Mg alloy component

Abstract

To provide Mg alloy components with excellent mechanical properties (such as hardness and tensile strength). [Solution] The Mg alloy member of the present invention contains, by mass%, Mn: 0.50% to 1.50%, Zn: 0.05% to 0.50%, Ca: more than 1.00% to 2.50%, with the remainder being Mg and unavoidable impurities. The Mg alloy member of the present invention can be manufactured by a process comprising a casting step of obtaining a cast material by casting to a desired alloy composition, a heat treatment step of heat treatment of the cast material, and a strain application step of extrusion or forging.

Description

Technical Field

[0001] The present invention relates to a Mg (magnesium) alloy member.

Background Art

[0002] Mg has excellent specific strength although its specific gravity is lighter than, for example, aluminum. Therefore, by adding additive elements to Mg to alloy it, its practical application to various uses has been progressing. As Mg alloys, for example, Mg-Al-Zn based alloys in which mechanical properties and formability are improved by adding additive elements such as Al (aluminum) and Zn (zinc) are known.

[0003] Patent Document 1 discloses a Mg-based alloy sheet material that is an Mg alloy excellent in room temperature strength and contains at least one of four elements of Mn, Al, Ca, Li, and Zn, or in addition to these four elements, further contains two elements of Sn and / Bi, and the balance consists of Mg and inevitable components.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the problem was to realize further excellent mechanical properties. Therefore, an object of the present invention is to provide a Mg alloy member excellent in mechanical properties such as hardness.

Means for Solving the Problems

[0006] To achieve the aforementioned objectives, the present invention provides a magnesium alloy component characterized by containing, by mass%, Mn: 0.50% to 1.50%, Zn: 0.05% to 0.50%, Ca: more than 1.00% to 2.50%, with the remainder being Mg and unavoidable impurities.

[0007] It is desirable that the ignition temperature obtained by differential thermal analysis be 900°C or higher.

[0008] It is desirable that the Vickers hardness be 60 HV or higher, and the corrosion rate measured in accordance with JIS-H0541 be 10 mm / year or less.

[0009] According to the present invention, Mg alloy members with excellent mechanical properties can be obtained. In particular, because Al is not included, even if Ca is included, Al-Ca intermetallic compounds are not formed, so a decrease in ductility can be suppressed.

[0010] Furthermore, increasing the amount of calcium (Ca) can raise the ignition temperature and improve flame retardancy.

[0011] Furthermore, the high calcium content increases hardness and improves corrosion resistance. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide Mg alloy members with excellent mechanical properties (such as hardness and tensile strength). [Brief explanation of the drawing]

[0013] [Figure 1] A diagram showing the process for manufacturing Mg alloy components. [Figure 2] Stress-strain curve after high-temperature forging. [Modes for carrying out the invention]

[0014] The Mg alloy component of the present invention contains, by mass%, Mn: 0.50% to 1.50%, Zn: 0.05% to 0.50%, Ca: more than 1.00% to 2.50%, with the remainder being Mg and unavoidable impurities. It is desirable that the ignition temperature obtained by differential thermal analysis be 900°C or higher. It is desirable that the Vickers hardness be 60 HV or higher, and the corrosion rate measured in accordance with JIS-H0541 be 10 mm / year or less.

[0015] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a diagram showing the manufacturing process of an Mg alloy member according to the present invention. As shown in Figure 1, an Mg alloy member can be manufactured by a process comprising a casting process to obtain a cast material by casting to a desired alloy composition, a heat treatment process to heat-treat the cast material, and a strain application process to apply strain to the cast material. The strain application process is not particularly limited as long as it can apply strain to the cast material, such as by drawing processes such as extrusion or forging. In the following description, the concentration of each element can be measured by ICP.

[0016] First, the components are blended so that, in terms of mass percent (hereinafter the same), Mn: 0.50% to 1.50%, Zn: 0.05% to 0.50%, and Ca: more than 1.00% to 2.50%, with the remainder being Mg and unavoidable impurities.

[0017] Mn is added to enhance ductility. If the Mn content is less than 0.50%, sufficient ductility cannot be ensured. Conversely, if the Mn content exceeds 1.50%, it can lead to a decrease in ductility. Furthermore, it is preferable that the Mn content is in the range of 0.60% to 1.40%, and more preferably in the range of 1.00% to 1.40%. Zn is incorporated to improve strength. If the amount of Zn is less than 0.05%, sufficient strength cannot be ensured. Also, if the amount of Zn exceeds 0.50%, there is a problem of reduced ductility. Further, Zn is preferably contained in the range of 0.10% or more and 0.50% or less, and more preferably in the range of 0.13% or more and 0.40% or less. Ca is incorporated to improve hardness, flame retardancy, and corrosion resistance. If the amount of Ca is 1.00% or less, sufficient hardness etc. cannot be ensured, and the flame retardancy may also be inferior. Also, if the amount of Ca exceeds 2.50%, there is a problem of reduced ductility. Further, Ca is preferably contained in the range of more than 1.00% and 2.00% or less, and more preferably in the range of 1.40% or more and 2.00% or less.

[0018] That is, in the case of the Mg alloy member of the present embodiment, by setting the optimal composition of Mn, Zn, and Ca, the desired mechanical properties can be achieved without containing Al. Furthermore, the corrosion resistance and flame retardancy can be improved. By containing Mn in the range of 0.50% to 1.50% or less and Zn in the range of 0.05% to 0.50% or less, mechanical properties such as strength can be ensured. Since Al is not contained, the formation of the Al-Ca intermetallic compound is prevented, so that the reduction in ductility can be prevented, and the amount of Ca can be increased, so that the corrosion resistance and flame retardancy (increase in the ignition temperature) can also be improved.

[0019] These raw materials are melted and cast. Then, it is cooled and solidified. The cooling rate is adjusted so that the crystal grain size after casting is 100 μm or more (the dendrite width is about 10 μm). Although the appropriate cooling rate varies depending on the composition, the cooling rate is set so that the crystal grain size is 100 μm or more according to the composition.

[0020] For the obtained casting, a heat treatment process such as a solution treatment and / or an aging heat treatment is performed, and a strain application process is performed, whereby a processed material of the Mg alloy member can be obtained. For example, as the strain application process, an extruded material of the Mg alloy member can be obtained by performing warm extrusion. In this case, the conditions of the heat treatment process are preferably such that the casting is held at 450°C to 550°C for 0.5 to 24 hours. As the conditions of the warm extrusion performed in the strain application process, extrusion is preferably performed such that the extrusion ratio is 5 to 25 (i.e., the ratio A1 / A2 of the vertical cross-sectional area A2 after extrusion to the vertical cross-sectional area A1 cut perpendicular to the extrusion direction before extrusion is 5 to 25), the extrusion temperature is 200°C to 400°C, and the extrusion speed is 5 m / min to 50 m / min, and more preferably 10 m / min to 20 m / min.

[0021] Further, the Mg alloy member of the present embodiment may also be a forged material produced through forging in addition to extrusion as the strain application process. The forging temperature is not particularly limited, and cold, warm, and hot forging can be appropriately selected. In the case of ordinary castings and extruded materials, heat treatments such as solution treatment and aging treatment are performed. However, when forging is performed as the strain application process, forging that applies high-temperature compressive strain to the casting obtained in the casting process may be performed. In this case, the treatment temperature of the forging is a temperature at which recrystallization does not occur, and for example, it can be 200°C or higher and 350°C or lower, and more preferably 250°C or higher and 350°C or lower. Also, the strain rate is 1×10 -3 / s or less. Further, the compressive strain is preferably 0.2 or more and 1.0 or less, and more preferably 0.2 or more and 0.5 or less. If the compressive strain is small, the effect of the high-temperature compressive strain is small. Also, if the compressive strain is too large, cracks or the like will occur in the sample during forging, and a sound forged material cannot be obtained.

[0022] The Mg alloy member obtained as described above can obtain, for example, a 0.2% proof stress of 300 MPa or more and an elongation of 7% or more.

[0023] Furthermore, the above-mentioned Mg alloy material can achieve an ignition temperature of 900°C or higher. In other words, high flame retardancy can be obtained. This ignition temperature can be evaluated by differential thermal analysis. Such flame retardancy can be obtained particularly when the amount of Ca added exceeds 1.0%.

[0024] Furthermore, the above-mentioned Mg alloy member preferably has a Vickers hardness of 55 HV or higher, and more preferably 60 HV or higher. Such hardness can be achieved by having a Ca addition amount of more than 1.0% and by appropriately adjusting the ratio of Ca to Zn. For example, high hardness can be ensured by setting the ratio of Zn to Ca to 0.5 or less.

[0025] Furthermore, as a strain-inducing process, forged materials produced through forging may be simply referred to as "high-temperature forged materials" if they are produced through high-temperature forging (a process that applies high-temperature compressive strain). Also, extruded materials obtained through warm extrusion as a strain-inducing process may be simply referred to as "extruded materials."

[0026] Furthermore, the above-mentioned Mg alloy components can achieve corrosion resistance with a corrosion rate of 10 mm / year or less, as measured in accordance with JIS-H0541. This effect can be achieved by appropriately adjusting the amounts of Zn and Ca. [Examples]

[0027] As an example, extruded materials of a Mg alloy containing Mn, Zn, and Ca were prepared, and their elongation and tensile properties were evaluated.

[0028] Extruded material was produced by hot extrusion of a cast material. First, the alloy composition was adjusted to the desired composition, and the casting process involved melting the alloy in an iron crucible to obtain the cast material. This was followed by a heat treatment process to apply heat to the cast material, and a strain application process to extrude the solution-treated cast material. In the casting process, 99.9% pure Mn, 99.9% pure Zn, and Mg-Ca alloy were weighed to obtain the desired alloy composition of the cast material. The casting was performed in an argon atmosphere with a melting temperature of 700°C and a holding time of 5 minutes, using an iron mold with a diameter of 50 mm and a height of 200 mm. In the heat treatment process, the cast material was solution-treated at 500°C for 24 hours. In the strain application process, hot extrusion was performed under the conditions of an extrusion ratio of 25, an extrusion temperature of 300°C, and an extrusion speed of 0.2 mm / sec.

[0029] The elongation (%) and 0.2% proof stress (MPa) were evaluated using the obtained extruded material. The 0.2% proof stress was measured by cutting a round bar test specimen of L10mm × φ2.5mm from the extruded material, with an initial strain rate of 1 × 10⁻⁶. -3 The evaluation was performed using the / s parameter. The results are shown in Table 1.

[0030] [Table 1]

[0031] As shown in Table 1, it was confirmed that all alloys No. 1-1 to 1-5 had a 0.2% yield strength of 300 MPa or higher.

[0032] Next, high-temperature forged materials of Mg alloys containing Mn, Zn, and Ca were prepared using the following method, and their hardness, corrosion resistance, and ignition temperature were evaluated.

[0033] To achieve the desired alloy composition, 99.9% pure Mn, 99.9% pure Zn, and Mg-Ca alloy were weighed, placed in a crucible, and subjected to multiple argon purging cycles. The mixture was then held at 850°C for 1 minute under an argon atmosphere and cast into an iron mold. A high-temperature forged material was then produced by forging the obtained cast material to impart a high-temperature compressive strain of 0.5. The compression temperature during forging was set to 300°C.

[0034] Hardness was measured using a micro-Vickers hardness tester (test load: 200 gf). Corrosion resistance was evaluated by assessing the corrosion rate using a saltwater erosion test (compliant with JIS-H0541). The test temperature was room temperature. The ignition temperature (°C) was measured using TG-DTA. The measurement conditions were: sample mass: 10-20 mg, temperature range: room temperature to 1100°C, heating rate: 10°C / min, and measurement atmosphere: air.

[0035] Figure 2 shows the nominal stress-nominal strain curves in the forging test. The vertical axis represents nominal stress, and the horizontal axis represents nominal strain. Table 2 shows the compositions A to F and the forging conditions. The test temperature was 300°C in all cases.

[0036] [Table 2]

[0037] Strain rate is 1 × 10 -2 Except for A, which is 0.5 / s, applying a compressive strain of 0.5 did not cause a stress decrease, and after yielding, a monotonic increase in stress due to work hardening was observed. Table 3 shows the results of evaluating the hardness of cast material (before forging) and high-temperature forged material.

[0038] [Table 3]

[0039] As described above, by appropriately applying high-temperature compressive strain, high hardness can be achieved without solution treatment or other processes. The reason why high-temperature forged materials have higher hardness is presumed to be mainly due to the refinement of crystal grain size accompanying recrystallization.

[0040] Table 4 shows the evaluation results for hardness, corrosion resistance, and ignition temperature of high-temperature forged materials.

[0041] [Table 4]

[0042] As shown in Table 4, all alloy compositions No. 2-1 to 2-7 were confirmed to have a hardness (HV) of 60 HV or higher in the high-temperature forged material. Furthermore, it was confirmed that the high-temperature forged material was harder than the cast material. On the other hand, No. 2-8 to No. 2-10, which had a lower Ca content, had a hardness of less than 60 HV.

[0043] Regarding corrosion resistance, the corrosion rate (mm / year) was 15 mm / year or less for the alloy compositions shown in Nos. 2-1 to 2-6 and Nos. 2-8 to 2-10. On the other hand, No. 2-7 had slightly lower corrosion resistance due to the overall high amount of added elements. Note that a high amount of Zn may reduce corrosion resistance; therefore, when considering corrosion resistance, a low Zn content, for example less than 0.40%, and preferably 0.30% or less, is preferable.

[0044] Furthermore, when the ignition temperatures of No. 2-5, 2-6, and 2-7 were evaluated, all of them had ignition temperatures of 800°C or higher, and in particular, No. 2-5 and 2-6 had higher ignition temperatures than No. 2-7. Also, since No. 2-5 and 2-6 have a lower Zn content than No. 2-7, a lower Zn content is preferable when aiming for higher ignition temperatures.

[0045] Although embodiments of the present invention have been described above with reference to the attached drawings, the technical scope of the present invention is not limited to the embodiments described above. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these will naturally also fall within the technical scope of the present invention.

Claims

1. In mass percent, Mn: 0.50% or more and 1.50% or less, Zn: 0.05% or more and 0.50% or less, Ca: more than 1.00% and less than 2.50% A magnesium alloy member characterized by containing [a certain substance], with the remainder being magnesium and unavoidable impurities.

2. The Mg alloy member according to claim 1, characterized in that the ignition temperature obtained by differential thermal analysis is 900°C or higher.

3. The Mg alloy member according to claim 1, characterized in that it has a Vickers hardness of 60 HV or more and a corrosion rate of 10 mm / year or less as measured in accordance with JIS-H0541.

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