AlSiMgX MASTER ALLOY AND USE OF THE MASTER ALLOY IN THE PRODUCTION OF AN ALUMINIUM ALLOY

Abstract

The invention relates to an AlSiMgX master alloy, especially suitable for increasing the Magnesium concentration of aluminium foundry alloy melts. The invention also relates to a process for increasing the Mg content of aluminium foundry alloys by use of the AlSiMgX master alloy in preparing a target aluminium alloy. The AlSiMgX master alloy comprises: Mg 1.3-6.5 wt %, Si 6.5-11.5 wt %, Cu 0-1 wt %, Mn 0-1.0 wt %, Fe0.40 wt %, Ti0.18 wt %, Sr0.10 wt %, balance Al and incidental impurities.

Claims

1. An AlSiMgX master alloy for increasing the content of Mg in an aluminium base alloy in the preparation of a target aluminium alloy, the AlSiMgX master alloy comprises: Mg 1.3-6.5 wt %; Si 6.5-11.5 wt %; Cu 0-1.0 wt %; Mn 0-1.0 wt %; Fe0.40 wt %; Ti0.18 wt %; Sr0.10 wt %; and balance Al and incidental impurities.

2. The AlSiMgX master alloy according to claim 1, wherein the content of Si is 6.5-7.5 wt %, or 9.0-11.5 wt %.

3. The AlSiMgX master alloy according to claim 1, wherein the content of Si is 6.5-11.5 wt % and the content of Mn is 0.4-0.8 wt %.

4. The AlSiMgX master alloy according to claim 3, wherein the content of Si is 6.5-8.5 wt %, or 9.0-11.5, and the content of Mn is 0.4-0.8 wt %.

5. The AlSiMgX master alloy according to claim 1, wherein the content of Si is 6.5-7.5 wt % and the content of Cu is 0.2-0.7 wt %.

6. The AlSiMgX master alloy according to claim 1, wherein the content of Sr is 0.02-0.04 wt %.

7. The AlSiMgX master alloy according to claim 1, wherein the content of Fe is 0.15 wt %.

8. The AlSiMgX master alloy according to claim 1, wherein the content of Ti is 0.05-0.15 wt %.

9. The AlSiMgX master alloy according to claim 1, wherein the Mg content is 1.3-5.5 wt %; 1.3-2.5 wt %; 1.5-2.5 wt %; 1.5-2.0 wt %; 2.0-3.0 wt %; 2.5-3.5 wt %; 3.4-4.0 wt %; 4.0-5.5 wt %; 4.5-5.5 wt %, or 4.0-4.6 wt %.

10. The AlSiMgX master alloy according to claim 1, wherein the master alloy is based on 3xx alloy (according to the Aluminium Association designation system), EN AC-42xxx, EN AC-43500 (AlSi10MnMg) or EN AC-45500 (AlSi7Cu0.5 Mg) alloy (according to European Standard EN1706 and/or EN 1676), having an increased Mg concentration compared to the said standard alloys.

11. The AlSiMgX master alloy according to claim 1, where the AlSiMgX master alloy is in the form of an ingot, rod, wire, pellet, or briquet, foil, waffle, button, rod, powder or splatter.

12. (canceled)

13. A method for increasing the content of Mg in an aluminium base alloy in the preparation of a target aluminium alloy, the method comprises providing an AlSiMgX master alloy according to claim 1; providing an aluminium base alloy having essentially the same composition as the AlSiMgX master alloy except the Mg concentration being lower compared to the Mg concentration of the AlSiMgX master alloy; adding a predetermined amount of the AlSiMgX master alloy to the aluminium base alloy, thereby increasing the Mg content of the aluminium base alloy while keeping the concentration of any other alloying elements essentially unchanged.

14. The method according to claim 13, comprising adding the AlSiMgX master alloy to a melting furnace, prior to, during, or after melting the aluminium base alloy.

15. The method according to claim 13, comprising adding the AlSiMgX master alloy to a transport crucible, prior to, during, or after being filled with molten aluminium base alloy.

16. The method according to claim 13, comprising adding the AlSiMgX master alloy to a holding or casting furnace, prior to, during, or after the aluminium base alloy is being poured in.

17. The method according to claim 13, comprising adding the AlSiMgX master alloy to a continuously melting furnace, wherein the AlSiMgX master alloy is periodically fed to the furnace to compensate Mg-loss.

18. The method according to claim 13, wherein the AlSiMgX master alloy is added in the form of an ingot, rod, wire, pellet, or briquet, foil, waffle, button, rod, powder or splatter.

19. A method for preparing an AlSiMgX master alloy according to claim 1, the method comprises the steps: providing an aluminium base alloy in solid or molten state; optionally, determining the concentration, in weight percent, of each alloying element in the aluminium base alloy; adding an appropriate amount of Mg into the aluminium base alloy to obtain a desired concentration of Mg in the AlSiMgX master alloy, optionally, adjusting the amount of any other alloying elements selected from the group consisting of Si, Cu, Fe, Mn, Ti and Sr by adding an appropriate amount of the alloying element(s) to the aluminium base alloy to obtain the desired composition of the AlSiMgX master alloy, if necessary, adjusting temperature to provide fluidity for casting, and casting the AlSiMgX master alloy into an ingot, rod, wire, pellet, or briquet.

20. The method according to claim 19, where the aluminium base alloy is chosen from a 3xx series alloy (according to the nomenclature of the Aluminium Association designation system); EN AC-42xxx alloy; EN AC-43500 alloy (AlSi10MnMg) or EN AC-45500 alloy (AlSi7Cu0.5 Mg) (according to European Standard EN1706 and/or EN 1676).

21-22. (canceled)

23. Use of an AlSiMgX master alloy according to claim 1, wherein a predetermined amount of the AlSiMgX master alloy is added to an aluminium base alloy to increase the content of Mg, while the concentration of any other alloying elements in the aluminium base alloy are essentially unchanged.

Description

DETAILED DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 illustrates the mechanical properties of AlSi7 in T6 temper as a function of the Mg-content.

DETAILED DESCRIPTION OF THE INVENTION

[0046] The present disclosure relates to an AlSiMgX master alloy especially suitable for increasing the Mg content of aluminium foundry alloy melts. The AlSiMgX master alloys according to the present disclosure is therefore especially suitable for usage in a process for preparing target aluminium alloys. Preferably, the AlSiMgX master alloy contains overall the same alloying elements and essentially in the same concentrations that are desired in the target aluminium alloy, except for a higher content of Mg.

[0047] The AlSiMgX master alloy according to the present disclosure comprises: [0048] Mg 1.3-6.5 wt %; [0049] Si 6.5-11.5 wt %; [0050] Cu 0-1.0 wt %; [0051] Mn 0-1.0 wt %; [0052] Fe0.40 wt %; [0053] Ti0.18 wt %; [0054] Sr0.10 wt %; the rest being Al and incidental impurities.

[0055] The AlSiMgX master alloy is used in a process for preparing a target aluminium alloy by addition of an appropriate amount of the above AlSiMgX master alloy to an aluminium base alloy.

[0056] The composition of any particular AlSiMgX master alloy according to the present disclosure depends upon the composition of the desired target aluminium alloy, which also corresponds with the composition of the base aluminium alloy. Except for the concentration of Mg, the AlSiMgX master alloy shall have essentially the same concentrations of alloying elements (alloying elements selected from the group consisting of Si, Cu, Fe, Mn, Ti and Sr) as the target alloy. By essentially the same concentrations is meant that the concentrations of the said alloying elements (except Mg) in the AlSiMgX master alloy corresponds with the target aluminium alloy, such that the resulting concentration of the said alloying elements in the target aluminium alloy, after addition of the AlSiMgX master alloy to a base aluminium alloy, have generally corresponding concentration except the concentration of Mg which is increased in the target aluminium alloy compared to the base alloy. For a given aluminium base alloy, an AlSiMgX master alloy of the invention can be prepared. It should be appreciated that the weight percent concentration of each alloying element in the base alloy can be identified by techniques, generally known in the art.

[0057] The AlSiMgX master alloy may be used in a process for preparing a target aluminium alloy by addition of the AlSiMgX master alloy to an aluminium base alloy. A preferred aluminium base alloy may be selected from the 3xx series, as designated by the Aluminium Association or from other European or national foundry alloys. The aluminium base alloy may be an EN AC-42xxx, EN AC-43500 (AlSi10MnMg) or EN AC-45500 (AlSi7Cu0.5 Mg) alloy, according to European Standard EN1706 and/or EN1676. The base alloy, to which the AlSiMgX master alloy is added, determines the alloying elements and their concentration in the AlSiMgX master alloy.

[0058] The Mg concentration in the AlSiMgX master alloy is from 1.3 to 6.5 wt %. In some applications, the Mg concentration in the AlSiMgX master alloy may range from 1.3 to 5.5 wt %, or 1.3 to 4.5, or 1.3 to 2.5 wt %, or 1.5 to 2.5 wt %, or 1.5 to 2.0 wt %, or 2.0 to 3.0 wt %, or 2.5 to 3.5 wt %, or 3.4 to 4.0 wt %, or 4.0 to 5.5 wt %, or 4.5 to 5.5 wt %, or 4.0 to 4.6 wt %. The concentration of Mg in the AlSiMgX master alloy generally depends on the desired increase of Mg in the target aluminium alloy, compared with the base aluminium alloy.

[0059] The Si concentration in the AlSiMgX master alloy is from 6.5 to 11.5 wt %. In some examples, the Si concentration in the AlSiMgX master alloy may range from 6.5 to 7.5 wt %. Some gravity and low-pressure aluminium casting alloys are of the AlSi7Mg-type, hence AlSiMgX master alloys having between 6.5-7.5 wt % Si are especially suited for such AlSi7Mg-type alloys. In another example, the Si concentration in the AlSiMgX master alloy may range from 9 to 11.5 wt % which are particularly suitable for addition to AlSi10Mg-type alloys. An AlSiMgX master alloy comprising from 6.5 to 11.5 wt % Si, e.g. from 6.5 to 8.5 wt % Si, or from 9.0 to 11.5 wt % Si, together with 0.4 to 0.8 wt % Mn are especially suitable for additions to AlSiMnMg-type alloys, such as AlSi7MnMg-type and AlSi10MnMg-type alloys. Furthermore, an AlSiMgX master alloy comprising from 6.5 to 7.5 wt % Si and 0.2 to 0.7 wt % Cu are especially suitable for addition to AlSi7MgCu0.5 type alloys.

[0060] The Fe concentration in the AlSiMgX master alloy should be 0.40 wt % or less, such as 0.15 wt % or less.

[0061] The Ti concentration in the AlSiMgX master alloy should be 0.18 wt % or less, such as between 0.05 and 0.15 wt %.

[0062] The Sr concentration in the AlSiMgX master alloy should be 0.10 wt % or less, such as between 0.02-0.04 wt %.

[0063] It should be appreciated that the composition of the AlSiMgX master alloy may be varied by combining the exemplified ranges of the alloying elements, and within the generally defined composition according to the appended claims.

[0064] The AlSiMgX master alloys of the present disclosure are prepared according to generally known techniques of production of foundry alloys. Commercially pure aluminium, scrap aluminium alloy, including recycled aluminium metal, or a combination thereof, as well as the alloying elements of the respective base alloy can be used as the starting material. The AlSiMgX master alloy is preferably based on a 3xx series alloy (according to the nomenclature of the Aluminium Association designation system), EN AC-42xxx, EN AC-43500 (AlSi10MnMg) or EN AC-45500 (AlSi7Cu0.5 Mg) alloy (according to European Standard EN1706 and/or EN 1676), having an increased Mg concentration compared with the said standard base alloys. A sufficient amount of magnesium is used to provide the calculated final concentration of magnesium in the AlSiMgX master alloy. After the final element has been added, it is desirable to immediately adjust the temperature so as to provide fluidity for casting and, depending on furnace stirring characteristics, provide a product that, when cast, is of consistent chemistry from the beginning to the end of the charge so as to remove concerns about segregation.

[0065] The casted AlSiMgX master alloy may be further processed or the final step in its preparation may be modified so as to produce the AlSiMgX master alloy in any desirable form. Such forms include foil, waffle, ingot, button, rod, wire, pellet, powder, briquet, and splatter. However, in many applications the preferred form of the AlSiMgX master alloy is an ingot. The ingot can be in a corresponding shape and/or size of the ingots used for the base alloy ingots. Another preferred form of the AlSiMgX master alloy is a continuous cast (direct chill) ingot, where the developing Mg-containing phases are small in size and well distributed due to the high solidification rate. An AlSiMgX master alloy ingot wherein the Mg-containing phases are small in size and well distributed facilitates a rapid dissolution of the master alloy when added to a molten aluminium base alloy.

[0066] The AlSiMgX master alloy according to the invention is used in the preparation of final target aluminium alloys. The AlSiMgX master alloy can be added to a melting furnace (prior to, during, or after melting), to the melt in a transport crucible or in a holding or casting furnace. For example, for a single furnace melting system, where the cast alloy is cast from the melting furnace, the base aluminium alloy is often prepared by using pre-alloyed foundry aluminium alloy ingots. Alternatively, the base aluminium alloy may be prepared, using commercially pure aluminium, scrap aluminium alloy, including recycled aluminium metal, or a combination thereof as well as the required alloying elements. Sufficient material is added until the basic charge weight is achieved, except for the amount of the AlSiMgX master alloy which may be added subsequently. The temperature is raised to above the melting point, typically between 70 and 800 C. Then an appropriate amount of AlSiMgX master alloy material may be added to achieve the desired final chemistry of the target alloy. Advantageously, the surface of the molten aluminium base alloy is skimmed clean of any oxides before the AlSiMgX master alloy addition.

[0067] Alternatively, depending on the expected nominal Mg-content calculated based on the composition of the input material (base aluminium alloy) an appropriate amount of AlSiMgX master alloy can also be added to the input material prior to melting in order to directly achieve the desired Mg-content after complete melting of the input and the AlSiMgX master alloy materials.

[0068] In another example, the AlSiMgX master alloys according to the present disclosure can be added to continuously melting furnaces such as shaft furnaces or chip-melting furnaces, where the normal expected Mg-loss due to burn-off during melting is usually quite well known. Depending on the hourly melting capacity and the necessary compensation of the Mg-loss or desired increase of the Mg-content, AlSiMgX master alloy ingots can be fed into the melt, e.g. in regular periods.

[0069] In a further example, the AlSiMgX master alloys according to the present disclosure can be added to the base aluminium alloy in a holding or casting furnace as the base alloy metal is being poured in. This provides a stirring action and minimizes the time and temperature for making alloying additions, thereby minimizing oxidation of some alloying elements, especially Mg. An alternative where the AlSiMgX master alloy is added to a filled holding furnace appropriate stirring would be needed.

[0070] In still another alternative, the AlSiMgX master alloys according to the present disclosure can be added outside of the melting furnace, such as in a transport crucible, so that the base alloy melt composition in the melting furnace is not affected. Preferably the addition of the AlSiMgX master alloy takes place into the empty transport crucible before it is being filled or to the melt in a transport crucible prior to an eventual rotor degassing process. Again, this provides stirring action and minimizes the time and temperature for making alloying additions, thereby minimizing oxidation of some alloying elements.

[0071] In a preferred embodiment of the invention the AlSiMgX master alloy is in the form of ingots having a size and a Mg-concentration that results in a stepwise and/or fixed increase of the Mg concentration when one or more AlSiMgX master alloy ingots are added to a certain amount of base aluminium alloy. The AlSiMgX master alloy ingots may have a weight of 6.5 kg, 7.5 kg or 9.2 kg, which sizes corresponds to commonly used base aluminium ingots. Addition of one AlSiMgX master alloy ingot to a certain amount of the base aluminium alloy may increase the Mg concentration in the target aluminium alloy by e.g. 0.1 wt % (percentage point). Table 1 shows examples of AlSiMgX master alloy ingots sizes and Mg ranges resulting in a fixed Mg increase (in wt %) in target aluminium alloys by addition of one ingot to 1000 kg base alloy. Using such standardized AlSiMgX master alloy ingot system facilitates and simplifies the production of target aluminium alloys. It should be noted that Table 1 only illustrates example alloys for better understanding the invention. The examples illustrated in Table 1 should therefore not be construed as limiting for the present invention since there are a variety of possible master alloy compositions within the defined claim scope in the appended claims.

TABLE-US-00001 TABLE 1 Desired Mg increase in target alloy by adding 1 Mg range in Ingot weight ingot to 1000 kg of melt master alloy [kg] [wt %] [wt %] 6.5 0.01 1.7-2.1 6.5 0.02 3.4-3.8 6.5 0.03 4.8-5.2 7.5 0.01 1.5-1.9 7.5 0.02 2.9-3.3 7.5 0.03 4.2-4.6 9.2 0.01 1.3-1.7 9.2 0.02 2.5-2.9 9.2 0.03 3.5-3.9

[0072] The following examples illustrate the use and advantages of the AlSiMgX master alloys according to the present disclosure. The illustrating examples should not be construed as limiting for the present invention.

[0073] The first illustrating example concerns a 3xx base alloy containing nominally 7 wt % Si, 0.12 wt % Fe, 0.12 wt % Ti 0.02 wt % Sr, and 0.28 wt % magnesium, balance Al. In order to fulfil required strength requirements, the Mg concentration shall be increased to 0.29 wt %. By adding an AlSiMgX master alloy ingot of 6.5 kg having the same nominal composition as the base alloy, but with 1.9 wt % Mg to 1000 kg of the above-described base alloy melt will nominally increase the Mg-content of the melt by 0.01 wt %, i.e. to a final Mg content of 0.29 wt %. In the same way, the addition of two ingots would nominally increase the Mg-content by 0.02 wt %. A calculated nominal loss in melt temperature of approx. 7.5 degrees per added ingot to a 1000-kg-melt has to be taken into consideration. The time for melting and complete dissolution of the AlSiMgX master alloy ingot can be expected to be within 2-3 minutes. Pouring the liquid base alloy onto the master alloy ingot or stirring (e.g. by a rotor degassing treatment) would further decrease the melting and dissolution time.

[0074] The second illustrating example concerns a 3xx base alloy containing nominally 7 wt % Si, 0.12 wt % Fe, 0.12 wt % Ti, 0.02 wt % Sr, and 0.28 wt % magnesium, balance Al. In order to fulfil required strength requirements, the Mg concentration shall be increased to 0.32 wt %. By adding two AlSiMgX master alloy ingots of 6.5 kg having the same composition as the base alloy, but with 3.8 wt % Mg to 1000 kg of the above-described base alloy melt will nominally increase the Mg-content of the melt by 0.04 wt % i.e. to a final value of 0.32 wt %.

[0075] The AlSiMgX master alloys of the present invention provide several advantages over conventional methods of adding Mg to aluminium alloys. The AlSiMgX master alloys provide a concentrated amount of Mg in the proper proportion that is required to produce the specific target alloy, thereby allowing the desired composition to be reached with the addition of only one master alloy. Due to finely distributed Mg-phases the AlSiMgX master alloys provide high solution rates, thereby reducing furnace cycle time or process time. The AlSiMgX master alloys reduce losses, e.g. caused by burn-off, and furthermore, they reduce melt treatment time, both due to faster dissolution and easier handling compared with the traditional methods. The AlSiMgX master alloys also provide, in certain instances, more consistent chemistry control due to more reliable yield compared to addition of pure Mg or binary AlMg alloys. These advantages result in increased efficiency and decreased manufacturing costs for shape-casting foundries.

[0076] The following examples relate to AlSiMgX master alloys according to the disclosure:

Example 1

[0077] 233.1 kg of an AlSi7Mg alloy was prepared in an electric resistance furnace. The temperature of the melt was 740 C. The composition of the alloy analyzed with Optical Emission Spectroscopy (OES) is given in table 2. The Mg concentration was 0.309 wt %.

[0078] An AlSiMgX master alloy according to the invention was added to the 233.1 kg melt. The composition of the AlSiMgX master alloy is given in table 2. The Mg concentration of the master alloy was 1.37 wt %. An amount of master alloy (5.009 kg) representing a theoretical increment in Mg concentration of 0.0223 wt %. was added to the melt. After dissolution of the master alloy the Mg concentration increased by 0.0249 wt %, giving an estimated yield of 111.5%. A person skilled in the art would conclude the deviation from 100% yield would be due to uncertainty in the chemical analyses (OES).

TABLE-US-00002 TABLE 2 Weight Si Mg Fe Ti Sr Others each Alloy [kg] [wt %] [wt %] [wt %] [wt %] [wt %] [wt %] AlSi7Mg 233.1 7.40 0.3091 0.1250 0.1143 0.0248 <0.01 (base alloy) Master alloy 5.009 7.50 1.37 0.1240 0.1031 0.0377 <0.01 AlSi7Mg 238.1 7.40 0.3340 0.1270 0.1149 0.0251 <0.01 (target alloy) Expected Mg increment 0.0223 in AlSi7Mg [wt %] Observed Mg increment 0.0249 in AlSi7Mg [wt %] Yield [%] 111.5

Example 2

[0079] 1.585 kg of an AlSi7Mg alloy was melted in an electric resistance furnace. The temperature of the melt was 720 C. The composition of the alloy analyzed with OES is given in table 3. The Mg concentration was 0.3043 wt %. An AlSiMgX master alloy according to the invention was added to the 1.585 kg melt. The composition of the master alloy is given in table 3. The Mg concentration of the master alloy was 1.37 wt %. An amount of master alloy (0.1592 kg) representing a theoretical increment in Mg concentration of 0.0973 wt %. was added to the melt. After dissolution of the master alloy the Mg concentration increased by 0.0957 wt %, giving an estimated yield of 98.4%. Again, the deviation from 100% yield can be explained by OES analysis uncertainty.

TABLE-US-00003 TABLE 3 Weight Si Mg Fe Ti Sr Others each Alloy [kg] [wt %] [wt %] [wt %] [wt %] [wt %] [wt %] AlSi7Mg 1.5850 6.96 0.3043 0.0989 0.1343 0.0251 <0.01 (base alloy) Master alloy 0.1592 7.50 1.37 0.1240 0.1031 0.0377 <0.01 AlSi7Mg 1.7442 6.98 0.4000 0.1014 0.1392 0.0250 <0.01 (target alloy) Expected Mg increment 0.0973 in AlSi7Mg [wt %] Observed Mg increment 0.0957 in AlSi7Mg [wt %] Yield [%] 98.4

Example 3

[0080] In a wheel foundry, a transport crucible was filled with 891 kg of an AlSi7Mg melt from a melting furnace. The weight of the melt was determined by weighing the crucible before and after filling. The composition of the alloy analyzed with Optical Emission Spectroscopy (OES) is given in table 4. The Mg concentration was 0.3021%. An AlSiMgX master alloy according to the invention was added to the 981 kg melt. The composition of the AlSiMgX master alloy is given in table 4. The Mg concentration of the master alloy was 1.37 wt %. One ingot of the master alloy (9.2 kg) representing a theoretical increment in Mg concentration of 0.011 wt % was added to the melt prior to a degassing treatment of four minutes. In an OES sample taken just after the treatment, the Mg concentration increased to 0.3142 wt %, i.e. by 0.0121 wt %, giving an estimated yield of 111%. A person skilled in the art would conclude the deviation from 100% yield would be due to uncertainty in the chemical analyses (OES).

TABLE-US-00004 TABLE 4 Weight Si Mg Fe Ti Sr Others each Alloy [kg] [wt %] [wt %] [wt %] [wt %] [wt %] [wt %] AlSi7Mg 891 7.4658 0.3021 0.1126 0.1203 0.0211 (base alloy) Master alloy 9.2 7.4950 1.37 0.1240 0.1031 0.0377 <0.01 Upgraded 900.2 7.4952 0.3142 0.1153 0.1232 0.0204 AlSi7Mg (target alloy) Expected Mg increment 0.0109 in AlSi7Mg [wt %] Observed Mg increment 0.0121 in AlSi7Mg [wt %] Yield [%] 111.0

[0081] The three examples show that the composition of the target alloy has essentially the same composition of the alloying elements as the base alloys, except the amount of Mg which is increased to the desired concentration.

[0082] The specific details described in the context of the various example embodiments are not intended to be construed as limitations. The disclosed examples and alternatives of the invention may be readily combined, without departing from the scope as defined in the appended claims.