JP3916452B2 - High corrosion resistance magnesium alloy and method for producing the same - Google Patents

Description

【００５５】
【発明の効果】
本発明によれば、特別な防蝕処理を施すまでもなく、耐蝕性に優れたマグネシウム合金が得られる。
【図面の簡単な説明】
【図１】含有する希土類元素（Ｒ．Ｅ．）と腐蝕速度との関係を示す棒グラフである。
【図２】Ｒ．Ｅ．の含有量と腐蝕速度との関係を示すグラフであり、同図（ａ）は（Ｃｅ＋Ｌａ）量との関係を示し、同図（ｂ）はＭｍ量との関係を示す。
【図３】Ｍｎの含有量と腐蝕速度との関係を示すグラフである。
【図４】Ａｌの含有量と腐蝕速度との関係を示すグラフである。
【図５】Ｚｎの含有量と腐蝕速度との関係を示すグラフである。
【図６】冷却速度と腐蝕速度との関係を示す棒グラフである。
【図７】マグネシウム合金の腐蝕試験後の様子を示す写真であり、同図（ａ）は本発明に係るマグネシウム合金のものであり、同図（ｂ）は従来のマグネシウム合金のものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a highly corrosion-resistant magnesium alloy having excellent corrosion resistance and a method for producing the same.
[0002]
[Prior art]
Magnesium is the lightest and most specific metal in practical metals, has abundant resources, and is excellent in recyclability. For this reason, magnesium is a promising metal material in recent years where weight reduction and reduction of environmental load are strongly demanded, and magnesium or magnesium alloys are being used in various products in various fields.
[0003]
For example, in the field of vehicles such as automobiles, covers made of magnesium alloys, wheels, and the like have been developed, and energy saving and improvement of exercise performance are achieved with the weight reduction. Also in the field of electrical equipment, magnesium (or its alloys) is used in cases such as notebook computers and mobile phones, thereby further reducing the weight and recycling of mobile equipment.
[0004]
However, magnesium is a very active metal, and is the most potential base metal among practical metals (that is, a metal having a high ionization tendency), and magnesium itself forms a dense oxide film having corrosion resistance. There is nothing. For this reason, not only pure magnesium but also conventional magnesium alloys have very poor corrosion resistance.
[0005]
For this reason, it has been practically necessary to provide a corrosion-resistant coating such as a chemical conversion coating, an anodic oxide coating, plating or painting on the surface of a magnesium alloy or the like. However, separately forming such a corrosion-resistant film is a factor of high cost. Even if the corrosion-resistant film is formed, if the base material is exposed due to scratches or the like, corrosion proceeds newly from that portion, and stable corrosion resistance cannot be obtained.
[0006]
Therefore, research and development have been conducted on magnesium alloys that do not require such special corrosion-resistant coatings but have improved their own corrosion resistance. For example, Japanese Patent Application Laid-Open No. 5-171333 discloses “Zn by weight: 1.0 to 6.0%, Misch metal: 0.1 to 2.0%, Zr: 0.1 to 2.0%, "Magnesium alloy characterized by containing Si; 0.1 to 3.0%, Al; 0.1 to 6.0%, the balance being composed of Mg and inevitable impurities" is disclosed. And according to the publication, this Mg-Al-Zn-R. E. Alloys based on R.I. E. In the early stages of corrosion. E. A rich protective film is formed to improve corrosion resistance.
[0007]
[Problems to be solved by the invention]
However, in the publication, the degree of corrosion resistance is not clarified, and it is unclear whether a magnesium alloy having the above composition has practically sufficient corrosion resistance. Moreover, there is no disclosure about the specific composition of the misch metal contained in the magnesium alloy, and it is unclear which element in the misch metal is effective in improving the corrosion resistance.
[0008]
In general, in the case of a multi-component magnesium alloy, there are many cases where it does not work effectively even if an alloy element effective for corrosion resistance is added. Even if the corrosion resistance is improved, if it does not reach a practical level, a corrosion prevention treatment is eventually required, and the cost of the magnesium alloy member cannot be reduced. Accordingly, sufficient corrosion resistance cannot be obtained unless a proper amount of appropriate alloy elements are combined. In addition, the structure of the magnesium alloy also affects the corrosion resistance. Therefore, it cannot be considered that satisfactory corrosion resistance was obtained with the magnesium alloy disclosed in the above publication.
[0009]
In JP-A-6-172948 and JP-A-7-11371, Mg—Al—Zn—R. E. Although -Mn-based alloys are disclosed, none of them is intended to improve the corrosion resistance, and it is unlikely that a highly corrosion-resistant magnesium alloy will be obtained with the disclosed compositions.
[0010]
The present invention has been made in view of such circumstances. In other words, it does not need to be subjected to a corrosion-resistant treatment for forming a special corrosion-resistant film, and exhibits excellent corrosion resistance by itself. For example, even in an as-cast state, it exhibits a sufficiently high corrosion resistance in practical use. An object is to provide a magnesium alloy.
[0011]
[Means for Solving the Problems]
Therefore, as a result of extensive research and trial and error, the present inventor has found a new element effective for improving the corrosion resistance of a magnesium alloy and an appropriate amount thereof, and has completed the present invention.
(Highly corrosion-resistant magnesium alloy)
That is, the highly corrosion-resistant magnesium alloy of the present invention comprises 2 to 8% by mass of Al, 0.1 to 1.5% by mass of Mn, Ce and / or La, when the total is 100% by mass. and rare earth elements including 0.1-0.9 wt% in total (R. E.), the remainder Ri Do from Mg and inevitable impurities, dendrite cell size is characterized Rukoto such from 50μm following tissue.
[0012]
The magnesium alloy of the present invention comprises Al, Mn and specific R.D. E. By including a proper amount, it is possible to exhibit excellent corrosion resistance without adding a separate corrosion-resistant film. Although it is not necessarily clear why the magnesium alloy of the present invention exhibits such excellent corrosion resistance, the present state of the present invention is thought to be as follows based on the present inventors' hard research.
[0013]
The inventor has found a relatively small amount of R.P. E. Is very effective in improving the corrosion resistance of the magnesium alloy of the present invention; E. Among these, it has been newly found that Ce and La are particularly effective elements. And this Ce or La forms a protective film (for example, a surface oxide film) close to a passive film different from the conventional one on the surface of the magnesium alloy by forming a compound with Mg, Al, and Mn. I'm thinking about it.
[0014]
However, it seems that stable corrosion resistance cannot always be obtained only by the presence of such a protective coating. This is because unavoidable impurities such as iron (Fe), nickel (Ni), and copper (Cu) mixed during manufacture can cause corrosion (corrosion starting point).
[0015]
In the case of the magnesium alloy of the present invention, an appropriate amount of Mn is contained in addition to Ce and La. Ce, La, and Mn effectively remove impurities such as Fe that cause corrosion (corrosion start point). As a result, the effect of the protective coating appears effectively, and it is considered that the magnesium alloy of the present invention has exhibited significantly superior corrosion resistance due to the synergistic effect of both. Details of this mechanism will be described later.
[0016]
Thus, a product using the magnesium alloy of the present invention can have practically sufficient corrosion resistance without being subjected to a special anticorrosion treatment. For example, when the magnesium alloy of the present invention is used in a cast product such as a die-cast product that requires cost reduction, it can be used even in an as-cast state, which is very preferable.
(Manufacturing method of highly corrosion resistant magnesium alloy)
In addition to the magnesium alloy, the present invention can be grasped as a manufacturing method thereof.
[0017]
That is, in the present invention, when the total is 100% by mass, Al is 2 to 8% by mass, Mn is 0.1 to 1.5% by mass, and Ce and / or La is 0.1 to 0. 9 wt%, consists of a raw material preparation step to the remainder Mg and inevitable impurities, and dissolution step of dissolving the raw material after the raw material preparation step, a solidifying step of solidifying by cooling the molten metal after the dissolution step, the The solidification step may be a method for producing a highly corrosion-resistant magnesium alloy characterized in that the cooling rate is a step of 2 ° C./s or more .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in more detail with reference to embodiments. The contents described below are applicable not only to the magnesium alloy itself of the present invention but also to the production method thereof.
(1) Corrosion mode and mechanism It is considered that the magnesium alloy of the present invention is different in corrosion mode and mechanism from conventional magnesium alloys. In this regard, what is currently conceivable will be described below.
[0019]
It is known that the corrosion resistance of the Mg—Al alloy improves as the Al addition amount increases. This is because the Mg-Al compound formed in the alloy has the effect of suppressing corrosion, and at the same time, Al dissolves in the oxide film on the surface, and dense alumina (or spinel) with high corrosion resistance. This is considered to form a film.
[0020]
However, since the magnesium alloy containing only Al shows a large concentration segregation, the local corrosion of the linear or network shape starts from the low Al concentration portion or the impurity compound (Al-Fe compound). Can occur violently.
[0021]
On the other hand, when a small amount of Ce, La (or Mm) is added to the Mg—Al alloy, the local corrosion is suppressed, and the corrosion resistance of the magnesium alloy is greatly improved. And even if the magnesium alloy slightly corrodes, it will cause uniform corrosion. This is presumably because impurities were removed by the presence of Ce and / or La, and in addition, the surface film was strengthened against corrosion.
[0022]
However, most of the added Ce or La forms a compound of Al (Mg) -Ce or Al (Mg) -La in the Mg alloy. Since these compounds are compounds having a noble corrosion potential with respect to Mg, there is a possibility that the corrosion resistance of the magnesium alloy may be lowered when the content thereof is increased.
[0023]
The magnesium alloy of the present invention is made of Al, R.I. E. In addition to (Ce, La), Mn is further contained. Mn forms a compound of Al (Mg) -Ce-Mn or Al (Mg) -La-Mn. Since these compounds are compounds having a corrosion potential close to that of Mg, it is possible to suppress a decrease in corrosion resistance due to the aforementioned Al (Mg) -Ce or Al (Mg) -La compound.
[0024]
Moreover, this Mn is likely to be combined with Fe, which is an inevitable impurity that has a very bad influence on the corrosion resistance. On the other hand, Ce and La are easy to combine with Ni. That is, Fe and Ni in the alloy are easily dissolved in an Al (Mg) -Ce-Mn or Al (Mg) -La-Mn compound, or a new compound is easily formed. Thus, Mn, Ce, and La also suppress the adverse effect of these impurities on the corrosion resistance of the magnesium alloy.
(2) Component composition Next, based on the above, each component element will be described in detail.
(1) R.R. E.
The rare earth element includes a large number of elements, but the element effective for corrosion resistance in the present invention is Ce or La. The results of examining this are shown in FIG. FIG. 1 shows an example in which 0.5% of Mm, Ce, La, and Nd are added based on an Mg-6% Al-0.3% Mn alloy. E. The corrosion rates when no is added are shown in comparison. In addition, the manufacturing method and corrosion test method of each magnesium alloy will be described in detail in the following examples (hereinafter the same). From FIG. E. In particular, it has been clarified that Ce and La are particularly effective elements for improving the corrosion resistance.
[0025]
Next, the magnesium alloy of the present invention only needs to contain either Ce or La or both at the same time. And the total content should just be 0.1-0.9 mass% (henceforth "%" only). This is because if it is less than 0.1%, sufficient corrosion resistance cannot be obtained, and if it exceeds 0.9%, the corrosion resistance starts to decrease. The total of Ce and / or La is more preferably 0.15 to 0.8%, and further preferably 0.15 to 0.5%. About the relationship between this content and corrosion resistance (corrosion rate), the result of having investigated about the Mg-6% Al-0.3% Mn-x% (Ce + La) alloy which is an example is shown to Fig.2 (a).
[0026]
Thus, even if Ce and La are effective elements for improving the corrosion resistance, Mm containing them is often used in industrial production processes from the viewpoint of cost. Therefore, it is preferable that the raw material preparation step in producing the magnesium alloy of the present invention is a step using Mm as a raw material for Ce and / or La.
[0027]
At this time, when Mm of Ce: 52%, La: 25%, Nd: 16%, Pr: 5% is used, the magnesium alloy of the present invention has an Mm of 0.2 to 1%, further 0.3. It should be ~ 0.5%. FIG. 2B shows the result of examining the relationship between the Mm content and the corrosion resistance of an example of an Mg-6% Al-0.3% Mn-x% Mm alloy.
[0028]
R.A. E. When the amount is increased, castability is lowered, but the castability is not deteriorated as long as it is within the above composition range of the present invention. For this reason, the magnesium alloy of this invention is preferable as a magnesium alloy for casting.
▲ 2 ▼ Mn
As described above, Mn is an element effective for removing impurities such as Fe that cause corrosion, and it is very effective to contain 0.1 to 1.5% of Mn.
[0029]
The relationship between the Mn content and the corrosion resistance (corrosion rate) is shown in FIG. 3 for an example of an alloy of Mg-6% Al-x% Mn-0.5Mm% (Mm is the above composition). As can be seen from FIG. 3, when Mn is less than 0.1%, the improvement in corrosion resistance cannot be expected so much, and when it exceeds 1.5%, the amount of the noble compound having a slightly corrosive potential increases in composition, resulting in corrosion resistance. Sex begins to decline. And it is more preferable when Mn is 0.2 to 1.0%, more preferably 0.2 to 0.5%.
[0030]
In many cases, Mn is usually precipitated and removed by forming an Al—Mn—Fe compound in the molten metal. Even if it remains in the alloy, since the potential difference between the Al—Mn—Fe compound and Mg is small, corrosion caused by Fe is greatly suppressed. Thus, according to the magnesium alloy of the present invention, the deterioration of corrosion resistance due to the inevitable impurity Fe is remarkably suppressed.
[0031]
R. E. Has an effect of removing impurities, and Al-Mn-Fe- (Ni) -R. E. The potential difference between the (Mm) compound and Mg is also small. Therefore, even if the Fe content of the impurity is relatively increased with respect to the Mn content, or even if the Ni content is increased, sufficient corrosion resistance can be obtained by adding Mm. Conceivable.
▲ 3 ▼ Al
Al is an element that improves the corrosion resistance of the magnesium alloy in cooperation with Ce and La, and it is very effective to contain Al in an amount of 1 to 8%.
[0032]
The relationship between Al content and corrosion resistance (corrosion rate) was examined for an example of an Mg-x% Al-0.3% Mn-0.5Mm% (Mm is the above composition) alloy in FIG. Show. As can be seen from FIG. 4, when Al is less than 1%, the corrosion resistance cannot be improved so much, and when it exceeds 8%, the corrosion resistance starts to decrease. It is more preferable that Al is 2 to 8%, 2 to 6%, and further 4 to 6%.
[0033]
In addition, it is generally said that the corrosion resistance improves as a relatively large amount of Al is contained. This is because the amount of Al in the surface coating increases, the amount and thickness of the highly corrosion-resistant alumina coating increase, and the Mg-Al compound formed in the alloy contributes to the improvement in corrosion resistance. It is thought that there is. However, according to the magnesium alloy of the present invention, due to the presence of Ce and La, the protective film is sufficiently strengthened even with a small amount of Al of about 1 to 3%, and it seems that the corrosion resistance is improved. Rather, the amount of Al exceeding 10% causes R.D. E. It is considered that the amount of (Ce, La) is deficient and the strengthening of the protective film is weakened.
(4) Zn
The magnesium alloy of the present invention can obtain sufficient corrosion resistance even if it does not contain Zn, but if it contains 1% by mass or less of Zn, its corrosion resistance is further improved. This is because a small amount of Zn is considered to be effective for improving the corrosion resistance of the magnesium alloy of the present invention which shows a uniform corrosion by solid-dissolving in Mg to lower the corrosion potential of Mg.
[0034]
As a result of examining the relationship between the Zn content and the corrosion resistance (corrosion rate), an alloy of Mg-6% Al-x% Zn-0.3% Mn-0.5Mm% (Mm is the above composition) is an example. Is shown in FIG. As can be seen from FIG. 5, when Zn exceeds 1%, the corrosion resistance starts to slightly decrease. It is more preferable that Zn is 0.1 to 0.8%, further 0.2 to 0.5%.
(3) In the case of structure pure Mg (or Mg alloy not containing Al), the grain boundary can be the starting point of corrosion. Therefore, the finer the crystal grain size, the easier the corrosion occurs, and the larger the crystal grain size, the more corrosion resistance. is there. In the case of an Mg—Al alloy, the formed Mg—Al compound is effective for corrosion resistance, and the finer the crystal grain size and dendrite cell size, the more effective the corrosion resistance. This is because the compound crystallizes between dendrite cells and the like.
[0035]
The same applies to this alloy, and it has been confirmed that the smaller the crystal grain size and dendrite cell size, the better the corrosion resistance.
[0036]
For example, the dendrite cell size is preferably 50 μm or less, 40 μm or less, and more preferably 30 μm. The dendrite cell size here is an average dendrite cell size. The average dendrite cell size is determined by a method of determining the average dendrite cell size by measuring the number of dendrite cells crossing a line segment of a certain length from the structure photograph (line segment method, Hen's method).
[0037]
A cast structure having such a dendrite cell size can be obtained, for example, by setting the solidification step in producing the magnesium alloy of the present invention to a cooling rate of 2 ° C./s or more, further 5 ° C./s or more. .
[0038]
The cooling rate at the time of casting is important not only for adjusting the dendrite cell size but also for controlling the solid solution of each alloy element in the Mg alloy, the formation of a compound with Mg, and the form thereof.
[0039]
About the relationship between this cooling rate and corrosion resistance (corrosion rate), the result of investigating about an alloy of Mg-4% Al-0.3% Mn-0.5Mm% (Mm is the above composition) as an example is shown in FIG. . As can be seen from FIG. 6, when the cooling rate is less than 1 ° C./s, the corrosion resistance of the magnesium alloy is insufficiently improved, whereas when the cooling rate exceeds 2 ° C./s, the corrosion resistance is sufficiently improved.
(4) Corrosion rate The magnesium alloy of the present invention is not only different in corrosion mode from the conventional magnesium alloy but also has extremely high corrosion resistance. As an example of indicating the corrosion resistance, in this specification, the corrosion rate by a 5 mass% saline immersion test is used. According to this, the magnesium alloy of the present invention, the corrosion rate of 0.1mg / (cm ² · day) or less, and ^{further, 0.08mg / (cm 2 · day} ) or less, 0.05mg / (cm ² · day) or less, and 0.03 mg / (cm ² · day) or less. The corrosion rate of JIS ADC12 alloy which is a general casting aluminum alloy is 0.11 mg / (cm ² · day). Therefore, the magnesium alloy of the present invention has a corrosion resistance equal to or higher than that of the aluminum alloy.
[0040]
The 5% by mass saline immersion test will be described later.
(5) Use Since the magnesium alloy of the present invention has excellent corrosion resistance, it can be used for various products. In particular, the magnesium alloy of the present invention can be used for a member in a wet environment where the use of the conventional magnesium alloy is restricted.
[0041]
In particular, since the magnesium alloy of the present invention has a corrosion resistance equal to or higher than that of the casting aluminum alloy as described above, various aluminum alloy products can be replaced with products using the magnesium alloy of the present invention.
[0042]
Specifically, the magnesium alloy of the present invention can be used for various cases, automobile wheels, and the like. In addition, since the excellent corrosion resistance is exhibited without the anticorrosion treatment, the cost of the magnesium alloy member can be reduced. Of course, this does not exclude the further application of the anticorrosion treatment to the magnesium alloy of the present invention.
[0043]
【Example】
Next, an Example is given and this invention is demonstrated more concretely.
(Manufacture of test pieces)
In order to specifically examine the corrosion resistance of the magnesium alloy according to the present invention, sample Nos. Listed in Table 1 were used. 1-15 and sample no. C1 to C12 were produced by the following method.
[0044]
First, commercially available pure Mg (99.93%), pure Al (99.99%), Mg-3.3% Mn alloy, pure Zn (99.99%), and Mm were prepared as raw materials. Mm prepared here has the above-described composition. The unit is mass% (the same applies hereinafter).
[0045]
Next, these raw materials were appropriately combined so as to have the composition shown in Table 1 (raw material preparation step). Sample No. 14, 15 and sample no. In C9, pure Ce (99%), pure La (99%), and pure Nd (99%) were used without using Mm.
[0046]
These raw materials were dissolved in a crucible made of stainless steel (SUS430), sufficiently stirred and maintained at 750 ° C. (dissolution step). At this time, the flux was not used, but dissolved while blowing a small amount of sulfur hexafluoride (SF ₆ ) gas.
[0047]
In addition, first, a magnesium ingot is melted in a crucible made of SUS430, and various alloy elements may be added thereto. In this case, the raw material preparation step and the dissolution step are performed simultaneously.
[0048]
The molten metal having different component compositions was cast into a 50 × 120 × 5 mm plate casting using a vertical die casting machine (solidification step). The cooling rate at this time was 80 ° C./s.
(Evaluation)
{Circle around (1)} A test piece of 20 × 20 × 3 mm was cut out from the plate-shaped casting obtained by the above-described method, and the entire surface was polished with # 800 SiC paper. The polished test piece was immersed in a 5 mass% NaCl aqueous solution (25 ° C.) for 100 hours to perform a corrosion test.
[0049]
The weight of this test piece was measured before and after the corrosion test. In addition, the corrosion product adhering to the test piece surface was removed with 20% chromium oxide aqueous solution after the test. The corrosion rate (mg / (cm 2 · day)) for each test piece was calculated from the weight change. The corrosion rate is also shown in Table 1.
[0050]
Sample No. C12 shows the result of a similar corrosion test performed on a test piece made of JIS ADC12 alloy, which is a general casting aluminum alloy.
(2) Sample No. Nos. 1 to 15 show that the corrosion rate is much smaller than 0.11 (mg / (cm 2 · day)) of the aluminum die cast product (sample No. C12), and the corrosion resistance is very excellent.
[0051]
The sample containing Mm contains both Ce and La. 14 and 15 include only one of them. However, it is understood that the corrosion resistance is sufficiently improved by including at least one of Ce and La. On the other hand, R.I. E. Even sample No. containing only Nd. C9 did not improve the corrosion resistance as shown in FIG. Sample No. As can be seen from C7 and C8, when Ce or La is not contained or the amount thereof is extremely small, improvement in corrosion resistance can hardly be expected.
[0052]
Sample No. There is little content of Al like C10, or sample no. Even if the content of Mn is small as in C11, the improvement in corrosion resistance cannot be expected.
(3) Sample No. 2 and sample no. FIGS. 7 (a) and 7 (b) show surface observation photographs after immersion of C7 in a 5% NaCl aqueous solution for about 250 hours and removal of corrosion products adhering to the surface of each specimen with a chromium oxide aqueous solution. It was. The size of each test piece at this time was 20 mm × 20 mm × 3 mm.
[0053]
Sample No. In the case of the C7 magnesium alloy, it can be seen from FIG. 7B that the test piece shows local corrosion in a linear or mesh shape. On the other hand, sample No. In the case of No. 2 magnesium alloy, it can be seen from FIG. 7A that such a form of corrosion is not observed and shows uniform corrosion. Therefore, it seems that the corrosion mechanism of both is clearly different, and according to the magnesium alloy according to the present invention, it is clear that the conventional local corrosion of linear or network is suppressed.
[0054]
[Table 1]

[0055]
【The invention's effect】
According to the present invention, a magnesium alloy having excellent corrosion resistance can be obtained without performing a special anticorrosion treatment.
[Brief description of the drawings]
FIG. 1 is a bar graph showing the relationship between the contained rare earth element (RE) and the corrosion rate.
FIG. E. It is a graph which shows the relationship between content of and the corrosion rate, The same figure (a) shows the relationship with (Ce + La) amount, The same figure (b) shows the relationship with Mm amount.
FIG. 3 is a graph showing the relationship between the Mn content and the corrosion rate.
FIG. 4 is a graph showing the relationship between Al content and corrosion rate.
FIG. 5 is a graph showing the relationship between Zn content and corrosion rate.
FIG. 6 is a bar graph showing the relationship between cooling rate and corrosion rate.
FIG. 7 is a photograph showing a state after a corrosion test of a magnesium alloy. FIG. 7 (a) shows a magnesium alloy according to the present invention, and FIG. 7 (b) shows a conventional magnesium alloy.

Claims (6)

When the total is 100% by mass,
And 2-8 wt% of aluminum (Al),
0.1 to 1.5 mass% manganese (Mn);
A total of 0.1-0.9% by weight of cerium (Ce) and / or lanthanum (La),
The remainder Ri is Do from magnesium and (Mg) and inevitable impurities,
High corrosion resistant magnesium alloy dendrite cell size is excellent in corrosion resistance characterized by Rukoto such from 50μm following tissue. When the total is 100% by mass,
2-8 mass% aluminum (Al),
0.1 to 1.5 mass% manganese (Mn);
A total of 0.1-0.9% by weight of cerium (Ce) and / or lanthanum (La),
The balance consists of magnesium (Mg) and inevitable impurities,
Furthermore, 1 mass% or less of zinc (Zn) is included.
A highly corrosion-resistant magnesium alloy with excellent corrosion resistance. The high corrosion-resistant magnesium alloy according to claim 1 or 2 , wherein the total of Ce and / or La is 0.15 to 0.5 mass%. The highly corrosion-resistant magnesium alloy according to claim 1 or 2 , wherein a corrosion rate by a 5 mass% saline immersion test is 0.1 mg / (cm ² · day) or less. When the total is 100% by mass, Al is 2 to 8% by mass, Mn is 0.1 to 1.5% by mass, Ce and / or La is 0.1 to 0.9% by mass in total, and the balance is Raw material preparation step for Mg and inevitable impurities;
A dissolution step of dissolving the raw material after the raw material preparation step;
It becomes the melt after the dissolution step from the solidifying step of solidifying by cooling,
The solidification step is a step of setting a cooling rate to 2 ° C./s or more, and a method for producing a highly corrosion-resistant magnesium alloy. 6. The method for producing a highly corrosion-resistant magnesium alloy according to claim 5 , wherein the raw material preparation step is a step of using misch metal (Mm) as a raw material for the Ce and / or La.

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