MXPA99005252A - Composition of strontium base alloys that have a reduced fusion temperature and method to manufacture the mi - Google Patents

Abstract

A base alloy is provided with 20-80% strontium, preferably 0.01-2.0% aluminum and / or copper, and the remainder essentially zinc plus impurities, and a method for preparing the same, and a method for modifying the microstructure of non-ferrous alloys with the alloy of

Description

COMPOSITION OF STRONTIUM BASE ALLOY THAT HAS TEMPERATURE OF REDUCED FUSION TEMPERATURE AND METHOD TO MANUFACTURE THE SAME BACKGROUND OF THE INVENTION The present invention relates to a base alloy containing strontium and its manufacture and use for the control of the microstructure in aluminum, zinc and magnesium base alloys. It is known in the art that strontium is a superior and permanent modifier of the aluminum-silicon component of eutectic and hypoeutectic aluminum-silicon die-cutting alloys, ie, less than 12.6 weight percent silicon. The addition of strontium modifies the morphology of the eutectic phase to produce a fine fibrous microstructure, instead of the lamellar structure similar to acicular plate «which is typically found in unmodified alloys, therefore results in an alloy with mechanical properties, Improved ductility and impact resistance. Reference may be made, for example to US Patents 3,446,170 and 3,567,429, the Glen Patent 1,829,816 and K.

Al er et al. "Experiences with the Permanent Modification of Al-Si Casting Alloys", published in Aluminum, 49 (5), 362-367 (1972) Other alloy systems have also found benefits of strontium additions. For example, US Patent 3,926,690 to Morris et al., Discloses that the addition of 0.01-0.5% strontium or calcium to an aluminum-magnesium-silicon alloy provides an alloy with improved extrusion properties. U.S. Patent 4,394,348 to Hardy et al., Discloses that the use of a base alloy containing strontium peroxide provides a finer grain alloy. In "Modification of Intermetallic Phases by Strontium in Aluminum Wrought Alloys", by M.H. Mulzimoglu et al., It was reported that the strontium additions have a modifying effect on several intermetallic phases of aluminum alloys of the series 6061, 5182 and lxxx. However, there are difficulties involved in the addition of strontium. Strontium is usually added to alloys in the form of a base alloy. The use of pure strontium metal is limited to the extent that it is easily oxidized in a humid atmosphere and in the presence of an oxide layer the dissolution rate of the strontium in the desired melt is inhibited. In the present practice, such alloys of strontium to alloys are often made using a master alloy containing strontium. Contact powders containing strontium-silicon are described in U.S. Patent No. 4,108,646. U.S. Patent 1,520,673 discloses an aluminum-silicon-strontium base alloy. A strontium-silicon-aluminum base alloy is described in U.S. Patent 4,009,026. U.S. Patent 4,937,044 describes a strontium-magnesium-aluminum base alloy. Most of the strontium-containing base alloys used for modification of aluminum-silicon alloys are manufactured in the form of aluminum-strontium binary base alloys; however, this gets disadvantages, and other systems also have disadvantages. Thus, for example, the use of these base alloys has always been impeded by the low melting rates or dissolution of low temperature applications. The following illustrative base alloys rejuvenate, all reportedly, addition at melting temperatures "exceeding 725 ° C in order to obtain acceptable dissolution rates and strontium recovery: (1) base alloy containing 10 percent in weight of strontium and 90 weight percent of aluminum; (2) base alloy "containing 10 percent by weight of strontium, 14% by weight of silicon and 76 percent by weight of aluminum; (3) base alloy containing 90 percent by weight of strontium and 10 percent by weight of aluminum; Y (4) base alloy "containing 40 percent by weight of strontium, 35 percent by weight of aluminum and 25 percent by weight of magnesium. In addition, the pure metallic strontium as well as the base alloys containing high concentrations of strontium in alpha phase, such as 90 percent by weight of strontium and 10 percent by weight of aluminum, without very reactive with the atmosphere and require special packaging to avoid oxidation and degradation of the base alloy. This special bond is usually aluminum, which has a melting temperature of 660 ° C, which further prevents the base alloys from melting or a dissolution rate at lower temperatures. Many applications that use non-ferrous alloys operate with the molten metal bath at extremely low temperatures. As an example, molten metal temperatures of 620 ° C are common in die casting operations. In addition, steel coating lines that apply a coating containing 57.5% aluminum, 41% zinc and 1.5% silicon typically operate with a molten metal bath temperature of 600 ° C. Therefore, there is a significant need in the industry for a base alloy containing strontium which can easily melt or dissolve at lower metal temperatures and which is non-reactive and stable in the atmosphere in order to avoid difficulties of processing and the need for a special protective packaging.

BRIEF DESCRIPTION OF THE INVENTION Therefore, a main objective of the present invention is to provide a strontium-containing base alloy for use as a strontium additive to non-ferrous alloy systems, also to provide a method for modifying the microstructure of non-ferrous alloys with the alloy of base, and a method to prepare such alloys. A further object of the present invention is to provide a base alloy and a method as mentioned in the foregoing, wherein the alloy has a low melting temperature and a rapid dissolution rate in molten metal. A further object of the present invention is to provide a method and a base alloy as mentioned above for addition of the base alloy to non-ferrous melted alloys at bath temperatures less than about 700 ° C, and lower than about 660 ° C, and even less than about 600 ° C. A further object of the present invention is to provide a method and a base alloy as mentioned above, wherein the base alloy has a relatively high density, which upon addition to the molten bath, promotes subsurface immersion of the molten bath and in this way the loss of strontium due to oxidation is minimized.

A further object of the present invention is to provide a method and base alloy as in the foregoing, wherein the base alloy is not subjected to oxidation and degradation when exposed to moisture and normal atmospheric conditions. A further object of the present invention is to provide a method and base alloy as mentioned above, wherein the base alloy does not require a protective packing.

A further object of the present invention is to provide a method and base alloy as mentioned above, wherein the base alloy can be die cut into conventional ingot and button type products, and wherein the base alloy has a low ductility which allows it to be further processed into granules or powders. A further object of the present invention is to provide a method and base alloy as mentioned above, wherein the base alloy can be provided in many forms for addition to molten non-ferrous alloys, such as (a) ingot, (b) button, (c) pellet, (d) granule, (e) powder, (f) compact or briquettes of granules or powder, (g) powder for coating by injection or molding, and (h) wire or rod with core.

In accordance with the present invention, it has now been found that the objects and advantages of the present invention can be easily obtained. The base alloy of the present invention consists essentially, in percent by weight, of between 20-80% strontium, desirably between 30 and 40 weight percent of strontium, with the remainder consisting of zinc plus impurities. Preferably, the base alloy also includes in percent by weight, from 0.01-2.0% each of a material "selected from the group" consisting of aluminum and copper and mixtures thereof, and preferably from 0.1 to 0.5. % of each of such materials. Throughout the present specification all percentages are by weight. The present invention also relates to a method for modifying the microstructure of non-ferrous alloys by providing a melt of an alloy which is selected from the group consisting of aluminum base alloys, magnesium base alloys and zinc base alloys, and adding the base alloy mentioned above to them.

The present invention also relates to a process for preparing a base alloy, which comprises: preparing a base alloy "consisting essentially of between 20-80% strontium, with the remainder constructed of zinc plus impurities, including steps of providing a bath of molten metal containing zinc and 0.01-2.0% of each of materials that are selected from the group consisting of aluminum, copper and mixtures thereof; and adding the strontium requirement amount to the molten metal bath, whereby losses due to oxidation are reduced. Desirably, strontium is added to molten metal baths after the addition of the material thereto. The additional objects and advantages of the present invention will appear in the following.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES According to the present invention, the base alloy contains 20-80% strontium and preferably 30-40% strontium. In addition, the base alloy desirably contains from 0.01-2.0% aluminum and / or copper, and preferably from 0.1-0.5% aluminum and / or copper. Strontium-zinc base alloys containing more than 40% strontium are reactive with the atmosphere and, in the absence of special packaging, exhibit degradation with respect to time. Strontium-zinc base alloys with less than 30% strontium have increased melting and solidification properties. The addition of aluminum and / or copper as mentioned above, minimizes the oxidation and generation of slag during the manufacture and punching of the base alloy and provides a base alloy that has minimal reactivity with the atmosphere and does not require a protective packing special to avoid degradation. The base alloy of the present invention modifies the microstructure of non-ferrous alloys such as aluminum, magnesium and zinc base alloys by adding the base alloy to a molten metal bath of the non-ferrous alloy. The base alloy of the present invention particularly modifies the eutectic aluminum-silicon component in the eutectic and hypoeutectic aluminum-silicon die-cutting alloys, and also modifies the eutectic phase of silicon in aluminum-zinc-silicon alloys. Therefore, the eutectic component is modified to produce a fine fibrous microstructure. In addition, in forged and die-cast alloys based on aluminum, the base alloy of the present invention modifies the plate-like Al5FeSi beta phase to the Chinese writing phase Al8Fe2Si alpha, and changes the morphology of the Mg2Si phase of Chinese writing to form similar to needles. In addition, in secondary aluminum casting alloys, the base alloy of the present invention reduces the size of the mud particles, that is, the intermetallic phase having Fe complex present in these alloys. Even more, the base alloy of the present invention reduces the grain size and concentrates the microporosity of shrinkage in magnesium-based alloys. According to the process of the present invention, a base alloy containing between 20-80% strontium is prepared, with the remainder consisting of zinc plus impurities, by providing a bath of molten metal containing zinc and from 0.01-2.0 % of each of aluminum and / or copper, and add the strontium requirement amount to the molten metal bath. Desirably, the aluminum and / or copper is added to the molten metal bath before the addition of the strontium. Advantageously, the above procedure reduces oxidation in the upper part of the melt and reduces strontium losses due to oxidation. In addition, when the alloy is emptied, it has been found that the present process again reduces oxidation on the surface of the resulting product and results in solidification with little oxidation. These are important advantages. The features and advantages of the present invention will become more readily apparent from a consideration of the following illustrative examples.

Example I - Preparation of Base Alloy The following example is an example of the process for preparing the base alloy of the present invention. In this example, the strontium content is between 20-80% with the contents of strontium, zinc, aluminum and copper as established in the following examples. The required amount of zinc is melted in an oven and 0.01-2.0% aluminum or copper is added to the melt. The oven temperature is adjusted to approximately 540 ° C. A gas blanket is applied to the furnace using an inert gas to additionally protect the melt from excessive oxidation and generation of slag. The required amounts of strontium metal are added to the melt slowly and increasingly, and the melt is stirred to ensure homogeneity. The oven temperature is adjusted to approximately 650 ° C. The resulting base alloy is emptied into the desired product form, eg pellets, buttons, ingots, etc. The base alloy of the preferred composition is brittle and can be further processed into powders or granules using conventional methods. Similarly, the powder or the granules can be further processed into compact materials or briquettes or into core wire or into rod product forms. Alternatively, if desired, a portion of the content zinc can be retained and added at the end of the alloy sequence to suspend the melt at pouring temperatures.

Example II - Speed of Volume Dissolution of the Base Alloy of Sr-Zn-X "in a Si-Al Alloy 12.5% 10 The method described previously in Example I is used to produce a series of alloys of Sr-Zn -X of the present invention to evaluate their respective dissolution rates in volume. The tests are carried out in a Si-Al alloy at 12.5% at a temperature of 625-650 ° C. Representative samples of each base alloy are placed in a cage which is then pushed under the surface of the melt. The cage is periodically removed and visually inspected to determine the degree of dissolution which has been produced. In addition to the Sr-Zn-X base alloy compositions, binary strontium and strontium pure metal base alloys were included for comparison. The products and chemical compositions evaluated, as well as the time required for dissolution, are given in Table I.

TABLE I Chemical composition of the alloys (% by weight) Time of dissolution of volume (minutes) Test Base Alloy Sr Zn Al Cu Si Dissolution time-comments (1) Commercial 10 - 90 No significant dispersion after 30 minutes (2) Commercial 10 - 76 14 No significant dispersion after 30 minutes (3) Commercial 90 - 10 No significant dispersion after 30 minutes (4) Strontium 100 No significant dispersion after metal 30 minutes (5) Zn-Sr-X 35 64 0.1 1-volume disappeared, semisolid dispersion (6) Zn-Sr-X 55 45 0.2 2-disappeared volumes, semisolid dispersion (7) Zn-Sr-X 62 38 0.2 2-disappeared volumes, semisolid dispersion (8) Zn-Sr-X 68 32 0.3 2-disappeared volumes, semisolid dispersion (9) Zn-Sr-X (1) 72 28 0.5 5-disappeared volumes, semisolid dispersion (10) Zn-Sr-X (2) 35 63 2-disappeared volumes, semisolid dispersion Note: () indicates an approximate value. (1) plus 0.0015% of Be. (2) plus 0.1% of Be.

Example III - Operation of the Sr-Zn Base Alloy as a Eutectic Silicon Modifier in a Si-Al Alloy 12.5% A Sr-Zn base alloy of the present invention is produced containing 33 weight percent strontium, 67 weight% zinc, according to the method of Example I. An alloy of 12.5 is prepared in the laboratory. 100% by weight of silicon and the rest of aluminum, and heated to a temperature of 650 ° C in a resistance furnace. The above base alloy is added to a Si-Al melt in an amount calculated to contribute a strontium addition of 0.02 weight percent. After maintaining the Al-Si melt for 2 minutes, a sample is emptied into a preheated cylindrical steel mold and evaluated to determine the degree of modification of eutectic silicon using conventional metallographic techniques. The procedure is repeated using Sr-Zn base alloys of the present invention "containing 34 and 35 weight percent strontium. Each of the above compositions of Sr-Zn produces a completely modified and fibrous eutectic silicon structure.

EXAMPLE IV - Operation of Sr-Zn Base Alloy as a Eutectic Silicon Modifier in Trosuel Castings of Al-Si-Cu-Zn Alloy A base alloy of 35 percent by weight of strontium, 65 percent by weight of zinc of the present invention is produced in the form of a button of 130 grams, according to the method of Example I and is evaluated as a modifier in an alloy cast in Al-Si-Cu-Zn die. The procedure involves adding the base alloy to a transfer crucible "containing an Al-Si alloy having a nominal chemical composition of 9.5 weight percent silicon, 2.9 weight percent copper, 2.4 percent by weight, zinc weight, 1.0 weight percent iron, 0.3 weight percent magnesium, and the rest aluminum. The temperature of the molten metal in the transfer crucible is 670 ° C. After the base alloy, the molten metal in the transfer crucible is flowed and degassed. This cycle consists of 2 minutes of flow injection, followed by 1 minute of rotary degassing using argon, for a total cycle time of 3 minutes during which the temperature of the molten metal decreases to 650 ° C. The molten metal is then transferred to the holding furnace of a cold chamber die-casting machine. The produced castings are examined using conventional metallographic techniques to evaluate the degree of eutectic modification of silicon that is obtained. It is found that the eutectic phase of silicon is completely modified and shows a structure of fibrous eutectic silicon. The strontium content in the castings varies from 0.007 to 0.010 percent by weight.

Example V - Operation of the Sr-Zn Base Alloy as a Al-Zn-Si Eutectic Silicon Modifier; Steel Coating Alloy The additions of strontium to coating lines of Al-Zn-Si using conventional base alloys is not possible due to the low temperature of the molten metal in the coating bath, which is typically maintained at about 600 ° C.

To evaluate the performance of the Sr-Zn base alloy, an Al-Zn-Si alloy containing 57.5 weight percent aluminum, 41 weight percent zinc and 1.5 weight percent is prepared in the laboratory. of silicon. The Al-Zn-Si alloy is maintained at a temperature of 600 ° C in a resistance furnace. A base alloy of 29 weight percent strontium, 71 weight percent zinc of the present invention is produced, according to the method of Example I and is added to the Al-Zn-Si melt in an amount calculated to contribute a strontium addition of 0.005 weight percent. After retaining the Al-Zn-Si melt for 5 minutes, samples are emptied and evaluated to determine the degree of modification of eutectic silicon. This is repeated with base alloy additions calculated to contribute strontium additions of 0.01 and 0.02 weight percent. The metallographic examination of the resulting microstructure shows that before the addition of the base alloy, the eutectic silicon shows an acrylic morphology, similar to sharp needles; typical of an unmodified structure. After the additions of the previous base alloy, the acrylic characteristics of the eutectic silicon begin to decompose and become more fibrous. The complete modification of the eutectic silicon is obtained at addition concentrations of 0.01-0.2 weight percent strontium. This invention may be embodied in other forms or may be carried out in other ways without departing from the spirit or essential characteristics thereof. Therefore, the present embodiment is considered in all its illustrative and non-limiting aspects, the scope of the invention is indicated by the appended claims, and all changes which are within the meaning and scope of equivalence are considered to be encompassed for the same.

Claims (19)

1. A base alloy, characterized in that it consists essentially of, in percent by weight, between 20-80% strontium, with the remainder consisting of zinc plus impurities.

2. The metal alloy according to claim 1, characterized in that it includes in weight percent from 0.01 to 2.0% each of a material that is selected from the group consisting of aluminum, copper and mixtures thereof.

3. The base alloy according to claim 2, characterized in that it includes from 0.1 to 0.5% of each such material.

4. The base alloy according to claim 1, characterized in that it includes 30 to 40% strontium.

5. The base alloy according to claim 1, characterized in that it is used to modify the eutectic component of eutectic and hypoeutectic aluminum-silicon casting alloys.

6. The base alloy according to claim 1, characterized in that it is used for addition to molten non-ferrous alloys which will melt and dissolve at temperatures below 600 ° C.

7. The base alloy according to claim 1, characterized by "that is used to modify the microstructure of forging and casting alloys based on aluminum.

8. The base alloy according to claim 1, characterized ponqué is used to reduce the size of an intermetallic phase having complex Fe present in the aluminum-based casting alloys.

9. The base alloy according to claim 1, characterized in that it is used to reduce the grain size and concentrate the microporosity of shrinkage in magnesium-based alloys.

10. A method for modifying the microstructure of non-ferrous alloys, characterized in that it comprises: providing a melt of an alloy which is selected from the group consisting of alloys based on aluminum, magnesium-based alloys and zinc-based alloys; and adding thereto a base alloy "consisting essentially of, in percent by weight, 20-80% strontium, with the remainder consisting of zinc plus impurities.

11. The method according to claim 10, characterized in that the base alloy includes, in percent by weight, 0.01 to 2.0% of each material that is selected from the group consisting of aluminum, copper and mixtures thereof.

12. The method according to claim 10, characterized in that the alloy is an aluminum-silicon casting alloy containing a eutectic component, which includes the step of modifying the eutectic component by the addition of the base alloy to the cast alloy of aluminum-silicon to produce a fine fibrous microstructure.

13. The method according to claim 10, characterized in that it includes the step of adding the base alloy to a molten metal bath of an aluminum-cast or forged alloy to modify the microstructure thereof.

14. The method according to claim 10, characterized in that it includes the step of adding the base alloy to a molten metal bath of an aluminum base cast alloy containing an intermetallic phase having Fe to reduce the size of the phase intermetallic

15. The method according to claim 10, characterized in that it includes the step of adding the base alloy to a bath of molten metal of a magnesium base alloy to reduce the grain size and concentrate the microporosity of shrinkage.

16. A process for preparing a base alloy, characterized in that it comprises: preparing a base alloy consisting essentially of, in percent by weight, between 20-80% strontium, with the remainder consisting of zinc plus impurities; which includes the steps of providing a bath of molten metal containing zinc and, in percent by weight, from 0.01-2.0% each of a material that is selected from the group consisting of aluminum, copper and mixtures thereof; and adding the strontium requirement amount to the molten metal bath, whereby losses due to oxidation are reduced.

17. The process according to claim 16, characterized in that it includes the step of adding the strontium to the molten metal bath after the addition of the material thereto.

18. The process according to claim 16, characterized in that it includes the step of providing the material in an amount from 0.1 to 0.5%.

19. The process according to claim 16, characterized by "including the step of adding a portion of the zinc content after the addition of strontium to suspend the melt at the pouring temperature.