JP2024514616A - Oxidation resistant Al-Mg high strength die casting alloy - Google Patents

Abstract

The present disclosure relates to a beryllium-free casting alloy suitable for casting operations. The casting alloy includes, in weight percent, one of Mg (about 1.0 to about 17.0), Fe (about 0.5 to about 1.8), Ca (about 0.003 to about 6.0) or Sr (about 0.003 to about 2.5), optionally a grain refiner, and the balance aluminum and unavoidable impurities. The casting alloy can be used in a method for producing aluminum cast products to reduce Mg loss and/or dross formation during casting operations.Selected Figure 3

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63/174,796, filed April 14, 2020, the entire contents of which are incorporated herein by reference. It is.

This disclosure relates to Al-Mg casting alloys suitable for casting operations such as high pressure vacuum die-casting operations.

The demand for structural die cast parts continues to increase in the automotive industry. Most of the existing alloys require heat treatment to produce products with good mechanical properties. Therefore, alloys that do not require heat treatment are required to reduce the manufacturing costs of structural die cast parts.

Al-Mg die casting alloys have attracted much interest due to their excellent mechanical properties in the as-cast state. To obtain sufficient solid solution strengthening, Al-Mg alloys are produced with high Mg additions (>3%). However, due to the strong affinity of Mg with oxygen, Al-Mg alloys undergo problematic oxidation that can result in significant dross formation and loss of Mg from the melt. Beryllium can be used to minimize oxidation because it forms a protective BeO layer at the air-metal interface that prevents further oxidation of Mg. However, the use of Be poses health risks to operators who inhale or come into contact with Be dust.

Therefore, the aluminum die casting market is seeking an alternative to Be in Al-Mg alloys that provides similar antioxidant benefits, but without the health risks. There is also a need to provide alloys that exhibit improved properties during casting operations, such as die soldering resistance. Additionally, there is a need to provide aluminum casting products that exhibit improved mechanical properties in the as-cast condition (temper F).

The present disclosure provides beryllium-free casting alloys. The casting alloy of the present disclosure includes Ca or Sr. In some embodiments, the cast alloy exhibits reduced Mg loss and/or reduced dross formation during casting operations. In some embodiments, the casting alloy also exhibits improved die seizure resistance during casting operations. In some embodiments, aluminum cast products made from cast aluminum alloys exhibit improved mechanical properties even in the as-cast condition.

According to a first aspect, the present disclosure provides a composition comprising, in weight percent:
Mg about 1.0 to about 17.0;
Fe about 0.5 to about 1.8;
one of: Ca from about 0.003 to about 6.0; or Sr from about 0.003 to about 2.5; and the balance being aluminum and inevitable impurities.
wherein the casting alloy does not include Be as an alloying element.

In one embodiment, the cast alloy further includes a grain refiner. In another embodiment, it further includes Ca. In yet another embodiment, the cast alloy includes from about 0.01 to about 0.3 weight percent Ca. In yet another embodiment, the cast alloy includes from about 3.0 to about 8.0 weight percent Mg. In yet another embodiment, the cast alloy includes about 4.0 to about 6.0 Mg. In yet another embodiment, the cast alloy includes from about 0.8 to about 1.8 weight percent Fe.

According to a second aspect, the present disclosure provides an aluminum casting product comprising the casting alloy described herein. In some embodiments, the cast aluminum is a structural automotive part. In additional embodiments, the aluminum cast product has one of the following properties: a tensile strength of at least about 200 MPa, a yield strength of at least about 100 MPa, an elongation of at least about 7%, and/or a VDA bending angle of at least about 30°. It has at least one of the following. In additional embodiments, the aluminum casting product includes Al ₄ Ca. In some further embodiments, the aluminum casting product has _four phases of Al ₁₃ Fe, _two phases of Al ₃ Mg, and Al ₄ Ca. In some additional embodiments, the aluminum casting product has Al ₄ Ca bonded with an Al ₃ Mg _two phase. In still additional embodiments, the aluminum cast product has AlMgCa phases at grain boundaries.

According to a third aspect, the present disclosure provides a method of producing an aluminum cast product, the method comprising casting the cast aluminum alloy described herein in a mold. In one embodiment, the method further comprises subjecting the cast aluminum alloy to high pressure vacuum die casting. In yet another embodiment, the method does not include a post-casting heat treatment step.

According to a third aspect, the present disclosure provides an aluminum casting product obtainable or obtainable by the methods described herein. In some embodiments, the cast aluminum is a structural automotive part. In additional embodiments, the aluminum cast product has one of the following properties: a tensile strength of at least about 200 MPa, a yield strength of at least about 100 MPa, an elongation of at least about 7%, and/or a VDA bending angle of at least about 30°. It has at least one of the following. In additional embodiments, the aluminum casting product includes Al ₄ Ca. In some further embodiments, the aluminum casting product has _four phases of Al ₁₃ Fe, _two phases of Al ₃ Mg, and Al ₄ Ca. In some additional embodiments, the aluminum cast product has Al ₄ Ca combined with an Al ₃ Mg _two- phase. In still additional embodiments, the aluminum cast product has AlMgCa phases at grain boundaries.

According to a fourth aspect, the present disclosure provides a method for limiting Mg loss and dross formation during a casting operation of an aluminum product compared to a control aluminum product, the method comprising adding one of about 0.003 to about 6.0 Ca or about 0.003 to about 2.5 Sr to a first aluminum alloy to obtain a casting alloy intended to be cast, the first aluminum alloy comprising, in weight percent:
Mg about 1.0 to about 17.0;
Fe from about 0.5 to about 1.8; and the balance aluminum and inevitable impurities.
and the first aluminum alloy and the cast alloy do not contain Be as an alloying element.

In some embodiments, the method further includes melting the cast alloy to obtain a molten cast alloy. In one embodiment, the first aluminum alloy further includes a grain refiner. In some additional embodiments, the method can be used to reduce Mg loss to less than about 12 weight percent when the molten cast alloy is held for at least 6 hours. In some further embodiments, the method can be used to reduce dross formation to less than about 7 weight percent when the molten cast alloy is held for at least 6 hours. In some embodiments, the method further includes casting the molten cast alloy to obtain a cast aluminum alloy. In still further embodiments, the method further includes subjecting the cast aluminum alloy to high pressure vacuum die casting. In some embodiments, the method does not include a post-casting heat treatment step. In some additional embodiments, the cast aluminum alloy includes Ca. In still further embodiments, the cast aluminum alloy includes about 0.01 to about 0.3 Ca. In additional embodiments, the first aluminum alloy includes from about 3.0 to about 8.0 Mg. In some further embodiments, the first aluminum alloy includes from about 4.0 to about 6.0 Mg. In yet another embodiment, the first aluminum alloy includes about 0.8 to about 1.8 Fe.

Having generally described the nature of the present invention, reference is now made to the accompanying drawings which illustrate preferred embodiments thereof.

Figure 1 shows the experimental procedure used in the example. Figure 2A shows a photograph of the HPVDC plate used in the example. The dashed line indicates the section used in the tensile tests presented in the example. FIG. 2B shows a diagram of the dimensions of the ASTM B557 tensile test specimen used in the examples. FIG. 3 shows photographs of changes in the melt surface during the course of the air exposure oxidation test (from left to right, after skimming, holding for 1 hour, holding for 2 hours, or holding for 20 hours). Figure 4A shows a photograph of the morphology of the solid dross. Figure 4B shows an electron microscope image of the dross, showing the energy dispersive X-ray analysis (EDX)-1 and EDX-2 grains. The scale bar is 20 μm. Figure 4C shows the EDX-1 results from Figure 4B. Figure 4D shows the EDX-2 results from Figure 4B. Figure 5A shows the weight percent of Mg in the base alloy (Ca, Sr, and/or a combination of Ca and Sr, stapled lines) over the course of 0 to 6 hours hold times in alloys containing 100 ppm Ca (■), 1000 ppm Ca (▲), 100 ppm Sr (X), or 1000 ppm Sr (●), and Figure 5B shows the percent Mg loss in the base alloy (Ca, Sr, and/or a combination of Ca and Sr) after a total hold time of 6 hours in alloys containing 100 ppm Ca, 1000 ppm Ca, 100 ppm Sr, or 1000 ppm Sr. FIG. 6 shows photographs of the typical appearance of molten Al-1.5Fe-5Mg base alloys containing no additives, only Ca, only Sr, and a combination of Ca and Sr after a holding time of 2 hours at 770° C. Figure 7 shows the total dross produced for the base Al-1.5Fe-5Mg alloy, the alloy with only Ca added, the alloy with only Sr added, or the alloy with a combination of Ca and Sr added after a total holding time of 6 hours. Indicates the amount (weight percent). The mechanical properties of the base Al-1.5Fe-5Mg alloy and the Ca-added (0.1) alloy are compared in Figure 8. The results are shown as tensile strength (left bar, MPa), yield strength (middle bar, MPa), elongation index (left bar, %), and quality index (■, MPa) for the two alloys compared. 9 compares the mechanical properties of Comparative Alloy 1, Comparative Alloy 2 (containing Be), and the Al-1.5Fe-5Mg0.1Ca alloy. Results are shown as tensile strength (left bar, MPa), yield strength (middle bar, MPa), elongation index (left bar, %), and quality index (■, MPa) for the three alloys compared. FIG. 10A shows a representative optical image of the base Al-1.5Fe-5Mg alloy. The arrows point to the porous areas in the material. The scale bar is 100 μm. FIG. 10B shows a representative optical image of the Al-1.5Fe-5Mg0.1Ca alloy. The scale bar is 100 μm. FIG. 10C shows a representative optical image of the base Al-1.5Fe-5Mg alloy. The scale bar is 20 μm. FIG. 10D shows a representative optical image of the Al-1.5Fe-5Mg0.1Ca alloy. The scale bar is 20 μm. Figure 11A shows a scanning electron microscope (SEM) image, EDX, and electron backscatter diffraction (EBSD) of the Al ₁₃ Fe ₄ phase found in the Al-1.5Fe-5Mg0.1Ca alloy. Figure 11B shows a scanning electron microscope (SEM) image and EDX of the Al ₃ Mg ₂ phase found in the Al-1.5Fe-5Mg0.1Ca alloy. Figure 11C shows a scanning electron microscope (SEM) image, EDX, and electron backscatter diffraction (EBSD) of the Al ₄ Ca component found in the Al-1.5Fe-5Mg0.1Ca alloy. Figure 11D shows a scanning electron microscope (SEM) image and EDX mapping of the Al-Mg-Ca phase found in the Al-1.5Fe-5Mg0.1Ca alloy. Figure 12 provides results showing the effect of Mg on the yield strength of the alloy.

Aluminum alloys offer an attractive solution to meet the lightweighting goals in the automotive industry for improved fuel economy and reduced _CO2 emissions. High pressure vacuum die casting (HPVDC) is widely used for the manufacture of aluminum structural components as a fast and economical near net shape manufacturing method. Alloys for structural die castings typically require good flow and die seizure resistance, high mechanical properties, and adequate corrosion resistance. Key challenges addressed by the industry are die seizure, blistering during solution treatment, and the need to combine strength and ductility. From a broad cost and quality standpoint, well-engineered aluminum alloys in tempers F and T5 are preferred.

Be is often used in Al-Mg casting alloys to limit or prevent oxidation. However, in the present disclosure, we have sought to replace Be in Al-Mg casting alloys intended for use in casting operations. Surprisingly, it has been found that the addition of Ca or Sr to Al-Mg casting alloys not only limits the oxidation of the alloy during casting operations, but also results in cast products exhibiting improved mechanical properties.

The cast aluminum alloy of the present disclosure contains either Ca or Sr. In some embodiments, the cast aluminum alloy does not include a combination of Ca and Sr. As indicated above, Ca and Sr limit oxidation of the alloy and, in some embodiments, improve casting conditions. When cast aluminum alloys are used to make cast products, in some embodiments it can also improve one or more mechanical properties of the cast product (in some embodiments, its as-cast state).

The cast aluminum alloy of the present disclosure may be any Al-Mg cast alloy suitable for casting operations. In one embodiment, the cast aluminum alloy of the present disclosure may be a 5xx.x aluminum alloy.

In some embodiments, Ca is present in the cast aluminum alloy at a weight percent of about 0.003 or greater. In some embodiments, Ca is present in the cast aluminum alloy at a weight percent of about 0.01 or greater. In some embodiments, Ca is present in the cast aluminum alloy at a weight percent of about 0.1 or greater. In additional embodiments, Ca is at least about 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03 , 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0 .7, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0, 5.0, or more weight percent. If Ca is present in the alloy, it is present in a weight percent of 6.0 or less. In some embodiments, Ca is about 6.0, 5.0, 4.0, 3.0, 2.0, 1.0, 0.9, 0.8, 0.7, 0.6 , 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0 Present in the alloy at a weight percent of .02 or less. In some specific embodiments, Ca is present in the alloy at a weight percent of about 0.01 to about 6.0. In additional embodiments, Ca is at least about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 , or greater weight percent. In some embodiments, Ca is about 6.0, 5.0, 4.0, 3.0, 2.0, 1.0, 0.9, 0.8, 0.7, 0.6 , 0.5, 0.4, 0.3, 0.2, or less by weight in the alloy. In some specific embodiments, Ca is present in the alloy at a weight percent of about 0.1 to about 6.0. In still other embodiments, Ca is at least about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0. Present in the alloy at a weight percent of 1, 0.2, or more. In still further embodiments, Ca is about 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, Present in the alloy at a weight percent of 0.02 or less. In still additional embodiments, Ca is about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 , or from 0.2 to about 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, or 0. It is present in the alloy at a weight percent of up to 0.02, such as from about 0.01 to about 0.3. In still other embodiments, Ca is present in the alloy at a weight percent of at least about 0.1, 0.2, or more. In still further embodiments, Ca is present in the alloy at a weight percent of about 0.3, 0.2 or less. In yet additional embodiments, Ca is present in the alloy at a weight percent from about 0.1 or 0.2 to about 0.3 or 0.2, such as from about 0.1 to about 0.3. weight percent, etc.

In some embodiments, Sr is present in the alloy at a weight percent of about 0.003 or greater. In some embodiments, Sr is present in the alloy at a weight percent of about 0.01 or greater. In some embodiments, Sr is present in the alloy at a weight percent of about 0.1 or greater. In some additional embodiments, Sr is present in at least about 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or more weight percent. If Sr is present in the alloy, it is present in 2.5 weight percent or less. In some embodiments, Sr is present in the alloy in a weight percent of less than or equal to 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, or less. In some specific embodiments, Sr is present in the alloy in a weight percent of from about 0.003 to about 2.5. In some additional embodiments, Sr is present in at least about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or more weight percent. In some embodiments, Sr is present in the alloy in a weight percent of about 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02 or less. In some specific embodiments, Sr is present in the alloy in a weight percent of about 0.01 to about 2.5. In some additional embodiments, Sr is present in a weight percent of at least about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or more. In some embodiments, Sr is present in the alloy in a weight percent of no more than about 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or less. In some specific embodiments, Sr is present in the alloy at about 0.1 to about 2.5 weight percent. In still other embodiments, Sr is present in the alloy at at least about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or 0.2 weight percent. In still further embodiments, Sr is present in the alloy at no more than about 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or less weight percent. In yet additional embodiments, Sr is present in the alloy in a weight percent of about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or 0.2 to about 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, or 0.02, such as from about 0.01 to about 0.3 weight percent. Sr is present in the alloy in at least about 0.1, 0.2, or more weight percent. In yet further embodiments, Sr is present in the alloy in a weight percent of about 0.3, 0.2, or less. In yet additional embodiments, Sr is present in the alloy in a weight percent of 0.1 or 0.2 to about 0.3 or 0.2, such as from about 0.1 to about 0.3 weight percent.

The cast aluminum alloys of the present disclosure include Mg to provide acceptable mechanical properties to the resulting cast product. Since the main strengthening mechanism of Mg is solid solution strengthening, addition beyond the solubility of Mg in aluminum does not further increase the mechanical properties of the corresponding aluminum cast product. Thus, the cast aluminum alloys of the present disclosure provide Mg at a weight percent of 17.0 or less. Mg is at least about 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12 present in the alloy at a weight percent of .0, 13.0, 14.0, 15.0, 16.0, or greater. Mg is approximately 17.0, 16.0, 15.0, 14.0, 13.0, 12.0, 11.0, 10.0, 9.0, 8.0, 7.0, 6. Present in the alloy at a weight percent of 0, 5.0, 4.0, 3.0, 2.0 or less. In one embodiment, Mg is about 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11 .0, 12.0, 13.0, 14.0, 15.0, 16.0 to about 17.0, 16.0, 15.0, 14.0, 13.0, 12.0, 11. Present in the alloy in weight percentages up to 0, 10.0, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.0, e.g. From about 1.0 to 17.0, and so on. In some embodiments, Mg is present in the alloy at a weight percent of at least about 3.0, 4.0, 5.0, 6.0, 7.0, or more. In some embodiments, Mg is present in the alloy at a weight percent of about 8.0, 7.0, 6.0, 5.0, 4.0 or less. In one embodiment, Mg is from about 3.0, 4.0, 5.0, 6.0, 7.0 to about 8.0, 7.0, 6.0, 5.0, 4.0 is present in the alloy at a weight percent of, for example, from about 3.0 to 8.0. In some embodiments, Mg is present in the alloy at a weight percent of at least about 4.0, 5.0, or more. In some embodiments, Mg is present in the alloy at a weight percent of about 6.0, 5.0 or less. In one embodiment, Mg is present in the alloy at a weight percent from about 4.0, 5.0 to about 6.0, 5.0, such as from about 4.0 to 6.0. .

The cast aluminum alloys of the present disclosure include Fe to provide die seizure resistance during casting operations. However, the amount of Fe present in the cast alloys of the present disclosure should be limited to avoid the formation of large iron phases that may be brittle and reduce the mechanical properties of the corresponding aluminum alloy product. Thus, Fe is present in the alloy at least about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or more by weight percent. Fe is present in the alloy at no more than about 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, or less by weight percent. In one embodiment, Fe is present in the alloy in a weight percent of from about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 to about 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, such as from about 0.5 to 1.8. In one embodiment, Fe is present in the alloy in a weight percent of at least about 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or more. Fe is present in the alloy in a weight percent of less than or equal to about 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, or less. In one embodiment, Fe is present in the alloy in a weight percent of from about 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 to about 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, such as from about 0.8 to 1.8.

Optionally, a grain refiner is included in the aluminum alloy of the present disclosure in the form of Ti, TiB, TiB, or TiC to solidify the aluminum alloy with a fine grain structure that is completely equiaxed. It's okay. If TiB is used as a grain refiner, the resulting B content in the alloy can be up to 0.05% by weight. If TiC is used as a grain refiner, the resulting C content in the alloy can be up to 0.01% by weight. The grain refiner can be added during the manufacture of the ingot to be remelted, or it can be added after remelting during the manufacture of the final casting.

The casting alloys of the present disclosure do not contain Be, either as an intentional additive or as an alloying element. If present, Be is considered to be an unavoidable impurity.
In some embodiments of the present disclosure, the cast alloy does not contain Cu, either as an intentional additive or as an alloying element, and thus, in some embodiments, Cu, if present, may be considered an unavoidable impurity.

The remainder of the aluminum alloy of the present disclosure is aluminum (Al) and unavoidable impurities. In one embodiment, each of the impurities is present at up to about 0.05 percent by weight, and the total unavoidable impurities are present at less than about 0.15 percent by weight.

The cast aluminum alloys of the present disclosure may be subjected to various casting operations, including but not limited to high pressure vacuum die casting (HPVDC), to obtain cast aluminum products. The presence of Ca or Sr, in some embodiments, may improve casting operations by reducing the amount of Mg loss and/or dross formation during holding of the molten aluminum alloy. In some embodiments, the presence of Ca or Sr may reduce Mg loss during melting to less than about 12 weight percent when the molten alloy is held for at least 6 hours (compared to the corresponding base alloy - Ca, Sr, and/or a combination of Ca and Sr). In some embodiments, the presence of Ca or Sr may reduce dross formation to less than about 7 weight percent when the molten alloy is held for at least 6 hours (compared to the corresponding base alloy without Ca and Sr).

The present disclosure therefore provides a method for producing an aluminum cast product from the cast aluminum alloys described herein. The method broadly involves casting the cast aluminum alloys described herein in a mold and, if desired, subjecting the cast aluminum alloy to high pressure vacuum die casting (HPVDC). In some embodiments, the method avoids the use of a post-casting heat treatment step. In such embodiments, the corresponding aluminum product is provided in the as-cast condition (e.g., temper F).

In some embodiments of the method, a cast aluminum alloy, which may be provided in the form of an ingot, is subjected to a melting process to obtain a molten aluminum alloy. The melting process includes heating and stirring the aluminum alloy, and optionally maintaining the molten aluminum alloy prior to casting. If dross is generated during the melting process (eg, during the holding process), the method may include removing the dross before casting. Once the molten aluminum alloy is obtained, it is cast in a mold to obtain an aluminum cast product. The casting process may include subjecting the cast aluminum alloy to a high pressure vacuum die casting process. In some embodiments, the method may include removing the aluminum casting product from the mold. In some embodiments, the method of manufacturing an aluminum cast product does not include a post-cast heat treatment step, and the aluminum cast product is obtained in an as-cast condition (eg, Temper F). However, in some embodiments, the method of producing cast aluminum may include one or more post-casting treatment steps (e.g., an annealing step, a strain hardening step, a solution heat treatment step, and/or a heat treatment step). process).

In embodiments where the aluminum product is a cast product, the method may also exclude any post-cast processing (eg, it may be provided as cast or as temper F). As another option, the method may include a post-casting heat treatment, such as, for example, a T5, T6, or T7 treatment (eg, a solution heat treatment step and an artificial aging step). In embodiments where the aluminum product is a cast product, the latter may be an automobile part, such as a chassis or a rotor.

In some embodiments, the casting alloys of the present disclosure can be used to reduce dross formation during casting operations. In some embodiments, the casting alloys of the present disclosure reduce the weight percent of dross generated during the melting process (e.g., during the holding process) to less than 7, 6, 5, 4, 3, 2, or 1% when the molten aluminum alloy is held for at least 6 hours.

In some embodiments, the casting alloys of the present disclosure can be used to reduce Mg loss during casting operations. In some embodiments, the casting alloys of the present disclosure reduce the weight percent of Mg loss during the melting process (e.g., during the holding process) to less than 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2% when the molten aluminum alloy is held for at least 6 hours.

In some embodiments, the method of the present disclosure may include adding Ca or Sr to aluminum or the first aluminum alloy to obtain a master alloy or a casting alloy of the present disclosure. In some embodiments, Ca or Sr is added to pure aluminum to obtain a master alloy. In such embodiments, the master alloy may then be used to produce a casting alloy of the present disclosure, and Mg, Fe, and optionally a grain refiner may be added. The pure aluminum or master alloy does not include Be as an alloying element, and if Be is present, it is considered an impurity. In some embodiments, Ca or Sr is added to a first aluminum alloy that includes Mg and Fe, and optionally a grain refiner, with the balance being aluminum and unavoidable impurities. The first aluminum alloy does not include Be as an alloying element, and if Be is present in the first aluminum alloy, it is considered an impurity.

The present disclosure also provides aluminum cast products obtainable or obtainable by the methods described herein. In the context of this disclosure, the term "aluminum cast product" can mean a final cast product (such as a structural auto part), or an intermediate ingot that can be further melted again into aluminum products of different shapes. In some embodiments, the aluminum casting product is a shock tower, A-pillar, B-pillar, or torque box. In some embodiments, the aluminum cast products of the present disclosure have improved tensile strength, yield strength, and quality index when compared to the properties of corresponding aluminum products that do not contain Ca or Sr (and optionally include Be). , VDA angle, and/or percent elongation. In some embodiments, improvements in tensile strength, yield strength, quality index, VDA angle, and/or percent elongation are seen in the as-cast condition (eg, Temper F) of the aluminum product.

In some embodiments, aluminum cast products produced from the casting alloys of the present disclosure have a tensile strength of at least about 200, 210, 220, 230, 240, 250 MPa, or more. In specific embodiments, aluminum cast products produced from the casting alloys of the present disclosure have a tensile strength of at least about 200 MPa. In some additional embodiments, aluminum cast products produced from the casting alloys of the present disclosure have a yield strength of at least about 100, 110, 120, 130, 140, 150 MPa, or more. In some additional embodiments, aluminum cast products produced from the casting alloys of the present disclosure have a yield strength of at least about 100 MPa. In some additional embodiments, aluminum cast products produced from the casting alloys of the present disclosure have an elongation of at least about 7, 8, 9, 10%, or more. In some additional embodiments, aluminum cast products produced from the casting alloys of the present disclosure have an elongation of at least about 7%. In some additional embodiments, aluminum cast products produced from the casting alloys of the present disclosure meet the angle of standard VDA (Verband der Automobilindustrie) 238-100 of at least about 30° or more.

The present invention will be more readily understood by reference to the following examples, which are given to illustrate the present invention and not to limit its scope.
EXAMPLES The present examples present the development of a novel aluminum alloy to provide exceptional mechanical properties and die-stick resistance for aluminum HPVDC structural components in as-cast temper applications. The microstructural evolution and mechanical properties were examined by scanning electron microscopy and tensile/bending tests. The relationship between microstructure and properties is analyzed, and the strengthening mechanism of the tested alloy is discussed. Based on the experimental results, the novel alloy demonstrates a promising solution for the as-cast application of HPVDC components.

As possible alternatives to Be, Ca and Sr were investigated for their effect on preventing oxidation of liquid Al-1.5Fe-5Mg alloy through observation and measurement of oxidation morphology, dross formation, and magnesium loss.

Molten Al-5Mg Oxidation Tests. Various additions of Ca and Sr in Al-1.5Fe-5Mg alloys were tested. The alloys were produced using P1020 aluminum, pure magnesium, and pure iron powders. The elements Sr and Ca were batched using master alloys of Al-10% Sr and Al-10% Ca. The chemical composition of these alloys was analyzed by optical emission spectroscopy (OES) and the results are shown in Table 1. The alloys were melted in the laboratory using a 350-kg electric resistance furnace.

The experimental procedure is presented in Figure 1. The procedure includes two steps, an alloy batching process and a holding process. A typical alloy batching process was used. More specifically, P1020 was placed in a furnace and batch processed with Fe and Mg. The molten metal was then stirred and degassed using argon. Flux salts were used to clean the melt during degassing. After degassing, Ca and Sr were added according to the chemical design in Table 1 at a ratio of 100 ppm to 0.3% for Ca and 100 to 1000 ppm for Sr. An interrupted thermal holding process was used to investigate the occurrence of oxidation during casting. The holding temperature of the metal was set at 770° C., which is the upper limit for typical casting. This test illustrates the effect of Ca and Sr on Al-Mg oxidation under the most severe oxidizing conditions, since the amount of oxidants formed on the liquid metal increases with temperature. As shown in Figure 1, alloying was followed by three hold times of 2 hours each. After each time, the appearance of the molten metal surface was photographed. A complete skimming of the metal surface was performed to quantify the amount of dross produced. Six OES samples were taken to assess magnesium loss. After each test, the crucible was thoroughly cleaned. The base Al-1.5Fe-5Mg alloy was tested for oxidation changes with extended heat hold times of up to 20 hours.

Properties and microstructural analysis of Al-Mg alloys. The effect of small amounts of Ca on the mechanical properties and bending ductility of Al-1.5Fe-5Mg alloys was studied. 3 mm thick plates obtained by high pressure vacuum die casting (HPVDC) were produced on a 260 t Buhler machine. The Al-1.5Fe-5Mg base alloy and the new Al-1.5Fe-5Fe0.1Ca alloy were cast. The chemical composition of the investigated alloys was determined using optical emission spectroscopy (OES) and the results are shown in Table 2.

Samples for tensile testing were cut from the cast blank (rectangular section in the center of the sample, as shown in Figure 2). The plate was then machined into the shape of the test sample with exact dimensions in accordance with the ASTM B557 standard. Tensile tests were conducted on ten as-cast tensile samples for each alloy. For bending tests, 60 x 60 mm square samples were machined from 3 mm HPVDC plates. Six samples of each alloy were tested according to the VDA 238-100 standard.

Metallographic samples were taken from as-cast HPVDC plates. Optical microscopy and scanning electron microscopy (SEM) were used to analyze the as-cast microstructure and identify intermetallic phases.

Effect of Ca and Sr on oxidation prevention of molten Al-Mg alloy. In order to understand the oxidation mechanism, the oxidation phenomenon of Al-Mg was tested. The effect of Ca and Sr on the oxidation prevention effect of Al-Mg alloy was investigated.

Oxidation properties of base Al-1.5Fe-5Mg alloy. Figure 3 shows the molten surface of Al-1.5Fe-5Mg alloy during heat holding at 770°C in air. The surface of the melt after sufficient skimming is very clean. After 1 hour of exposure, the surface shows partial popcorn-shaped oxidation near the crucible edge. After 2 hours of exposure, the surface of the melt is completely covered with popcorn-shaped oxides. The temperature of the metal rose to 800° C. due to the exothermic oxidation reaction between aluminum and magnesium. After 20 hours of exposure, the color of the oxide has partially turned black. The solid popcorn-shaped oxide has a porous morphology, as shown in FIG. 4A, which constitutes a large number of pores and oxide clusters (see FIG. 4B). EDX analysis shows that the dross is primarily composed of magnesium oxide (MgO) and spinel (MgAl ₂ O ₄ ).

Figures 5A and 5B show the change in Mg concentration during retention times from 0 to 6 hours, as well as the percent Mg loss after a total retention time of 6 hours. It can be seen that the base Al-1.5Fe-5Mg alloy suffered the highest Mg loss. The total Mg loss after 6 hours holding time is 0.63% by weight or 12.6% loss. The addition of Ca or Sr effectively reduced Mg loss during melting. Mg loss was less than 0.1 wt% or less than 2% loss for Ca-containing alloys and less than 0.3 wt% or less than 6% loss for Sr-containing alloys.

A combination of Ca and Sr. FIG. 6 shows the visual appearance of molten Al-1.5Fe-5Mg-based alloys with no additives, Ca only, Sr only, and a combination of Ca and Sr. Alloys containing both Ca and Sr have small corrugations. This characteristic is similar to that of Sr-containing alloys. The oxide layer appears thick. No porous dross is present. This result shows that the combination of Ca and Sr can help effectively counter the oxidation of Al-1.5Fe-5Mg.

Figure 7 shows the total amount of dross produced (% by weight of input) after a total holding time of 6 hours. Note that the combination of Ca and Sr effectively reduced dross formation. The alloy containing both Ca and Sr showed a dross formation of 2.1 wt%, which is higher than the dross formation of the base alloy (6.9 wt%) and the dross formation of the Sr-containing alloy (2.9 wt%). ) lower than However, the amount of dross generated is higher than that of the Ca-containing alloy (1.0% by weight).

In summary, Mg in Al-1.5Fe-5Mg has a strong affinity for oxygen. In the case of the base alloy, a thick oxide was observed on the melt surface. Both Ca and Sr showed good effects in preventing the oxidation of Al-1.5Fe-5Mg.

Mechanical properties. The properties of Al-1.5Fe-5Mg and Al-1.5Fe-5Mg0.1Ca were tested. Table 3 summarizes the tensile properties and VDA bending results for the as-cast test and reference alloys. Figure 8 shows the effect of Ca on the mechanical properties of Al-1.5Fe-5Mg alloy. It has been found that Al-1.5Fe-5Mg0.1Ca exhibits superior tensile properties compared to Al-1.5Fe-5Mg alloy. The Al-1.5Fe-5Mg0.1Ca alloy has higher tensile strength and ductility than the Al-1.5Fe-5Mg alloy. The alloy quality index (QI) calculated using the formula QI = UTS + 150 ^* log (El%) is 459 MPa for Al-1.5Fe-5Mg0.1Ca, which is higher than that of Al-1.5Fe-5Mg. is also 81 MPa or 21% higher. On the other hand, as shown in Table 3, the Al-1.5Fe-5Mg0.1Ca alloy gives better bending ductility than the Al-1.5Fe-5Mg alloy (bending ductility in Al-1.5Fe-5Mg0.1Ca angle 37.7° versus 29.0° in Al-1.5Fe-5Mg alloy). The results highlight the beneficial effect of Ca on the mechanical performance of Al-1.5Fe-5Mg0.1Ca alloy.

Figure 9 shows the mechanical properties of the new Al-1.5Fe-5Mg0.1Ca alloy in comparison with other commercially available die casting alloys (e.g., comparative alloys 1 and 2). The new alloy showed higher quality index values than comparative alloys 1 and 2. It had the highest tensile strength and yield strength overall.

Compared with Comparative Alloy 1 containing 7.5 wt% Si and 0.17 wt% Fe, the Al-1.5Fe-5Mg0.1Ca alloy had higher tensile strength and lower elongation. . The elongation was 11.5% for Comparative Alloy 1 compared to 10% for the Al-1.5Fe-5Mg0.1Ca alloy. Interestingly, the Al-1.5Fe-5Mg0.1Ca alloy exhibited better bending ductility than Comparative Alloy 1, compared to 32.4° for Comparative Alloy 1. The bending angle of the alloy was 37.7°. The Al-1.5Fe-5Mg0.1Ca alloy is believed to have similar or better ductility than Comparative Alloy 1. Regarding die seizure resistance, the Al-1.5Fe-5Mg0.1Ca alloy contains 1.5 wt% Fe, which reduces the tendency to stick compared to Comparative Alloy 1. , which is expected to significantly improve die life.

Compared to Comparative Alloy 2 Al-1.6Fe-4.2Mg-Be alloy, Al-1.5Fe-5Mg0.1Ca alloy exhibited higher strength but lower ductility. Without being bound by theory, this suggests that the Mg content in the Al-1.5Fe-5Mg0.1Ca alloy is higher (5.1 wt.% Mg) than comparative alloy 2 (4.3 wt.% Mg), which provided a higher solid solution strengthening effect. The ductility of the Al-1.5Fe-5Mg0.1Ca alloy can be improved by reducing the amount of Mg if higher elongation is required. Regarding the quality index of the alloy, the Al-1.5Fe-5Mg0.1Ca alloy showed a higher quality index value (459 MPa) than comparative alloy 2 (427 MPa). The Al-1.5Fe-5Mg0.1Ca alloy had overall better mechanical properties than Comparative Alloy 2. Regarding die seizure resistance, the Al-1.5Fe-5Mg0.1Ca alloy and Comparative Alloy 2 had similar Fe contents of 1.5 wt% vs. 1.6 wt%. The Al-1.5Fe-5Mg0.1Ca alloy is believed to perform similar to the comparative alloys in terms of die life.

Microstructural analysis of as-cast condition. To understand the strengthening mechanism of Ca in the Al-1.5Fe-5Mg alloy, microstructural analysis was performed on the as-cast plates. The results are shown in Table 10. Al-1.5Fe-5Mg exhibits shrinkage pores, while Al-1.5Fe-5Mg0.1Ca exhibits a microstructure without pores. Since Ca is very efficient in reducing Al-Mg oxidation, it makes sense that Al-1.5Fe-5Mg0.1Ca has fewer oxides and lower porosity.

Identification of phase morphology and chemistry was performed using SEM/EDX and EBSD analysis. The results are shown in FIG. Table 4 summarizes the different stable phases identified in the two alloys tested. The alloy matrix mainly consists of _two phases of Al ₁₃ Fe ₄ and Al ₃ Mg for the Al-1.5Fe-5Mg alloy, and Al ₁₃ Fe ₄ and Al ₃ Mg ₂ /Al ₄ Ca for the Al-1.5Fe-5Mg0.1Ca alloy. It consisted of phases. By adding Ca to the Al-5Mg-1.5Fe alloy, it is possible to form an Al ₄ Ca phase or an AlMgCa phase bonded to the Al ₃ Mg ₂ phase at the grain boundaries in the matrix. In addition, Ca appears to slightly modify the morphology of the iron-rich phase. In the microstructure of Al-1.5Fe-5Mg0.1Ca alloy, there are more partially fragmented script Fe phases with very non-uniform distribution. was observed. Small particles promote uniform deformation in tensile tests, resulting in higher elongation.

In addition, the effect of Mg addition on the mechanical properties of the alloy was also tested. Essentially, the tensile strength (UTS) and yield strength (YS) increased with increasing Mg content, as seen in Table 5 and Figure 12 below.

Although the present invention has been described in connection with specific embodiments thereof, it will be understood that the scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be accorded the broadest interpretation consistent with the entire disclosure.

Claims (31)

In weight percent,
from about 1.0 to about 17.0 Mg;
Fe from about 0.5 to about 1.8;
one of about 0.003 to about 6.0 Ca or about 0.003 to about 2.5 Sr; and
Residual amounts of aluminum and unavoidable impurities,
and does not contain Be as an alloying element. The cast alloy of claim 1 further comprising a grain refiner. The casting alloy according to claim 1 or 2, containing Ca. 4. The cast alloy of any one of claims 1-3, comprising about 0.01 to about 0.3 Ca. 5. The cast alloy of any one of claims 1-4, comprising about 3.0 to about 8.0 Mg. 6. A cast alloy according to any one of claims 1 to 5, comprising about 4.0 to about 6.0 Mg. A casting alloy according to any one of claims 1 to 6, containing about 0.8 to about 1.8 Fe. An aluminum casting product comprising a casting alloy according to any one of claims 1 to 7. A method of manufacturing an aluminum cast product comprising casting a cast alloy according to any one of claims 1 to 7 in a mold. 10. The method of claim 9, further comprising subjecting the cast aluminum alloy to high pressure vacuum die casting. The method according to claim 9 or 10, which does not include a post-casting heat treatment step. An aluminum cast product obtainable or obtainable by the method according to any one of claims 9 to 11. 13. Aluminum casting product according to claim 8 or 12, which is a structural automotive part. At least one of the following characteristics:
- a tensile strength of at least about 200 MPa;
a yield strength of at least about 100 MPa,
- an elongation of at least about 7%, and - a VDA bend angle of at least about 30°;
14. The aluminum cast product according to any one of claims 8, 12 and 13, having a 15. Aluminum casting product according to any one of claims 8, 12 to 14, comprising _Al4Ca . 16. Aluminum casting product according to any one of claims 8, 12 to 15, having _four phases of _Al13Fe , two phases of _Al3Mg and _two phases of _Al4Ca . 17. The aluminum cast product of claim 16 having _Al4Ca bonded with the _{Al3Mg two-} phase. The aluminum casting product according to any one of claims 8, 12 to 17, having an AlMgCa phase at the grain boundaries. A method for limiting Mg loss and dross formation during a casting operation of an aluminum product compared to a control aluminum product, the method comprising: from about 0.003 to about 6.0 Ca or from about 0.003 to about 2% by weight. .5 of Sr to a first aluminum alloy to obtain a cast alloy intended to be cast, said first aluminum alloy having a weight percent of:
about 1.0 to about 17.0 Mg;
about 0.5 to about 1.8 Fe, and the remaining amount of aluminum and unavoidable impurities;
, wherein the first aluminum alloy and the cast alloy do not contain Be as an alloying element. 20. The method of claim 19, wherein the first aluminum alloy further comprises a grain refiner. The method of claim 19 or 20, further comprising melting the casting alloy to obtain a molten casting alloy. 22. The method of claim 21, for reducing Mg loss to less than about 12 weight percent when the molten cast alloy is held for at least 6 hours. 22. The method of claim 21, for reducing dross formation to less than about 7 weight percent when the molten cast alloy is held for at least 6 hours. The method of any one of claims 21 to 23, further comprising casting the molten casting alloy to obtain a cast aluminum alloy. The method of claim 24, further comprising subjecting the cast aluminum alloy to high pressure vacuum die casting. The method according to any one of claims 19 to 25, which does not include a post-casting heat treatment step. 27. A method according to any one of claims 19 to 26, wherein the cast aluminum alloy comprises Ca. The method of claim 27, wherein the cast aluminum alloy contains about 0.01 to about 0.3 Ca. 29. The method of any one of claims 19-28, wherein the first aluminum alloy comprises about 3.0 to about 8.0 Mg. 30. The method of any one of claims 19-29, wherein the first aluminum alloy comprises about 4.0 to about 6.0 Mg. The method of any one of claims 19 to 30, wherein the first aluminum alloy contains about 0.8 to about 1.8 Fe.

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