Process for producing an aluminum-scandium-calcium alloy

Abstract

Calcium is added to an aluminum-scandium alloy to produce an aluminum-scandium-calcium alloy by combining aluminum, scandium, and the calcium in a melt, where the common melt is then quenched at a high velocity.

Claims

1. A method for adding calcium to an aluminum-scandium-magnesium-zirconium alloy for producing an aluminum-scandium-magnesium-zirconium-calcium alloy, the method comprising the steps: a) combining aluminum, scandium, magnesium, zirconium and calcium together in a common melt; and b) quenching the common melt by a rapid solidification process at a speed of more than 1000 K/s, wherein the calcium is added to the alloy in a ratio so that a density less than 2.6 g/cm.sup.3 is achieved, and wherein step a) comprises combining 0.2 wgt.-% to 3 wgt.-% scandium; 1.0 wgt.-% to 8.0 wgt.-% magnesium; 0.1 wgt.-% to 1.5 wgt.-% zirconium; 0.5 wgt.-% to 5 wgt.-% calcium; and a remainder being aluminum and undesirable contaminants together in the common melt.

2. The method according to claim 1, wherein the common melt is sprayed onto a substrate as a nozzle jet by a nozzle, wherein the substrate is cooled and rotated during the application of the common melt.

3. The method according to claim 1, wherein the substrate is rotated so quickly that the quenched common melt is spun off from the substrate from an impact region of the nozzle jet on the substrate.

4. The method according to claim 1, wherein the method is carried out under atmospheric conditions.

5. The method according to claim 1, wherein step a) comprises the step of: combining an aluminum-magnesium master alloy, an aluminum-scandium pre-alloy, or an aluminum-calcium pre-alloy into the common melt.

6. The method according to claim 1, further comprises combining, in addition to step a), additional admixtures of elements M.sup.1, M.sup.2, M.sup.3, M.sup.4 in amounts of 0.2 to 2.0 wgt.-% each, wherein M.sup.1 and M.sup.2 are each selected from the group consisting of copper, magnesium, manganese, silicon, iron, beryllium, lithium, chromium, zinc, silver, vanadium, nickel, cobalt and molybdenum, where M.sup.1 is different than M.sup.2, M.sup.3 is selected from the group consisting of zirconium, niobium, tantalum, hafnium and titanium, and M.sup.4 is selected from the group consisting of the rare earth metals.

7. The method according to claim 1, wherein the step of quenching the common melt by the rapid solidification process comprises quenching the common melt by the rapid solidification process at a speed of between 10,000 K/s to 10,000,000 K/s.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) An embodiment of the invention is explained in more detail in the following, based on the enclosed drawings. Therein is shown:

(2) FIG. 1 the combining of aluminum, scandium and calcium together in a melt;

(3) FIG. 2 the quenching of the common melt by spraying onto a cooled, rotating substrate;

(4) FIG. 3 a rear-side view of the substrate; and

(5) FIG. 4 the producing of an alloy band.

DETAILED DESCRIPTION

(6) FIG. 1 shows how the metals scandium 12 and calcium 14 are mixed into an aluminum-magnesium master alloy 17 comprising aluminum 15 and magnesium 16 in a common melting crucible 10. The melting crucible 10 has a nozzle 18 on the bottom side thereof which is separated from the melting crucible 10 by a closing device 19.

(7) In order to achieve holding times that are as short as possible, scandium 12 is added as an aluminum-scandium pre-alloy 20 and calcium 14 is added as an aluminum-calcium pre-alloy 21. The mixture is heated by induction heating 23 for melting. However, other suitable heating options for introducing the metals 12, 14, 15, 16 into the melt are also possible. After the metals 12, 14, 15, 16 input into the melting crucible 10 have melted, a common melt 22 is produced.

(8) FIG. 2 shows how the common melt 22 is sprayed onto a rotating substrate 24. To do so, the closing device 19 between the nozzle 18 and the melting crucible 10 is opened so that the common melt 22 can flow into the nozzle 18. The nozzle 18 sprays the common melt 22 in a nozzle jet 30 onto an impact region 32 on a surface 33 of the substrate 24. The substrate 24 is cooled on the side opposite the impact region 32 by a cooling device 34. The substrate 24 is rapidly rotated in the direction of the arrow O around the axis 35.

(9) The common melt 22 solidifies on the cooled substrate 24 at a high cooling velocity into an aluminum-scandium-calcium alloy 36. Due to the rapid rotation of the substrate 24 and the resulting forces, the aluminum-scandium-calcium alloy 36 that is produced is spun away from the surface 33 of the substrate 24 so that an alloy band 40 is produced.

(10) FIG. 3 shows the substrate 24 from a rear side 42, which is opposite the surface 33. Here, the cooling device 34 is arranged in the form of a cooling spiral. Water can be directed by the cooling spiral 44 in the direction of the arrow, for example, in order to cool the substrate 24. It is also possible, however, to use liquid nitrogen or other lower-melting media than water in order to achieve a greater temperature difference between the impacting nozzle jet 30 and the substrate 24.

(11) FIG. 4 shows a view of the surface 33 of the substrate 24. The substrate 24 is rotated in the direction of the arrow P so quickly that, due to the resulting forces, the solidified aluminum-scandium-calcium alloy 36 is spun away from the surface 38 as an alloy band 40.

(12) In the following example, the production of an AlScCa alloy semi-finished product is described.

(13) 2.0 wgt.-% calcium is added to an AlMg5.4Sc1.2Zr0.6Mn0.5 alloy according to the method described above. The alloy band is chopped into granulate and then degassed in a heatable device at 290 to 300° C. under cyclic flushing with vacuum at approximately 10 to 2 mbar and supplying of dry nitrogen and repeated vacuum suctioning. The degassing process is carried out five times and in doing so the granulate is compacted by means of a hydraulic press into a bolt having 98% gross density and 31 mm diameter and 25-30 mm length.

(14) The bolt is then overtwisted to 30 mm and subsequently pressed out into a 6 mm round bar in an extrusion device having a compression ratio of 25:1 at 325 to 335° C. Standardized round bar samples EN 10001 B6×30 are taken from the round bar and the strength is examined. The structural hardness according to the Brinell hardness testing method (HB2.5/6.5) can then additionally be determined on small discs from the 6 mm rod.

(15) The lower the material density, the greater the lightweight construction potential; this is a fixed design parameter when strength properties are otherwise constant. Material-based lightweight construction requires construction materials having high strength and low density; that is, high specific strength, also called breaking length. High-strength AlMgSc alloys have a density of 2.62 to 2.86 g/cm.sup.3 and a Mg content of 6.0 to 2.5 Gew.-%. AlMg materials, which are all written in field AA5XXX according to the American Al alloy key in their composition, are widely distributed due to their relatively low density and are very popular due to their good strength and processing properties. The magnesium portion of the alloy partially controls the strength of the mixed crystalline hardening, but at the same time also determines the density of the corresponding alloys, since magnesium 16 has a density of 1.74 g/cm.sup.3. This should be as low as possible, particularly in respect of lightweight construction concerns. The more magnesium 16 is found in the alloy, the lower the density. It is known that the adding of magnesium 16 to aluminum 15, and thus the consequential density reduction, is only sensible up to certain volumes, since otherwise negative properties such as brittleness and corrosion sensitivity heavily increase.

(16) For that reason, established—that is, industrially used—high-magnesium content aluminum materials generally have a magnesium content of under 6 wgt.-% (e.g. AA5059 or AA5083). The adding of lithium to the alloy is prior art; the adding of calcium 14 in AlMgSc alloys is not. The alternative to lowering the density—that is, the adding of lithium having a density of 0.52 g/cm.sup.3—was already developed in the 20's of the last century and technically implemented particularly from the late 70's in Russia. A further density reduction is thus possible by adding lithium (0.5 g/cm.sup.3) or calcium 14 (1.55 g/cm.sup.3) to the alloy. The adding of scandium 12 in connection with sufficiently rapid cooling after casting or during solidification enables in said materials, by means of defined heat control, e.g. downstream artificial aging in the temperature range between 250 and 400° C., a further strength increase of the precipitation hardening via a fully or partially coherent Al.sub.3Sc phase and/or dispersoid hardening if the Al.sub.3Sc phase becomes increasingly incoherent due to overaging.

(17) The density of AlMgSc plate and moreover of extrusion profiles is determined by the volume of magnesium 16, which is added to the alloy for mixed crystalline hardening of said material type. From this results a downward-limited minimum density in the case of more solid AlMgSc alloys. The adding of calcium 14, having a density of 1.55 g/cm.sup.3 and in a volume of more than 0.5 wgt.-%, is not previously known in high-strength aluminum-magnesium-scandium alloy concepts for applications in the transportation and aerospace fields.

(18) Since the solubility of calcium 14 in aluminum 15 is very low, the use of calcium 14 as a standard alloy element is prohibited at significant alloy volumes of greater than 0.5 wgt.-%. However, this only applies for the normal metallurgical production method, wherein a casting and solidification having slow cooling conditions occurs after smelting and immediately excretes an Al.sub.2Ca phase which embrittles the alloy.

(19) If a rapid solidification process, such as melt spinning, is carried out, the problem of the very limited solubility of calcium 14 in aluminum 15 and aluminum-magnesium alloys 17 can be overcome and calcium 14 remains substantially in solution. Sufficiently rapidly solidified aluminum-magnesium materials, alloyed with scandium 12 between 0.3 and 1.5 wgt.-% and therefore high-strength to highest strength and having a magnesium content between 1 and 10 wgt.-%, can be further density-reduced by adding calcium 14 in a range between 0.5 and 5 wgt.-% and thus increase their attractiveness as lightweight construction materials due to the high specific strength for all types of weight-driven applications, such as aircraft construction, vehicle construction, et cetera.

(20) As a result of the rapid cooling and solidification from the liquid phase, which is required so that increased volumes of scandium 12 can be dissolved in the aluminum material, the alkaline-earth element calcium 14 having a density of 1.54 g/cm.sup.3 can then be added to the aluminum-magnesium-scandium alloys and the density of said attractive, high-strength aluminum materials further reduces. High-strength aluminum-magnesium-scandium materials having reduced density of less than 2.6 g/cm.sup.3 can be achieved as profiles, although also high-strength aluminum-magnesium-scandium materials having reduced density of less than 2.6 g/cm.sup.3 as direct-generated (e.g. remelted by laser), close-contoured components, wherein the components are more efficient lightweight structures having high durability.

(21) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

REFERENCE LIST

(22) 10 Melting crucible 12 Scandium 14 Calcium 15 Aluminum 16 Magnesium 17 Aluminum-magnesium master alloy 18 Nozzle 19 Closing device 20 Aluminum-scandium pre-alloy 21 Aluminum-calcium pre-alloy 22 Common melt 23 Induction heating 24 Substrate 30 Nozzle jet 32 Impact region 33 Surface 34 Cooling device 25 Axis 36 Aluminum-scandium-calcium alloy 40 Alloy band 42 Rear side 44 Cooling spiral O Arrow P Arrow