JP5638222B2 - Heat-resistant magnesium alloy for casting and method for producing alloy casting - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a heat-resistant magnesium alloy and a method for producing an alloy casting, and more particularly to a heat-resistant magnesium alloy and a heat-resistant magnesium alloy casting for casting a prototype by sand mold casting in a prototype stage of a new product before mass production by die casting. It relates to the manufacturing method.

  Due to the growing needs for weight reduction in recent years, magnesium alloys that are lighter than aluminum alloys are attracting attention. This magnesium alloy is the lightest material among practical metal materials. In addition to the aircraft industry, which is seeking to reduce the weight of aircraft, the weight of the vehicle body (vehicle) is being further reduced with the heightened environmental awareness. It is especially attracting attention as a component material in various industries such as the automobile industry.

  Therefore, in response to such industry demands, there is a magnesium-aluminum-calcium heat-resistant magnesium alloy that is superior in mechanical properties such as heat resistance and mass-productivity by die casting to reduce production costs. (For example, refer patent document 1-patent document 4 etc.).

  In Patent Document 1, aluminum is 6 to 12% by weight, calcium is 0.05 to 4% by weight, rare earth elements are 0.5 to 4% by weight, manganese is 0.05 to 0.50% by weight, and tin is 0%. A heat-resistant magnesium alloy containing 1 to 14% by weight with the balance being magnesium and unavoidable impurities and excellent castability is disclosed. Further, zirconium is added to the heat-resistant magnesium alloy having such a component composition. A heat-resistant magnesium alloy excellent in heat resistance and castability containing at least one of 0.05 to 0.2% by weight and 0.03 to 0.2% by weight of carbon is disclosed.

  Patent Document 2 includes at least 86 wt% magnesium, 4.8 to 9.2 wt% aluminum, 0.08 to 0.38 wt% manganese, 0.00 to 0.9 wt% zinc, 0 A magnesium alloy containing 2 to 1.2 wt% calcium, 0.05 to 1.4 wt% strontium and 0.00 to 0.8 wt% rare earth element is disclosed.

  Patent Document 3 includes at least 85.4 wt% magnesium, 4.7 to 7.3 wt% aluminum, 0.17 to 0.60 wt% manganese, and 0.0 to 0.8 wt% zinc. , 1.8-3.2 wt% calcium, 0.3-2.2 wt% tin, 0.0-0.5 wt% strontium alloy is disclosed.

  Patent Document 4 describes a magnesium alloy containing 2 to 9% by weight of aluminum, 6 to 12% by weight of zinc, and 0.1 to 2.0% by weight of calcium, with the balance being magnesium and inevitable impurities. A magnesium alloy having a 0.2% proof stress of at least 140 MPa at room temperature and a Vickers hardness of 65 HV or more at room temperature in a state where solution treatment and artificial aging treatment are sequentially performed is disclosed.

JP 2005-68550 A JP 2004-238678 A JP 2004-238676 A JP 2002-266044 A

  By the way, newly designed new products such as oil pans, cylinder head covers, cylinder blocks, and other automotive parts are mass produced and put into practical use by high pressure die casting using heat-resistant magnesium alloy. At the development stage from design to practical use, a small number of prototypes with mechanical properties close to those in mass production are cast, thereby verifying newly designed parts, that is, as a state after assembling a single part or multiple parts It is essential to evaluate and confirm various functions and characteristics in advance.

However, when producing a prototype of a new product using a magnesium alloy according to the conventional technology, the implementation of the casting technology using the simplest sand mold among molds that can be cast at a low cost in a short time is realized. Since it has not been established, the prototype could not be prototyped without producing the same die casting mold as in mass production from the development stage (prototype stage) of the new product. .
For this reason, conventionally, it has been necessary to spend a development period on prototype casting, which results in an increase in development costs and a prolonged period of time, resulting in more development engineers from various industries such as the aircraft and automobile industries. There is a strong demand for the realization of a prototype casting technique that is inexpensive and can prototype a prototype in a short period of time and evaluate and confirm (test proof) mechanical properties. In other words, compared to molds, there was a strong desire to realize prototype casting technology for prototypes using sand molds that can be manufactured at low cost and in a short period of time.

Therefore, the present invention was created to solve the above-mentioned problems, and on the premise of mass production casting such as die casting, trial casting of a prototype in the design and development stage of a new product is inexpensive, and To realize by simple sand mold casting that can be done in a short period of time, to enable trial casting of prototypes that can obtain approximately 75% or more of mechanical properties of mass-produced products by die casting, by sand mold casting, etc. An object of the present invention is to provide an improved heat-resistant magnesium alloy and a method for producing a heat-resistant magnesium alloy casting.
Here, the mechanical properties of 75% or more of the die-casting product are as follows. The 0.2% proof stress in the static tensile test, which is considered to be the main requirement in the prototype function evaluation, is 75% or more compared to the die-casting. That means.

As a result of intensive research and various experiments over many years, the present inventor has found that the above-mentioned problems can be solved, and has completed the present invention.
That is, the heat-resistant magnesium alloy of the present invention is a heat-resistant magnesium alloy containing magnesium, aluminum, calcium,
9.20% by mass to 12.6% by mass of aluminum, 0.9 to 2.0% by mass of calcium, 0.0005 to 0.1000% by mass of manganese, and 0.10 to 0.45 of manganese (Mn) It is contained by mass and the balance consists of magnesium and inevitable impurities.

Here, the heat-resistant magnesium alloy of the present invention has the aluminum content exceeding 9.50 mass% to 10.5 mass%, the calcium content exceeding 1.2 mass% to 2.0 mass%, and the beryllium 0.0010-0. It is preferable that the content is 0.0100% by mass.
Further, the heat-resistant magnesium alloy of the present invention further includes 1.0% by mass or less of zinc or / and 0.60% by mass or less of strontium, 0.005% by mass or less of iron, 0.10% by mass or less of silicon, It is preferable to contain 0.020% by mass or less of nickel and 0.030% by mass or less of copper.

And in the manufacturing method of the heat-resistant magnesium alloy casting of the present invention, the heat-resistant magnesium alloy is melted, and the molten alloy is poured into a mold to cast the casting,
By refining the molten alloy with a flux at 630 to 670 ° C., degassing with an inert gas at 630 to 730 ° C., or leaving the molten alloy under a reduced pressure of 200 Torr or less. Among the degassing treatment, a treatment step for performing any one or more treatments, and after the treatment step, in the mold having an average temperature of the cavity surface of 45 ° C. or more at a melt temperature of 670 to 730 ° C. And a filling step of pouring the molten alloy.

  Here, the heat-resistant magnesium alloy has aluminum in excess of 9.20% by mass to 12.6% by mass, calcium in 0.9 to 2.0% by mass, beryllium in 0.0005 to 0.1000% by mass, and manganese in 0%. .10 to 0.45% by mass, the balance being composed of magnesium and inevitable impurities, aluminum exceeding 9.50% by mass to 10.5% by mass, calcium exceeding 1.2% by mass to 2.0 1% by mass, beryllium 0.0010 to 0.0100% by mass, zinc 1.0% by mass or less, strontium 0.60% by mass or less, iron 0.005% by mass or less, silicon It is preferable that 0.10% by mass or less, nickel is 0.020% by mass or less, and copper is 0.030% by mass or less.

  Further, the flux contains 10 to 15% by mass of calcium fluoride, 40 to 46% by mass of barium chloride, 6 to 11% by mass of potassium chloride, 30 to 38% by mass of magnesium chloride, and unavoidable impurities. Each of these powders was mixed, and this powder was charged and kneaded in the molten alloy within a range of 0.2 to 0.5 mass% of the total molten metal weight poured into the mold, and then for 20 minutes. It is preferable to continuously perform the stirring operation of the above molten alloy and the sedation of the molten metal for 5 minutes or more after the stirring operation.

The degassing process is performed by sending argon gas into the molten alloy at a flow rate of 3 to 10 liters / minute for 3 minutes or more, and the argon gas has a purity of 97% or more. In addition, feeding of the argon gas into the molten alloy is performed by immersing a gas supply pipe having a large number of fine holes through which argon gas is ejected as bubbles in the molten alloy, In addition, it is preferable that the mold is a sand mold and the mold main material contains 30% or more zircon sand.
In the method for producing a heat-resistant magnesium alloy casting of the present invention, it is preferable that the hydrogen content of the casting is 20 cc / 100 g Mg or less.

  According to the present invention, in newly designed new products, automotive parts such as oil pans, cylinder head covers, cylinder blocks, etc., the mechanical characteristics (axial force retention rate, tensile force) required according to the use of each of these parts. Strength, 0.2 proof stress, elongation, etc.), and trial casting of prototypes to check the castability in casting (fluidity, casting cracking, adherence to mold, etc.) with a simple sand mold It can be carried out. In other words, when designing and developing new products with new shapes and structures using heat-resistant magnesium alloys, mold plans for mass production of products by die-casting, etc., and their casting conditions, etc. in a short time using simple sand mold casting It is possible to find out.

It is a schematic explanatory drawing which shows typically the state which measures the axial force of the fastened bolt. It is explanatory drawing which shows the sample piece which evaluates a tensile characteristic.

[Heat-resistant magnesium alloy]
The heat-resistant magnesium alloy of the present invention has an aluminum (Al) content exceeding 9.21% by mass to 12.6% by mass, calcium (Ca) at 0.9 to 2.0% by mass, 0.0005 to 0.00999% by mass. Beryllium (Be), 0.10 to 0.45% by mass of manganese (Mn), with the balance being magnesium (Mg) as the main component and a small amount of inevitable impurities.
Further, the heat-resistant magnesium alloy of the present invention further comprises 1.0% by mass or less of zinc (Zn), 0.60% by mass or less of strontium (Sr), 0.005% by mass or less of iron (Fe), 0. It contains 10 mass% or less of silicon (Si), 0.020 mass% or less of nickel (Ni), and 0.030 mass% or less of copper (Cu).
Hereinafter, the reasons for limiting the composition will be described.

≪Aluminum over 9.21 mass% ～ 12.6 mass% ≫
Aluminum is an element that contributes to the improvement of corrosion resistance and castability, and also contributes to strengthening of the magnesium alloy and improves the mechanical strength of the cast product. Therefore, if the content is too small, the castability is significantly reduced. In particular, good fluidity (hot water flow) may not be obtained. On the other hand, if the content is excessive, the solid solution limit of aluminum in the matrix phase of the magnesium alloy may be exceeded, and the β (Mg17, Al12) phase crystallized in a non-equilibrium state remarkably increases. The toughness and ductility (elongation) of the steel may be reduced.
Therefore, it is important to set the aluminum content in the range of more than 9.21% by mass to 12.6% by mass, and preferably more than 9.50% by mass to 10.0%. It is in the range of 5% by mass.

≪Calcium 0.9-2.0 mass% ≫
When calcium coexists with aluminum in a magnesium alloy, an Al-Ca compound phase typified by Al ₂ Ca is crystallized and formed mainly at grain boundaries and cell boundaries during solidification, and these are thermally stable. Since the compound phase is an element that suppresses deformation and grain boundary sliding in the crystal grains and improves the high temperature strength (heat resistance) of the magnesium alloy, if the content is too small, an Al ₂ Ca phase is formed. And the effect of improving heat resistance is reduced. On the other hand, if the content is excessive, the toughness and ductility may be lowered to the extent that it cannot withstand practicality.
Therefore, it is important to set the calcium content in the range of 0.9 to 2.0% by mass in order to establish the present invention, and preferably in the range of 1.21 to 1.90% by mass. Is within.

≪Beryllium 0.0005 to 0.1000 mass% ≫
Beryllium is an element that plays a role in preventing oxidative combustion of the molten alloy of the heat-resistant magnesium alloy during melting, flux refining, degassing, holding the molten metal, and casting (while filling the molten alloy into the mold). The effect is due to the fact that beryllium has a lower free energy of formation of metal oxide than magnesium and is preferentially oxidized. For this reason, if the content is less than 0.0005% by mass, the amount of preferential oxidation of beryllium decreases, so that the oxidative combustion of the molten metal progresses significantly, and the fluidity (molten fluidity) during casting is reduced. To do. On the other hand, when the content is more than 0.1000% by mass, an excessively thick and strong protective film of beryllium oxide (BeO) is formed on the surface of the molten alloy, and the fluidity (hot water flowability) ) To cause poor hot water circulation, and the protective film becomes inclusions and mixes in the cast article, leading to deterioration of mechanical properties.
Therefore, it is important for the content of beryllium to be set within the range of 0.0005 to 0.1000% by mass in order to achieve the present invention, and preferably within the range of 0.0010 to 0.0100% by mass. It is.

≪Manganese 0.10 to 0.45 mass% ≫
Since manganese is an element that contributes to improving the corrosion resistance of the magnesium alloy, if the content is less than 0.10% by mass, the effect of improving the corrosion resistance is reduced. On the other hand, if the content is more than 0.45% by mass, the alloy cannot be completely dissolved in the molten alloy, and there is a fear that the toughness is reduced due to the formation of a fragile compound phase such as Al ₆ Mn.
Therefore, the content of manganese is important to establish the present invention within the range of 0.10 to 0.45% by mass, preferably within the range of 0.15 to 0.35% by mass. It is.

≪Zinc 1.0 mass% or less≫
When added to the Mg-Al alloy, zinc preferentially dissolves in the magnesium alloy matrix and contributes to solid solution strengthening, and the crystallization and precipitation β (Mg17, Al12) phase is fine. Since the element contributes to uniform dispersion, if the content is more than 1.0% by mass, the Mg-Zn-based crystallization phase and the accompanying low-melting multi-eutectic reaction may occur. If this multi-element eutectic reaction occurs, casting cracks during solidification may increase significantly.
Therefore, setting the zinc content to 1.0% by mass or less is important for establishing the present invention, and preferably 0.90% by mass or less.

≪Strontium 0.60% by mass or less≫
Strontium is an element advantageous for improving the heat resistance of a magnesium alloy by being uniformly dissolved in an Al—Ca-based compound phase typified by Al ₂ Ca. However, if the content is more than 0.60% by mass, the effect of improving heat resistance is saturated, and even if the content exceeds 0.60% by mass, there is no meaning. In addition, when the content is more than 0.60% by mass, an Al—Sr compound phase may be generated. Since this Al—Sr compound phase is fragile, there is a risk that mechanical properties such as strength and ductility of the magnesium alloy may be reduced.
Therefore, setting the strontium content to 0.60% by mass or less is important for achieving the present invention, and is preferably 0.40% by mass or less.

≪Iron 0.005 mass% or less≫
Since iron is an element that greatly affects the corrosion resistance of the cast product, if the content exceeds 0.005% by mass, the corrosion resistance of the cast product may be significantly reduced.
Therefore, it is important for the iron content to be set to 0.005 mass% or less in order to achieve the present invention, and the preferable content is 0.003 mass% or less.

≪Silicon 0.10 mass% or less≫
Silicon is not a harmful element as long as it is a trace amount, and does not bring about a significant change in the characteristics of the heat-resistant magnesium alloy. However, if the content exceeds 0.10% by mass, a Mg ₂ Si compound phase is formed, resulting in ductility and fatigue strength. Tends to decrease.
Therefore, it is important to set the content to 0.10% by mass or less in order to establish the present invention, and the preferable content is 0.07% by mass or less.

≪Nickel 0.020 mass% or less≫
Since nickel is an element that greatly affects the corrosion resistance of the cast product, if the content exceeds 0.002% by mass, the corrosion resistance of the cast product may be significantly reduced.
Therefore, setting the nickel content to 0.020% by mass or less is important for achieving the present invention, and the preferred content is 0.001% by mass or less.

≪Copper 0.030 mass% or less≫
Copper, like nickel, is an element that greatly affects the corrosion resistance of the cast product. Therefore, if the content exceeds 0.030% by mass, the corrosion resistance of the cast product may be significantly reduced.
Therefore, setting the copper content to 0.030% by mass or less is important for establishing the present invention, and the preferable content is 0.020% by mass or less.

≪Inevitable impurities≫
Examples of the inevitable impurities in the heat-resistant magnesium alloy according to the present invention include oxides such as lead (Pb), titanium (Ti), tin (Sn), and magnesium oxide (MgO).
Lead and titanium are not harmful elements as long as they are in trace amounts, and do not significantly change the properties of the heat-resistant magnesium alloy. However, if the content exceeds 0.01% by mass, an intermetallic compound phase is generated and ductility decreases. Tend to. Therefore, it is preferable to prepare (preparation) so as to be 0.01% by mass or less in the heat-resistant magnesium alloy.
Tin does not have a particularly great effect when added in a small amount, but when it is contained in an amount of 0.02% or more, it forms an Mg—Sn—Ca intermetallic compound phase that is stable at high temperatures. When the production amount of the intermetallic compound phase increases, Ca added for the purpose of improving heat resistance is consumed for the production of the Mg—Sn—Ca intermetallic compound phase, and the heat resistance of the system is relatively increased. This leads to a decrease in the Al ₂ Ca phase, which is the main heat-resistant strengthening phase of the alloy, and consequently to a decrease in heat resistance characteristics. Therefore, it is preferable to prepare so that it may become 0.01 mass% or less in a heat-resistant magnesium alloy.
Magnesium oxide is a non-metallic inclusion that primarily affects the melt flow during casting and the mechanical properties of the cast after casting, so an increase in content will proportionally balance these properties. It tends to decrease. Therefore, it is preferable to prepare so that it may become 1.0 mass% or less in a heat-resistant magnesium alloy.

Next, the heat-resistant magnesium alloy of the present invention will be specifically described with reference to examples.
In the main component magnesium, aluminum is more than 9.50% by mass to 10.5% by mass, calcium is 1.21 to 1.90% by mass, beryllium is 0.0010 to 0.0100% by mass, manganese is 0.15% ~ 0.35% by mass, containing inevitable impurities (oxides such as lead, titanium, tin, and magnesium oxide), further containing 1.0% by mass of zinc, 0.60% by mass or less of strontium, and iron Various Mg-Al-Ca alloys prepared by adding 0.005% by mass or less, silicon by 0.10% by mass or less, nickel by 0.020% by mass or less, and copper by 0.030% by mass or less were prepared ( Examples 1 to 6 in Table 1).
Then, a casting is cast from the prepared alloy of the present invention by a manufacturing method (sand mold casting) described later, and the castability of the various Mg-Al-Ca alloys at this time is observed, and the obtained various Mg-Al A test for evaluating mechanical properties was performed using a Ca-based alloy casting, and the results are shown in Table 2.
[Comparative example]

  Moreover, the content upper limit is exceeded in the content range of aluminum, calcium, and beryllium. And various Mg-Al-Ca type-alloys less than a content lower limit were prepared, respectively (Comparative Examples 1-6 of Table 1), and while obtaining the castability at the time of the casting by the manufacturing method mentioned later similarly to the above, it was obtained. Tests for evaluating mechanical properties were performed using various Mg-Al-Ca alloy castings, and the results are shown in Table 2.

[Method for producing heat-resistant magnesium alloy casting]
Below, the manufacturing method of this invention which casts a heat-resistant magnesium alloy casting using this various Mg-Al-Ca type | system | group alloy which consists of each composition of Examples 1-6 shown in Table 1 is demonstrated.
The production method of the present embodiment is a refining treatment with a flux at 630 to 670 ° C. or degassing with an inert gas at 630 to 730 ° C. with respect to a molten alloy of a heat-resistant magnesium alloy (alloy ingot). Among the treatment or the degassing treatment by leaving the molten alloy under a reduced pressure of 200 Torr or less, the temperature of the mold cavity surface is averaged after the treatment step of performing any one or more of these treatment steps. It is performed in a filling process in which molten alloy is poured into a mold at 45 ° C. or higher at a pouring temperature of 670 to 730 ° C.
Moreover, in the manufacturing method of a present Example, a sand mold is used as a casting_mold | template which pours molten alloy and manufactures a casting. This sand mold is manufactured by a mold base material containing 30% or more of zircon sand (ZrO ₂ , ZrO).

  And in the manufacturing method which concerns on a present Example, satisfy | filling each conditions of the refining process, the degassing process, the deaeration process, filling (pouring), and sand type which are demonstrated below is important in order to materialize this invention. .

≪Smelting treatment≫
Refining treatment by flux of molten alloys of the various Mg-Al-Ca alloys of Examples 1 to 6 shown in Table 1 (hereinafter, simply referred to as "molten metal"), that is, oxides by flux dispersion and stirring to the molten metal For the purpose of cleaning the molten metal by reactive adsorption to the flux of inclusions and inclusions, chloride formation, and gravity separation of the chloride (floating removal to the molten metal surface or precipitation to the molten metal bottom side) In order to remove inclusions in the molten metal, a refining treatment with flux at the molten metal temperature in the range of 630 to 670 ° C. is important.
The reason is that when the temperature is lower than 630 ° C., the reaction adsorption to the flux of inclusions and the generation of chloride do not proceed, and the cleaning process of the molten metal cannot be achieved. When the temperature is higher than 670 ° C., the reaction adsorption to the flux is promoted too much and the adsorption reaction of the normal magnesium alloy molten metal also proceeds. As a result, the molten metal becomes clean, but the molten metal itself is reduced. This is because the refining yield decreases.
Therefore, in the refining process of the molten metal by flux, setting the molten metal temperature within the range of 630 to 670 ° C. is important for establishing the production method of the present invention, and preferably within the range of 640 to 660 ° C. .

In the refining process, the flux is 10 to 15% by mass of calcium fluoride (CaF ₂ ), 40 to 46% by mass of barium chloride (BaCl ₂ ), and 6 to 11% by mass of potassium chloride (KCI). , 30 to 38% by mass of magnesium chloride (MgCl ₂ ) and unavoidable impurities are mixed, and this powder is 0.2 to 0.5 of the total molten metal weight poured into the mold. In order to establish the production method of the present invention, the molten metal is stirred and stirred for 20 minutes or less after the molten metal is charged and kneaded within the range of mass%, and the molten metal is calmed for 5 minutes or more after the stirring. Is important.
The reason for this is that if the amount of calcium fluoride, barium chloride, potassium chloride, or magnesium chloride is out of the above range, the viscosity of the flux itself will be easily changed and the adsorptivity of the oxide will be reduced. This is because the ability (the effect of removing inclusions in the molten metal) may be significantly reduced.
Therefore, the flux charged into the molten metal during the refining process is 10 to 15% by mass of calcium fluoride, 40 to 46% by mass of barium chloride, 6 to 11% by mass of potassium chloride, and 30 to 38% by mass. It is important for establishing the production method of the present invention that the powder is a powder in which both magnesium chloride and inevitable impurities are mixed.

In the refining process, the flux (powder) composed of the above blended components is charged into the molten metal within a range of 0.2 to 0.5 mass% of the total molten metal weight poured into the mold. In order to establish the production method of the present invention, it is important that the molten metal stirring operation within 20 minutes and the molten metal sedation for 5 minutes or more after the stirring operation are continuously performed.
The reason is that if the input amount is less than 0.2% by weight of the total molten metal weight, inclusion removal is insufficient, and if it is more than 0.5% by weight, not only does not contribute to the reaction, but also unnecessary flux components. Will increase, resulting in higher costs in actual production. Moreover, if the stirring reaction between the molten metal and the flux is not sufficiently completed within 20 minutes after being charged and kneaded into the molten metal, stirring exceeding 20 minutes becomes an unnecessary and wasteful work.
Therefore, in the refining process, the flux is charged and kneaded into the molten metal within a range of 0.2 to 0.5 mass% of the total molten metal weight to be poured, and then the molten metal is stirred for 20 minutes. In order to establish the production method of the present invention, it is important to continue the molten metal calming for 5 minutes or more after the stirring work.

≪Degassing treatment≫
In the degassing treatment of the molten metal with an inert gas, the inert gas is blown into the molten metal and bubbled, so that the hydrogen dissolved in the molten metal is adsorbed to the bubbles and floated and separated. Thereby, the effect of reducing the amount of hydrogen contained in the molten metal is brought about. In order to bring about the effect of reducing the hydrogen content, degassing with an inert gas at a molten metal temperature in the range of 630 to 730 ° C. is important.
The reason is that when the temperature is lower than 630 ° C., the viscosity of the molten metal is high, and because of the low temperature, the adsorption reaction does not proceed easily and the degassing effect becomes poor. When the temperature is higher than 730 ° C., the adsorption reaction proceeds and a degassing effect is obtained. However, hydrogen absorption and inclusion generation also progress on the foamed molten metal surface, and the degassing effect is reduced and the molten metal is contaminated. This is not preferable.
Therefore, in the degassing treatment with an inert gas, it is important to set the molten metal temperature within the range of 630 to 730 ° C. in order to establish the production method of the present invention, and preferably within the range of 640 to 660 ° C. is there.

Further, in the degassing process, the argon gas is sent into the molten metal at a flow rate of 3 to 10 liters / minute for 3 minutes or more, and the argon gas has a purity of 97% or more. This is important in establishing the manufacturing method of the invention.
The flow of argon gas to the molten metal at a flow rate of 3 to 10 liters / minute for 3 minutes or more is, for example, a condition for melting a molten metal weight of about 50 to 1000 kg and applying it to a holding furnace. Even if argon gas is fed into the molten metal at a flow rate and / or time longer than the conditions, the reduction of the hydrogen content in the molten metal has reached the limit level in the method according to the present invention, which is meaningless.
If the purity of the argon gas is less than 97%, the effect of reducing the amount of hydrogen contained in the molten metal is lowered, that is, the degassing effect is lowered. Therefore, it is important that the argon gas has a purity of 97% or more. It is.
In addition, the argon gas is fed into the molten metal by using a gas supply pipe having a large number of fine holes through which the argon gas is blown out as bubbles and immersing the gas supply pipe in the molten metal. Is preferred.

≪Degassing process≫
The main purpose is to clean the molten metal before casting by reducing unnecessary gas (gas) in the molten metal under reduced pressure. In order to effectively reduce gasification components such as nitrogen and hydrogen in the molten metal, there is a critical value of the degree of pressure reduction in addition to an appropriate molten metal temperature, 630 to 730 ° C., which is approximately 200 Torr or less. If it is 200 Torr or more, the degassing effect in the molten metal cannot be obtained remarkably.
Therefore, a deaeration process by leaving the molten metal under a reduced pressure of 200 Torr or less is effective, and is important for establishing the production method of the present invention.

≪Filling≫
In order to establish the production method of the present invention, it is important to pour molten metal having a melt temperature of 670 to 730 ° C. into a mold having an average cavity surface temperature of 45 ° C. or more.
The reason is that when the molten metal temperature is lower than 630 ° C. and the cavity surface temperature is 45 ° C. or lower, the fluidity of the molten metal is lowered and solidification is accelerated, so that it is impossible to completely fill the mold (cavity). There is a risk of causing so-called poor hot water.
Therefore, at the time of casting in which the molten metal after any one or more of the above-described refining treatment, degassing treatment, and degassing treatment is poured into a mold, the molten metal temperature is 670 to 730 ° C. Filling the mold with pouring into the mold at an average surface temperature of 45 ° C. or higher is important in establishing the production method of the present invention.

≪Sand mold≫
It is important for the production method of the present invention to contain 30% or more of zircon sand (ZrO ₂ , ZrO) as a sand mold main material.
That is, the sand mold usually uses silica sand (SiO ₂ ) as a mold main material. The heat-resistant magnesium alloy of the present invention is a so-called good castability material that fully considers castability (such as molten metal flowability, seizure, and casting cracks) at the alloy design stage. However, the alloy design suffers, and on the other hand, conventional refiners (all those with C-based compounds as refined nuclei) cannot refine the crystal grains of castings (improve mechanical properties, strength and elongation). In sand mold casting, which has a slower solidification rate than mold casting, the difference is most prominent.
Therefore, using 30% or more of zirconium sand, whose thermal conductivity coefficient is smaller than that of silica sand (which has good thermal conductivity), as a mold main material, solidifies faster than silica sand 100%. An increase in the number of crystal nucleation occurs, and as a result, a refined structure of the casting is obtained. That is, it becomes possible to cast a casting having excellent mechanical properties (axial force retention, tensile strength, 0.2 yield strength, elongation).
Therefore, it is important for the production method of the present invention to contain 30% or more of zircon sand (ZrO ₂ , ZrO) as a sand mold main material.

[Prototype production]
The various Mg-Al-Ca alloys of Examples 1 to 6 shown in Table 1 under the conditions of refining treatment, degassing treatment, degassing treatment, filling (pouring), and sand mold of the manufacturing method described above, comparative examples Manufacture of prototypes using 1 to 6 Mg-Al-Ca alloys was attempted under the following casting conditions.
Casting conditions Use mold: JIS-H5203 sand mold (4 test pieces, 4 pieces, molded with wooden mold)
Molten metal treatment: After melting alloy, flux refining: at 650-670 ° C
⇒ Ar degassing: 3 liters / minute x 5 minutes at 630-700 ° C
(If oxidation combustion is intense here, refining flux is sprayed)
⇒ Sedation: 5-10 minutes Molten metal filling: at 700-720 ° C
Prototype a: 150 × 150 × 3.5t (assuming average wall thickness at the time of trial production of actual parts)
Prototype b: 140 × 60 × 30t (assuming a thick part when prototyping an actual part)

[Evaluation]
And the test which evaluates the castability at the time of casting by the said casting conditions and the mechanical characteristic of the casting (prototypes a and b) obtained by this casting condition was done.

[Castability]
The castability under the above casting conditions was evaluated by two parameters of fluidity and casting crack that characterize the properties of the alloy in the casting process, and the results are shown in Table 2.

≪Liquidity≫
With regard to fluidity (hot water flow), during casting in which molten metal is poured into a mold, the amount of molten metal overflow and the amount of molten metal filled in a space such as a chill belt into which the molten metal flows are determined as evaluation criteria. The evaluation was divided into stages.
a. Good b. Slightly inferior c. Inferior

≪Casting crack≫
Cast cracks (occurrence of hot cracks) were evaluated by appearance inspection of the obtained castings (prototypes), judged by the presence or absence of cracks, and evaluated in the following three stages.
a. Almost none b. There is a little c. Yes

[Mechanical properties]
Moreover, as evaluation of the mechanical characteristics of the various Mg-Al-Ca-Be-Mn alloy castings (prototypes) of Examples 1 to 6 and Comparative Examples 1 to 6 shown in Table 1 obtained by the casting conditions described above. The axial force retention and tensile properties (tensile strength, 0.2% proof stress and elongation) were measured, and the results are shown in Table 2.

≪Axial force retention ratio≫
FIG. 1 is a conceptual explanatory view schematically showing a state in which an axial force of a bolt that has been fastened is measured.
As shown in FIG. 1, the axial force measurement is performed on a test material (seat surface outer diameter φ20 mm, inner diameter (bolt insertion hole) φ9 mm, thickness about 10 mm) 1 having a bolt insertion hole 1 a processed into a cylindrical shape. Maintained in an atmospheric furnace at 150 ° C. for 200 hours in a state of being fastened to a mating member 2 having a screw hole (M8.0 × P1.25) 2a through a washer 3 with a predetermined axial force by a bolt (with flange) 4 Then, the axial force retention (%) was evaluated by measuring the axial force of the bolt 4 after cooling to room temperature.
Here, the used counterpart material 2 is an aluminum alloy member of JIS standard ADC12 having a block shape of L50 × D25 × D25, and the washer 3 is an aluminum alloy having an outer diameter φ18 mm, an inner diameter φ9 mm, a thickness 3 mm, and A6061-T6. The bolt 4 is made of an iron alloy with M8 × P1.25 × 25 mm and strength classification 8.0-9.0. is there.

More specifically, as shown in FIG. 1, the bolt 4 is inserted into the bolt through hole of the specimen 1 through the washer 3, and the initial axial force 9.5 KN ( The bearing surface pressure is about 50 MPa). The axial force of the bolt 4 at this time was measured with a strain gauge 5 attached to the bolt 4 shown in FIG. And the fastening test piece which consists of the washer 3 which fastened the volt | bolt 4, the specimen 1 and the other party material 2 was accommodated in the atmospheric furnace, and it cooled to room temperature, after hold | maintaining high temperature on the conditions of 150 degreeC and 200 hours.
After cooling to room temperature, the axial force retention with respect to the initial axial force was determined by measuring the axial force of the bolt 4 again with the strain gauge 5. This axial force retention rate can be obtained as an average value of a plurality (approximately n = 3). The calculation formula is as follows.

Axial force retention rate (%) = (residual axial force after heating to 150 ° C. × 200 h and cooling to room temperature ÷ initial axial force before heating) × 100

Here, the fact that the axial force retention rate is 45%, for example, means that the axial force has decreased to an initial axial force of 9.5 KN × 0.45 due to high temperature retention at 150 ° C. for 200 hours. Is. Therefore, the case where the axial force retention rate exceeded 45% was evaluated as ◯, and the case where the axial force retention rate did not exceed was evaluated as ×.

[Tensile properties]
FIG. 2 is an explanatory view showing a test piece for evaluating tensile properties.
And the test which evaluates a tensile characteristic was done. The test condition at this time is an Instron type tensile test manufactured by Tsushima Seisakusho Co., Ltd. in an atmosphere of 20 to 25 ° C. with a test piece (test piece) cut and processed into the shape (approximate size) shown in FIG. The tensile strength (MPa), 0.2% proof stress (MPa), and elongation (%) were each evaluated by pulling at a crosshead speed of 1 mm / min using a machine.
Here, GL in the dimension display of the test piece shown in FIG. 2 represents the distance between the scores, and PP represents the length of the plane portion.

  Comparative Example 1 shown in Table 1 has an aluminum content lower than the lower content limit of the various Mg-Al-Ca alloys, and Comparative Example 2 has an aluminum content of the various Mg-Al-Ca alloys. It exceeds the upper limit of the content of. In Comparative Example 3, the calcium content is lower than the lower content limit of the various Mg-Al-Ca alloys, and in Comparative Example 4, the calcium content is the contents of the various Mg-Al-Ca alloys. It is above the upper limit. In Comparative Example 5, the beryllium content is lower than the lower content limit of the various Mg-Al-Ca alloys, and in Comparative Example 6, the beryllium content of the various Mg-Al-Ca alloys is included. It is above the upper limit.

As can be seen from Table 2, Comparative Example 1 and Comparative Example 4 have high values in the mechanical properties of axial force retention, tensile strength, 0.2% proof stress, and elongation, but the molten metal at the time of casting. The fluidity of the film was slightly inferior, and there was a problem in castability such as casting cracking and seizure, and the overall evaluation was x.
In Comparative Example 2, although the castability was improved as compared with Comparative Example 1, the axial force retention in the mechanical characteristics was low, and the overall evaluation was x.
In Comparative Example 3, although the castability was improved as in Comparative Example 2, the axial force retention and the 0.2% proof stress in the mechanical properties were low, and the overall evaluation was x.
Comparative Example 5 has a high value in mechanical properties, and although casting cracks do not occur at the time of casting, the fluidity of the molten metal at the time of casting is poor, and there are some problems with casting properties such as seizure. The overall evaluation was x.
In Comparative Example 6, the fluidity of the molten metal at the time of casting was poor, and there were some problems in casting properties such as seizure, and the 0.2% proof stress value was low in mechanical properties, and the overall evaluation was x. .

  In contrast to Comparative Examples 1 to 6, according to Examples 1 to 6, as shown in Table 2, the fluidity of the molten metal at the time of casting, the prevention of casting cracks and seizure, the axial force retention, the tensile strength It has a high value in the mechanical properties of 0.2% proof stress and elongation, and it has been confirmed that it is excellent overall.

As described above, it was confirmed that the heat-resistant magnesium alloy is suitable for sand mold casting, hardly adheres to the mold, hardly causes cracking in casting, and has excellent fluidity. As a result, on the premise of mass production casting such as die casting, prototype casting of a prototype in the design and development stage of a new product can be realized by simple sand mold casting that is possible at a low cost and in a short period of time. .
Moreover, the prototype which can obtain the mechanical characteristics (axial force retention, tensile strength, 0.2% yield strength, elongation) of 75% or more of the die cast product can be manufactured by simple sand casting.

The specific configuration of the embodiment of the present invention is not limited to the above-described embodiment, and even if there is a design change or the like without departing from the gist of the present invention described in claims 1 to 10. It is included in the invention.
As the heat-resistant magnesium alloy, in addition to the Mg-Al-Ca-based alloy described in detail in the above embodiment, for example, any of Mg-Al-Mn-based alloy, Mg-Zn-Mn-based alloy, or Mg-Al-Zn-Mn-based alloy For the purpose of improving heat resistance, one heat-resistant magnesium alloy containing at least one of Ca, Sr, ER, Si, and Sn can be cited as one alloy.
Then, using these heat-resistant magnesium alloys, it is possible to embody sand mold casting under the casting conditions in the manufacturing method described in detail in the above embodiment.

  Moreover, as a heat-resistant magnesium alloy, aluminum is more than 9.20 mass% to 12.6 mass%, calcium is 0.9 to 2.0 mass%, beryllium 0.0005 to 0.1000 mass%, and manganese is 0.10. -0.45 mass%, the balance is magnesium and inevitable impurities, and further, zinc is 1.0 mass% or less, iron is 0.005 mass% or less, silicon is 0.10 mass% or less, nickel is 0.00. A heat-resistant magnesium alloy containing 020% by mass or less and copper by 0.030% by mass or less can be exemplified.

Claims (8)

A heat-resistant magnesium alloy for casting containing magnesium, aluminum and calcium,
9.20% by mass to 12.6% by mass of aluminum, 0.9 to 2.0% by mass of calcium, 0.0005 to 0.1000% by mass of beryllium, and 0.10 to 0.45% by mass of manganese Containing , zinc, strontium, iron, nickel,
It contains 1.0% by mass or less of zinc, 0.60% by mass or less of strontium, 0.005% by mass or less of iron, 0.020% by mass or less of nickel, and the balance is composed of magnesium and inevitable impurities. Heat-resistant magnesium alloy for casting . 9.50% to 10.5% by weight of aluminum, 1.2% to 2.0% by weight of calcium, and 0.0010 to 0.0100% by weight of beryllium are contained. Item 2. The heat-resistant magnesium alloy for casting according to item 1. The heat-resistant magnesium alloy for casting according to claim 1 or 2, further containing silicon and copper, containing 0.10% by mass or less of silicon and 0.030% by mass or less of copper . Heat-resistant magnesium alloy. A manufacturing method for melting a heat-resistant magnesium alloy for casting according to any one of claims 1 to 3, and pouring the molten alloy into a mold to cast a casting,
With respect to the molten alloy, refining treatment with a flux at six hundred thirty to six hundred seventy ° C., degassing with an inert gas at six hundred thirty to seven hundred and thirty ° C., a degassing treatment by standing the molten alloy under a reduced pressure of not more than 200Torr and line intends process,
A filling step of pouring the molten alloy at a melt temperature of 670 to 730 ° C. into the mold having an average cavity surface temperature of 45 ° C. or higher after the treatment step ;
A method for producing a heat-resistant magnesium alloy casting, wherein the mold is a sand mold, and the mold main material contains 30% or more zircon sand . 10-15 mass% calcium fluoride, 40-46 mass% barium chloride, 6-11 mass% potassium chloride, 30-38 mass% magnesium chloride, and inevitable impurities are mixed in the flux. Made of powder,
After the powder is charged and kneaded into the molten alloy within a range of 0.2 to 0.5 mass% of the total molten metal weight poured into the mold, the molten alloy is stirred for 20 minutes or less. 5. The method for producing a heat-resistant magnesium alloy casting according to claim 4, wherein the molten metal calming is continued for 5 minutes or more after the stirring operation.   The degassing treatment is performed by sending argon gas into the molten alloy at a flow rate of 3 to 10 liters / minute for a time of 3 minutes or more, and the argon gas has a purity of 97% or more. A method for producing a heat-resistant magnesium alloy casting according to claim 4 or 5.   The feed of the argon gas into the molten alloy is performed by immersing a gas supply pipe having a large number of fine holes through which the argon gas is ejected as bubbles into the molten alloy. 6. A method for producing a heat-resistant magnesium alloy casting described in 6. The method for producing a heat-resistant magnesium alloy casting according to any one of claims 4 to 7, wherein the hydrogen content of the casting is 20 cc / 100 g Mg or less .

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