JP2007277660A - Magnesium alloy and die cast product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium alloy for casting having excellent casting properties and high strength, to provide a method for producing a die cast product using such the alloy, and to provide a magnesium die cast product. <P>SOLUTION: The magnesium alloy has a componential composition comprising, by mass, 4.0 to 13.0% Al, 0.1 to 15.0% Sn, 0.1 to 3.0% Zn and 0.05 to 0.60% Mn, and, if required, further comprising at least either 0.05 to 0.50% Zr or 0.01 to 0.50% Cu. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnesium alloy suitably used as, for example, an automobile body part, a method for producing a die-cast product using such a magnesium alloy, and a magnesium die-cast product by the production method.

In recent years, needs for weight reduction of materials used for vehicles such as automobiles and various industrial machines have increased, and magnesium alloys having the lowest density among practical alloys have attracted attention.
However, this magnesium alloy presents a problem that its strength is lower than that of a cast aluminum alloy material that has many achievements as a lightweight metal.

As such a magnesium alloy, for example, those disclosed in Patent Documents 1 to 3 are known.
Japanese Patent Laid-Open No. 7-3374 JP 2004-238676 A JP 2005-68550 A

  That is, Patent Document 1 contains 6.0 to 20.0% Sn (tin) and 0.2 to 2.0% Si (silicon) by mass ratio, and further Al (aluminum). And a magnesium alloy excellent in creep characteristics containing 4.0% or less of at least one of Zn (zinc).

  Further, according to Patent Document 2, the mass ratio is also at least 85.4% Mg (magnesium), 4.7 to 7.3% Al, 0.17 to 0.60% Mn (manganese) ), 0.0-0.8% Zn, 1.8-3.2% Ca (calcium), 0.3-2.2% Sn, 0.0-0.5% Sr (strontium) ) Containing magnesium alloys are described.

  In Patent Document 3, Al is 6 to 12%, Ca is 0.05 to 4%, RE (rare earth element) is 0.5 to 4%, and Mn is 0.05 to 0 in the same mass ratio. .50%, together with a magnesium alloy containing 0.1 to 14% Sn, and at least one of 0.05 to 0.2% Zr (zirconium) and 0.03 to 0.2% C (carbon) A magnesium alloy containing one is disclosed.

  However, the magnesium alloy described in Patent Document 1 contains Sn and Si as heat resistance enhancing elements in order to improve creep characteristics, but contains Sn but has a low Al content. Therefore, there is a problem that it is inferior in castability (hot water flow, casting). Further, although the magnesium alloy described in Patent Document 2 contains Sn as a castability improving element, since Ca is added, a brittle crystallized product may be formed at the crystal grain boundary. There is a tendency to be inferior in ductility.

And in the magnesium alloy of the said patent document 3, although heat resistance is improved by dissolving Sn in the alpha-Mg phase, although it contains Sn, Ca and rare earth elements are added. Therefore, a brittle crystallized product may be formed at the grain boundary in the same manner, and there is a problem that the ductility is inferior.
Furthermore, in such a magnesium alloy containing a rare earth element, an intermetallic compound is formed at the time of remelting, so that there is a problem that the recyclability is poor.

  The present invention has been made in view of the above-mentioned situation in conventional magnesium alloys, and the object of the present invention is to make a magnesium alloy made of such an alloy together with a high-strength magnesium alloy for casting excellent in castability. To provide die-cast products.

  In order to achieve the above object, the present inventors have conducted intensive studies on the additive component and the amount of addition to the magnesium alloy, and as a result, without adding Ca or rare earth elements, The inventors have found that the above problems can be solved by adding quantitative amounts of Sn, Zn, and the like, and have completed the present invention.

  That is, the present invention is based on the above knowledge, and the magnesium alloy of the present invention has a mass ratio of 4.0 to 13.0% Al (aluminum) and 0.1 to 15.0% Sn. (Tin), 0.1 to 3.0% Zn (zinc), and 0.05 to 0.60% Mn (manganese), and if necessary, further 0.05 to 0.50 % Zr (zirconium) and 0.01 to 0.5% Cu (copper), and the balance consists of Mg and inevitable impurities.

  And in the manufacturing method of the die-cast product of this invention, the said magnesium alloy is cast by the die-casting method, and it is made to give an aging treatment further as needed.

  Moreover, the die-cast product of this invention is manufactured by the said manufacturing method, Comprising: For example, it can apply to the various components for motor vehicles.

According to the present invention, the component composition of the magnesium alloy is, by mass ratio, Al: 4.0-13.0%, Sn: 0.1-15.0%, Zn: 0.1-3.0%, Mn : Since 0.05 to 0.60% is contained, a high-strength magnesium alloy excellent in castability can be obtained. By using the alloy, a high-strength die-cast product without casting defects can be easily obtained. Can get to.
Furthermore, if necessary, by adding at least one of 0.05 to 0.50% Zr and 0.01 to 0.50% Cu, in addition to the above, an excellent characteristic that the strength is improved. Will be demonstrated.

  Hereinafter, the magnesium alloy of the present invention will be described in more detail together with the reasons for limiting the chemical components. In the present specification, “%” represents mass percentage unless otherwise specified.

  Since the magnesium alloy of the present invention has the above component composition, it is excellent in strength and castability. The reason why the strength and castability are improved in the magnesium alloy is as follows. Can be considered.

That is, in the magnesium alloy of the present invention, Sn is added, which is dissolved in the primary crystal α-magnesium phase forming the magnesium alloy, and the strength of the alloy is improved by solid solution strengthening.
And Sn is known as a fluidity improving element in magnesium alloy molten metal, and based on good workability, it is possible to obtain a die-cast product free from defects such as poor hot water due to poor hot water flow and hot water boundaries. .

  In general, rare earth elements are often added to high-strength magnesium alloys, but such rare earth element-added alloys are inferior in recyclability because rare earth element-based intermetallic compounds are formed during remelting. (Such an intermetallic compound has a high melting point and cannot be recycled because it does not re-dissolve). However, in the present invention, since the hardness is improved by Sn without adding rare earth elements, it is excellent in recyclability. At the same time, since Sn is relatively cheaper than rare earth elements, the material cost is reduced.

  Next, together with the action of each component element in the magnesium alloy of the present invention, the reason for limiting the content will be described.

Al: 4.0 to 13.0%
Al is an element that contributes to improvement of castability, in particular, molten metal flow, and is effective for strengthening the alloy and improves mechanical properties.However, when it is excessively contained, toughness and strength are reduced, but when insufficient, Since the hot water flowability cannot be sufficiently improved, the Al content needs to be 4.0% or more and 13.0% or less.

Sn: 0.1-15.0%
Sn dissolves in the primary crystal α-magnesium matrix and contributes to improvement of strength by solid solution strengthening. In addition, according to the Mg—Sn phase diagram, Sn can be contained up to about 14.5% in the primary α-magnesium phase. Therefore, by performing an aging heat treatment, it is due to precipitation strengthening of the Mg ₂ Sn phase. Contributes to strength improvement.
However, when the Sn content is less than 0.1%, such an effect cannot be sufficiently obtained. On the other hand, when Sn is added excessively, toughness and strength are reduced, and Sn has a large specific gravity of about 7.3. Therefore, if Sn is excessive, the characteristics of the magnesium alloy as a lightweight alloy may be lost. Therefore, the Sn content is specified in the range of 0.1% to 15.0%.

Zn: 0.1-3.0%
Zn is an element effective in improving yield strength and elongation by solid solution strengthening and inducing age hardening to increase the effect of heat treatment, but if its content is less than 0.1%, The effect cannot be obtained sufficiently.
And as the Zn content increases, the tensile strength and proof stress at room temperature increase, but when the Zn content becomes excessive, the toughness and strength decrease on the contrary, the Zn content is 0.1% or more, It is necessary to be within the range of 3.0% or less.

Mn: 0.05 to 0.60%
Mn is an element that contributes to the improvement of corrosion resistance, but if the addition amount is small, the intended effect cannot be obtained, and because toughness and strength are reduced by excessive addition, the Mn content is 0.05% or more, It was specified in the range of 0.60% or less.

Zr: 0.05 to 0.50%
Cu: 0.01 to 0.50%
As described above, the magnesium alloy of the present invention contains Al, Sn, Zn, and Mn as essential components, but Zr and Cu are components that are effective for strength and ductility. Accordingly, in addition to the essential component elements, 0.05% and 0.01% or more and 0.50% or less can be added.
That is, by adding Zr in the range of 0.05 to 0.50%, it contributes to improvement in strength and ductility by crystal grain refinement, and Cu is added in the range of 0.01 to 0.50%. By doing so, the strength can be improved during the aging heat treatment. If these elements are out of the above range, the above effects cannot be obtained.

In the method for producing a die-cast product of the present invention, the magnesium alloy of the present invention is cast by a die-casting method, and the magnesium alloy has excellent molten metal flowability and good castability as described above. Therefore, a healthy die-cast product without defects can be manufactured with good workability.
At this time, it is desirable to preheat the die casting mold to about 100 to 250 ° C., for example, thereby improving the hot water flow.

Further, in the method for producing a die-cast product of the present invention, it is desirable to perform an aging treatment on a cast product obtained by die casting, and the strength of the product is greatly increased by age hardening based on precipitation of Mg ₂ Sn phase and β phase. Can be improved.
Further, prior to the aging treatment, the die casting product can be subjected to a solution treatment, whereby the aging treatment can be made more effective.

That is, heat treatment is performed when strength and ductility are required. However, since the cost is high, it is determined whether heat treatment is necessary according to the required performance.
In addition, as the solution treatment conditions, for example, after uniformly heating to 390 to 410 ° C., the solution is rapidly cooled by holding for about 2 to 24 hours, and the aging treatment conditions are 180 to 250 ° C. for 4 to 32 hours. An example of the condition for maintaining the degree can be illustrated.

  The die-cast product of the present invention is manufactured by the above-described manufacturing method. For example, various parts for automobiles, that is, body parts such as steering members, seat frames, door inners, back door inners, strut housings, It can be applied to chassis parts such as suspension members, frames, suspension link members and engine cradle.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(1) Magnesium alloy The following evaluation was performed using six kinds of magnesium alloys for the purpose of the chemical component composition shown in Table 1.

(2) Melting and Casting Six kinds of magnesium alloys shown in Table 1 were melted in the atmosphere using an electric resistance furnace. In addition, SF ₆ + CO ₂ mixed gas was used for preventing oxidation of the molten metal.
Further, in order to remove impurities, KgCL ₂ based flux was placed for 1% of the total melt weight and allowed to subside stirred for 10 minutes, die-casting die preheated to 200~250 ℃ (190 × 40 × The molten metal was cast into a 115 mm book mold).

(3) Heat treatment conditions and evaluation method DSC (Differential Scanning Calorimetry) analysis is performed, and based on the results, the solution treatment temperature is set to 400 to 410 ° C., which is about 15 ° C. lower than the solidification end temperature of the melt, and β (Mg _The solution treatment time for dissolving the ₁₇ Al ₁₂ ) phase was 24 hours. Further, the aging characteristics at 200 ° C. after the solution treatment were investigated, and the peak aging conditions were obtained.
Under these conditions, each casting was subjected to solution treatment and artificial aging treatment (T6 treatment), and a hardness test and a tensile test were performed at room temperature.

(4) Hardness test results FIG. 1 shows an aging curve at 200 ° C. after the solution treatment.
The Sn-added alloy showed an increase in hardness as compared with the base alloy, and in particular, it was confirmed that the hardness of the AZ91 alloy containing 9% Al increases as the Sn addition amount increases. .
However, since there is no significant change in the age hardening behavior until reaching the peak hardness in each alloy, the addition of Sn only contributes to solid solution strengthening and has a significant effect on the precipitation behavior of the β phase. It is thought that there is no.

(5) Tensile test results FIG. 2 shows the tensile properties of each alloy subjected to T6 treatment at an aging temperature of 200 ° C.
As is clear from this result, the proof stress increases as the amount of Sn added increases, and solid solution strengthening due to the addition of Sn appears remarkably.
In addition, as for the hot-water flow property, as a result of comparison by flow length, it was confirmed that the alloy system (AZT916) of Example 4 was improved by 15% with respect to the alloy system (AZ91) of Comparative Example 2.

It is a graph which shows the aging curve in 200 degreeC of the magnesium die-casting by each alloy melted in the Example. It is a graph which shows the influence of Sn addition amount on the tensile property after T6 process of the magnesium die casting by each alloy melted in the Example.

Claims (10)

  By mass ratio, 4.0-13.0% Al, 0.1-15.0% Sn, 0.1-3.0% Zn, 0.05-0.60% Mn A magnesium alloy characterized in that the balance consists of Mg and inevitable impurities.   By mass ratio, 4.0-13.0% Al, 0.1-15.0% Sn, 0.1-3.0% Zn, 0.05-0.60% Mn In addition, a magnesium alloy containing 0.05 to 0.50% Zr and / or 0.01 to 0.50% Cu, with the balance being Mg and inevitable impurities.   A method for producing a die-cast product, wherein the magnesium alloy according to claim 1 or 2 is formed into a cast product by a die-cast method.   4. The method for producing a die-cast product according to claim 3, wherein an aging treatment is applied to the obtained cast product.   The method for producing a die-cast product according to claim 3, wherein the cast product obtained is subjected to solution treatment and then subjected to aging treatment.   A die-cast product produced by the method according to any one of claims 3 to 5.   The die-cast product according to claim 6, wherein the die-cast product is a body part of an automobile.   The die cast product according to claim 7, wherein the die cast product is a steering member, a seat frame, a door inner, a back door inner, or a strut housing.   The die-cast product according to claim 6, wherein the die-cast product is a chassis part of an automobile.   The die cast product according to claim 9, wherein the die cast product is a suspension member, a frame, a suspension link member, or an engine cradle.

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