HIGH-STRENGTH AND CORROSION-RESISTANT MAGNESIUM ALLOY MATERIAL AND METHOD FOR FABRICATING SAME

TECHNICAL FIELD

The present disclosure relates to a magnesium alloy material and method for fabricating the same, and in particular relates to a high strength and corrosion-resistant magnesium alloy material and method for fabricating the same.

BACKGROUND

Magnesium is one of the most abundant elements on the Earth. Commercially available pure magnesium can reach a purity of more than 99.8%. Magnesium has a low density, and is 35% lighter than aluminum and 78% lighter than steel. In the age of pursuit of lightweight, magnesium and its alloys have become increasingly attractive engineering materials.

Due to the unstable chemical properties of magnesium, pure magnesium cannot meet the requirements of most engineering applications. In order to improve the comprehensive properties of magnesium, many attempts have been made to add various alloying elements to magnesium for the production of magnesium alloy products. Through the addition of alloying elements, the mechanical properties of magnesium have been significantly improved.

However, despite the improvement in mechanical properties, alloying elements usually lead to an increase in corrosion rate of magnesium alloys. The main reasons are: first, magnesium is a metal with highly active chemical properties, and the addition of alloying elements usually leads to the formation of some second phases in its microstructure, resulting in the formation of microscopic cathodes, which accelerates the corrosion of the magnesium alloy matrix. Secondly, magnesium has a limited ability to support the cathode reaction (hydrogen evolution reaction, HER). Among all metal elements, magnesium has one of the lowest density of current exchange in hydrogen evolution reaction. Therefore, when there are other inerter metal alloying elements or impurities (such as copper, nickel, iron) present, the corrosion rate of magnesium alloy will be greatly accelerated.

In addition, unlike other alloy systems such as some aluminum alloys and stainless steel systems with good corrosion properties, magnesium alloys cannot be passivated by incorporating sufficient alloying elements to form a dense oxide layer. The basic reason is that many alloying elements have limited solid solubility in magnesium. Although some elements (such as lithium and yttrium) have certain solubility in magnesium, the addition of such elements cannot result in the formation of a more corrosion-resistant inert oxide film on the surface of the magnesium alloy. On the contrary, the addition of such elements usually results in the formation of an even more active oxide layer.

Based on above, the addition of alloying elements usually leads to an increase in the corrosion rate of magnesium. Although alloying elements can enhance mechanical properties, the negative effects thereof on corrosion properties limit the application of magnesium alloys.

In view of the foregoing, it is desired to obtain a magnesium alloy material that not only has high strength, but also has strong corrosion resistance.

SUMMARY

One of the objectives of the present disclosure is to provide a high strength and corrosion-resistant magnesium alloy material, which not only has high strength, but also has strong corrosion resistance.

In order to achieve the above objective, the present disclosure provides a high strength and corrosion-resistant magnesium alloy material, which comprises 0.01-1.2 wt % of Ge and 0.01-1.2 wt % of Zn.

In some embodiments of the present disclosure, the design principle of adding Ge and Zn is as follows.

Germanium (Ge): Pure germanium is a shiny, hard metal with a grey-white color, and belongs to the carbon group. The chemical properties of germanium are similar to that of tin and silicon of the same group. Germanium is insoluble in water, hydrochloric acid, or diluted caustic alkali solution, but is soluble in aqua regia, concentrated nitric acid or sulfuric acid. Germanium is amphoteric, and is therefore soluble in molten alkali, peroxide alkali, alkali metal nitrate or carbonate. Germanium is rather stable in the air and reacts with oxygen to form GeO₂at 700° C. or higher, and reacts with hydrogen at 1000° C. or higher. When germanium is added to magnesium, an Mg₂Ge intermetallic compound phase with column-shaped morphology is formed. This second phase can strengthen the magnesium alloy and affect the corrosion resistance of the magnesium alloy. When the content of Ge is low, the formed second phase can delay corrosion and strengthen the alloy, significantly improving the corrosion resistance and the strength of the alloy. However, due to the very low solubility of Ge in Mg, the addition of excess Ge may embrittle the alloy. When the Ge content exceeds 1.18%, coarse bulk Mg₂Ge second phase aggregates at the grain boundary and also occurs inside the grain and significantly deteriorates the corrosion resistance, mechanical strength and plasticity of the alloy. Therefore, in the high strength and corrosion-resistant magnesium alloy material according to the present disclosure, the percentage by weight of Ge is limited to 0.01-1.2 wt %. Preferably, the percentage by weight of Ge is 0.02-1.18 wt %.

Zinc (Zn): Zinc has both solid solution strengthening and aging strengthening effects. By adding an appropriate amount of Zn to the magnesium alloy, a variety of Mg—Zn phases can be formed, thereby improving the strength (such as yield strength and tensile strength), plasticity, ductility, melt fluidity, and casting performance of the magnesium alloy. However, if excessive amount of Zn is added, the fluidity of the Zn alloy will be greatly reduced and microporosity or hot cracking tend to occur in the magnesium alloy. Therefore, in the high strength and corrosion-resistant magnesium alloy material according to the present disclosure, the percentage by weight of Zn is limited to 0.01-1.2 wt %. Preferably, the percentage by weight of Zn is 0.02-1.2 wt %.

Further, the high strength and corrosion-resistant magnesium alloy material according to the present disclosure has a microstructure including an a-Mg phase and a column-shaped Mg₂Ge intermetallic compound phase.

Further, the high strength and corrosion-resistant magnesium alloy material according to the present disclosure has a yield strength of more than 260 MPa and a corrosion weight loss of less than 0.8 mg/(cm²day).

Another objective of the present disclosure is to provide a high strength and corrosion-resistant magnesium alloy material, which not only has high strength, but also has strong corrosion resistance.

In order to achieve the above objective, the present disclosure provides a high strength corrosion-resistant magnesium alloy material, comprising the following chemical elements in percentage by weight:

Ge: 0.01˜1.2%;
Zn: 0.01˜1.2%;

at least one of Mn, Ca, Zr, Sr, and Gd with a total weight percentage of ≤3%, wherein the percentage by weight of a single element is ≤0.8%; and

the balance of Mg and other inevitable impurities.

The high strength and corrosion-resistant magnesium alloy material according to the present disclosure comprises at least one of Mn, Ca, Zr, Sr, and Gd in addition to the aforementioned 0.01-1.2 wt % of Ge and 0.01-1.2 wt % of Zn. The main design principle of the material is as follows. Mn, Ca, Zr, Sr, and Gd can all affect the grain size and the strength and type of crystal texture in the microstructure of the alloy, and improve the ductility and formability of magnesium alloy deformable materials. However, when these alloying elements are excessive, a large amount of second phases will form and coarsen into large-sized second phases in the alloy, thereby reducing the plasticity and the strength of the alloy, and causing intensified microcell corrosion. In addition, as the solubility of calcium in magnesium is less than 1%, the addition of a large amount of calcium will embrittle the grain boundaries and reduce the corrosion resistance of magnesium alloys. Therefore, in the high strength and corrosion-resistant magnesium alloy material according to the present disclosure, the total percentage by weight of Mn, Ca, Zr, Sr, and Gd is limited to ≤3%, and the percentage by weight of a single element is limited to ≤0.8%. In addition, it should be noted that the design principles of adding Ge and Zn herein are the same as described above, and is not repeated herein.

Further, the high strength and corrosion-resistant magnesium alloy material according to the present disclosure further comprises at least one of Al, Cu, Si and Fe in a total weight percentage of ≤2%, wherein the percentage by weight of a single element is ≤0.5%, and the percentage by weight of a single element is ≤0.5%.

The high strength and corrosion-resistant magnesium alloy material according to the present disclosure further comprises at least one of Al, Cu, Si and Fe. The design principle is that Al, Cu, Si and Fe can all improve the ductility and formability of magnesium alloy sheets. However, when these alloying elements are excessive, a large amount of second phases will form and coarsen into large-sized second phases in the alloy, thereby reducing the plasticity and the strength of the alloy, and causing intensified microcell corrosion. Therefore, in the high strength and corrosion-resistant magnesium alloy material according to the present disclosure, the total percentage by weight of Al, Cu, Si and Fe is limited to ≤2%, and the percentage by weight of a single element is limited to ≤0.5%. Preferably, the total percentage by weight of Al, Cu, Si and Fe is ≤0.5%, and the percentage by weight of a single element is ≤0.05%. Within the above ranges, the plasticity and the mechanical properties of the magnesium alloy will be significantly improved, and the corrosion resistance will also be significantly enhanced.

Further, in the high strength and corrosion-resistant magnesium alloy material according to the present disclosure, the total amount of the inevitable impurities is less than 100 ppm.

In an embodiment of the present disclosure, in addition to the a-Mg phase and the column-shaped Mg₂Ge intermetallic compound phase, the microstructure of the high strength and corrosion-resistant magnesium alloy material further comprises other intermetallic compound phase formed by magnesium and other alloying elements (e.g. Mn, Ca, Zr, Sr, Gd, etc.) added in small amounts.

Correspondingly, another objective of the present disclosure is to provide a method for fabricating the above-mentioned high strength and corrosion-resistant magnesium alloy material. The high strength and corrosion-resistant magnesium alloy material fabricated by the method not only has high strength, but also has strong corrosion resistance.

In order to achieve the above objective, the present disclosure provides a method for fabricating the high strength and corrosion-resistant magnesium alloy material, comprising the steps of: smelting, solid solution heat treatment and extrusion, wherein in the extrusion step, the extrusion temperature is 180-350° C., the extrusion rate is 0.1-10 mm/s, and the extrusion ratio is 10:1-30:1. When the extrusion temperature is lower than 180° C., the mold wears a lot, the spindle is difficult to squeeze, and cracks appear on the surface of the profile. When the extrusion temperature is higher than 350° C., the grains become significantly larger, resulting in a significant decrease in strength. When the extrusion speed is too fast or the extrusion ratio is too high, the surface of the material cracks easily. When the extrusion speed is too slow or the extrusion ratio is too low, the production efficiency is too low.

In the fabricating method according to the present disclosure, during the smelting step, in some embodiments, the raw material is heated and melted in an SF₆protective atmosphere, and the molten magnesium alloy liquid is poured into a preheated mold to cool. The fabricating method according to the present disclosure allows the microstructure of the prepared high strength and corrosion-resistant magnesium alloy material to include an α-Mg phase, a Mg₂Ge intermetallic compound phase, and other intermetallic compound phases formed by other added alloying elements and magnesium.

Further, in the method for fabricating the high strength and corrosion-resistant magnesium alloy material according to the present disclosure, in the solid solution heat treatment step, the solid solution heat treatment temperature is 350-450° C., and the treatment time is 10-24 h.

Compared with the prior art, the high strength and corrosion-resistant magnesium alloy material and the fabricating method thereof according to the present disclosure have the following beneficial effects:

(1) The mechanical properties and corrosion resistance of the high strength and corrosion-resistant magnesium alloy material according to the disclosure is significantly improved by the addition of Zn, Ge and other alloying elements.

(2) The high strength and corrosion-resistant magnesium alloy material according to the present disclosure has a yield strength of more than 260 MPa and a corrosion weight loss of less than 0.8 mg/(cm²day).

(3) The method for fabricating the high strength and corrosion-resistant magnesium alloy material according to the present disclosure significantly improves the strength and corrosion resistance of the high strength and corrosion-resistant magnesium alloy material according to the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a scanning electron microscope image in backscattered electron (BSE) mode of Comparative Example 2.

FIG. 2 shows a scanning electron microscope image in backscattered electron (BSE) mode of the high strength and corrosion-resistant magnesium alloy material of Example 3.

FIG. 3 shows a scanning electron microscope image in backscattered electron (BSE) mode of the high strength and corrosion-resistant magnesium alloy material of Example 4.

FIG. 4 shows an energy spectrum analysis image of Comparative Example 2.

FIG. 5 shows an energy spectrum analysis image of the high strength and corrosion-resistant magnesium alloy material of Example 3.

FIG. 6 shows an energy spectrum analysis image of the high strength and corrosion-resistant magnesium alloy material of Example 4.

FIG. 7 shows an electron backscatter diffraction image of Comparative Example 2.

FIG. 8 shows an electron backscatter diffraction image of the high strength and corrosion-resistant magnesium alloy material of Example 3.

FIG. 9 shows an electron backscatter diffraction image of the high strength and corrosion-resistant magnesium alloy material of Example 4.

FIG. 10 shows the grain size distribution of the high strength and corrosion-resistant magnesium alloy materials of Examples 3 and 4, and Comparative Example 2.

FIG. 11 shows the potentiodynamic polarization measurement results of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Examples 1-2 in a 0.1 M sodium chloride solution.

FIG. 12 shows the cathodic polarization measurement results of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Examples 1-2.

FIG. 13 shows the results of weight loss and hydrogen evolution measurements of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4, Comparative Examples 1-2, and commercial AZ91 magnesium alloy.

FIG. 14 shows a scanning electron microscope image (at low magnification) in the secondary electron (SE) mode of Comparative Example 1 after immersion.

FIG. 15 shows a scanning electron microscope image (at high magnification) in the secondary electron (SE) mode of Comparative Example 1 after immersion.

FIG. 16 shows a scanning electron microscope image (at low magnification) in the secondary electron (SE) mode of Comparative Example 2 after immersion.

FIG. 17 shows a scanning electron microscope image (at high magnification) in the secondary electron (SE) mode of Comparative Example 2 after immersion.

FIG. 18 shows a scanning electron microscope image (at low magnification) in the secondary electron (SE) mode of the high strength and corrosion-resistant magnesium alloy material of Example 3 after immersion.

FIG. 19 shows a scanning electron microscope image (at high magnification) in the secondary electron (SE) mode of the high strength and corrosion-resistant magnesium alloy material of Example 3 after immersion.

FIG. 20 shows a scanning electron microscope image (at low magnification) in the secondary electron (SE) mode of the high strength and corrosion-resistant magnesium alloy material of Example 4 after immersion.

FIG. 21 shows a scanning electron microscope image (at high magnification) in the secondary electron (SE) mode of the high strength and corrosion-resistant magnesium alloy material of Example 4 after immersion.

FIG. 22 shows the cathode current density measurement results of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Examples 1-2 when the anode current density is 0.025-2.5 mA/cm².

FIG. 23 shows the cathode current density measurement results of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Examples 1-2 when the anode current density is 2-24 mA/cm².

FIG. 26 shows the microhardness measurement results of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Example 2.

FIG. 27 shows the engineering stress-strain curves of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Example 2.

DETAILED DESCRIPTION

The embodiments of the present invention will be further described below in conjunction with the drawings and examples. However, the explanation and description are not intended to unduly limit the technical solutions of the present invention.

Examples 1-17 and Comparative Examples 1-2

Table 1-1 and Table 1-2 list the percentage by weight (wt %) of each element in Examples 1-17 and Comparative Examples 1-2.

TABLE 1-1

(wt %, and the balance is Mg and other inevitable impurities)

Mn, Ca,

Zr, Sr,

and Gd

No.
Ge
Zn
Mn
Ca
Zr
Sr
Gd
in total

E1
0.30
1.00
0.01
0.05
—
—
—
0.06

E2
0.50
1.00
0.02
0.01
—
—
0.01
0.04

E3
0.30
1.00
0.02
0.8
—
—
—
0.82

E4
0.50
1.00
0.05
0.5
—
—
—
0.55

E5
0.03
1.2
0.02
—
0.5
—
0.8
1.32

E6
0.21
0.05
0.8
0.2
0.5
—
0.4
1.9

E7
0.75
0.2
0.8
0.7
0.7
—
0.8
3

E8
0.86
0.5
0.02
0.2
—
—
—
0.22

E9
0.27
0.08
0.8
0.5
0.01
—
—
1.31

E10
0.08
1.0
0.02
0.5
0.5
—
—
1.02

E11
0.05
1.2
0.02
0.5
0.5
0.1
—
1.12

E12
0.52
0.2
0.1
0.8
—
—
—
0.9

E13
0.02
0.4
0.02
0.8
—
—
0.4
1.22

E14
0.66
0.5
0.02
0.8
0.5
—
—
1.32

E15
1.16
0.04
0.02
0.8
0.8
0.8
—
2.42

E16
1.06
0.4
0.02
0.8
0.8
—
0.01
1.63

E17
1.18
0.02
0.02
0.8
0.5
0.01
0.4
1.73

CE1
0.002
0.005
0.01
0.001
—
—
—
0.011

CE2
0.002
1
0.02
0.001
—
—
—
0.021

TABLE 1-2

(wt %, and the balance is Mg and other inevitable impurities)

Al, Cu,
Inevitable

Si, Fe
impurities

in
in total
Micro-

No.
Al
Cu
Si
Fe
total
(ppm)
structure

E1
0.011
0.001
0.02
0.004
0.036
90
α-Mg, Mg₂Ge

and Mg₂Ca

phases

E2
0.011
0.001
0.02
0.004
0.036
80
α-Mg, Mg₂Ge

and Mg₂Ca

phases

E3
0.011
0.001
0.02
0.005
0.037
90
α-Mg, Mg₂Ge

and Mg₂Ca

phases

E4
0.011
0.001
0.02
0.004
0.036
90
α-Mg, Mg₂Ge

and Mg₂Ca

phases

E5
0.007
0.002
0.02
0.004
0.033
80
α-Mg, Mg₂Ge

and MgZr

phases

E6
0.010
0.002
0.02
0.004
0.036
90
α-Mg, Mg₂Ge,

Mg₂Ca

and MgZr

phases

E7
0.010
0.002
0.02
0.004
0.036
60
α-Mg, Mg₂Ge,

Mg₂Ca, MgGd

and MgZr

phases

E8
0.010
0.002
0.02
0.005
0.037
90
α-Mg, Mg₂Ge

and Mg₂Ca

phases

E9
0.007
0.002
0.02
0.004
0.033
60
α-Mg, Mg₂Ge

and Mg₂Ca

phases

E10
0.012
0.002
0.02
0.004
0.038
70
α-Mg, Mg₂Ge,

Mg₂Ca,

MgZr phases

E11
0.013
0.002
0.02
0.005
0.04
90
α-Mg, Mg₂Ge,

Mg₂Ca, MgZr

and Mg₂Sr

phases

E12
0.011
0.002
0.02
0.004
0.037
60
α-Mg, Mg₂Ge

and Mg₂Ca

phases, etc.

E13
0.010
0.002
0.02
0.005
0.037
90
α-Mg, Mg₂Ge,

Mg₂Ca,

and Mg₂Gd

phases, etc.

E14
0.015
0.002
0.02
0.004
0.041
60
α-Mg, Mg₂Ge,

MgZr, and

Mg₂Ca

phases, etc.

E15
0.013
0.002
0.02
0.004
0.039
70
α-Mg, Mg₂Ge,

Mg₂Ca and

Mg₂Sr phases

E16
0.013
0.002
0.02
0.005
0.04
90
α-Mg, Mg₂Ge

and Mg₂Ca

phases

E17
0.008
0.002
0.02
0.004
0.034
60
α-Mg, Mg₂Ge,

Mg₂Ca, Mg₂Gd

and Mg₂Sr phases

CE1
0.005
0.002
0.02
0.006
0.033
70
α-Mg phase

CE2
0.013
0.001
0.02
0.005
0.039
80
α-Mg, and MgZn

phases

The fabrication method of Examples 1-17 and Comparative Examples 1-2 is as follows (specific process parameters are listed in Table 2):

1) Mixing the raw materials uniformly in a steel crucible according to the ratio of elements in Table 1-1 and Table 1-2.

2) Smelting: heating and melting the mixture in SF₆protective atmosphere, and pouring the molten magnesium alloy liquid into a preheated mold to cool.

3) Solid solution heat treatment.

4) Extrusion.

TABLE 2

Specific process parameters in the fabrication method

of Examples 1-17 and Comparative Examples 1-2.

Extrusion

Solid solution treatment
Extrusion

Extrusion

Temperature
Time
Temperature
Extrusion
rate

No.
(° C.)
(h)
(° C.)
ratio
(mm/s)

E1
400
24
320
20:1
0.1

E2
400
24
340
26:1
0.9

E3
400
24
300
12:1
0.8

E4
400
24
330
16:1
0.6

E5
450
10
300
20:1
6

E6
400
10
200
25:1
8

E7
420
20
250
28:1
5

E8
400
18
2320
18:1
2

E9
420
12
250
16:1
1

E10
440
22
350
12:1
0.5

E11
380
20
320
15:1
0.2

E12
360
22
300
20:1
0.1

E13
370
20
340
18:1
10

E14
360
18
250
15:1
0.2

E15
390
16
190
20:1
0.6

E16
400
14
180
10:1
5.5

E17
420
12
350
30:1
8.0

CE1
400
24
300
12:1
0.8

CE2
400
24
330
16:1
0.6

Performance tests were conducted on the high strength and corrosion-resistant magnesium alloy materials of Examples 1-17 and Comparative Examples 1-2. Their yield strength and corrosion weight loss value in 0.1 M NaCl solution in 24 hours were measured.

The yield strength is measured by a tensile test in accordance with ASTM E-8 standard. The yield strength is the stress corresponding to 0.2% strain. The experimental platform is Instron 4505. The stretching rate is 10⁻³/s. The initial length of the extensometer is 10 mm. The length of the parallel part of the stretched sample is 22 mm.

The corrosion weight loss is measured according to ASTM-G1-03 standard. The sample is a cube with a side length of 5 cm. The surface of the sample is polished with a 1200 grid sandpaper, then the sample is immersed in a 0.1 M NaCl solution at 25° C. for 24 hours. After immersion, the sample surface is cleaned to remove the corrosion. The sample is weighed after drying. The results are listed in Table 3.

TABLE 3

Yield strength (MPa)
Corrosion weight loss (mg/cm²/day)

E1
285
0.72

E2
310
0.78

E3
288
0.60

E4
320
0.70

E5
328
0.69

E6
316
0.75

E7
320
0.73

E8
306
0.77

E9
270
0.78

E10
280
0.75

E11
265
0.63

E12
295
0.58

E13
279
0.68

E14
286
0.65

E15
275
0.60

E16
266
0.62

E17
265
0.72

CE1
70
10.5

CE2
255
1.8

It can be seen from Table 3 that, the high strength and corrosion-resistant magnesium alloy material of Examples 1-17 with a yield strength of higher than 260 MPa and a corrosion weight loss of less than 0.8 mg/(cm²day) has superior mechanical properties and corrosion resistance compared to Comparative Examples 1-2. Thus, the high strength and corrosion-resistant magnesium alloy material has a wide range of application prospects.

As can be seen from FIGS. 1 to 6, the microstructure of Comparative Example 2 consists of a single α-Mg phase. In contrast, column-shaped Mg₂Ge intermetallic compound phase and small amount of Mg₂Ca compound are observed in the microstructure of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4

As can be seen from FIGS. 7 to 9, the electron backscatter diffraction measures the grain size of the prepared alloy. The grain structure of Comparative Example 2 has uniform size and shape, with an average grain size of 1.2 μm. A bimodal particle size distribution is observed in the high strength and corrosion-resistant magnesium alloy materials of Examples 3 and 4, and the microstructures thereof comprises column-shaped grains with an average grain size of 10-22 μm.

FIG. 10 shows the grain size distribution of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Example 2, wherein Mg-1Zn represents Comparative Example 2, Mg-1Zn-0.3Ge represents Example 3, and Mg-1Zn-0.5Ge represents Example 4.

It can be seen from FIG. 10 that when the content of germanium in the alloy increases from about 0.3% to about 0.5%, the proportion of column-shaped grains with large size increases significantly, which indicates that the content of germanium in the alloy can affect the formation of column-shaped grains with large size.

In order to reveal the influence of the addition of alloying elements on the electrochemical performances of the magnesium alloy, potentiodynamic polarization measurement and cathode polarization measurement are conducted on Comparative Examples 1-2 and the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4. The specific results are shown in FIGS. 11 and 12, wherein Mg represents Comparative Example 1 (where the trace amounts of Ge and Zn can be ignored), Mg-1Zn represents Comparative Example 2, Mg-1Zn-0.3Ge represents Example 3, and Mg-1Zn-0.5Ge represents Example 4.

As can be seen from FIG. 11, due to the increase of Zn content, the corrosion potential of the high strength and corrosion-resistant magnesium alloy material of Comparative Example 2 increases by about 50 mV compared with Comparative Example 1. In addition, due to the increase of germanium content, the corrosion potentials of the high strength and corrosion-resistant magnesium alloy materials of Examples 3 and 4 is reduced to about −1.67 V_SCE.

As can be seen from FIG. 12, the cathode reaction rate of Comparative Example 2 is higher than that of Comparative Example 1, indicating that the increase of Zn improves the cathode kinetics. On the contrary, the increase of Ge leads to a decrease in the cathode current density of the high strength and corrosion-resistant magnesium alloy materials of Example 3 and Example 4, indicating that Ge alloying offsets the effect of Zn alloying and significantly reduces the potential dynamics of the cathode.

By incorporating FIG. 11 and FIG. 12, it can be seen that the high strength and corrosion-resistant magnesium alloy materials of Example 3 and Example 4 show an anode kinetics similar to that of Comparative Example 1. The change of corrosion potential of Example 3 and Example 4 are mainly due to the change of cathode kinetics.

In order to verify the long-term corrosion performance of magnesium alloys, long-term (24 h) immersion test is conducted on Comparative Examples 1-2 and Examples 3-4 and commercial AZ91 magnesium alloy at open circuit potential in a 0.1 M sodium chloride solution. The results are shown in FIG. 13, wherein Mg represents Comparative Example 1, AZ91 represents commercial AZ91 magnesium alloy, Mg-1Zn represents Comparative Example 2, Mg-1Zn-0.3Ge represents Example 3, and Mg-1Zn-0.5Ge represents Example 4 in the x-coordinate.

As can be seen from FIG. 13, under the conditions of immersion test, the weight loss and hydrogen evolution rate of the high strength and corrosion-resistant magnesium alloy materials of Example 3 and Example 4 are about an order of magnitude smaller than those of Comparative Example 1 and commercial AZ91 magnesium alloy, which proves that the addition of Zn and Ge can reduce the corrosion rate of Mg.

After long-term (24 h) immersion test of Comparative Examples 1-2 and Examples 3-4 at open circuit potential in a 0.1 M sodium chloride solution, the corrosion products were washed with a chromic acid solution (i.e., 200 g/L chromium trioxide, 10 g/L silver nitrate and 20 g/L barium nitrate) to show the degree of corrosion, and then the surface morphology was observed.

As can be seen from FIGS. 14 to 21, after the immersion test, the corrosion morphology of the high strength and corrosion-resistant magnesium alloy materials of Examples 3 and 4 are different from that of Comparative Example 1 and Comparative Example 2. Discrete surface corrosion sites were observed in Example 3 and Example 4, while widespread “filamentous” corrosion was observed in Comparative Example 1 and Comparative Example 2. Thus, Zn and Ge enhance the anti-corrosion ability of magnesium alloys and inhibit the rate of cathode reaction (i.e., hydrogen evolution reaction).

The influence of alloying on cathode activation (difference effect) of magnesium is further evaluated by constant current potential experiment. As shown in FIG. 22, the sample is anodic polarized in a gradual increment of 0.025-2.5 mA/cm²cycle, and a fixed negative potential (−2 V_SCE) is kept in each anodic polarization period to measure the cathode current density maintained on the anodic polarized surface (i.e., applied dissolution current density). As shown in FIG. 23, the sample is anodic polarized in a gradual increment of 2-24 mA/cm²cycle, and a fixed negative potential (−2 V_SCE) is kept in each anodic polarization period to measure the cathode current density maintained on the anodic polarized surface (i.e., applied dissolution current density). In FIG. 22 and FIG. 23, Mg represents Comparative Example 1, Mg-1Zn represents Comparative Example 2, Mg-1Zn-0.3Ge represents Example 3, and Mg-1Zn-0.5Ge represents Example 4.

As can be seen from FIG. 22, the cathode current density measured in Example 3 and Example 4 are 2-3 times lower than those of Comparative Example 1 and Comparative Example 2, indicating that the addition of Ge inhibits the activation of magnesium cathode.

As can be seen from FIG. 23, a similar trend can be observed when the experiment is repeated with a higher anode polarization current density (2-24 mA/cm²). Thus, the high strength and corrosion-resistant magnesium alloy materials of Example 3 and Example 4 show the potential as fine electrode materials due to their good corrosion resistance performance, low self-reaction (corrosion) rate, and little hydrogen evolution.

FIG. 24 shows the anode dissolution current density of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Examples 1-2 in 0.1 M sodium chloride during open circuit potential (OCP) and potentiodynamic polarization (PDP) by inductively coupled plasma optical emission spectrometer (ICP-OES), wherein Mg represents Comparative Example 1, Mg-1Zn represents Comparative Example 2, Mg-1Zn-0.3Ge represents Example 3, and Mg-1Zn-0.5Ge represents Example 4.

It can be seen from FIG. 24 that Example 3 and Example 4 exhibit the lowest anode dissolution current density during both OCP and potentiodynamic polarization.

FIG. 25 shows the relationship between the anode dissolution current density and the anode potential of the high strength and corrosion-resistant magnesium alloy materials of Examples 3-4 and Comparative Examples 1-2, wherein Mg represents Comparative Example 1, Mg-1Zn represents Comparative Example 2, Mg-1Zn-0.3Ge represents Example 3, and Mg-1Zn-0.5 Ge represents Example 4.

As can be seen from FIG. 25, for Comparative Examples 1-2 and Examples 3-4, the anode dissolution current density increases logarithmically as the anode potential increases. It shall be noted that the kinetics of the anode reaction of Examples 3-4 is lower than those of Comparative Examples 1-2. The slopes of curves derived from ICP-OES polarization analysis are listed in Table 4.

TABLE 4

No.
Slope (V/μA · cm²)

E3
0.0168

E4
0.0234

CE1
0.0114

CE2
0.0106

It can be seen from Table 4 that the addition of small amount of the above-mentioned alloying elements inhibits the kinetics of the magnesium anode.

FIG. 26 shows the microhardness measurement results of Comparative Example 2 and Examples 3-4. FIG. 27 shows the engineering stress-strain curves of Comparative Example 2 and Examples 3-4. In FIG. 26 and FIG. 27, Mg-1Zn represents Comparative Example 2, Mg-1Zn-0.3Ge represents Example 3, and Mg-1Zn-0.5Ge represents Example 4.

It can be seen from FIG. 26 that as the Ge content increases, the hardness of the alloy increases from 50HV1 in Comparative Example 2 to 83HV1 in Example 4.

It can be seen from FIG. 27 that as the Ge content increases, the yield strength of the alloy increases from about 255 MPa in Comparative Example 2 to about 320 MPa in Example 4.

It should be noted that the portion of prior art in the protection scope of the present invention is not limited to the embodiments given herein. All prior art that does not contradict the solutions of the present invention, including but not limited to the previous patent documents, prior publications, prior applications, etc., can all be included in the protection scope of the present invention.

In addition, the combination of the technical features in the present disclosure is not limited to the combination described in the claims or the combination described in the specific examples. All technical features described herein can be freely combined in any way, unless contradicts between each other.

It should also be noted that the above-listed embodiments are only specific examples of the present invention. Obviously, the present invention should not be unduly limited to such specific embodiments. Changes or modifications that can be directly or easily derived from the present disclosure by those skilled in the art are intended to be within the protection scope of the present invention.

HIGH-STRENGTH AND CORROSION-RESISTANT MAGNESIUM ALLOY MATERIAL AND METHOD FOR FABRICATING SAME

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