DE3208702A1 - Process for producing heat-resistant dispersion-hardened aluminium alloys - Google Patents

Abstract

The invention relates to a process for producing heat-resistant dispersion-hardened aluminium alloys which are ductile even at high temperatures. Hitherto it was only possible to produce such alloys by cooling the melt after adding the silicide-forming metals by granulation at very high speed and then processing the granular material by rolling or extruding to form a semifinished product. It is proposed to add silicide-forming metals in the form of alkali-metal fluoride compounds or as a mixture of metal-fluoride compounds with alkali-metal compounds to a melt composed of 0.5 to 19% by weight of silicon, the remainder, including the usual unavoidable impurities, being aluminium, at less than 900 DEG C and then to cast the melt within not more than 30 minutes to produce mouldings or blocks. In this way, mouldings or semifinished products can be produced much more economically.

Description

PROCESS FOR THE MANUFACTURING OF WARM RESISTANT DISPERSION HARDENED

ALUMINUM CONVERSIONS The invention relates to a method for the production of heat-resistant, dispersion-hardened materials, even at high temperatures ductile aluminum alloys.

Such a method has become known from DE-PS 12 48 302. In this case, a metal disilicide or silicon and a are used to melt aluminum Disilicide-forming metal added and a proportion of 2 to 12% by volume of the metal disilicide generated in the alloy and then the alloy by dividing it into granules with a speed> 5000C / s and cooled the granulate by rolling or Extrusion processed into semi-finished products.

The major disadvantage of this and other known methods of manufacture the desired aluminum alloys is that to achieve the required fine distribution of the silicides heat the melt both high and very quickly must freeze.

The required high solidification rates are achieved only by dividing the melt into fine droplets and spraying it against cooled surfaces will. A granulate is obtained from which only through a series of further process steps, like cold compaction, extrusion and Forging, work pieces made can be. An immediate production of molded parts or cast blocks for the manufacture of semi-finished products by rolling or extrusion is not possible.

In addition, the production of the granules in the technical Scale still encounters considerable difficulties because of the sprayed particles the melt tend to stick to the cooling surfaces. To provide flawless Cooling surfaces, the production must be interrupted again and again, so that the production significant amounts of granules is very expensive.

There has therefore long been a need for a method with the heat-resistant, dispersion-hardened molded parts that are ductile even at high temperatures or blocks for semi-finished products from aluminum alloys can be made without that the detour via granulation of the melt must be taken. Of this The problem was set out in the present invention.

To solve the problem, it is proposed that in a melt of 0.5 Up to 19% by weight silicon, the remainder aluminum including common, unavoidable impurities, 0 at less than 900 C silicide-forming metals such as Cr, Ti, Th, Ce, V, Nb, Ta, W, Zr or Mo in the form of alkali fluoride compounds or as a mixture of metal fluoride compounds with alkali compounds and then add the melt within no more than 30 minutes to cast into moldings or blocks.

In this way, moldings or blocks for semi-finished products can be produced in which the silicide-forming metals in the required fine and uniform Distribution exist without the otherwise necessary extremely high solidification rates be respected have to. The procedure also has the advantage that the aluminum melt does not have to be overheated as much as in the case of the previously known Process for dissolving the refractory, silicide-forming metals required is.

The process therefore allows moldings to be produced directly or ingots in a very economical way.

Since the melting temperature can be kept lower, i.e. not must be increased above the specified addition temperature, there is also the advantage the energy saving the further improvement that the melt to a lesser extent Gases, especially hydrogen, absorbs, which has an unfavorable effect on the quality of the material would.

Another advantage of the method according to the invention is that that instead of the silicide formers added in metallic form in the conventional process whose compounds are added, which are much cheaper.

In particular, however, the proposed method is advantageous because because now workpieces can be produced directly as cast parts, i.e. with a substantial less processing effort and significantly better output, measured as weight of the finished part to the weight of raw materials used. This affects of course also very favorably on the energy required to manufacture the workpieces.

In FIG. 1, the method according to the invention is once again the conventional one Processes compared in the form of a flow chart, showing the advantages mentioned are apparent to the person skilled in the art without further explanation.

Metals like V, Nb, Ta, Cr, Mo or W can also be in the form of a mixture from oxides and alkali or alkaline earth oxides be admitted. Further it is possible to use the metals as alkali vanadates, niobates, tantalates, chromites, -Molybdates or -wungstates or as mixtures of these compounds with alkali or to add alkaline earth oxides.

Metals such as V, Nb, Ta, Mo and W can also be added alone as oxides will.

Preferably the metals become less at a temperature of zero added than 800 C to the melt. It is particularly advantageous if the melt is cast within no more than 10 minutes after the addition of the metals. According to the invention, the silicide-forming metals should be added in such an amount that they are essentially completely set as silicides and that the aluminum alloy does not contain more than 12% free silicon.

As particularly suitable for the production of thermal and / or mechanical The following alloys have proven to be highly loaded pistons for reciprocating engines: a) Al + 5% Cr + 3% Si b) Al + 2% V + 3% Si c) Al + 4 8 V + 5% Si Will a Requires reduced thermal expansion of the piston, the three mentioned Alloys further silicon are added, each up to 12% additional to the specified quantities.

The chromium is used in a particularly advantageous manner as chromium trifluoride added in a mixture with alkali and alkaline earth fluoride. A particularly cheap one The form of addition for the vanadium is the technically pure vanadium pentoxide in the form of "flakes".

In cast form, these materials surpass conventional ones Piston cast alloys based on AlSil2CuNiMg with regard to heat resistance (static and dynamic) and thermal shock resistance quite considerably. Will the silicide-containing Extruded alloys, so is their superiority over the extruded AlSil2CuNiMg even bigger.

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Claims (7)

PATENT CLAIMS 1. Process for the production of heat-resistant, dispersion-hardened, ductile aluminum alloys even at high temperatures, characterized that in a melt of 0.5 to 19% by weight silicon, the remainder including aluminum common, unavoidable impurities at less than 900 C, silicide-forming Metals such as Cr, Ti, Th, Ce, V, Nb, Ta, W, Zr or Mo in the form of alkali fluoride compounds or added as a mixture of metal fluoride compounds with alkali compounds and that the melt then becomes moldings within not more than 30 minutes or blocks is cast. 2. The method according to claim 1, characterized in that the metals such as V, Nb, Ta, Cr, Mo or W in the form of a mixture of oxides and alkali or Alkaline earth oxides are added. 3. The method according to claim 1, characterized in that the metals as alkali vandates, niobates, tantalates, chromites, molybdates or tungstates or added as mixtures of these compounds with alkali or alkaline earth oxides will. 4. The method according to claim 1, characterized in that the metals, such as V, Nb, Ta, Mo, W are added as oxides. 5. The method according to any one of claims 1 to 4, characterized in that that the metals are preferably at a temperature of less than 8000C of the melt be admitted. 6. The method according to any one of claims 1 to 5, characterized in that that the melt is preferably within no more than 10 minutes after the addition the metal is poured. 7. The method according to any one of claims 1 to 6, characterized in that that the silicide-forming metals are added in such an amount that they are essentially completely set as a silicide and that the aluminum alloy contains no more than 12% free silicon.