JP2011509350A - Magnesium alloy - Google Patents

Abstract

Magnesium-based alloy, 2 to 5% by weight, rare earth elements (the alloy contains lanthanum and cerium as rare earth elements, the lanthanum content is greater than the cerium content); 0.2 to 0.8% zinc; 0-0.15% aluminum; 0-0.5% yttrium or gadolinium; 0-0.2% zirconium; 0-0.3% manganese; 0-0.1% calcium; 0-25 ppm beryllium; incidental Magnesium-based alloy, with the exception of magnesium, the rest being magnesium.
[Selection] Figure 1

Description

  The present invention relates to a magnesium-based alloy, and more specifically to a magnesium-based alloy that can be cast by a high pressure casting method (HPDC).

  With the growing need to limit fuel consumption and reduce harmful emissions to the atmosphere, car manufacturers are trying to develop more fuel-efficient vehicles. Reducing the overall weight of the vehicle is key to achieving this goal. The primary contributor to vehicle weight in any vehicle is the engine and other components of the transmission mechanism. The most important component of the engine is a cylinder block that makes up 20-25% of the total engine weight. In the past, significant weight savings have been made by introducing aluminum alloy cylinder blocks to replace conventional gray cast iron blocks, and if magnesium alloys are used that can withstand the temperatures and stresses generated during engine operation. A further weight loss on the order of 40% could be achieved. It is necessary to develop such an alloy that combines the desired high temperature mechanical properties with a cost-effective manufacturing process before the production of a viable magnesium engine block can be considered.

  HPDC is a very productive process for mass production of light alloy components. Although the casting integrity of sand casting and low pressure / gravity die casting processes is generally higher than HPDC, HPDC is a less expensive technology for larger volume production. HPDC is gaining high acclaim among North American car manufacturers and is the primary process used to cast aluminum alloy engine blocks in Europe and Asia. In recent years, the search for high temperature magnesium alloys has mainly focused on the HPDC processing path and several alloys have been developed. HPDC is considered to be a good option for achieving high productivity and thus reducing manufacturing costs.

Patent document 1 is weight,
1.5-4.0% rare earth elements (one or more),
0.3-0.8% zinc,
0.02-0.1% aluminum,
4-25 ppm beryllium,
0-0.2% zirconium,
0-0.3% manganese,
0-0.5% yttrium,
The present invention relates to a magnesium-based alloy composed of 0-0.1% calcium, except for incidental impurities, the remainder being magnesium.

  The alloy according to Patent Document 1 showed excellent high-temperature creep characteristics, but it was found that it was somewhat difficult to cast by die casting. The inventors have found that the fluidity and hot cracking resistance during casting and the oxidation resistance of the molten alloy are improved by increasing the proportion of lanthanum in the alloy according to US Pat. confirmed.

  Throughout this specification, the expression “rare earth” is understood to mean the element of atomic number 57-71, ie any of lanthanum (La) to lutetium (Lu), or a combination of these elements. I want.

International Publication No. 2006/105594 Pamphlet

The present invention is a magnesium-based alloy, 2 to 5% by weight rare earth element (this alloy contains lanthanum and cerium as rare earth elements, the lanthanum content being greater than the cerium content);
0.2-0.8% zinc;
0.02 to 0.15% aluminum;
0-0.5% yttrium or gadolinium;
0-0.2% zirconium;
0-0.3% manganese;
0-0.1% calcium;
Provided is a magnesium-based alloy consisting of 0-25 ppm beryllium, with the remainder being magnesium except for incidental impurities.

Comparison of creep curves for Alloy A to Alloy F (all included) tested under the same conditions at 177 ° C. and 90 MPa. Comparison of creep curves of Alloys G and H and Alloy X tested under the same conditions at 177 ° C. and 90 MPa tensile load. a) Photograph of a malleable mold part with three small overflows (see left hand side of the photo) and a three-part spout (see right hand side of the photo). b) Photograph of the as-cast surface finish of an HPDC part cast using the alloy H of the present invention. Comparison of internal defect structures of (a) Alloy I and (b) Alloy J (c) Alloy H of the present invention cast into parts (see FIG. 2) under the same processing conditions. Approximate temperature vs. solid fraction curve (fs) for Alloys I and H based on Gulliver-Scheil model calculations using each phase diagram of each individual rare earth assuming complete mixing. Comparison of the surface quality of (a) Alloy I and (b) Alloy H. Comparison of creep curves for Alloy K to Alloy P (all included) tested under the same conditions at 177 ° C. and 90 MPa.

In a first aspect, the present invention is a magnesium-based alloy, 2 to 5% by weight of a rare earth element (this alloy contains lanthanum and cerium as rare earth elements, the lanthanum content being greater than the cerium content);
0.2-0.8% zinc;
0.02 to 0.15% aluminum;
0-0.5% yttrium or gadolinium;
0-0.2% zirconium;
0-0.3% manganese;
0-0.1% calcium;
Provided is a magnesium-based alloy consisting of 0-25 ppm beryllium, with the remainder being magnesium except for incidental impurities.

  The total lanthanum and cerium content of this alloy is preferably 1.5 to 3.5% by weight, more preferably 1.8 to 3.0%, most preferably 2.0 to 2.8%. While not wishing to be bound by theory, the lanthanum and cerium also improve the malleability and creep strength of the alloy. Again, without wishing to be bound by theory, a lanthanum content greater than the cerium content further improves the malleability of the alloy, particularly the hot cracking resistance of the alloy. A higher ratio of lanthanum to cerium typically gives the alloy greater ductility and greater resistance to hot cracking. Typically, a higher total lanthanum and cerium content is beneficial to the creep resistance of the alloy, with a decrease in the ductility of the alloy.

  The rare earth element content of the alloy may optionally contain neodymium, and in that embodiment, the rare earth element content is primarily lanthanum, cerium and neodymium. Although not wishing to be bound by theory, the inclusion of neodymium improves the creep resistance of this alloy. However, the neodymium content of the alloy may be reduced to improve the malleability of the alloy, particularly its resistance to hot cracking. When present, this neodymium content is preferably 0.5-2.0%, more preferably 0.5-1.5%, more preferably about 1% by weight of the alloy.

  The various rare earth elements are typically derived from lanthanum misch metal containing lanthanum, cerium, optionally neodymium, small amounts of praseodymium (Pr) and traces of other rare earths. In another embodiment, the rare earth element is derived from cerium misch metal and pure lanthanum may be used together to provide a lanthanum content greater than the cerium content. For alloys that require a low cerium content, these rare earth elements may be derived from a commercially pure source of lanthanum.

  The neodymium may be derived from one or both of the above-mentioned misch metals, a pure source of neodymium, didymium (neodymium rich neodymium-praseodymium alloy), or any combination thereof.

  Yttrium is an optional ingredient that may be included. While not wishing to be bound by theory, the inclusion of yttrium is believed to be beneficial for both melt protection and creep resistance. However, the yttrium content of the alloy may be reduced to improve the malleability of the alloy, particularly its resistance to hot cracking. When present, the yttrium content is preferably 0.005 wt% to 0.5 wt%, more preferably 0.01 to 0.4 wt%, more preferably 0.05 to 0.3 wt%, most preferably Is 0.1 to 0.2% by weight.

  The lanthanum or cerium misch metal from which these rare earth elements are derived may optionally contain yttrium. The yttrium content may thus be derived from these misch metals. Yttrium may be derived from a pure source of yttrium content, a magnesium-yttrium master alloy, or any combination of these with or without the misch metal.

  Gadolinium is an optional ingredient that may be included. While not wishing to be bound by theory, the inclusion of gadolinium is believed to be beneficial for both the creep and oxidation resistance of the melt. Gadolinium addition may be performed instead of yttrium addition. However, this gadolinium addition may be performed in combination with yttrium addition. When present, the gadolinium content is preferably 0.005% to 0.5% by weight, more preferably 0.01 to 0.4% by weight, more preferably 0.05 to 0.3% by weight, most preferably 0.1 to 0.2% by weight.

  Preferably, the alloys according to the invention contain at least 94.0% magnesium, more preferably 95-96% magnesium, most preferably about 95.3-95.7% magnesium.

  The zinc content is 0.2-0.8% by weight, preferably 0.2-0.6%, more preferably about 0.4%.

  The aluminum content is preferably 0.05 to 0.15% by weight, more preferably 0.08 to 0.12% by weight, more preferably about 0.1% by weight. While not wishing to be bound by theory, it is believed that the inclusion of these small amounts of aluminum in the alloys of the present invention improves the creep properties of the alloys.

  The beryllium content is 0-25 ppm. If present, this beryllium content is preferably 4-20 ppm, more preferably 4-15 ppm, more preferably 6-13 ppm, such as 8-12 ppm, but when yttrium is present, it is preferred that no beryllium is present. . This is because yttrium has a similar effect to beryllium at low yttrium levels. If present, beryllium will typically be introduced as an aluminum-beryllium master alloy, such as an Al-5% Be alloy. While not wishing to be bound by theory, inclusion of beryllium is believed to improve the castability of the alloy. Again, not wishing to be bound by theory, the inclusion of beryllium improves the oxidation resistance of the molten alloy, and in particular also improves the retention of rare earth elements in this alloy from reduction by oxidation. Conceivable.

  Reduction of the iron content can be accomplished by the addition of zirconium that precipitates iron from the molten alloy. Accordingly, the zirconium content specified herein is the residual zirconium content. However, it should be noted that zirconium may be incorporated in two different stages. Firstly during the production of the alloy and secondly after remelting of the alloy prior to casting. Preferably, the zirconium content will be the minimum amount required to achieve satisfactory iron removal. Typically, the zirconium content will be less than 0.1%.

  Manganese is an optional component of the alloy. If present, the manganese content will typically be about 0.1%.

  Calcium (Ca) is an optional component that may be included in situations where adequate molten metal protection is not possible, especially through control of the cover gas atmosphere. This is especially true when a closed system is not involved in the casting process.

  Ideally, the incidental impurity content is zero, but it should be understood that this is virtually impossible. Accordingly, it is preferred that this incidental impurity content be less than 0.15%, more preferably less than 0.1%, more preferably less than 0.01%, and even more preferably less than 0.001%.

  In a second aspect, the present invention provides an engine block for an internal combustion engine manufactured by high pressure casting the alloy according to the first aspect of the present invention.

  In a third aspect, the present invention provides a component of an automotive transmission mechanism formed from an alloy according to the first aspect of the present invention.

  The component of this transmission mechanism may be an engine block or a part of the engine, such as a cover, oil pan or bracket.

  The transmission mechanism component may be a transmission housing or another transmission component.

  Although specific reference is made to the conduction mechanism above, it should be noted that the alloys of the present invention may be used in other high temperature and low temperature applications. Although specifically referred to above as HPDC, the alloys of the present invention may be cast by techniques other than HPDC, including thixomolding, thixocasting, mold casting and sand casting. Please keep in mind.

  In a fourth aspect, the present invention provides an article formed from the alloy according to the first aspect of the present invention.

Example 1
The high Nd type die casting alloy has the following composition:
1.8 wt% Nd
0.7% by weight Ce
0.4 wt% La
0.6 wt% Zn
The rest Mg.

  The alloy was removed from the cover gas protection protected by the trademark known as AM-cover by immersing a cylinder with a 10 mm diameter hole in the bottom. 2 l / min of dry air was introduced at the top of the cylinder. The bottom surface of the cylinder was immersed in the molten alloy to a depth of 50 mm, and the surface state of the molten metal was observed.

  For this high Nd alloy, the new melted surface turned black almost instantaneously and a flaming magnesium bloom occurred shortly thereafter.

  Addition of 53 ppm yttrium via 43% yttrium-57% magnesium master alloy to the melt dramatically changed the oxidation behavior of the melt. When the cylinder was inserted into the melt, the surface of the melt remained bright and shiny for 50 seconds, but after that spot-like combustion started. The addition of 250 ppm yttrium was also excellent in resistance to the start of combustion.

  A similar effect is experienced when gadolinium is added to the melt instead of yttrium. Although 310 ppm of gadolinium addition was sufficient to delay the onset of spot burning in the 60 second cylinder test, it was not as efficient as yttrium for this purpose.

It has been observed that the higher lanthanum type of the alloy behaves differently than the high Nd type. A pilot work was conducted on the high La type oxidation behavior of the alloy containing:
1.6 wt% La
0.9 wt% Nd
1.1 wt% Ce
0.6 wt% Zn
The rest Mg.

  The cylinder test described above was also used here. Upon removal of the melt from this protective atmosphere and into the dry air, the alloy remained shiny and shiny after 40 seconds without any signs of oxidation or combustion. This alloy had a molten metal protection behavior similar to the high Nd type of the alloy with the addition of 50-100 ppm yttrium. Addition of yttrium to this high La version of the alloy was not necessary for melt protection purposes.

Example 2
Ten alloys were prepared and the chemical analysis of these alloys is shown in Table 1 below. These rare earth elements were added as cerium-based misch metal (which contained cerium, lanthanum and some neodymium) and elemental lanthanum and neodymium. Yttrium and zinc were added in their elemental form. Beryllium was added as an aluminum-beryllium master alloy. Aluminum was added as elemental aluminum alone as this master alloy supplemented with elemental aluminum or without beryllium added. Zirconium was added by a Mg-Zr master alloy guarded by the trademark known as AM-cast. The balance of the alloy was magnesium except for accidental impurities. Standard melt handling procedures were used throughout the preparation of these alloys.

表１ − 調製された合金（ＮＡ：分析せず）

Table 1-Prepared alloys (NA: not analyzed)

  FIG. 1 shows the creep results for alloys A, B, C, D, E and F at 177 ° C. and 90 MPa. This set of creep curves shows the dramatic effect of compositional variations on the creep performance in the alloys of the present invention. The control alloy (Alloy A) exhibits a relatively low creep resistance under the imposed test conditions, enters tertiary creep at the very beginning of this test (<50 hours), and 1 when the test is completed at 600 hours. Finished with 3% creep strain. This was consistent with previous results for other alloy types that did not contain an Al / Be addition for molten metal protection.

  The addition of yttrium (about 0.05% by weight) substantially improved the creep response (Alloy B). Both Alloy A and Alloy B reached 0.1% creep strain at approximately the same time, 62 hours and 60 hours, respectively, but the onset of tertiary creep was delayed until much later in the test for Alloy B.

  The addition of a small amount of aluminum (about 0.03% by weight) resulted in a significant improvement in creep response (Alloy C). The alloy did not reach 0.1% creep strain under approximately 500 hours under the imposed test conditions and did not appear to have entered tertiary creep until the end of the test (600 hours). With an additional amount of aluminum (about 0.06 wt%), further improvement in creep properties was observed (Alloy D) and no 0.1% creep strain was reached during the duration of this test ( 0.04% creep strain after 600 hours). As the aluminum content was further increased (alloy E, about 0.1 wt%), creep resistance began to decline (0.1% creep strain at about 190 hours), but still still relatively good it was thought. Finally, when the aluminum content was significantly increased (Alloy F, about 0.6 wt%), the creep response of this alloy was completely aggravated. Alloy F was considered to have very low creep resistance under the imposed test conditions. These results confirm that aluminum is an important microalloying additive in obtaining excellent creep properties.

FIG. 2 shows the creep results for alloys G and H for 177 ° C. and 90 MPa. Alloys G and H both delayed tertiary creep to the point where the duration of the test was exceeded. As shown in FIG. 2, the creep resistance of alloy H is prepared according to WO 2006/105594 and by weight,
0.68% zinc,
1.89% neodymium,
0.56% cerium,
0.33% lantern,
<0.005% yttrium,
0.05% aluminum,
<5ppm iron,
It is advantageously compared to Alloy X, which has a composition of 12 ppm beryllium and the remainder is magnesium except for incidental impurities.

  Tensile properties were measured according to ASTM E8 at 20 and 177 ° C. in air using an Instron universal tester. Prior to testing, the samples were held at temperature for 10 minutes. The specimen had a circular cross section (diameter 5.6 mm) and a gauge length of 25 mm.

  Table 2 shows the results of tensile tests on various samples of the alloy.

Table 2-Tensile test data

  It is pointed out that both Alloy G and Alloy H had very good malleability. The processing range for obtaining a normal casting is much wider for these two alloys than for the alloy X mentioned above. For good casting quality, the alloy requires low susceptibility to hot cracking, good mold filling properties, and low susceptibility to defect formation at the intersection of the flow fronts in the mold.

  A malleability test mold was developed to evaluate the malleability of a wide range of alloys by high pressure casting (HPDC). A cast from this mold is shown in FIG. Since this mold was designed to have a complex shape, it would be extremely difficult to produce a good quality high pressure casting using this mold. FIG. 3 (a) shows a three-part gate system channel (known as “runner” in the art) on the right hand side of the casting, through which the molten alloy flows into the mold. . "Overflow" can be seen on the opposite side (left hand side) of the casting runway. This overflow and runner are destroyed after casting.

  A cast of alloy H was produced using this malleability test mold. The quality of the as-cast surface of this cast alloy H is shown in FIG.

Example 3
Alloys I, J and H (see Table 1, Example 2) were cast by high pressure casting using the malleability test mold mentioned in Example 2 above, and lanthanum for malleability of this alloy And the effect of cerium was studied.

  FIG. 4 shows the internal defect structure of the same cross section of a cast product of (a) Alloy I, (b) Alloy J, and (c) Alloy H. Alloy I (0.66 wt% cerium, 0.37 wt% lanthanum) was found to have a large amount of internal cracks after casting. In Alloy J (0.68 wt% lanthanum, 0.28 wt% cerium), changing the ratio of lanthanum to cerium until greater than 1: 1 reduces the amount of internal cracks and reduces the overall quality of this casting. The improvement can be seen in FIG. 4 (b). Further improvements in malleability include greater total lanthanum and cerium content (1.7 wt% lanthanum, 1.1 wt% cerium) and lanthanum to cerium ratio greater than 1: 1 and reduced neodymium content (in Alloy I). 1.62% by weight neodymium and alloy H with 0.7% by weight neodymium compared to 1.69% by weight in alloy J). For the cast alloy H, almost no internal cracks were observed. It can also be seen in FIG. 4 (c) that alloy H has good resistance to internal flow defect formation and hot cracking.

  While not wishing to be bound by theory, a possible reason for this second observation is that Gulliver − uses a phase diagram of magnesium and each of the individual rare earth elements, assuming complete mixing within the alloy. This can be explained with reference to FIG. 5, which shows the temperature vs. solid fraction curve for alloys I and H based on the Scheil model calculation. It can be seen that alloy H, which has a higher lanthanum content than alloy I, has a shorter solidification range. This is known to reduce the susceptibility of this alloy to hot cracking. Alloy H also has an increased amount of eutectic mixture than Alloy I. This is evidenced by the last part of the solidification of these alloys taking place at the same temperature. For alloy H, this occurs for a larger fraction of this alloy and therefore for a longer period of time compared to alloy I. This further reduces the sensitivity of alloy H to hot cracking. It is pointed out that lanthanum is more efficient than cerium in changing the solidification properties to reduce the susceptibility of this alloy to hot cracking. This is because for alloys having the same total cerium and lanthanum content, the eutectic ratio is higher when solidifying the lanthanum-rich alloy and the eutectic temperature is also higher.

  Again, not wishing to be bound by theory, the reduction in flow line when high pressure casting using alloy H compared to alloy I may also contribute to the reduction of internal cracks in alloy H. high. A flow line is formed between the HPDCs where the flow of molten alloy from the runner to this mold meets the flow of other runners. Oxidation of the alloy occurs on the surface of these streams that meet and form a visible flow line of the oxidized alloy in the casting. While not wishing to be bound by theory, it is believed that the higher yttrium content in alloy H is responsible for this effect. This is because it improves the recovery of beryllium from the master alloy additive and also affects the oxidation rate of beryllium from the molten alloy.

  FIG. 6 illustrates the improved surface appearance of HPDC castings from (a) Alloy I and (b) Alloy H, with a much improved lanthanum and beryllium content alloy (Alloy H). It has a surface appearance.

Example 4
Five additional alloys were prepared to study the effect of neodymium addition. These alloys were prepared according to the procedure described above in Example 2. Table 3 below presents the chemical analysis of these additional alloys (K-P).

Table 3 Prepared alloys

  FIG. 7 shows the creep results for Alloy K to Alloy P at 177 ° C. and 90 MPa. It can be seen from FIG. 7 that the creep response improves with increasing neodymium content of the alloy (see Table 3). Alloy K, Alloy M, Alloy N and Alloy P also have very similar compositions in all other alloying elements except for this neodymium content. These curves show that the neodymium content in this alloy should be greater than about 0.5% by weight in order to obtain a creep response suitable for high temperature applications.

Claims (23)

Magnesium alloy, by weight,
2-5% rare earth elements (the alloy contains lanthanum and cerium as rare earth elements, the lanthanum content being greater than the cerium content);
0.2-0.8% zinc;
0-0.15% aluminum;
0-0.5% yttrium or gadolinium;
0-0.2% zirconium;
0-0.3% manganese;
0-0.1% calcium;
Magnesium-based alloy consisting of 0-25 ppm beryllium, with the remainder being magnesium, excluding incidental impurities.   The magnesium-based alloy according to claim 1, wherein the ratio of lanthanum to cerium in the alloy is greater than 1: 1.   The magnesium-based alloy according to claim 1 or 2, wherein the alloy also contains neodymium as a rare earth element.   The magnesium-based alloy according to claim 3, wherein the lanthanum content of the alloy is greater than the neodymium content.   The magnesium-based alloy according to claim 3 or 4, wherein the cerium content of the alloy is larger than the neodymium content.   The magnesium-based alloy according to any one of claims 3 to 5, wherein a total lanthanum and cerium content of the alloy is larger than the neodymium content.   The magnesium-based alloy according to any one of claims 3 to 6, wherein the neodymium content of the alloy is 0.5 to 2.0% by weight.   The magnesium-based alloy according to any one of claims 3 to 6, wherein the neodymium content of the alloy is 0.5 to 1.5% by weight.   The magnesium-based alloy according to any one of claims 1 to 8, wherein a total lanthanum and cerium content of the alloy is 1.5 to 3.5% by weight.   The magnesium-based alloy according to any one of claims 1 to 9, wherein a total lanthanum and cerium content of the alloy is 1.8 to 3.0% by weight.   The magnesium-based alloy according to any one of claims 1 to 10, wherein a total lanthanum and cerium content of the alloy is 2.0 to 2.8% by weight.   The magnesium-based alloy according to any one of claims 1 to 11, wherein the yttrium content is 0.005 to 0.5% by weight.   The magnesium-based alloy according to any one of claims 1 to 12, wherein the gadolinium content is 0.005 to 0.5% by weight.   The magnesium-based alloy according to any one of claims 1 to 13, wherein the alloy is composed of at least 94% magnesium by weight.   The magnesium-based alloy according to any one of claims 1 to 14, wherein the zinc content is 0.2 to 0.6% by weight.   The magnesium-based alloy according to any one of claims 1 to 15, wherein the aluminum content is 0.05 to 0.15% by weight.   The magnesium-based alloy according to any one of claims 1 to 16, wherein the zirconium content is less than 0.1% by weight.   The magnesium-based alloy according to any one of claims 1 to 17, wherein the beryllium content is 8 to 12 ppm by weight.   The magnesium-based alloy according to any one of claims 1 to 18, wherein the manganese content is approximately 0.1% by weight.   The magnesium-based alloy according to any one of claims 1 to 19, wherein the incidental impurities in the alloy are less than 0.15% by weight.   An engine block for an internal combustion engine manufactured by high-pressure casting the alloy according to any one of claims 1 to 20.   A component of a conduction mechanism formed from the alloy according to any one of claims 1 to 20.   21. An article formed from the alloy of any one of claims 1-20.

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