JP5709063B2 - Heat-resistant magnesium alloy - Google Patents

Description

  The present invention relates to a magnesium alloy having excellent heat resistance.

  Magnesium alloys obtained by adding elements such as aluminum to magnesium are lightweight and easy to process, and are used in various fields. For example, an AZ-based alloy to which Al—Mn—Zn is added has excellent proof stress, tensile strength, and the like, and is useful for applications that require mechanical strength. In addition, an AS-based alloy to which Al—Mn—Si is added is also known as an alloy with further improved heat resistance.

  However, an AS-based alloy has a limit in heat resistance, and as a method for further improving this, a magnesium alloy in which high temperature characteristics are improved by adding Ca is known.

  For example, Patent Document 1 describes a magnesium alloy in which Al is added in an amount of 2 to 10 wt%, Ca is added in an amount of 1.4 to 10 wt%, and Ca / Al ≧ 0.7. The Mg / Ca compound is easily crystallized by adjusting the Ca / Al ratio to 0.7 or more, and the strength at high temperatures is improved.

  Patent Document 2 describes a magnesium alloy in which 2 to 6 wt% Al and 0.5 to 4 wt% Ca are added and Ca / Al ≦. This is because when the amount of Ca is too large as in Patent Document 1, seizure to the mold is likely to occur, and the elongation also decreases, so the amount of the Mg—Ca compound is suppressed to an appropriate range.

Japanese Patent Laid-Open No. 06-25790 JP 09-272945 A

  However, even these magnesium alloys of Patent Documents 1 and 2 have applications in which the creep resistance is not sufficient, and there is a demand for a magnesium alloy having excellent mechanical strength at high temperatures. Accordingly, an object of the present invention is to obtain an alloy further excellent in heat resistance in an Al—Mn-based magnesium alloy excellent in mechanical strength.

  Al is 3.0 mass% or more and 7.0 mass% or less, Mn is 0.1 mass% or more and 0.6 mass% or less, Ca is 1.5 mass% or more, Si contains 0.4 mass% or more, The magnesium alloy with Ca / Si ≧ 2.0 (mass ratio) has solved the above problem.

  When Si is 0.5% by mass or more and Ca is 2.0% by mass or more, a magnesium alloy having further improved creep characteristics is easily obtained. Further, the mass ratio of Ca / Si is more preferably 2.5 or more, and creep resistance is further improved when it is 3.0 or more.

  This magnesium alloy has high creep resistance even in an environment of 170 ° C. or higher, can suppress creep strain to 0.20% or less, and can be used as a material having excellent mechanical strength even at high temperatures.

The graph which plotted the result of the creep distortion with respect to Ca / Si ratio in an Example

The present invention will be described in detail below.
The present invention is a magnesium alloy containing at least Al, Mn, Ca and Si and having excellent creep resistance.

  The magnesium alloy according to the present invention is required to contain 3.0% by mass or more of Al and is preferably 5.5% by mass or more. If the Al content is too small, the decrease in the melting point of the magnesium alloy is small, and when preparing the alloy or when the alloy is used for casting, a high temperature is required. It becomes easy to cause burn-in. If it is 3.0 mass% or more, a certain amount of workability can be ensured, and if it is 5.5 mass% or more, sufficient workability can be ensured by the combination with Si described later. On the other hand, if there is too much Al, the β phase is precipitated and the creep resistance tends to be lowered, and it is necessary to be 7.0% by mass or less, and 6.5% by mass or less. The problem can be almost ignored.

  The magnesium alloy according to the present invention needs to contain 0.1% by mass or more of Mn, and preferably contains 0.3% by mass or more. This is because Mn has an effect of removing Fe, which is an impurity in the molten metal, to suppress a decrease in corrosion resistance, and if it is too small, the ease of corrosion derived from Fe cannot be ignored. On the other hand, the Mn content needs to be 0.6% by mass or less. If the amount is too large, a large amount of manganese precipitates alone and becomes brittle and the strength decreases.

  The magnesium alloy according to the present invention needs to contain 1.5% by mass or more of Ca, and preferably 2.0% by mass or more. It is because heat resistance improves by containing Ca, but the effect will become inadequate if it is less than 1.5 mass%. When the content is 2.0% by mass or more, this heat resistance becomes more reliable. On the other hand, if Ca is excessively present, cracks and seizure are likely to occur during casting, and therefore it is preferably 6.0% by mass or less, and more preferably 4.5% by mass or less.

  The magnesium alloy according to the present invention needs to contain 0.4% by mass or more of Si, and preferably 0.5% by mass or more. Si has an effect of lowering the melting point together with the above Al, and if it is too small, workability is lowered and it becomes difficult to use for casting. On the other hand, when the amount of Si added is 2.0% by mass or more, a coarse Mg—Si compound is generated and becomes brittle, and the strength is reduced. More preferably, it is 0 mass% or less.

  In the magnesium alloy according to the present invention, the mass ratio of Ca and Si to be contained needs to be 2.0 or more, preferably 2.5 or more, and more preferably 3.0 or more. The larger the Ca / Si ratio, the better the creep resistance. This ratio has no particular upper limit in the Ca and Si content ranges described above, and is preferably as high as possible.

  The magnesium alloy according to the present invention may contain inevitable impurities in addition to the above elements. The inevitable impurities are unavoidably contained due to problems in production or raw materials. The content of the magnesium alloy according to the present invention needs to be in a range that does not hinder the properties, and is preferably less than 0.2% by mass per element, and the smaller the content, the more preferable.

  However, among other elements, it is preferable that the content of Group 2 elements other than the above Ca and Mg, that is, Be, Sr, Ba, and Ra is as low as possible. Specifically, even if these are added together, it is preferably less than 0.05% by mass, and each individual element is preferably less than the detection limit. This is because these Group 2 elements are expensive and cause cost increase. In particular, Ba reacts with Al to form an Al—Ba compound, but its eutectic temperature is 528 ° C., which is lower than the eutectic temperature of 545 ° C. of the Al—Ca compound, and decomposes at a lower temperature to reduce creep resistance. I will let you. In addition, other Group 2 elements may produce unexpected compounds and deteriorate properties.

  The magnesium alloy according to the present invention can be prepared by a general method using a raw material containing the above element so as to be in the above mass% range. In addition, said mass ratio and mass% are not ratio and% in a raw material, but ratio and% in the prepared alloy and the product which manufactured it by casting etc.

  The magnesium alloy according to the present invention is easy to use for casting because the melting point is moderately suppressed and seizure hardly occurs. It can also be used for wrought material. In any case, products manufactured using the magnesium alloy according to the present invention have good creep resistance under high temperature conditions.

  The example which actually prepared the magnesium alloy concerning this invention is shown. Magnesium alloys were prepared so that the content of elements other than Mg would be the mass% described in each of Table 1 below, and each alloy was tested based on the creep test method defined in JIS Z 2271. A creep tester manufactured by Yonekura Seisakusho Co., Ltd .: CR-20KN was used, the test temperature was 175 ° C., the applied stress was 50 MPa, and the creep strain (%) after 100 hours was measured. The results are also shown in Table 1. Creep strain ≦ 0.15% was evaluated as ◎, 0.15% <creep strain ≦ 0.20% as ○, and 0.20% <creep strain as ×.

  In Comparative Examples 1 to 4, Ca is less than 1.5% by mass, and in Comparative Examples 2 to 5, the Ca / Si mass ratio is less than 2.0. FIG. 1 is a graph in which the data of these examples and comparative examples are plotted with Ca / Si on the horizontal axis and creep strain (%) on the vertical axis.

Claims (3)

Al is 5.5 mass% or more and 7.0 mass% or less, Mn is 0.1 mass% or more and 0.6 mass% or less, Ca is 1.5 mass% or more and 6.0 mass% or less , Si is 0.5 mass%. Magnesium alloy containing not less than 0.8% by mass and not more than 0.8% by mass , the balance being Mg and inevitable impurities, and the Ca / Si mass ratio being not less than 2.0. Ca is 2.0 mass% or more of magnesium alloy according to claim 1.   The magnesium alloy according to claim 1 or 2, wherein the mass ratio of Ca / Si is 2.5 or more.

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