KR20190098307A - Magnesium alloy having excellent strength and corrosion resistance and manufacturing method for the same - Google Patents

Abstract

The present invention relates to a magnesium alloy comprising calcium (Ca) and manganese (Mn) as a main component, and having a very low corrosion rate and high yield strength by using a multi directional forging process. According to the present invention, the magnesium alloy is characterized in that a magnesium comprising 0.2-1.5 wt% of Ca and 0.1-1.0 wt% of Mn is forged and processed in three or more axial directions having different directions from each other.

Description

Magnesium alloy with high strength and corrosion resistance and its manufacturing method {MAGNESIUM ALLOY HAVING EXCELLENT STRENGTH AND CORROSION RESISTANCE AND MANUFACTURING METHOD FOR THE SAME}

The present invention relates to a magnesium alloy with improved strength and corrosion resistance, more specifically, calcium (Ca) and manganese (Mn) as a main component, using a multi directional forging process, very low It relates to a magnesium alloy having a corrosion rate and high yield strength and a method of manufacturing the same.

Magnesium alloy has high specific strength and low density, and because of its degradability in vivo, it is considered to be a very suitable material for light body, electronic products, and biomaterials.

In particular, magnesium has a biodegradability with strength, processability, and ductility, attracting attention as the most suitable biodegradable material among metals, and recently, magnesium alloys have been used for some of the fixing screws for bonding bones. have.

On the other hand, the biodegradation rate of the biodegradable material should proceed in proportion to the regeneration rate of the tissue. If the degradation rate is too fast and the stability is lost before the damaged tissue is repaired, it may not perform the proper function of the medical device. If the decomposition rate is too slow, it causes problems such as complications. Therefore, control of the degradation rate of biodegradable magnesium is an essential factor in the design of medical devices using biodegradable magnesium.

By the way, magnesium has the advantage of having a certain strength and easy molding, but because of its low corrosion resistance in vivo, dissolving too quickly has become a major cause of preventing application to various medical devices.

1. Republic of Korea Patent Publication No. 2010-0053480 2. Korean Patent Publication No. 2010-0123428

The present invention is to solve the problem to provide a magnesium alloy with improved strength and corrosion resistance and its manufacturing method.

One aspect of the present invention for solving the above problems is a magnesium alloy forging a magnesium alloy containing Ca: 0.2 to 1.5% by weight and Mn: 0.1 to 1.0% by weight in three or more axial directions having different directions from each other To provide an alloy.

Another aspect of the present invention for solving the above problem is to prepare a billet by melting and casting a magnesium alloy containing Ca: 0.2 to 1.5% by weight and Mn: 0.1 to 1.0% by weight, the billet 200 to 500 Heat-treating at 0.5 ° C. for 0.5-48 hours, preheating the heat-treated billet to 200-600 ° C., extruding or processing the pre-heated billet at an extrusion ratio of 5: 1 to 20: 1, extrusion or processing It is to provide a method for producing a magnesium alloy, comprising the step of performing the forging step sequentially at least one magnesium alloy in three or more directions having different directions at 150 ~ 350 ℃.

The magnesium alloy according to the present invention not only has excellent strength, but also has improved corrosion resistance and can be suitably used particularly for biomaterials.

1 is a schematic diagram schematically showing a multi-directional forging process.
2 is a graph showing the tensile test results of the magnesium alloy prepared by the extrusion process, and the magnesium alloy prepared according to the embodiment of the present invention.
3 is a graph showing the corrosion rate of the magnesium alloy prepared by the extrusion process, and the magnesium alloy prepared according to an embodiment of the present invention.
4 is a graph showing the yield strength and corrosion resistance of a known magnesium alloy and the magnesium alloy prepared according to the embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings for the embodiment of the present invention will be described the configuration and operation.

In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In addition, when a part is said to "include" a certain component, this means that it may further include other components, except to exclude other components unless otherwise stated.

The magnesium alloy according to the present invention is characterized by forging a magnesium containing 0.2 to 1.5% by weight of Ca and 0.1 to 1.0% by weight of Mn in three or more axial directions having different directions from each other.

The reason for limiting the components of the magnesium alloy according to the present invention as follows is as follows.

Calcium (Ca)

Calcium (Ca) is an element that controls the texture and microstructure of the extruded material, and serves to improve the tensile strength and formability at room temperature, and was added by 0.2 to 1,5% by weight due to the limitation of solid solution. If the content of calcium (Ca) is less than 0.2% by weight, the effect of enhancing the grains is insufficient because the effect of grain refinement is insufficient, and when it is added in excess of 1.5% by weight, the yield strength is increased by forming various secondary products. Since corrosion resistance falls rapidly due to the occurrence of galvanic corrosion, it is preferable to add it within the said range, and more preferable range is 0.6 to 0.8 weight%.

Manganese (Mn)

Manganese (Mn) reacts with iron (Fe), which adversely affects the corrosion resistance of magnesium alloys, to form Fe-Mn compounds, which are filtered out by sludge to lower the iron (Fe) content of magnesium alloys. As an element that improves the corrosion resistance, less than 0.1% by weight of iron (Fe) removal effect is not sufficient, when added in excess of 1.0% by weight of the manganese phase is generated galvanic corrosion to lower the corrosion resistance It is preferable to add in the said range, and a more preferable range is 0.4 to 0.6 weight%.

Moreover, in order to improve strength and corrosion resistance, it is preferable that the average grain size of the magnesium alloy which concerns on this invention is 10 micrometers or less, More preferably, it is 2-4 micrometers.

In addition, the minimum tensile strength of the magnesium alloy according to the present invention is 200MPa or more, the corrosion rate is 1mm / y.

In addition, the magnesium alloy according to the invention is characterized in that it is produced through the following (1) ~ (5) process.

(1) preparing a billet by melting and casting a magnesium alloy containing Ca: 0.2 to 1.5% by weight and Mn: 0.1 to 1.0% by weight

(2) heat-treating the billet at 200-500 ° C. for 0.5-48 hours

(3) preheating the heat-treated billet to 200 ~ 600 ℃

(4) extruding or processing the preheated billet at an extrusion ratio of 5: 1 to 20: 1

(5) performing the forging process of the extruded magnesium alloy at least once in three or more directions having different directions from 150 ~ 350 ℃

The heat treatment of step (2) is for homogenizing the cast product, it is preferable to perform within the temperature and time range.

The preheating of step (3) is for facilitating extrusion, and it is preferable to carry out within the temperature and time range to perform a subsequent extrusion process.

Extrusion ratio of the extrusion process of step (4) is less than 5: 1 because it is difficult to increase the strength, it is because it is difficult to perform the process if more than 20: 1.

When the forging process is out of the temperature range, it is difficult to obtain a healthy forging product, and the forging process is advantageous in obtaining excellent strength and corrosion resistance in three or more different directions. In addition, in view of improving corrosion resistance, the forging process may be more preferably performed at 250 ~ 350 ℃.

In addition, the forging process may be preferably repeatedly performed one or more times in three directions, which are orthogonal to each other, in the x direction, the y direction, and the z direction.

EXAMPLE

Manufacture of Magnesium Alloy

A magnesium alloy containing 0.65 wt% Ca and 0.53 wt% Mn was dissolved using an electric furnace under a protective gas of CO ₂ and SF ₆ , followed by casting to prepare a billet.

For homogenization of the cast billet, it was heat treated at 340 ° C. for 12 hours and then cooled in air. After the heat treatment, the magnesium alloy was processed into cylindrical billets for extrusion.

The billet was preheated and extruded at 280 ° C. for 30 minutes immediately before extrusion. At this time, the extrusion ratio was 10: 1 and the size of the cross-sectional area was 22 × 22 mm. Rectangular cubes cut from the extruded material are 22 × 22 × 28 mm in size and are multi-directional (x-axis, y-axis, z with an Instron 5582 machine at an initial strain of 3 × 10 ⁻³ s ⁻¹ , as shown in FIG. 1. Axial three directions) forging, and the cumulative strain after 9 forgings was 2.7.

During multidirectional forging, the process temperatures were varied between 220 ° C (sample name, MDF220) and 300 ° C (sample name MDF300).

Specifically, in the multi-directional forging, as shown in FIG. 1, after performing the first forging (1st pass) in the z-axis direction, performing the second forging (2nd pass) in the y-axis direction, and performing the third in the z-axis direction. After performing the 3rd pass, the process was repeated two more times, for a total of nine forgings.

Samples obtained through the forging process were polished up to 1200 times using sandpaper to remove the deformed surface.

Tensile and Corrosion Test

In addition to the forging manufactured by the above process, for comparison, the sample (sample name, extrusion) extruded in parallel with the first direction of the multi-directional forging of magnesium alloy was analyzed.

Tensile testing of each sample was performed with an R & B universal machine, the results are shown in Table 1 below.

Sample name Average grain size
(Μm) Yield strength
(MPa) The tensile strength
(MPa) Elongation
(%) Extrusion 2.8 168.1 190.2 3.1 MDF220 2.0 202.7 241.0 12.3 MDF300 3.5 174.1 223.2 16.9

As shown in Table 1 and Figure 2, the yield strength increased rapidly as the average grain size decreased. In general, grain boundaries have an important effect of preventing dislocation propagation, and thus the highest yield strength and tensile strength were obtained in the MDF220 sample having the smallest grain size with the smallest grain size.

On the other hand, in the multi-directional forging process, the grain size increased as the process temperature increased from 220 ° C to 300 ° C, and thus yield strength tended to decrease somewhat.

In the case of two samples (MDF220, MDF300) prepared by the method according to the embodiment of the present invention, it can be seen that not only the tensile strength was improved but also the elongation was remarkably improved as compared with the simple extruded sample. Therefore, the magnesium alloy according to the present invention can be utilized in the field of biomaterials using high strength properties.

Each sample was cut to a thickness of 3 mm, and the corrosion behavior was analyzed using hydrogen generation amount and mass change. At this time, in order to reduce the surface roughness effect on corrosion, all exposed surfaces were polished using 400-2000 SiC sandpaper, and then ultrasonic cleaning was performed in ethanol.

Corrosion resistance was measured by corrosion rate of different materials through hydrogen generation, mass loss and polarization method.

First, the corrosion rate using the hydrogen generation amount was calculated from the following [Formula 1].

[Equation 1]

Where VH (mL) is the generated hydrogen volume, A (cm2) is the surface area of the sample, and t (d) is the immersion time)

Hydrogen generation of the sample after extrusion and multidirectional forging are shown in FIG. 3. As can be seen in Figure 3, the hydrogen generation amount and the corrosion rate can be seen that the magnesium alloy after the multi-directional forging process according to the present invention was the lowest.

Among the samples subjected to the multi-directional forging process, the MDF300 which performed the forging process at 300 ° C. showed a lower corrosion rate than the MDF220 which performed the forging process at 220 ° C.

4 is a graph showing the yield strength and corrosion resistance of a known magnesium alloy and the magnesium alloy prepared according to the embodiment of the present invention. As confirmed in FIG. 4, it is confirmed that the magnesium alloy according to the present invention exhibits a corrosion rate lower than that of most known magnesium alloys and even high purity magnesium, thereby obtaining very improved corrosion resistance.

From these results, it can be seen that the magnesium alloy according to the present invention can achieve considerable strength with a corrosion rate comparable to or lower than that of pure magnesium. Such magnesium alloys can be suitably used for biomaterials requiring high strength and corrosion resistance.

Claims (7)

A magnesium alloy processed by forging magnesium containing 0.2 to 1.5% by weight of Ca and 0.1 to 1.0% by weight of Mn in three or more axial directions having different directions. The method of claim 1,
The magnesium alloy contains 0.2% to 1.5% by weight of Ca and 0.1% to 1.0% by weight of Mn, and comprises magnesium and inevitable impurities. The method according to claim 1 or 2,
Magnesium alloy, the average grain size of the magnesium alloy is 5㎛ or less. The method according to claim 1 or 2,
The tensile strength of the magnesium alloy is 200MPa or more, the corrosion rate is less than 1mm / y, magnesium alloy. Preparing a billet by melting and casting a magnesium alloy including Ca: 0.2 to 1.5% by weight and Mn: 0.1 to 1.0% by weight;
Heat-treating the billet at 200-500 ° C. for 0.5-48 hours,
Preheating the heat-treated billet to 200 ~ 600 ℃,
Extruding the preheated billet at an extrusion ratio of 5: 1 to 20: 1,
Comprising the step of performing the forging process of the extruded magnesium alloy at least once in three or more directions having a different direction from 150 ~ 350 ℃,
Method for producing magnesium alloy. The method of claim 5,
The forging process is repeatedly performed one or more times in sequence in three directions, which are orthogonal to each other in the x direction, the y direction and the z direction. The method according to claim 5 or 6,
The forging process is carried out at 200 ~ 350 ℃, manufacturing method of magnesium alloy.

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