KR100519721B1 - High strength magnesium alloy and its preparation method - Google Patents

Abstract

A high-strength magnesium alloy containing 3-10 wt.% Zn and 0.25-3.0 wt.% Mn, the balance being inevitable impurities and Mg. The high-strength magnesium alloy may further include 1-6 wt.% Al, further, 0.1-4.0 wt.% Si or 0.1-4.0 wt.% Si and 0.1-2.0 wt.% Ca together. It may further include. The high strength magnesium alloy according to the present invention has improved hardness and strength, and excellent elongation characteristics at room temperature. In addition, in the present invention, in adding Mn to the molten magnesium, a Zn-Mn mother alloy is added by a solvent-free dissolution method, and a method of producing and processing a high-strength magnesium alloy obtained by processing and heat-treating the obtained cast material. Provide process conditions.

Description

High strength magnesium alloy and its manufacturing method {HIGH STRENGTH MAGNESIUM ALLOY AND ITS PREPARATION METHOD}

The present invention relates to a high-strength magnesium alloy and a method of manufacturing the same, and more particularly, by improving the mechanical properties including strength, hardness, and elongation by adding a specific alloying element or by changing the manufacturing conditions including a specific heat treatment, The present invention relates to a magnesium alloy having high strength and elongation and an economical manufacturing method thereof.

Among the magnesium alloys, an alloy exhibiting the best aging reinforcement behavior is an Mg-Zn-based alloy, and the alloy has the advantages of relatively good strength and ductility after aging treatment and easy processing and welding. On the other hand, since micropores are generated during casting due to Zn addition, it has a disadvantage that it is difficult to apply to casting processes such as die casting.

In addition, unlike other magnesium alloys, Mg-Zn-based alloys have limitations in terms of strength improvement because they are not easy to refine the structure through alloy element addition and overheating, and this has been a limiting factor in terms of commercialization.

In order to overcome this problem, studies have been conducted to add some alloying elements to the Mg-Zn binary alloy. Examples are as follows.

In 1947 JP Doan and G. Ansel proposed a method to improve the strength of alloys by adding Zr to refine the grains of Mg-Zn alloys (JP Doan and G. Ansel, Trans, AIME, vol. 171 (1947), pp. 286-295). However, it is difficult to add Zr to the molten magnesium due to the high melting point of Zr.

In addition, a method of adding rare earth metals such as La, Ce, Nd, or Th is also known. This method has advantages of suppressing fine pores, improving strength at high temperatures, and improving weldability, but are conventionally used. The disadvantage is that the manufacturing cost is very high compared to other magnesium alloys.

In 1987, W. Unsworth and JF King reported that the addition of Cu could improve ductility by miniaturizing β ₁ ', the main strengthening precipitation phase of Mg-Zn alloys (W. Unsworth and JF King, Magnesium Technology, The Inst. of Metal, 1987, pp. 25-35). However, the addition of Zn and Cu has a limit that the elongation at room temperature is difficult to exceed 10% although there is a difference depending on the addition amount.

Table 1 below shows a comparison table of properties of commercial casting alloys and processing alloys.

It can be seen from Table 1 that the alloy for commercial processing is superior in yield strength, tensile strength, and elongation as compared with commercial casting alloys. However, it is difficult to obtain an alloy having a combination of high strength and high elongation even in the existing commercial processing alloy. That is, in the case of a high strength alloy having a tensile strength of more than 300 MPa, the elongation is difficult to exceed 10%. In addition, Zn and Zr-added alloys exhibiting excellent properties in terms of strength have been reported to have many restrictions in the manufacturing process for Zr addition.

In addition, U. S. Patent No. 4,997, 662 shows the properties of magnesium produced by the quench coagulation method. The yield strength, tensile strength, and elongation of the alloys produced by the quench coagulation method are increased. It is very expensive and its scope of application is limited.

1A is a microstructure photograph of an Mg-Zn binary alloy extruded material Z6.

1B and 1C are microstructure photographs of Mg-Zn-based alloy extruded materials ZM61 and ZAM621 to which Mn is added or Al and Mn are added according to the present invention.

1D and 1E illustrate the fineness of Mg-Zn-based alloy extruded materials (ZAM631 + 2.5Si, ZAM631 + 2.5Si + 0.4Ca) to which Al, Mn, and Si are added or Al, Mn, Si, and Ca are added according to the present invention. Organization picture.

2 is a graph showing the aging hardening behavior during the aging treatment of the Mg-Zn binary alloy extruded material Z6.

Figure 3 shows the aging hardening behavior of the Mg-Zn-based alloy extruded material (ZM61, ZAM621) to which Mn is added or Al and Mn added in accordance with the present invention is a double of the Mg-Zn binary alloy extruded material (Z6) It is a graph compared with the aging hardening behavior at the time of aging treatment.

Figure 4 shows the age hardening behavior of Mg-Zn-based alloy extruded materials (ZM61, ZAM621) added Mn, or Al and Mn added in accordance with the present invention during the double aging treatment Mg-Zn binary alloy extruded material It is a graph shown in comparison with the age hardening behavior when (Z6) is treated under the same conditions.

5 is a double aging treatment of Mg-Zn-based alloy extruded material (ZAM631 + 2.5Si, ZAM631 + 2.5Si + 0.4Ca) to which Al, Mn and Si is added or Al, Mn, Si and Ca are added according to the present invention. A graph showing the aging hardening behavior of.

FIG. 6 shows tensile properties at room temperature of Mg-Zn alloy extruded materials ZM61 and ZAM621 added with Mn or Al and Mn according to the present invention. It is a graph compared with property.

7 is a tensile at room temperature of the Mg-Zn-based alloy extruded material (ZAM631 + 2.5Si, ZAM631 + 2.5Si + 0.4Ca) to which Al, Mn and Si is added or Al, Mn, Si and Ca are added according to the present invention. It is a graph showing the property.

8 is a cross-sectional view of the tensile properties of Mg-Zn binary alloy extruded material (Z6) at room temperature during the double aging treatment of Mg-Zn-based alloy extruded materials (ZM61, ZAM621) to which Mn is added or Al and Mn added according to the present invention. This graph is compared with the tensile properties at room temperature during the double aging treatment.

9 is a double aging treatment of Mg-Zn-based alloy extruded material (ZAM631 + 2.5Si, ZAM631 + 2.5Si + 0.4Ca) to which Al, Mn and Si is added or Al, Mn, Si and Ca are added according to the present invention. It is a graph showing the tensile properties at room temperature.

10 is a Mg-Zn binary alloy of the Mg-Zn-based alloy extruded material (ZM61, ZAM621) to which Mn is added or Al and Mn added in solution according to the present invention and then the tensile properties at room temperature during the double aging treatment It is the graph shown compared with the tensile property at normal temperature when the extruded material Z6 is processed on the same conditions.

11 is a Mg-Zn binary alloy of the Mg-Zn-based alloy extruded material (ZM61, ZAM621) to which Mn is added or Al and Mn added (5% stretch) after stretching 5% It is the graph shown compared with the tensile property at normal temperature when the extruded material Z6 is processed on the same conditions.

The present invention improves the microstructure and precipitation behavior of the structure by improving alloying properties such as hardness, strength and elongation by adding an alloy element that is cheaper than the alloy element added to the Mg-Zn-based alloy, and improves the formability. It is an object to provide an alloy.

In addition, an object of the present invention is to provide a method for producing a high-strength magnesium alloy having excellent elongation to strength for the alloy produced by deriving the optimum heat treatment conditions in the production of high-strength magnesium alloy and economical manufacturing conditions therefor.

In order to achieve the above object, the present invention provides a high-strength magnesium alloy composed of 3 to 10 wt.% Zn, 0.25 to 3.0 wt.% Mn, and a remainder composed of unavoidable impurities and Mg.

The magnesium alloy may additionally contain 1 to 6 wt.% Of Al, and additionally, 0.1 to 4.0 wt.% Of Si or 0.1 to 4.0 wt.% Of Si and 0.1 to 2.0 wt.% Of Ca. It may be. In addition, the Al content is preferably less than the Zn content.

In addition, the Zn content is 5.0 ~ 7.0wt.%, The Mn content is 0.75 ~ 2.0wt.%, The Si content is 1.5 ~ 3.0wt.%, The Ca content is 0.3 ~ 1.0wt.% More preferred.

That is, the core of the present invention is to provide a high-strength magnesium alloy having high strength and elongation by lowering the yield strength by improving the yield strength by adding Al as an alloying element to the Mg-Zn-based alloy to improve workability.

Furthermore, this invention provides the manufacturing method of the said high strength magnesium alloy which adds Zn-Mn mother alloy in adding Mn to a molten magnesium.

Preferably, the high-strength magnesium alloy is made of a cast material by adding Zn-10-20 wt.% Mn master alloy at 670-720 ° C., Zn or Zn and Al in molten magnesium, or Zn- in magnesium molten metal. 10-20 wt.% Mn master alloy is added at 670-720 ° C., Mg-Si master alloy is added, and Zn, Zn and Al and / or Ca are added to form a cast material.

Further, the cast material made as described above is preferably homogenized at 340 to 410 ° C. for 6 to 12 hours to prepare a billet, and the billet is preheated at 150 to 400 ° C. for 30 minutes to 2 hours and then processed. Can be.

More preferably, after the above-described processed material is subjected to the primary aging treatment at 70 to 100 ° C. for 24 to 96 hours, the secondary aging treatment may be performed at 150 to 180 ° C. for 48 hours or more.

In addition, solution treatment may be performed at 340 to 410 ° C for 6 to 12 hours before the double aging treatment, or 3 to 7% stretching may be performed before the double aging treatment.

The reason why the composition range of the alloying element in the present invention is limited as described above is as follows.

Zinc (Zn): 3-10 wt.%

Zn is 6.2wt.% At 340 ° C in the maximum solid solubility in Mg matrix, and when 3.0wt.% Or more is added, Zn forms acicular precipitated phase through heat treatment, thereby exhibiting aging strengthening behavior. Generally, the addition amount is determined based on the amount employed, and aging strengthening behavior can be maximized by adding about 5.0 ~ 7.0 wt.% Close to the maximum solution. If less than 3.0wt.% Is added, this is less than the solid solution at the normal aging temperature, so that the formation of precipitated phase is weak and hardly expected to be enhanced. If more than 10.0wt.% Is added, equilibrium precipitation at grain boundaries is achieved. This encouragement can lead to degradation of mechanical properties. Therefore, the addition range of Zn in the present invention is limited to 3 ~ 10wt.%, Preferably 5.0 ~ 7.0wt.%.

Manganese (Mn): 0.25-3.0 wt.%

Mn is 2.2wt.% At 650 ° C, the maximum solubility of Mg in the Mg matrix, so that the solid solution rapidly decreases due to the temperature drop, and is present in the form of α-Mn in the Mg matrix. In general, commercially available Mg alloys are known to contribute to the improvement of corrosion resistance by adding 0.1 wt.% Or more of Mn, and when added for purposes other than corrosion resistance, for example, for reinforcement, the alloy system is added at 0.25 to 2.0 wt.% This contributes to the strength improvement of the alloy. In particular, in the present invention, by adding Mn, the precipitated phase of the binary Mg-Zn alloy is refined during aging treatment after solution treatment of the workpiece, thereby improving the strength and the elongation. Therefore, when Mn was added for the purpose of strengthening the alloy in the present invention, the minimum amount was set to 0.25 wt.%. On the other hand, considering the maximum solubility of Mn and the manufacturing process of the alloy, the addition of a large amount of Mn is difficult to add by the general dissolution process, and in the case of Mn added more than 3.0wt.%, Most are present in the form of α-Mn in the matrix. It is not preferable in terms of manufacturing cost since the excess amount is irrelevant to the improvement of the properties of the alloy at all. As a result, the addition range of Mn in the present invention is limited to 0.25 ~ 3.0wt.%, Preferably 0.75 ~ 2.0wt.%.

Aluminum (Al): 1-6 wt.%

Al has a maximum solid solubility of about 12 wt.% At 437 ° C., and Mg-Al binary alloy is known to form Mg ₁₇ Al ₁₂ precipitated phase upon thermal treatment. In the present invention, Al was not added for the purpose of forming the precipitated phase, but was added for the improvement of the Mg-Zn related acicular precipitated phase which is the main reinforcement phase in the Mg-Zn-Mn ternary alloy. Therefore, the addition amount was determined in the range not forming Mg-Al-based precipitated phase in consideration of the heat treatment section such as the aging temperature and the content of the main alloy element Zn added. That is, in the aging temperature section, the Al solid solution in the Mg matrix represents approximately 1 wt.%, And the lower Al addition limit was set to 1.0 wt.%. As described above, Al is the Zn content in the Zn content limited in the present invention. The upper limit of addition was limited to 6.0 wt.% In order to suppress the formation of Mg-Al-based precipitated phase in excess. On the other hand, when Al is added more than Zn, the Mg-Al-based precipitated phase, that is, the Mg ₁₇ Al ₁₂ phase is very likely to precipitate. The precipitated phase is coarsened at the grain boundaries or precipitates within the grain boundaries depending on the heat treatment temperature. The precipitated phases are very fragile in strength and provide a fracture path when the material is destroyed to cause a decrease in strength. Therefore, it is preferable that Al content is below Zn content. According to the present invention, the addition of Al showed an effect of finely acicular precipitated phase without solution treatment. The yield strength was slightly decreased, but a significant improvement in tensile strength and elongation was obtained. Yield strength decreased and tensile strength tended to increase.

Silicon (Si): 0.1-4.0 wt.%

Si has little solid solution in the Mg matrix, and forms Mg ₂ Si phase when added as an alloying element. These compounds can obtain a dispersion strengthening effect by adjusting the shape and size of the workpiece during the manufacturing process and the heat treatment process. Also in the present invention, the dispersion strengthening effect can be obtained by adding Si to the Mg-Zn-Al-Mn employee alloy. However, when the Si content is less than 0.1 wt.%, The effect of Si addition cannot be expected, and when the Si content exceeds 4.0 wt.%, The elongation is reduced due to the formation of coarse Mg ₂ Si. Therefore, the addition range of Si in the present invention is limited to 0.1 ~ 4.0wt.%, Preferably 1.5 ~ 3.0wt.%.

Calcium (Ca): 0.1-2.0 wt.%

In the case of Si-added alloys, the addition of Ca can reduce the grain size of the alloy and improve the shape of the Mg ₂ Si phase. To this end, Ca was added to the Mg-Zn-Al-Mn alloy added with Si in the present invention. If the Ca content is less than 0.1 wt.%, The improvement effect of the Mg ₂ Si phase cannot be expected. In addition, considering that the maximum solubility of Ca in the Mg matrix is 1.34 wt.% At 516 ° C, when the Ca content exceeds 2.0 wt.%, The formation of the Mg ₂ Ca precipitated phase at the grain boundary, in addition to the improvement effect of the Mg ₂ Si phase, This will cause a decrease in strength. In the present invention, the preferred range of Ca content that can particularly effectively control the size of the Mg ₂ Si phase in the Mg-Zn-Al-Mn alloy was 0.3 to 1.0 wt.%. As a result, the effect of improving the strength and elongation was obtained. Therefore, the addition range of Ca in the present invention is limited to 0.1 ~ 2.0wt.%, Preferably 0.3 ~ 1.0wt.%.

In addition, the main impurities in the Mg alloy are mainly limited by adversely affecting the corrosion resistance of the alloy rather than deterioration of mechanical properties. Commonly known impurities include Fe, Ni, and Cu. In particular, in the case of Cu, in the Mg-Al-based alloy which is generally used, the corrosion resistance is adversely affected, but in the Mg-Zn-based alloy according to the present invention, It doesn't affect anything. Therefore, impurities that can be mainly limited in the Mg-Zn-based alloys include Fe and Ni, and generally the allowance is limited to a maximum of 0.005 wt.% From a conservative point of view. Here, in the case of Fe, the adverse effects can be excluded by the addition of Mn, by lowering the content ratio Fe / Mn value to 0.032 or less in the Mg alloy can minimize the adverse effects of Fe. In the present invention, since Mn is basically added, if the above conservative tolerance is observed, the adverse effect of Fe on the corrosion resistance can be effectively excluded. On the other hand, the content of the other impurities including the Fe, Ni and Cu is generally limited to a maximum of 0.3wt.% In the Mg alloy based on the total amount.

One of the most important features of the manufacturing method according to the present invention using the solvent-free dissolution method together with the specific composition as described above is Mn, which has a very high melting point and cannot be directly dissolved in magnesium molten metal at a general alloy manufacturing process temperature. It is added in the form of Zn-Mn master alloy. Early in the development of magnesium alloys, Mn was added in the form of flux. That is, magnesium molten metal has a risk of ignition when the surface is exposed to air, so that a material that serves to block the air is used. Mn is contained in the molten material to diffuse the Mn into the molten metal by diffusion. It was added by infiltration. However, this method has a lot of difficulties in the production of the target alloy due to the constraint of the addition amount and difficult to control the impurity content. On the other hand, after dissolving the solvent-free dissolving method of applying a protective gas to the surface of the molten magnesium alloy in general, Mn was mainly added in the form of a Mg-Mn mother alloy. That is, the magnesium molten metal is heated to a high temperature at which Mn can be directly dissolved in an inert gas atmosphere so that the molten magnesium does not ignite, and an Mg-Mn mother alloy is separately prepared, and an alloy is prepared by the solventless dissolution method using the mother alloy. At this time, Mn is added to the target amount. However, the method using the Mg-Mn master alloy requires expensive separate dissolution equipment that can control the atmosphere in the manufacture of the master alloy, and also has a large amount of magnesium loss in the production of the master alloy due to the high vapor pressure of magnesium at a high temperature. It will raise the unit price. Accordingly, the present inventors have found that when the solvent-free dissolution method is adopted, Mn can be added by adding to the molten magnesium in the form of a low melting point Zn-Mn mother alloy. This makes it possible to eliminate the possibility of ignition of magnesium molten metal and a large amount of material loss, thereby making it possible to manufacture magnesium alloys economically and to easily control impurities.

The melting point of magnesium is Zn-Mn master alloy in consideration of securing sufficient fluidity of molten magnesium at a temperature of about 650 ℃ or at least 670 ℃ and increasing the risk of ignition when the temperature of magnesium flux exceeds 720 ℃. The temperature range of the molten magnesium to be added is preferably limited to 670 ~ 720 ℃, the composition of the Zn-Mn master alloy that can be sufficiently dissolved in the temperature range is preferably limited to Zn-10 ~ 20wt.% Mn. Do. More preferably stirring should be done.

The addition of Si is carried out in the form of a Mg-Si master alloy. In this case, the preferable temperature range is preferably limited to 700 to 720 ° C in consideration of the high melting point of the master alloy and the suppression of ignition of the molten magnesium surface. In this case, stirring is more preferable.

The addition of the scarce Zn is carried out either alone or with Al, and optionally Ca can also be added. In this case, it is preferable to carry out after-cooling in order to reduce the loss of Zn with high vapor pressure at the alloy manufacturing temperature. The furnace cooling may be performed up to about 670 ° C. in view of the fluidity of the magnesium molten metal. More preferably, stirring is also required at the time of their addition.

After that, it is made of a cast material, in this case it is preferable to make the cast material after the furnace is cooled to 660 ℃ ~ 670 ℃ in order to suppress the heat of the Mg molten metal as much as possible.

In addition, it is preferable to perform a homogenization treatment to remove the segregation of the alloying elements and the resulting nonuniformity of the processed material that can occur during casting, for the alloy casting material produced by the above method. Homogenization treatment temperature and time are set to 6 ~ 12 hours at 340 ~ 410 ℃ based on Mg-Zn binary system diagram in consideration of conditions under which Zn, the main alloying element, can be sufficiently dissolved, and the thermal stability of the alloy itself. It became.

The cast material is processed into billets for extrusion and preheated at 150 to 400 ° C. for 30 minutes to 2 hours, followed by extrusion, rolling, forging, shaving and drawing in the same temperature range. It is preferable. In general, magnesium alloy is not able to secure the workability at room temperature, the high-temperature processing is performed to obtain a healthy workpiece, the processing temperature was set in a range that can ensure the integrity of the workpiece through the experiment.

It is preferable to perform the secondary aging treatment for the processed workpiece selectively at 70-100 degreeC for 24 to 96 hours, then immediately at 150-180 degreeC for 48 hours or more. This double aging maximizes the effect of precipitation phase contributing to reinforcement by performing primary aging at the temperature below GP zone solvus temperature of β ₁ 'phase, which is the main precipitation phase, in Mg-Zn alloy. To do so. Therefore, in the present invention, the first aging temperature section is limited to 70-100 ° C., which is a section slightly lower than the GP zone solvus temperature, which is generally known as β ₁ ', and the aging time is determined to a certain degree through GP zone formation through hardness measurement. The interval was set enough to expect the hardness improvement. On the other hand, in the present invention, the secondary aging temperature range is set to 150 ~ 180 ℃, it takes a lot of time to reach the maximum hardness at a temperature of less than 150 ℃ causing problems in the process, the maximum hardness at temperatures exceeding 180 ℃ Is reached quickly, but the maximum hardness decreases.

In addition, in the present invention, before the double aging treatment, in order to maximize the effect of the precipitated phase that contributes to the strength, the solution treatment is performed for 6 to 12 hours at 340 ~ 410 ℃, which is a temperature range in which the precipitated phase that may occur during the processing process exists as a solid solution It is more preferable to carry out. The temperature range and time were set with reference to the Mg-Zn binary system diagram in consideration of the conditions under which the precipitated phases due to the main alloying element Zn are sufficiently dissolved and the thermal stability of the alloy itself.

On the other hand, in this invention, it is more preferable to stretch before the said double aging treatment. In general, the range of stretching during processing heat treatment for strengthening the alloy is limited from the elastic region to the region below the maximum strength by the strain test of the alloy before heat treatment. Therefore, in the present invention, the range was limited to 3 to 7% through a tensile test.

In accordance with the present invention, the elongation to strength can be improved as compared to existing commercially available alloys and also high strength magnesium alloys can be produced at lower cost. That is, compared with the conventional commercial extrusion alloys shown in Table 1, compared with the ZC71 alloy showing the maximum strength level, it is possible to obtain a more than twice the elongation improvement while maintaining a similar strength level. In addition, high-strength can be obtained in a state in which an alloy element such as Zr, which is difficult to handle and expensive as a radioactive element such as Th, and an alloy element such as Zr, which is difficult to be added in the manufacturing process, is excluded. In addition, by adding Mn, which was previously added in the form of Mg-Mn mother alloy, in the form of Zn-Mn mother alloy, it is possible to reduce material loss in process and lower manufacturing costs. The significant working effects of the present invention will become more apparent from the following description based on the accompanying drawings and examples.

Best Mode for Carrying Out the Invention

Hereinafter, a high strength magnesium alloy according to the present invention will be described in more detail with reference to Examples.

Examples 1-11

In accordance with the present invention, an alloy casting having the nominal composition of Table 2 was prepared. A steel crucible was used, using a solvent-free dissolution method in which the CO ₂ + 0.5% SF ₆ mixed gas was applied to the molten surface at a flow rate of 2 L / min when dissolving the alloy. Mn was added at 700 ° C. in the form of a Zn-15 wt.% Mn master alloy, and then stirred for 5 minutes using a stirrer. After the furnace was cooled to 670 ° C., Zn, Zn, and Al were added together and stirred for 2 minutes. In the case of adding Si, Si was added in the form of Mg-10wt.% Si mother alloy and stirred at 720 ° C. for 10 minutes. After stirring, the furnace was cooled to 670 ° C, and Zn or Zn and Al or Ca were added thereto, followed by stirring for 2 minutes. Thereafter, the molten metal was annealed to 660 ° C., and then an alloy casting material was manufactured by directly immersing the entire crucible in water at room temperature.

For the purpose of controlling the microstructure of the alloy casting material prepared as described above, after homogenizing the alloy casting material for 12 hours at 340 ~ 410 ℃ to prepare a billet, preheated for 30 minutes at 320 ~ 360 ℃ after the container of the extrusion device The die was set at 320 to 360 ° C. and then extruded to form an alloy extrusion.

Figures 1a, 1b and 1c is a photograph of the surface microstructure of the Z6, ZM61 and ZAM621 alloy extruded material made as described above and Figures 1d and 1e is a microstructure of the ZAM631 + 2.5Si and ZAM631 + 2.5Si + 0.4Ca alloy extruded material thus produced It is a photograph. Referring to the drawings, the grain size of the existing magnesium alloy Z6 alloy (grain size) was about 22㎛, the grain size of the ZM61 alloy and ZAM621 alloy according to the present invention was about 12㎛ and 8㎛, respectively. In addition, the grain sizes of the ZAM631 + 2.5Si alloy and the ZAM631 + 2.5Si + 0.4Ca alloy were about 12 µm and 6 µm, respectively.

Therefore, when 1wt.% Mn is added to the existing Mg-Zn alloy, the grain size of the microstructure decreases by about 1/2, and 1wt.% Mn and 2wt.Al are added to the existing Mg-Zn alloy. The grain size decreased by about one third. When 0.4 wt.% Of Ca was added to ZAM631 + 2.5Si, the grain size was 6 µm, which is about 2/3 of ZAM621. As a result, it can be seen that the grain size of the alloy according to the present invention is reduced by about 2/3 in the case of Mn and Al addition and about 3/4 in the case of the addition of Si and Ca.

2 is a graph showing the aging hardening behavior during the aging treatment of the Mg-Zn binary alloy extruded material Z6. Alloy aging material Z6 was subjected to single and double aging treatments for the purpose of maximizing hardness and strength improvement. That is, the Z6 alloy extruded material was aged at 90 ° C. for 48 hours as primary aging, and then treated with varying time from 180 ° C. to 384 hours as secondary aging. The aging hardening behavior is shown in FIG. 2. Referring to the drawings, it can be seen that the maximum hardness of the alloy is increased and the time to reach the maximum hardness is shortened in the dual aging treatment.

Figure 3 shows the aging hardening behavior of the Mg-Zn-based alloy extruded material (ZM61, ZAM621) to which Mn is added or Al and Mn added in accordance with the present invention is a double of the Mg-Zn binary alloy extruded material (Z6) It is a graph compared with the aging hardening behavior at the time of aging treatment. Aging of Z6, ZM61, and ZAM621 alloys was carried out for 48 hours at 70 ° C. as the primary aging in an extruded state, followed by aging treatment at different temperatures from 150 ° C. to 384 hours as the secondary aging. The aging hardening behavior is shown in FIG. 3. Referring to the drawing, ZAM621 alloy having 2 wt.% Al and 1 wt.% Mn added to Z6 alloy is about 35% higher than the Z6 alloy. It can be seen that there is approximately 20% hardness improvement in the state. However, ZM61 alloy containing only Mn in Z6 alloy had high hardness in the extruded state, but hardening did not occur as aging progressed, and the maximum hardness was lower than that of Z6 alloy.

Figure 4 shows the aging hardening behavior during double aging treatment after solution treatment of Mg-Zn-based alloy extruded materials (ZM61, ZAM621) to which Mn is added or Al and Mn is added, according to the present invention, Mg-Zn binary alloy It is the graph shown compared with the age hardening behavior when the extruded material Z6 was processed on the same conditions. Z6, ZM61, and ZAM621 alloy extruded materials were first subjected to a solution treatment for 12 hours while maintaining a temperature of 380 to 410 캜, followed by a double aging treatment. The age hardening behavior is shown in FIG. 4. Referring to the drawing, the overall hardness was improved during the age hardening process by adding Mn or Al and Mn to the Z6 alloy. A hardness improvement of more than% could be obtained. In particular, the aging hardening behavior of ZM61 alloy containing only Mn showed a significant difference from the aging hardening behavior under heat treatment conditions without the solution treatment before the double aging treatment. And Mn appeared similar to ZAM621 alloy added simultaneously.

5 is a double aging treatment of Mg-Zn-based alloy extruded material (ZAM631 + 2.5Si, ZAM631 + 2.5Si + 0.4Ca) to which Al, Mn and Si is added or Al, Mn, Si and Ca are added according to the present invention. A graph showing the aging hardening behavior of. After the aging was carried out at 70 ° C. for 48 hours as the primary aging in the extruded state, it was subjected to aging treatment at different temperatures at 150 ° C. as the secondary aging. Referring to Figures 3 and 5, by simultaneously adding 2.5 wt.% Si and 0.4 wt.% Ca to the ZAM631 alloy, the maximum hardness is reached with a hardness improvement of approximately 12% at maximum double aging at 150 ° C. It can be seen that the time was significantly reduced.

FIG. 6 shows tensile properties at room temperature of Mg-Zn alloy extruded materials ZM61 and ZAM621 added with Mn or Al and Mn according to the present invention. Referring to the drawings, it can be seen that the yield strength and the maximum tensile strength in the extruded state were significantly increased by adding Mn or Al and Mn to the Z6 alloy. In addition, an excellent elongation of 25% or more was obtained by processing the alloy using extrusion, and specific results thereof are shown in Table 3 above.

7 is a tensile at room temperature of the Mg-Zn-based alloy extruded material (ZAM631 + 2.5Si, ZAM631 + 2.5Si + 0.4Ca) to which Al, Mn and Si is added or Al, Mn, Si and Ca are added according to the present invention. It is a graph showing the property. Referring to the drawings, it can be seen that the maximum tensile strength in the extrusion state was increased by adding 2.5 wt.% Si and 0.4 wt.% Ca to the ZAM631 agreement. In addition, an elongation of 16% or more was obtained by processing the alloy using extrusion. The specific results are shown in Table 3 above.

8 is a cross-sectional view of the tensile properties of Mg-Zn binary alloy extruded material (Z6) at room temperature during the double aging treatment of Mg-Zn-based alloy extruded materials (ZM61, ZAM621) to which Mn is added or Al and Mn added according to the present invention This graph is compared with the tensile properties at room temperature during the double aging treatment. Tensile properties of Z6, ZM61 and ZAM621 alloy extruded materials were aged at 70 ° C. for 48 hours as primary aging, and then aged at 150 ° C. for 96 hours as secondary aging. Referring to the drawing, the yield strength and the maximum tensile strength of the alloy were increased and the elongation was similar due to the double aging compared to the tensile curve without the double aging treatment. Tensile properties of the alloys shown in the tensile test after the double aging treatment are shown in Table 4 above.

9 is a double aging treatment of Mg-Zn-based alloy extruded material (ZAM631 + 2.5Si, ZAM631 + 2.5Si + 0.4Ca) to which Al, Mn and Si is added or Al, Mn, Si and Ca are added according to the present invention. It is a graph showing the tensile properties at room temperature. Tensile properties of the alloy extruded material were aged at 70 ° C. for 48 hours as the primary age, and then aged at 150 ° C. for 24 hours as the secondary age. The tensile properties are shown in FIG. 9. Referring to the drawings, the extruded material (ZAM631 + 2.5Si, ZAM631 + 2.5Si + 0.4Ca) containing 2.5wt.% Si, 2.5wt.% Si and 0.4wt.% Ca compared to the alloy without double aging treatment Remarkably large yield strength and maximum tensile strength increase effect can be obtained. The specific results are shown in Table 4 above.

Referring to Table 4, the tensile property of the alloy (ZM61) in which Mn is added to the Z6 alloy is slightly increased compared to the Z6 alloy by double aging treatment. In addition, the alloy (ZAM621) in which Al and Mn were simultaneously added to the Z6 alloy was superior to the Z6 alloy due to the double aging treatment. In particular, the maximum tensile strength was significantly increased. All the alloys showed good elongation even after the double aging treatment.

10 is a Mg-Zn binary alloy of the Mg-Zn-based alloy extruded material (ZM61, ZAM621) to which Mn is added or Al and Mn added in solution according to the present invention and then the tensile properties at room temperature during the double aging treatment It is the graph shown compared with the tensile property at normal temperature when the extruded material Z6 is processed on the same conditions. The Z6, ZM61, and ZAM621 alloy extruded materials were subjected to solution treatment at 380 ~ 410 ° C for 12 hours, and then aged at 70 ° C for 48 hours as primary aging, and then aged at 150 ° C for 96 hours as secondary aging. Tensile properties are shown in FIG. Referring to the drawings, in the case of solution treatment before the double aging treatment, the yield strength and the maximum tensile strength of the ZM61 alloy increased significantly, and the elongation was similar to that of the Z6 alloy. In addition, the yield strength of ZAM621 alloy was lower than that of ZM61, but the maximum tensile strength was similar. In particular, the elongation was significantly increased. In the case of double aging after the solution treatment, the tensile properties of the alloys are shown in Table 5 below.

On the other hand, when comparing the alloy extruded material with the double aging treatment and the double aging treatment after the solution treatment, the strength of the ZM61 alloy was significantly increased by the solution treatment before the double aging treatment, but Z6 and ZAM621 In the case of alloys, only a slight increase in strength can be obtained. Elongation was significantly reduced in Z6 and ZM61 alloys by solution treatment before double aging, but similar levels were observed in ZAM621 alloys.

11 is a Mg-Zn binary alloy of the Mg-Zn-based alloy extruded material (ZM61, ZAM621) to which Mn is added or Al and Mn added (5% stretch) after stretching 5% The graph shows the comparison with the tensile property at normal temperature when the extruded material Z6 is processed on the same conditions. After 5% stretching of Z6, ZM61 and ZAM621 alloy extruded material, aging was performed at 70 ° C. for 48 hours as the primary aging, and then aged at 150 ° C. for 96 hours as the secondary aging. As a result, the tensile properties thereof are shown in FIG. 11. Referring to the drawings, in the case of ZAM621 alloy, the strength level was improved as compared with the case where no stretching was performed, and the elongation was 20% or more. In addition, it was possible to improve the overall strength of the alloy by stretching the extruded material before double aging. Particularly, in the case of ZAM621 alloy, the elongation was greatly increased while showing the strength level comparable to that of the solution-treated ZM61 alloy by performing only the stretching without the solution treatment before the double aging treatment. In the case of double aging treatment after the alloy extruded material was stretched 5%, the room temperature tensile properties of each alloy are shown in Table 6 below.

According to the present invention, Mn is added to the Mg-Zn binary alloy, or Al and Mn are added together, and Si or Si and Ca are added together to form a workpiece having reduced grain size, and heat treatment and heat treatment are performed at room temperature. It is possible to provide a magnesium alloy with improved hardness and strength and an improved elongation.

Claims (17)

As Mg-Zn-Mn-based alloy, A high-strength magnesium alloy containing 3-10 wt.% Zn for forming a precipitated phase in an alloy, and 0.25-3.0 wt.% Mn for strengthening the precipitated phase, the balance being inevitable impurities and Mg. The high strength magnesium alloy according to claim 1, further comprising 1-6 wt.% Al. The high strength magnesium alloy according to claim 2, further comprising 0.1 to 4.0 wt.% Si. 4. The high strength magnesium alloy according to claim 3, further comprising 0.1 to 2.0 wt.% Of Ca. 3. The high strength magnesium alloy of claim 2, wherein the Al content is less than or equal to the Zn content. delete delete The high strength magnesium alloy according to claim 3 or 4, wherein the Si content is 1.5 to 3.0 wt.%. The high strength magnesium alloy of claim 4, wherein the Ca content is 0.3-1.0 wt.%.  Prepare the molten magnesium in an inert gas atmosphere, Zn-10-20 wt.% Mn master alloy was added to the molten metal at 670-720 DEG C as a Mn component, Shortage of Zn is added to the molten metal, It is made of a casting material from the molten metal mixed with the Mn and Zn components, Homogeneous treatment of the casting material to produce a billet, Preheating the billet and then processing Method for producing a high strength magnesium alloy, characterized in that.  The method for producing a high strength magnesium alloy according to claim 10, further comprising Al or Ca.  The method for producing a high strength magnesium alloy according to claim 10, wherein the Mg-Si mother alloy is further added to the molten magnesium.  The method for producing a high strength magnesium alloy according to claim 10, wherein the addition of Zn is performed after the furnace is cooled to reduce the loss of Zn having a high vapor pressure at the alloy production temperature. The method of claim 10, wherein the cast material is homogeneous treatment for 6 to 12 hours at 340 ~ 410 ℃ to prepare a billet, the billet is a high-strength magnesium, characterized in that after preheating for 30 minutes to 2 hours at 150 ~ 400 ℃ Method of producing an alloy. The high-strength magnesium alloy according to claim 14, wherein the processed material is subjected to a primary aging treatment at 70 to 100 ° C. for 24 to 96 hours, followed by a secondary aging treatment at 150 to 180 ° C. for 48 hours or more. Manufacturing method. The method for producing a high strength magnesium alloy according to claim 15, wherein a solution treatment is performed for 6 to 12 hours at 340 to 410 캜 before the double aging treatment. The method of producing a high strength magnesium alloy according to claim 15, wherein 3 to 7% of stretching is performed before the double aging treatment.