MXPA99004710A - Iron additive for alloying non-ferrous alloys - Google Patents

Abstract

The present invention concerns additives for non-ferrous, liquid metals. The additives consist of compacted bodies of essentially pure iron particles.

Description

ADDITIVE OF IRON FOR ALLOY OF NON-FERROUS METALS DESCRIPTIVE MEMORY Iron is generally considered an unwanted impurity in aluminum. However, small amounts of iron (0.15-1.8%) in aluminum influence the mechanical properties of aluminum and facilitate the rotation of thin aluminum sheets. Aluminum with an increased iron content can also be used in profiles, since the iron improves the extrusion properties. Aluminum produced by electrolysis contains small amounts of iron that originate in the anodes of the electrolytic cell. Said iron content is not sufficient to produce the adequate aluminum for the sheets and profiles, and therefore iron must be added. In the manufacture of iron-containing aluminum, the iron addition can be made in the form of a fragment or pieces of iron and a main Al-Fe alloy containing about 5-30% by weight of iron. Iron powder and iron-based tablets are also used because of the advantages they offer in the form of shorter dissolution time. The addition of the pulverulent materials can be done by injection together with a conveyor by means of a lance. The powder is injected into a cauldron, the storage furnace or the melting furnace. The The temperature of the aluminum mixture is maintained on the scale of 720-760 ° C, which is the normal alloy temperature regardless of the alloy method applied. The higher temperatures can be used, but this does not result in a reduction in the dissolution time of the iron powder. A very important property of the iron powder to be used in the injection process is its particle size. The particles that are very small follow the gas bubbles to the waste at the melting surface and can also cause dusting problems at various stages of the process. Particles that are very large do not dissolve fast enough. It is also important that the surface of the particles be substantially free of oxide layer which, if present, can deteriorate the wetting of the particles by the fused aluminum and in this way block or decrease their dissolution. In addition and as indicated above, the injection procedure requires special equipment. When iron powder tablets are used, they are simply thrown into the aluminum melt, through which they sink and dissolve. Some users manufacture the tablets themselves, but there are also commercially available tablets. The so-called alloy tablets contain 75-80% of the alloy metal which in addition to Fe can be Mn, Cr, Cu, Ti, Pb, Ni or Zn. The rest is pure aluminum plus the right flows to accelerate the dissolution and to protect the alloy metal as it dissolves. The Tablets are made of a suitable weight and composition that do not have to be weighed before being used to ensure the proper dosage. It has been found that previous methods based on the addition of iron-based powders or tablets can be considerably improved if the iron is added to the metal melt in the form of solid bodies of compacted iron particles, consisting essentially of pure iron. . In this context, the term "non-ferrous metal" includes metals selected from the group consisting of aluminum, copper and copper-based alloys. By using an additive consisting of iron particle bodies compacted according to the invention, the rate of dissolution of the iron in the non-ferrous metal melt can be faster. From the above follows the increase in productivity due to the shorter periods in the melting temperature. The use of compacted iron bodies also implies that less energy is consumed. Also due to the purity of the compacted iron bodies, fewer inclusions are formed and therefore less subsequent purification treatment is required, which simplifies the manufacture of the mixed metal. The advantages obtained by using the compacted bodies according to the present invention are unexpected and very considerable in view of what is taught in the U.S. patent. 3 935 004, which discloses that the compacted bodies of alloying agents, which have been tested for addition to the fused aluminum, were not effective. Specifically, said patent describes that alloying additives Compacted for aluminum alloy metals should contain a casting agent as an important ingredient. Said preferred additive must also contain bonding materials. The compacted bodies according to the present invention are quite the opposite and should not include any casting or bonding agent. The new compacted iron bodies can be manufactured from an atomized iron powder or a sponge iron powder, such as AHC100.29 or M40, M80, M100, M120, W100.25, W40.24 or A40S, all available from Hóganás AB, Sweden. In contrast to the alloy additives described in WO94 / 17217, it is not involved in any melting step when compacted bodies are prepared from the solid or sponge atomized iron powders according to the present invention. The density of the compacted bodies must be high enough so that the bodies do not disintegrate during the control and transportation and so that the bodies do not float on the surface of the metal bath. In this way, the densities should be at least 4, preferably at least 5 g / m 3. The preferred density range is between 5.1 and 6.7 g / cm3. To this end, the powders are compacted, for example, in a conventional mill at a pressure of at least 200 MPa and with a maximum of 500 MPa, the preferred range being between 250 and 400 MPa. The resistance to the crude product of the compacted body should preferably be at least 5 MPa, most preferably at least 10 MPa. The influence of the pressure of Compaction in the solubility or recovery speed can be observed in figure 1. An adequate thickness of the compacted body obtained from the milling operation can vary between 0.5 and 4 mm. The body is subsequently converted to an adequate size. The detachment can be carried out in a conventional mill at a size of at least 50 mm2, preferably at least 100 mm2. It is also possible to add the compacted bodies in the form of larger pieces or strips or any other suitable form. The important factors are also the oxygen and carbon contents of the compacted iron bodies. According to one embodiment of the invention which is spatially suitable for use in place of the iron powder tablets currently used, the oxygen content should be between 0.3 and 2%, and preferably the oxygen content varies between 0.5. and 1.5% by weight of the compacted iron bodies. The carbon content must be between 0.02 and 0.75%, and preferably the carbon content must vary between 0.05 and 0.5% by weight of the compacted iron bodies. In this case, the iron powder is suitably an un-annealed sponge iron powder. In an alternative embodiment of the invention, where it is important that the number of inclusions be maintained at a lower level, the amount of oxygen and carbon must be even lower. When a sponge iron is used in this alternative, the amount of oxygen may vary between 0. 1 and 1.5 and preferably between 0.15 and 1.0% by weight. The carbon content should vary between 0.001 and 0.20 and preferably between 0.002 and 0.15% by weight. The most preferred material for obtaining low amounts of inclusions is an atomized iron powder having an oxygen content of between 0.03 and 1.5, preferably between 0.1 and 1.0% by weight. The carbon content should vary between 0.0001 and 0.02, preferably between 0.002 and 0.15% by weight. These compacted bodies with low oxygen content and low carbon content are particularly interesting for high quality products. When the non-ferrous metal is aluminum, it is preferred that the temperature of the molten metal material be between 680 ° and 780 ° C, and most preferably between 700 ° and 750 ° C. Figure 2 describes the solubility rates at different temperatures for bodies compacted to 19 tons. The first step in the practical application of the iron bodies or flakes is to calculate the necessary amount of iron to reach the specified Fe content of the Al-Fe material. In this calculation the Fe yield is set at 10% of iron added. The Fe material is then added to the melting furnace in a loose form, and in case it spreads on the entire surface of the molten aluminum material. Alternatively packages are added in bags containing a predetermined amount of flakes. After the addition, a stirring operation is started and continued until the iron dissolves completely.

An investigation has been carried out that refers to the correlation between the properties of the iron powder and the dissolution rate in fused aluminum. From this investigation you can report the following. Six iron powder products were included in accordance with Table 1 below. Samples 1-3 consisted of uncondensed loose powders that are not within the scope of the present invention and samples 4-6 are examples of compacted bodies according to the present invention. TABLE 1 * Commercially used tablet available from London & Scandinavian Metallurgical Co Limited, London, and which includes flow agents in addition to iron. Each type of iron powder was compacted into small cylinders measuring 4 mm in diameter and 7 mm in height. The pressure used was sufficient to prevent the separation of the compact cylinders. The mass of a cylinder was 400-450 mg and the amount of aluminum in each test was 70 g, so that the final iron content after completing the dissolution of the iron cylinder was just 0.7%. The iron additive according to the invention was used as a single particle of flakes of adequate size. The tests were carried out in a reaction chamber having a diameter of 50 mm, which was heated in an oven. An aluminum crucible with the dimensions of 40 mm in diameter and 60 mm in height was filled with solid, pure aluminum parts (99.7% Al). The crucible was placed in a holder that could be moved vertically in the reaction chamber. The compact iron cylinder was placed in an aluminum fastener and introduced into the reaction chamber and suspended above the aluminum in the crucible by means of thin steel suspension wire from an electrobalance, by which the weight changes they could be recorded with very high sensitivity (detection limit 1 μg). The test was carried out in a very pure argon atmosphere, and oxidation of the iron or aluminum samples during the heating sequence could not be detected. The temperature in the reaction chamber was controlled by a thermocouple. When the desired reaction temperature was reached (in most tests 720 ° C), the aluminum crucible with the molten aluminum material was pushed so that the iron sample was immersed in the fusion. The weight changes of the test sample were recorded in a five-second interval during the dissolution studies. The results of the dissolution test were recorded in the following Table 2, which shows the weight loss of the iron sample as a percentage of its initial weight as a function of time. This percentage is called "recovery".

TABLE 2 * Commercial tablet used, available from London < & Scandinavian Metallurgical Co Limited, London, which includes flow agents in addition to iron. The reduction of the temperature of the molten aluminum material of the normally applied 720 to 700 ° C increases the dissolution time and substantially reduces the recovery, while an increase to 750 ° C has only a marginal effect.

The compacted iron bodies mentioned above consist of leaflets approximately 2 mm thick with a size of only 15x15 mm. The following table 3 describes the amount of inclusions.

TABLE 3 * Commercially used tablet available from London & Scandinavian Metallurgical Co Limited, London, and which includes flow agents in addition to iron. ** Product prepared in accordance with document W094 / 17217.

The small amounts of inclusions in samples 5 and 6 according to the present invention clearly indicate that said products may be an interesting alternative for the FeAl Waffle, whose manufacture it is more complicated than the manufacture of the compacted bodies according to the present invention. Although it is described with particular reference to the addition of iron flakes to liquid aluminum, it is obvious that the iron flakes according to the invention can also be added to other non-ferrous fused metals such as copper and copper alloys.

Claims (12)

NOVELTY OF THE INVENTION CLAIMS

1. - An additive for non-ferrous metals, liquid, characterized in that the additive consists of compacted bodies of essentially pure particles of atomized iron or sponge.

2. The additive according to claim 1, further characterized in that the compacted body has a density of at least 4, preferably at least 5g / cm3.

3. The additive according to any of claims 1 or 2, further characterized in that the compacted body does not include any auxiliary agent such as flow agents or binding agents.

4. The additive according to any of claims 1 to 3, further characterized in that the particles are sponge iron particles that include between 0.3 and 2.0%, preferably between 0.5 and 1.5% by weight of oxygen, and between 0.02 and 0.75%, preferably 0.05 and 0.5% by weight of carbon.

5. The additive according to any of claims 1 to 4, further characterized in that the particles are sponge iron particles including 0.1 and 1.5%, preferably between 0. 15 and 1.0% by weight of oxygen, and between 0.0001 and 0.2%, preferably 0.002 and 0.15% by weight of carbon.

6. The additive according to any of claims 1 to 3 further characterized in that the iron particles are atomized iron particles including 0.03 and 1.5, preferably between 0. 1 and 1.0% by weight of oxygen, and between 0.0001 and 0.20, preferably between 0. 002 and 0.15% by weight of carbon.

7. The additive according to any of the preceding claims, further characterized in that the compacted body has the shape of a leaflet.

8. The additive according to any of the preceding claims, further characterized in that it is added to the liquid metal selected from the group consisting of alloys based on Al, Cu, Cu, preferably aluminum.

9. The additive according to any of the preceding claims, further characterized in that the compacted body has a thickness between 0.5 and 4 mm and a size of at least 50 mm2, preferably at least 100 mm2.

10. The additive according to any of the preceding claims, further characterized in that the compacted body has a green resistance of at least 5 MPa.

11. - The use of a compacted body according to any of the preceding claims as an additive for non-ferrous metals, liquids such as aluminum.

12. The method of alloy iron in aluminum comprising the steps of adding compacted bodies of essentially pure particles of atomized iron or sponge according to any of claims 1 to 10 to an aluminum melting bath and subjecting the mixture obtained to a mixture during a sufficient period to complete the dissolution of the bodies.