Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
  • C22C23/04—Alloys based on magnesium with zinc or cadmium as the next major constituent
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
  • B22D21/002—Castings of light metals
  • B22D21/007—Castings of light metals with low melting point, e.g. Al 659 degrees C, Mg 650 degrees C
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
  • C22C23/06—Alloys based on magnesium with a rare earth metal as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon

Definitions

• the present invention relates to a magnesium alloy material and a method for manufacturing the same and particularly to a magnesium alloy material having high mechanical strength and a method for manufacturing the same.
• magnesium alloy materials have the lowest density among alloys in practical use, lightweight and high strength and accordingly have been promoted for applications to chassis of electric products, wheels of automobiles, underbody parts, peripheral parts for engines, and the like.
• Patent Document 3 and Patent Document 4 are known to have a long period stacking ordered structure (LPO) in a structure and to have high mechanical characteristics.
• Patent Document 1 Japanese Patent Application Laid-Open (JP-A) No. 06-041701
• Patent Document 2 JP-A No. 2002-256370
• Patent Document 3 International Publication No. 2005/052204 Pamphlet
• Patent Document 4 International Publication No. 2005/052203 Pamphlet
• Non-Patent Document 1 Lecture Summary, the 108th Conference of Japan Institute of Light Metals, P42-45 (2005)
• the invention has been completed to provide a magnesium alloy material excellent in mechanical characteristics without using specific manufacturing facilities and processes and a method for manufacturing the same.
• the invention provides a magnesium alloy material having the following configuration. That is, the magnesium alloy material is an Mg-Zn-RE alloy containing, as an essential component, Zn and at least one of Gd, Tb, and Tm as RE, and balance of Mg and unavoidable impurities, and in the alloy structure of the Mg-Zn-RE alloy, stacking faults of a thickened two-atomic layer of Zn and RE are formed.
• the magnesium alloy material is an Mg-Zn-RE alloy containing, as an essential component, Zn and at least one of Gd, Tb, and Tm as RE, and balance of Mg and unavoidable impurities, and in the alloy structure of the Mg-Zn-RE alloy, stacking faults of a thickened two-atomic layer of Zn and RE are formed.
• the magnesium alloy material contains the stacking faults, so that the tensile strength, 0.2% proof strength, and elongation (elongation ratio) are improved as compared with those having a long period stacking ordered structure (LPO) .
• the alloy structure of the Mg-Zn-RE alloy contains recrystallized grains which have an average crystal grain diameter of 5 ⁇ m or less and a surface area ratio of 35% or more with respect to the above-mentioned alloy structure.
• the fine recrystallized grains in the metal structure improve the mechanical characteristics and the tensile strength, 0.2% proof strength, and elongation are improved.
• Zn is preferably in a component range of 0.5 to 3% by atom and RE is preferably in a component range of 1 to 5% by atom.
• a method for manufacturing the magnesium alloy material involves a casting step of forming a cast material by casting an Mg-Zn-RE alloy containing, as an essential component, Zn and at least one of Gd, Tb, and Tm as RE, and balance including Mg and unavoidable impurities, a solution treatment step of carrying out solution treatment for the cast material, and a heat treatment step of carrying out heat treatment in prescribed conditions for the cast material subjected to the solution treatment and the above-mentioned heat treatment step is carried out in a condition satisfying -14.58 [In (x) ] + 532.32 ⁇ y ⁇ -54.164 [In (x) ] + 674.05 and 0 ⁇ x ⁇ 2, wherein y denotes the heat treatment temperature (K) and x denotes the heat treatment time (h) .
• the precipitates of Mg and RE become in a solid-solution state by the solution treatment and further the heat treatment step is carried out in the heat treatment condition of the prescribed range, so that the stacking faults of the thickened two-atomic layer of Zn and RE can be formed in the alloy structure (mother phase) of the Mg-Zn-RE alloy and accordingly tensile strength, 0.2% proof strength and elongation can be improved.
• the method involves a casting step of forming a cast material by casting an Mg-Zn-RE alloy containing Zn as an essential component, at least one of Gd, Tb, and Tm as RE, and the rest including Mg and unavoidable impurities, a solution step of carrying out solution treatment for the above-mentioned cast material, a heat treatment step of carrying out heat treatment for the cast material subjected to the solution treatment in prescribed conditions, and a plasticity processing step of carrying out plastic processing of the above-mentioned heat-treated cast material and the above-mentioned heat treatment step is carried out in conditions satisfying -14.58[In(X)] + 532.32 ⁇ y ⁇ -54.164 [In (x) ] + 674.05 and 0 ⁇ x ⁇ 2, wherein y denotes the heat treatment temperature (K) and x denotes the heat treatment time (h) .
• K heat treatment temperature
• x denotes the heat treatment time (h)
• the precipitates of Mg and RE are in a solid-solution state by the solution treatment and further the heat treatment condition is adjusted to be in the prescribed range, so that the stacking faults of the thickened two-atomic layer of Zn and RE can be formed in the alloy structure (mother phase) of the Mg-Zn-RE alloy and accordingly the tensile strength, 0.2% proof strength and elongation can be improved. Further, execution of the plastic processing generates a large number of fine recrystallized grains in the alloy structure and the tensile strength, 0.2% proof strength and elongation can be improved more.
• a magnesium alloy material and its manufacturing method according to the invention have the following excellent effects.
• the magnesium alloy material contains stacking faults of the thickened two-atomic layer of Zn and RE in the alloy structure (mother phase) , the tensile strength, elongation, and 0.2% proof strength at a prescribed elongation ratio can remarkably be improved as compared with those having a long period stacking ordered structure. Further, if extrusion (plasticity) processing is carried out, since fine crystal grains are generated in the alloy structure, mechanical characteristics too high to be achieved generally can be obtained. Therefore, the magnesium alloy material can be used also, for example, automotive parts, particularly, parts such as pistons or the like which are required to have very severe mechanical characteristics .
• the magnesium alloy material Since the method for manufacturing the magnesium alloy material involves heat treatment in condition of the prescribed range after the solution treatment, the magnesium alloy material contains the stacking faults of the thickened two-atomic layer of Zn and RE in the alloy structure (mother phase) . Therefore, the magnesium alloy material provided with the tensile strength, elongation, and 0.2% proof strength at a prescribed elongation ratio improved as compared with those of a conventional material can be produced efficiently by common manufacturing facilities or processes.
• the heat treatment temperature and the heat treatment time are adjusted in a condition satisfying -14.58[ln(x)] + 532.32 ⁇ y ⁇ -54.164 [In (x) ] + 674.05 and 0 ⁇ x ⁇ 2, wherein y denotes the heat treatment temperature (K) and x denotes the heat treatment time (h) , so that the magnesium alloy material provided with improved tensile strength, elongation, and 0.2% proof strength at a prescribed elongation ratio in a widened range (as compared with those of a magnesium alloy material having the long period stacking ordered structure) can be manufactured.
• Figs. 1 (a) and 1 (b) are TEM photographs of the state that the stacking faults are formed in the metal structure of the magnesium alloy material of the invention observed by a low magnification transmission electron microscope.
• Fig. 2 is a TEM photograph of the stacking faults observed in the magnesium alloy material of the invention by a high-resolution transmission electron microscope.
• Fig. 3 is a STEM photograph of the stacking faults in the magnesium alloy material of the invention observed by a high-angle scattered annular dark field method.
• Fig. 4 is a TEM photograph of the state that the long period stacking ordered structure is formed in the metal structure of a conventional magnesium alloy material observed by a low magnification transmission electron microscope.
• Fig. 5 is a flow chart showing a method for manufacturing the magnesium alloy material of the invention.
• Fig. 6 is a graph schematically showing the relations of temperature and time in the solution treatment and heat treatment of the magnesium alloy material of the invention.
• Fig. 7 is a graph showing the region of stacking faults formed in the metal structure at the heat treatment temperature and heat treatment time in the condition of the invention.
• Figs. 8 (a) to 8 (c) are TEM photographs showing the state of the metal structure by heat treatment at 673K for 0.5 hours and 1 hour and at 523K for 2 hours for the magnesium alloy material of the invention.
• Figs. 9 (a) to 9(c) are TEM photographs showing the state of the metal structure by heat treatment at 723K for 2 hours, at 673K for 10 hours, and at 773K for 10 hours for the magnesium alloy material of the invention and the conventional magnesium alloy material.
• Fig. 10 is a TEM photograph for comparing the states of the metal structures by heat treatment at 673K for 0.5 hour, at 673K for 10 hours, and at 773K for 10 hours for the magnesium alloy material of the invention and the conventional magnesium alloy material.
• Figs. 11 (a) to 11 (c) are graphs showing the relation of 0.2% proof strength and elongation, the relation of tensile strength and elongation, and the relation of tensile strength and 0.2% proof strength before extrusion processing successively to the heat treatment step for the magnesium alloy material of the invention and the conventional magnesium alloy material.
• Figs. 12 (a) to 12 (c) are graphs showing the relation of 0.2% proof strength and elongation, the relation of tensile strength and elongation, and the relation of tensile strength and 0.2% proof strength in the case of executing extrusion processing successively to the heat treatment step for the magnesium alloy material of the invention and the conventional magnesium alloy material.
• Fig. 13 is a graph showing the correlation of the surface area ratio of the recrystallized grains in the metal structure and mechanical characteristics for the magnesium alloy material of the invention.
• Fig. 14 (a) is a TEM photograph showing the microstructure after the plastic processing in one example of conventional heat treatment conditions for the conventional magnesium alloy material
• Fig. 14 (b) is a TEM photograph showing the microstructure after the plastic processing in one example of heat treatment conditions of the invention for the magnesium alloy material of the invention.
• Fig. 15 (a) is a TEM photograph showing the microstructure after the plastic processing in the heat treatment at 773K for 10 hours for the conventional magnesium alloy material
• Fig. 15 (b) is a TEM photograph showing the microstructure after the plastic processing in heat treatment at 673K for 0.16 hour for the magnesium alloy material of the invention.
• Fig. 16 (a) is a TEM photograph showing the microstructure after the plastic processing in the heat treatment at 673K for 0.5 hour for the conventional magnesium alloy material and 16 (b) is a TEM photograph showing the microstructure after the plastic processing in heat treatment at 673K for 1 hour for the magnesium alloy material of the invention.
• Fig. 17 is a graph showing the relation of heat treatment temperature and the heat treatment time including the magnesium alloy material of the invention.
• Fig. 18 is a block chart showing the respective steps for evaluating mechanical characteristics in the case of explaining Examples of the invention.
• Figs . 19 (a) to 19 (d) are TEM photographs in the case a cast ingot to be used in Examples of the invention are subjected to heat treatment at the respective temperatures for respective times .
• Figs . 20 (a) to 20 (c) are TEM photographs in the case a cast ingot to be used in Examples of the invention are subjected to heat treatment at 673K for respective times.
• LPO long period stacking ordered structure
• Figs. 1 (a) and 1 (b) are TEM photographs of the state that the stacking faults are formed in the metal structure of a magnesium alloy material observed by a low magnification transmission electron microscope;
• Fig. 2 is a TEM photograph of the stacking faults observed in the magnesium alloy material by a high-resolution transmission electron microscope;
• Fig. 3 is a STEM photograph of the stacking faults in the magnesium alloy material observed by a high-angle scattered annular dark field method;
• Fig. 4 is a TEM photograph of the state that the long period stacking ordered structure is formed in the metal structure of a conventional magnesium alloy material observed by a low magnification transmission electron microscope.
• a magnesium alloy material 1 is an Mg-Zn-RE alloy containing Zn as an essential component, at least one of Gd, Tb, and Tm as RE (rare earth metals) , and the rest including Mg and unavoidable impurities, and herein an example containing Gd will be described. As shown in Figs. 1 to 3, the magnesium alloy material 1 contains stacking faults 2 of thickened two-atomic layer of Zn and RE in the alloy structure (mother phase) .
• the magnesium alloy material 1 contains stacking faults 2 including drawing type stacking faults in the two atomic layer where zinc (Zn) and rare earth (RE) elements are thicked (two atomic layer thickened) in the two atomic layer in the bottom face of the ⁇ -magnesium mother phase and the solute elements are thus thicked (the stacking faults will be described later) .
• stacking faults 2 including drawing type stacking faults in the two atomic layer where zinc (Zn) and rare earth (RE) elements are thicked (two atomic layer thickened) in the two atomic layer in the bottom face of the ⁇ -magnesium mother phase and the solute elements are thus thicked (the stacking faults will be described later) .
• the bottom face of the alloy structure means the alloy surface side in the mother phase, that is, both faces of the upper and lower side in the mother phase
• the observation direction is in parallel to the a-axis of the mother phase crystals and in the electron diffraction pattern, streaks derived from the stacking faults but not from the long period stacking ordered structure can be observed in the c-axis direction.
• the observation direction is in parallel to the a-axis of the mother phase crystals and it can be understood that the stacking faults are drawing type stacking faults.
• the observation direction is in parallel to the a-axis of the mother phase crystals and it can be understood that the solute atoms are thicked in the two atomic layer.
• numberless stacking faults 2 are shown in the form of thin lines as shown in Fig. 1.
• Fig. 3 thicking by two atoms can be understood and it can be understood that it is the stacking faults 2.
• Gd is contained as RE
• the two layer thick is thick by Zn atoms and Gd atoms.
• the precipitates of Mg 3 Gd are precipitated in the magnesium alloy material 1 (not-illustrated) .
• the precipitates of Mg 3 Gd form solid-solution (solution) by solution treatment and the stacking faults 2 are formed by this solid solution and heat treatment.
• the stacking faults 2 in the magnesium alloy material 1 are drawing type stacking faults 2 by thick by the RE atom and Zn atom in the two atomic layer and the stacking direction is not particularly determined.
• the long period stacking ordered structure 3 shown in Fig. 4 is formed by stacking the RE atom and Zn atom in the c-axial direction of the magnesium mother phase crystal in certain cycles and thus the long period stacking ordered structure 3 and the stacking faults 2 can clearly classified in terms of the stacking direction and the cyclic property.
• Zn is defined in a range of 0.5 to 3 at.% here.
• the stacking faults 2 are formed by solid solution and heat treatment of Mg 3 Gd (Mg 3 Zn 3 Tb2 or Mg 24 Tm 5 ) or the stacking faults 2 may be formed by solid solution and heat treatment of Mg 3 Gd (Mg 3 Zn 3 Tb 2 or Mg 2 -JTm 5 ) and at the same time the long period stacking ordered structure 3 may be mixed.
• a prescribed amount of RE consisting of at least Gd, Tb, and Tm in the magnesium alloy material 1 is required. If the total amount of at least one of Gd, Tb, and Tm in the magnesium alloy material 1 is less than 1 at.%, Mg 3 Gd (Mg 3 Zn 3 Tb2 or Mg 2 ⁇ m 5 ) and the stacking faults 2 cannot be formed and if the total amount exceeds 5 at.%, not only the not only the strength cannot be improved corresponding to the addition amount, but also Mg 3 Gd precipitated in grain boundaries is increased and the elongation is lowered. Accordingly, the total content of RE, at least one of Gd, Tb, and Tm, in the magnesium alloy material 1 is defined in a range of 1 to 5 at.%.
• the magnesium alloy material 1 has a composition on the basis of % by atom, defined by a composition formula Mgi O o-a-bZn a RE b (in the composition formula, 0.5 ⁇ a ⁇ 3; 1 ⁇ b ⁇ 5) .
• components other than the above-described components may be added within a range of unavoidable impurities in a range that the effect of the magnesium alloy of the invention is not affected and for example, Zr, which contributes to fineness, in an amount of 0.1 to 0.5 at.% may be added.
• Fig. 5 is a flow chart showing a method for manufacturing a magnesium alloy
• Fig. 6 is a graph schematically showing the relation of temperature and time of solution treatment and heat treatment of a magnesium alloy.
• a magnesium alloy material 1 is first cast in a casting step Sl .
• the magnesium alloy material 1 has a composition formula Mgi O o-a-bZn a RE b and contains Gd as RE.
• the cast material is subjected to solution treatment (solid solution formation of RE) in a solution treatment S2.
• the temperature of the solution treatment at that time is, as an example, 793K, and the solution treatment is carried out for 2 hours.
• a compound of Mg and Gd (Tb, Tm) formed by the casting is dissolved in a matrix and forms a solid solution by the solution treatment.
• the solution treatment is preferably carried out at 773K or higher for 2 hours or longer.
• the heat treatment step S3 of carrying out heat treatment for the cast material subjected to the solution treatment is carried out in prescribed conditions. Execution of the heat treatment step S3 forms the stacking faults 2 and at the same time precipitation of the long period stacking ordered structure 3 and precipitates of Mg 3 Gd (Mg 3 Zn 3 Tb 2 or Mg 24 Tm 5 ) and Mg 3 Zn 3 Gd 2 may sometimes coexist.
• the heat treatment step S3 is carried out in condition of the range satisfying -14.58[ln(x)] + 532.32 ⁇ y ⁇ -54.164[ln(x)] + 674.05 and 0 ⁇ x ⁇ 2, wherein y denotes the heat treatment temperature (K) and x denotes the heat treatment time (h) .
• Fig. 7 is a graph showing the regions of the stacking faults to be formed in the metal structure at the heat treatment temperature and heat treatment time
• Figs. 8 (a) to 8(c) are TEM photographs showing the state of the metal structure of the magnesium alloy material obtained by heat treatment at 673K for 0.5 hour and 1 hour and at 523K for 2 hours.
• FIG. 9 (a) to 9(c) are TEM photographs showing the state of the metal structure of the magnesium alloy material obtained by heat treatment at 723K for 2 hours, at 673K for 10 hours, and at 773K for 10 hours.
• Fig. 10 is a TEM photograph for comparing the states of the metal structures for magnesium alloy materials obtained by heat treatment at 673K for 0.5 hour, at 673K for 10 hours, and at 773K for 10 hours.
• Figs. 8, 9 and 10 are all photographed with the same scale and correspond to a part of the plot of Fig. 7.
• the range in which the stacking faults 2 are mainly formed is the " range of the above-mentioned prescribed heat treatment condition.
• the range of the heat treatment condition is defined by calculating the curve equation approximating the range surrounded with the solid line of Fig. 7, based on the calculated curve equation. That is, the range surrounded with the solid line is approximately the range of the heat treatment condition.
• formation of the long period stacking ordered structure 3 or precipitation of Mg 3 Gd precipitates may occur in combination with the stacking faults 2. It is made possible to entirely improve the tensile strength, 0.2% proof strength, and elongation for the magnesium alloy material 1 by forming mainly the stacking faults 2 (reference to Examples)
• stacking faults 2 are mainly formed in the case where the heat treatment temperature is 673K and the heat treatment time is set to be respectively 0.5 hour and 1 hour and the heat treatment temperature is 523K and the heat treatment time is set to be 2 hours. Further, as shown in Fig. 9, formation of the stacking faults 2 is not observed in the case where the heat treatment is carried out at a heat treatment temperature of 723K and for a heat treatment time of 2 hours, at 673K for 10 hours, and at 773K for 10 hours. Furthermore, as shown in Fig. 10, stacking faults are formed in the case where the heat treatment temperature is 673K and the heat treatment time is 0.5 hour, and no stacking fault is formed at 673K for 10 hours and at 773K for 10 hours.
• the cast product subjected to the heat treatment is next subjected to the plastic processing step S4 for plastic processing, based on the necessity.
• the plastic processing of the plastic processing step S4 may be extrusion processing or forging processing.
• the plastically processed plastic-processing product is provided with remarkably improved tensile strength, 0.2% proof strength, and elongation (elongation ratio) .
• Figs. 11 (a) to 11 (c) are graphs showing the relation of 0.2% proof strength and elongation, the relation of tensile strength and elongation, and the relation of tensile strength and 0.2% proof strength before extrusion processing successively to the heat treatment step for the magnesium alloy materials.
• 12 (a) to 12 (c) are graphs showing the relation of 0.2% proof strength and elongation, the relation of tensile strength and elongation, and the relation of tensile strength and 0.2% proof strength in the case of executing extrusion processing successively to the heat treatment step for magnesium alloy materials (extruded materials) .
• the magnesium alloy material 1 having the stacking faults 2 has stable data in the condition and is excellent in balance between the 0.2% proof strength and elongation, balance between the tensile strength and elongation, and balance between the relation of tensile strength and 0.2% proof strength.
• the mechanical properties are high as a whole .
• the magnesium alloy material 1 subj ected to the extrusion processing which is the plastic processing step S4, shows high tensile strength, 0.2% proof strength, and elongation values as compared with those which is not subjected to the extrusion processing.
• the magnesium alloy material 1 provides the formation of the stacking faults 2 in the case where the tensile strength, 0.2% proof strength, and elongation are improved in the heat treatment step S3 and the plastic processing step S4 and also in the case where precipitates of Mg 3 Gd (Mg 3 Zn 3 Tb2 or Mg 2 ⁇ m 5 ) and the long period stacking ordered structure 3 are precipitated in addition, if the stacking faults 2 are formed, the tensile strength, 0.2% proof strength, and elongation are improved.
• Mg 3 Gd Mg 3 Zn 3 Tb2 or Mg 2 ⁇ m 5
• Fig. 13 shows the correlation between the surface area ratio of the recrystallized grains in the metal structure and mechanical properties. As shown in Fig. 13, as the surface area ratio of the recrystallized grains 4 is higher, the 0.2% proof strength tends to be improved more. It is preferable to have the strength at 35% surface area ratio or higher. Further, the average crystal grain diameter can be measured by observation with an optical microscope and calculation by an average crystal grain surface area method standardized in ASTM.
• Fig. 14 (a) is a TEM photograph showing the microstructure after the plastic processing in one example of conventional heat treatment conditions for the conventional magnesium alloy material
• Fig. 14 (b) is a TEM photograph showing the microstructure after the plastic processing in one example of heat treatment conditions of the invention for the magnesium alloy material of the invention
• Fig. 15 (a) is a TEM photograph showing the microstructure after the plastic processing in the heat treatment at 773K for 10 hours and Fig.
• FIG. 16 (a) is a TEM photograph showing the microstructure after the plastic processing in the heat treatment at 673K for 0.5 hour and Fig. 16 (b) is a TEM photograph showing the microstructure after the plastic processing in heat treatment at 673K for 1 hour.
• the extrusion conditions of Figs. 15 and 16 are an extrusion ratio of 10 and an extrusion speed of 2.5 mm/sec. As shown in Figs. 14 to 16, in the heat treatment conditions of the invention, it can be understood that a large number of recrystallized grains
• the step may be carried out in accordance with the uses of the magnesium alloy material 1.
• the magnesium alloy material 1 after the plastic processing may be processed by cutting or the like into a prescribed shape to obtain a product.
• the method for manufacturing the magnesium alloy material 1 is described here as a method involving a series of steps from the casting step Sl to the plastic processing step S4, the series of steps may be only from the casting step Sl to the heat treatment step S3 and the plastic processing step S4 may be carried out in the purchaser side whose purchases the product.
• Fig. 17 is a graph showing the relation of heat treatment temperature and the heat treatment time.
• Fig. 18 is a block chart showing the respective steps for evaluating mechanical properties .
• Figs. 19 (a) tol9(d) are TEM photographs in the case where each cast ingot is subjected to heat treatment at the respective temperatures for the respective times.
• Figs. 12 (a) to 20 (c) are TEM photographs in the case where each cast ingot is subjected to heat treatment at a temperature of 673K for the respective times.
• An Mg-Zn-Gd alloy containing 1 at.% of Zn, 2 at.% of Gd, and the rest including Mg and unavoidable impurities as a magnesium alloy material was loaded to a melting furnace and melted by a flux refining. Successively, the thermally melted material was cast by a casting die as shown in Fig.
• Fig. 17 for Examples: that is, the heat treatment was carried out for short times of 0.16 hour, 0.33 hour, 0.5 hour, 1 hour, and 2 hours.
• Fig. 18 collectively shows solution treatment and heat treatment as heat treatment.
• a test was carried out for the magnesium alloy material in total of 24 types, as specimens, relevant to the above-mentioned respective temperatures and times .
• Fig. 19 (a) it was found that only stacking faults appeared in the matrix together with the Mg 3 Gd phase in the metal structure state in the case where merely solution treatment was carried out.
• the structure configuration was changed by heat treatment carried out thereafter and as shown in Fig. 19 (b), the metal structure state was found containing precipitates of stacking faults at a high density and Mg 3 Gd coexisting together in the case of a heat treatment at 773K for 0.16 hour.
• TEM photographs of microstructures of specimens of 673K * 0.16 hour, 673K * 0.5 hour and 673K x 1 hour are shown in Figs. 20 (a) to 20 (c) .
• Fig. 20 (a) to 20 (c) it was found that the stacking faults were precipitated at high density and Mg 3 Gd coexisting together in metal structures in the case of the heat treatment conditions.
• Tables 1 and 2 shows those treated in conditions within the scope of the invention defined as Examples 1 to 7 among the specimens shown in Fig. 17 and those treated in the representative conditions out of the scope of the invention defined as Comparative Examples 1 to 6 among the specimens shown in Table 17 together with the conditions of the respective steps, structure states, 0.2% proof strength, tensile strength, and elongation.
• Table 1 shows those before the plastic processing (S4) was carried out and Table 2 shows those after the plastic processing (S4) was carried out.
• magnesium alloy material As described above, it is made possible to use a magnesium alloy material as a material excellent in the mechanical properties even if the magnesium alloy material is an Mg-Zn-RE alloy by precipitating stacking faults.

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