu, Co, etc. may adversely affect the corrosion resistance, so management is required to be 0.005% by weight or less.

In addition, when the average grain size of the microstructured grains exceeds 10 µm, the strength and formability of the material are lowered, so that the grain size average grain size of the microstructured grains is preferably 10 µm or less.

In addition, the increase in texture intensity in magnesium alloys inhibits formability in the case of magnesium having a low slip system, and the texture intensity of the (0002) surface, which is the base surface, is 2.5 or less. If not, since it is difficult to implement press formability comparable to that of aluminum alloy, 2.5 or less is preferable, and more preferably 2.2 or less.

In addition, when the melt temperature of the step (b) is less than the temperature at which the liquid fraction is 70% or less, the viscosity of the melt increases, so that the melt solidifies before contacting the cooling roll of the step (c) and does not exit the roll. Since the process cannot be performed when the temperature to be ignited is exceeded, the molten metal temperature should be maintained in the above range.

In addition, if the cooling rate of the molten metal in the step (c) is less than 10 ² K / s, there is a problem that the cooling rate is slow, there is no significant difference in the microstructure of the general mold casting method and the flow of the molten metal before the casting can be unstable, If it exceeds 10 ³ K / s, it is difficult to reach it commercially except for the quench solidification method, which obtains a very thin ribbon form, so it is preferable to keep it at 10 ² to 10 ³ K / s. Maintaining the gap between the rolls of 10 mm or less is also advantageous for obtaining the cooling rate as described above. In the present invention, the fast cooling rate as in step (c) not only refines the cast structure and reduces segregation, but also finely disperses the intermetallic compounds in the matrix that play a detrimental role in tensile properties when the cooling rate is slow. Rather, it can play a beneficial role. In addition, since it is possible to manufacture a relatively thin plate in the casting step compared to other casting methods, it is possible to reduce the rolling reduction rate and the rolling pass in the rolling process, thereby minimizing the texture generated in the rolling process, which adversely affects press formability. The anisotropy of the plate can be reduced.

In addition, in the thin cast alloy sheet material, it is preferable to perform the solution treatment because the unevenness of the processed material may occur due to segregation of alloy elements that may occur during casting, and the solution treatment temperature and time are the main alloy elements. It is set in consideration of the diffusion of Zn, secondary dendrite arm spacing (SDAS), and the incidence of melting and oxidation measured by DTA / DSC, and should be performed under conditions of 1 to 24 hours at 300 to 490 ° C. Sufficient solution treatment results can be obtained.

In addition, the preheated temperature range (processing temperature range) may not be maintained when the solution-treated magnesium alloy sheet is preheated at 300 to 400 ° C. and then rolled to a required thickness of 1 to 45% per pass with a heated rolling roll. In this case, it is preferable to maintain the preheating temperature range because it is difficult to obtain a healthy plate, and it is preferable to keep the reduction rate per pass in the range of 1 to 45% because the aggregate structure develops and the moldability decreases as the reduction amount increases. .

In addition, if the heat treatment is not performed for 0.5 to 4 hours at 300 ~ 490 ℃ after rolling, it is not possible to sufficiently remove the characteristic non-uniformity after processing, it is preferable to maintain the above conditions.

In addition, in order to improve the room temperature tensile characteristics, it may comprise the step of performing the aging treatment for 1 to 96 hours at 150 ~ 200 ℃ heat-treated magnesium alloy plate material after the rolling, which is most This is because the tensile properties can be improved efficiently.

According to the present invention, unlike the conventional manufacturing method of commercial magnesium alloy sheet material, the alloy component suitable for the twin roll type sheet casting method, grain refinement and intermetallic compound formation and volume fraction control by thin sheet casting and subsequent heat treatment or processing heat treatment Through the conventional commercial magnesium alloy sheet, the strength and room temperature as well as the elongation and formability is improved to provide a room temperature forming magnesium sheet that can be widely applied to the automotive and electronics industry.

Moreover, according to the manufacturing method of the magnesium alloy plate material which concerns on this invention, since a manufacturing process number is reduced compared with the conventional manufacturing process of a plate material, a magnesium alloy plate material can be manufactured at low cost compared with the conventional commercial magnesium alloy plate material. In addition, since the final reduction can be greatly reduced, it is possible to minimize the formation of the aggregate structure, from which an improved press formability can be obtained.

1 is a schematic view of a sheet casting apparatus for producing a magnesium alloy sheet used in an embodiment of the present invention.
Figure 2 is a schematic diagram showing the evaluation method of the limit dome height of the magnesium alloy sheet according to the present invention.
Figure 3 shows the microstructure of the thin plate cast magnesium plate according to an embodiment of the present invention observed with an optical microscope after 1 hour heat treatment at 440 ℃.
Figure 4 shows the microstructure observed by the optical microscope after 30 minutes solution treatment at 440 ℃ after rolling a thin sheet cast magnesium alloy sheet according to an embodiment of the present invention.
Figure 5 shows the microstructure observed by transmission electron microscope after 30 minutes solution treatment at 440 ℃ after rolling 0.95Zn, 0.9Ca alloy.
Figure 6 shows the microstructure observed by transmission electron microscope after 30 minutes solution treatment at 350 ℃ after rolling a 5.99Zn, 0.98Ca alloy.
Figure 7 shows the deformation of the specimen before and after the solution treatment after 30 minutes solution treatment at 440 ℃ after rolling 0.95Zn, 0.9Ca alloy using EBSD.
FIG. 8 shows the deformation of the specimens before and after the 30 minute solution treatment at 350 ° C. after rolling the 5.99 Zn and 0.98Ca alloys using EBSD.
9A and 9B show the results of analysis of a basal pole figure of a magnesium alloy sheet manufactured according to an embodiment of the present invention, respectively.
Figure 10 shows the (0002) aggregate strength and LDH of the magnesium alloy sheet according to the embodiment and the comparative example of the present invention.

The singular forms used to describe the embodiments of the present invention are intended to include the plural forms as well, unless the phrases clearly indicate the opposite. And “includes” embodies a particular property, region, integer, step, operation, element, and / or component, and the presence or addition of another particular property, region, integer, step, operation, element, component, and / or group. It is not excluded.

Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, the commonly used terms defined in advance are ideal unless they are additionally interpreted and defined as having a meaning consistent with the related technical literature and the presently disclosed contents. It is not interpreted in a very official sense.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of a method for producing a magnesium alloy plate and a magnesium alloy plate manufactured using the same, but the present invention is not limited to the following embodiments. Therefore, it will be apparent to those skilled in the art that the present invention may be variously modified without departing from the technical spirit of the present invention.

[Manufacture of Magnesium Alloy Plate]

First, a magnesium alloy molten metal was prepared by dissolving a pure Mg (99.9%), a pure Zn (99.9%), and a Mg-3 wt% Ca master alloy under a CO ₂ and SF ₆ mixed gas atmosphere. At this time, the content ratio of each component in the prepared molten metal was set to the composition of Table 1 below.

Composition (% by weight) Zn Ca Mg 0.95 0.9 Honey. 3.43 0.82 Honey. 5.99 0.98 Honey.

1 is a schematic view of a twin roll sheet casting apparatus used in the embodiment of the present invention. As shown in FIG. 1, a twin roll plate casting apparatus includes a melting furnace 10, a nozzle 20, and two cooling rolls 30.

Specifically, the casting method using the twin roll type sheet casting apparatus is specifically, a temperature of about 70% of the molten metal dissolved in the above composition in the induction melting furnace 10 under a CO ₂ and SF ₆ mixed gas atmosphere (about 650). At a temperature of about 950 ° C. up to the temperature before the molten metal is ignited, and then transferred to the nozzle 20. In this case, if the temperature of the molten metal is too high, a liquid phase may exist inside the plate that has passed through the cooling roll, and thus, in the embodiment of the present invention, the melt is transferred to the nozzle 20 while maintaining the temperature below 750 ° C, specifically 710 ° C. .

The molten metal whose temperature is maintained at 710 ° C. is injected through the nozzle 20 between two cooling rolls 30 being cooled by a cooling device (not shown) provided in the twin roll sheet casting device. At this time, the gap between the two cooling rolls was maintained at about 2mm and the rotational speed of the cooling roll was maintained at about 4m / min during the injection of the molten metal. The casting speed of the molten metal was cast to be 200 ~ 300K / s under such conditions. Through the same casting method, a magnesium alloy sheet having a length of about 5 m, a width of about 70 mm, and a thickness of about 2 mm was obtained.

The plate material thus cast was subjected to the following processing heat treatment as follows. First, the cast plate was subjected to solution treatment at 440 ° C. for 1 hour. The solution treatment is to remove as much as possible the casting structure and segregation generated during casting before rolling, and to avoid defects caused by uneven grains or segregation during rolling.

Next, the solution-treated board | plate material was preheated to 300 degreeC, and hot rolling was performed by the rolling roll heated to 200 degreeC.

During hot rolling, rolling was carried out at 50% of the final reduction ratio in 5 passes while giving a rolling reduction ratio of 10% per pass, and after obtaining a sheet having a final thickness of about 1 to 0.7 mm, the rolled sheet was used as shown in Table 2 below. After the emulsification treatment, an aging treatment was performed for T6 heat treatment.

[Microstructure of Magnesium Plate]

The microstructure of the plate produced as described above was analyzed. Figure 3 is a photograph of the magnesium alloy sheet cast as described above after heat treatment at 440 ℃ for 1 hour to observe the microstructure of the specimen with an optical microscope.

Figure 4 is a photograph of the microstructure after the solution treatment for 30 minutes at 440 ℃ after rolling the magnesium alloy sheet prepared by the present invention with an optical microscope. As shown in FIG. 4, after the solution treatment after rolling, the average grain size of the microstructure is about 11 μm, and fine precipitated phases are evenly distributed throughout the microstructure.

5 and 6 are photographs of the magnesium alloy plate produced by the present invention, respectively, and then rolled and subjected to a solution-treated microstructure with a transmission electron microscope.

In the embodiment of the present invention, the precipitated phase is formed differently according to the amount of Zn. When prepared by fixing Ca at 1% by weight and changing the Zn content to about 1, 4, 6% by weight, as shown in FIG. 5, when Zn is 0.95% by weight, Mg ₂ Ca phase was formed, and Zn When the content of 6% by weight (4% by weight or more) can be seen in Figure 6 that the Mg ₆ Zn ₃ Ca ₂ phase is formed. Although there is a difference between these precipitated phases, as shown in Table 3 below, it is considered that there is no difference in formability due to the difference in precipitation phase.

7 and 8 show the backscattering electron diffraction (EBSD) of the solution-treated microstructure after rolling 0.95 Zn, 0.9 Ca and 5.99 Zn, 0.98 Ca in the magnesium alloy sheet produced by the present invention, respectively. Deformation behavior is analyzed using As can be seen from these figures, the degree of change of the grain orientation before and after the deformation is different, and due to this difference, it is estimated that the formability of 0.95 Zn and 0.9 Ca is higher than other alloys in the embodiments of the present invention. .

As described above, it can be seen that the method of manufacturing the magnesium alloy sheet according to the embodiment of the present invention can obtain a precipitated phase evenly dispersed in the microstructure by a simple process of the hot extrusion process compared with the conventional method.

In addition, as shown in Table 2, as the content of Zn increases, the heat treatment temperature is set to be lower, which is an optimum temperature at which the precipitated phase is evenly distributed in each grain for each embodiment of the present invention, which is higher than the temperature. When heat treatment for a long time at a temperature, the grain boundary is partially dissolved, and a large amount of precipitated phases are distributed in the grain boundary, thereby impairing room temperature tensile properties and formability.

[Evaluation of Physical Properties of Magnesium Plate]

In order to evaluate the tensile properties of the cast and post-processed magnesium alloy sheet prepared as described above, a tensile specimen having a gauge length of 12.6 mm, a gauge width of 5 mm, and a thickness of 1 mm was fabricated, and a strain of 6.4 × 10 ^-4 s ^-1 was obtained. Tensile testing was conducted at speed.

In addition, in order to evaluate the press formability of the manufactured magnesium alloy sheet material, a limit dome height (LDH) test was performed. FIG. 2 schematically illustrates a method for obtaining a selected limit dome height (LDH) value as an index for evaluating formability (particularly pressability) of a magnesium alloy sheet in an embodiment of the present invention.

In the limit dome height test, a disk-shaped test piece having a diameter of 50 mm and a thickness of 0.7 mm was prepared, a test piece was inserted between the upper die and the lower die, and the specimen was fixed with a force of 5 kN. Then, a strain was applied at a speed of 0.1 mm / sec using a spherical punch having a diameter of 27.5 mm, the punch was inserted until the disc-shaped specimen was broken, and the deformation height at the fracture was measured. The limit dome height test was carried out not only for the examples of the present invention but also for the magnesium alloy plates (AZ31 H24, ZW41) and aluminum plates (Al 5052) that are currently commercially available for comparison.

Table 2 shows the tensile and molding properties measured by the above method.

Composition (% by weight) Heat treatment Crystal grain
size
(um) UTS
(MPa) YS
(MPa) EL
(mm) LDH
(mm) Remarks Zn Ca Mg 0.95 0.9 Honey. 440 ℃ / 1h + 5pass + 440 ℃ / 30m 11.6 229.5 151.7 11.4 8.8 Example 470 ℃ / 2h + 5pass + 470 ℃ / 30m 20 222.7 126.9 13.1 8 Example 470 ℃ / 2h + 5pass + 380 ℃ / 30m 7.8 236 168.4 13.8 6.6 Example 3.43 0.82 Honey. 400 ℃ / 1h + 5pass + 400 ℃ / 30m 11.2 258.2 151.9 14.5 7.1 Example 380 ℃ / 4h + 5pass + 380 ℃ / 30m 13.2 254.4 158.8 15.5 7.4 Example 5.99 0.98 Honey. 350 ℃ / 1h + 5pass + 350 ℃ / 30m 10.9 258.9 163.6 17.2 7.5 Example 380 ℃ / 4h + 5pass + 380 ℃ / 30m 12.7 258.4 152.4 14.3 8 Example 380 ℃ / 4h + 5pass + 300 ℃ / 1h - 247.7 154 14.8 8.6 Example Commercial AZ31B H24 - 290 220 15 2.7 Comparative example ZW41 4 223 89 21 6.6 Comparative example Al 5052 29.2 189 82 16.9 7.7 Comparative example

As a result of the test, as shown in Table 2, the commercially available magnesium alloy AZ31B H24 LDH is only 2.7mm, ZW41 LDH, known as a good magnesium moldability is 6.6mm, which is much better than AZ31B H24 The LDH of the aluminum alloy Al 5052, which is better in formability than magnesium, showed an excellent 7.7 mm compared with the two kinds of magnesium alloys.

In comparison, the magnesium alloy sheet produced according to the embodiment of the present invention exhibited an LDH of 6.6 to 8.8 mm. Considering that the larger the LDH, the higher the moldability, the magnesium alloy prepared through the examples of the present invention not only shows three times or more excellent moldability as compared with the commercial AZ31 H24 alloy, but also has excellent moldability in the related art. Compared with the ZW41 alloy known to represent, it can be seen that the LDH is greatly improved in some examples. Moreover, even when compared to the Al 5052 series of aluminum, which is a material having excellent moldability compared to magnesium, the moldability is excellent in some embodiments.

9A and 9B show the results of analysis of a basal pole figure of a magnesium alloy sheet manufactured according to an embodiment of the present invention, respectively. In general, in the case of magnesium alloy sheet, the pole plane of the basal plane becomes stronger during the rolling process, and the increase of the texture strength is due to the slip system. Less magnesium impairs formability.

Accordingly, many conventional studies have been conducted on various processes and heat treatments to lower the maximum intensity of such a basal pole and to have random textrue.

Composition (% by weight) Heat treatment E _U (mm) LDH (mm) (0002)
texture intensity Remarks Zn Ca Mg 0.95 0.9 Honey. 440 ℃ / 1h + 5pass + 440 ℃ / 30m 11.4 8.8 2.0 Example 3.43 0.82 Honey. 400 ℃ / 1h + 5pass + 400 ℃ / 30m 14.5 7.1 2.0 Example 5.99 0.98 Honey. 350 ℃ / 1h + 5pass + 350 ℃ / 30m 17.2 7.5 2.1 Example Commercial AZ31 H24 15 2.7 - Comparative example AZ31 15.9 4.1 9.3 Comparative example ZW41 21 6.6 3.0 Comparative example Al 5052 16.9 7.7 - Comparative example

However, the magnesium alloy sheet according to the embodiment of the present invention shows a low intensity (see FIG. 9A) of 3.8 in the case of the texture of the base surface even after rolling. The low intensity (see FIG. 9B) of case 2.0 is shown. As shown in Table 3, it shows a low intensity (intensity) compared to the conventional magnesium plate.

In addition, FIG. 10 shows the ratio of the base face (0002) texture and the pyramid face (10-11) texture of the embodiment and the comparative example of the alloy, in the case of the magnesium alloy sheet according to this embodiment The structure is relatively strong and has a lower value than that of the AZ31 alloy. This means that a random texture is formed in the magnesium alloy sheet according to the embodiment.

By further heat treatment (aging hardening) to the alloy of Table 2, it is possible to produce a high-strength magnesium alloy compared to the yield strength after the solution treatment. Table 4 below compares the tensile properties after the additional age hardening treatment and the tensile properties of the magnesium plate and the commercially available AZ31 H24 prepared in the same manner as the examples of the present invention magnesium alloys.

Composition (% by weight) Heat treatment UTS (MPa) YS
(MPa) EL
(mm) Remarks Zn Ca Mg 0.95 0.9 Honey. 440 ℃ / 1h + 5pass + 440 ℃ / 30m + 150 ℃ / 16h 252.4 194.2 8 Example 470 ℃ / 2h + 5pass + 470 ℃ / 2h + 150 ℃ / 48h 256.4 186.9 9.2 Example 470 ℃ / 2h + 5pass + 470 ℃ / 2h + 200 ℃ / 1h 256.3 201.3 7.2 Example 3.43 0.82 Honey. 400 ℃ / 1h + 5pass + 400 ℃ / 30m + 150 ℃ / 8h 262.7 180.5 16.2 Example 380 ℃ / 4h + 5pass + 380 ℃ / 4h + 150 ℃ / 16h 245.1 172.3 11.6 Example 380 ℃ / 4h + 5pass + 380 ℃ / 4h + 200 ℃ / 1h 253.7 174.7 15.9 Example 5.99 0.98 Honey. 350 ℃ / 1h + 5pass + 350 ℃ / 30m + 150 ℃ / 24h 263.7 175.8 13.9 Example 380 ℃ / 4h + 5pass + 380 ℃ / 4h + 150 ℃ / 48h 278.6 208.8 12 Example 380 ℃ / 4h + 5pass + 380 ℃ / 4h + 200 ℃ / 8h 262.5 205 8.4 Example Commercial AZ31 B H24 290 220 15 Comparative example AZ31 235 131 15.9 Comparative example ZW41 223 89 25.5 Comparative example

As can be seen in Table 4, the magnesium alloy sheet according to the embodiment of the present invention has a considerably superior tensile strength compared to the same thin cast magnesium alloy sheet, and some examples of the magnesium alloy has a tensile strength of commercial AZ31 H24 A comparatively low degree is shown.

As described above, the magnesium alloy sheet according to the embodiment of the present invention may simultaneously control high formability and high mechanical properties so as to have mechanical properties comparable to those of aluminum, which is a lightweight metal, by heat treatment after rolling.

First, since the casting and hot rolling processes are simultaneously performed in one process through the twin-roll thin plate casting method, which is a method of manufacturing magnesium alloy sheet of the present invention, it is economical and provides a very fast cooling rate compared to the prior art, thereby making it possible to refine the particles. It can be improved.

In addition, the conventional magnesium alloy plate is relatively less strength than heat-treated aluminum, but the alloy plate according to the embodiment of the present invention can be applied to the automotive and structural materials industry that requires a high strength plate by implementing a relatively high strength In addition, due to the excellent moldability compared to the conventional magnesium can be used in a variety of fields that require a complex type plate that is not applied to the conventional magnesium alloy plate.

10: melting furnace
20: Nozzle
30: cooling roll

Claims

Zn: less than 0.95 to 3% by weight, Ca: 0.1 to 5% by weight, consisting of the remaining unavoidable impurities and magnesium, high forming magnesium alloy sheet, characterized in that the limit dome height (LDH) is 7mm or more.

The method of claim 1,
Magnesium alloy sheet material, characterized in that the Ca content of 0.5 to 3% by weight.

3. The method according to claim 1 or 2,
The high-forming magnesium alloy sheet material, characterized in that the average grain size of the microstructure of the magnesium alloy sheet material is 10㎛ or less.

3. The method according to claim 1 or 2,
Highly magnesium alloy sheet, characterized in that the limit dome height (LDH) of the magnesium alloy sheet is 8mm or more.

delete

3. The method according to claim 1 or 2,
High strength magnesium alloy sheet, characterized in that the aggregate intensity (texture intensity) of the (0002) surface of the magnesium alloy sheet is less than 2.5.

(a) preparing a molten alloy of an alloy comprising Zn: less than 0.95 to 3% by weight and Ca: 0.1 to 5% by weight, the remainder being inevitable impurities and magnesium;
(b) maintaining the molten metal in a temperature range from a temperature at which the liquid fraction is 70% to a temperature before the molten metal is ignited;
(c) injecting the molten metal maintained in the temperature range between two rotating cooling rolls to form a thin sheet of magnesium alloy sheet;
(d) solution treatment of the cast magnesium alloy plate at 300 to 490 ° C. for 1 to 24 hours;
(e) preheating the solution-treated magnesium alloy sheet to 300 to 400 ° C. and then rolling it to a required thickness of 1 to 45% per pass with a heated rolling roll; And
(f) performing a solution treatment for 0.5 to 4 hours at 300 to 490 ° C. after the rolling;
It includes, The method of producing a high-forming magnesium alloy sheet material of the limit dome height (LDH) 7mm or more after the solution treatment.

The method of claim 7, wherein
In step (c), the gap between the two cooling rolls is maintained at 1 to 5 mm and the rotational speed of the cooling roll is maintained at 0.2 to 20 m / min during injection of the molten metal, thereby cooling the molten metal to 10 ² to 10 ³ K / s. Method for producing a highly formed magnesium alloy sheet, characterized in that to be.

9. The method according to claim 7 or 8,
The Ca content is 0.1 to 3% by weight manufacturing method of the high-forming magnesium alloy sheet, characterized in that.

9. The method according to claim 7 or 8,
And further performing aging treatment on the solution-treated magnesium alloy sheet at 150 to 200 ° C. for 1 to 72 hours after the rolling.

9. The method according to claim 7 or 8,
The method of manufacturing a highly formed magnesium alloy sheet, characterized in that the addition of Ca is carried out by adding a Mg-Ca mother alloy.