WO2003080881A1

WO2003080881A1 - Process for the production of al-fe-v-si alloys

Info

Publication number: WO2003080881A1
Application number: PCT/IN2002/000071
Authority: WO
Inventors: Kanai Lal Sahoo; Subramaniam Sivaramkrishnan Chittur
Original assignee: Council Of Scientific And Industrial Research
Priority date: 2002-03-26
Filing date: 2002-03-26
Publication date: 2003-10-02
Also published as: US20030185701A1

Abstract

The present invention relates to an improved process for the production of high strength and high wear resistant Al-Fe-V-Si alloys. The present invention comprises modifying/blocking primary intermetallic phases as well as interdendritic silicide phases by treating the melt with elemental magnesium or magnesium bearing master alloys to get a structure containing uniform distribution of intermetallic phases. The uniform distribution of primary and interdendritic phases are obtained with addition of magnesium or magnesium bearing master alloys because morphology of the interface changes resulting in the creation of more nuclei. It also breaks dendrite of the primary particles leading to structural change and fine particles. The present invention is useful for the industries engaged in production of high strength wear resistant aluminium alloys which are widely used in aerospace, transport and other engineering sectors. The process comprises the following steps: (i) melting pure aluminium, Al-Fe-V, Al-Si master alloys at a temperature in the range of 800 to 1000 °C to obtain a melt of Al-Fe-V-Si in the following composition ranges. Fe=8 to 10 wt %, V=0.8 to 1.0 wt%, Si=0.8 to 1.7 wt % and balanced Al; (ii) degassing the said melt; (iii) adding magnesium or magnesium bearing master alloys in the range of 0.05 -1.0 wt % to the degassed melt; (iv) pouring the resultant melt in a die to obtain a casting followed by cooling; (v) heating the casting obtained to a temperature in the range of 350 to 500 °C; (vi) hot rolling/extrusion of the homogenized casting in the temperature range of 250 to 500 °C.

Description

PROCESS FOR THE PRODUCTION OF AI-Fe-V^Si ALLOYS Field of the invention

The present invention relates to an improved process for the production of high strength and high wear resistant Al-Fe-N-Si alloys. The present invention will be useful for the industries engaged in production of high strength wear resistant aluminium alloys which are widely used in aerospace, transport and other engineering sectors. Background of the invention

In the general melting and casting process, the wide differences of densities and melting point of Al, Fe, N and Si couple with low diffusivity of Fe, N in Al pose problems in producing cast homogeneous structure. Al-Fe-N-Si alloys are generally produced and shaped through a costly technique or rapid solidification - powder compacting - extrusion/rolling route. In the prior art rapid solidification processes, such as atomization and melt spinning are used to obtain rapidly solidified alloy powders or ribbons respectively.

US Patent No. 2,963,780 discloses a method for obtaining improved tensile strength at 350°C in aluminium based alloys (see also: US Patent No. 2,967,351; US Patent No.

3.462.248). The alloys are formed by atomization of the liquid metals into finely divided droplets by high velocity gas streams. The droplets are then rapidly cooled to obtain the desired alloys. In atomization process the molten alloy is impacted by a high energy fluid for obtaining powders. The powders are cold pressed, degassed followed by hot consolidation (E.J. Lavemia, J.D Ayers, T.S. Srivatsan, International Materials Review, vol. 37, No. 1

(1992), 1-44). Then it is hot worked for obtaining final product. The melt spinning process employed a high pressure shock wave of gas to propel a small droplet of melt against a clean rotating metal wheel to produce a brittle ribbon or thin sheet. The ribbons are pulverized to obtain powder. The powders may be cold pressed and sintered or consolidated and heat treated (E.J.Lavernia, J.D. Ayers, T.S. Srivatsan, International Materials Review, vol. 37,

No.l (1992), 1-44). Then it is extruded or rolled to make material for final product. US Patent

4,347,076 discloses formation of high strength aluminum alloys at temperatures of about

350°C obtained by rapid solidification techniques. However, alloys obtained herein have low engineering ductility at room temperature and thus cannot be used in structural applications where a minimum tensile elongation of about 3% is required, for example in gas turbines.

Rapid solidification techniques are however, capital intensive and require high skill of operation because:

(i) the cooling rate is very high (10 to 10) which is difficult to achieve unless huge capital cost equipment is used (ϋ) the powders/ribbons so obtained are not of uniform size leading to deterioration of mechanical properties (iii)the steps of consolidation of the rapidly solidified alloy powders/melt spin ribbons and process to shape give additional cost to the technique (iv)the product capacity is limited to a small size only because the ribbon or powder so obtained are compacted or sintered to a small for obtaining homogeneous structure. It is therefore important to produce alloys which overcome the above problems associated with the art, and at the same time where the manufacturing processes are not capital intensive. Objects of the invention

The main object of the present invention is to establish melting treatment process for the production of cast and mechanically worked high strength and high wear resistant Al-fe- N-Si alloys leading to superior properties.

It is an object of the invention to provide a process for the production of Al-Fe-N-Si alloy in cast route whose mechanical properties are comparable with those of identical alloy made by the known process as mentioned above. Summary of the invention

Accordingly, the present invention provides a process for the production of high strength and high wear resistant Al-Fe-N-Si alloy which comprises (i) melting pure aluminum, Al-Fe-N, Al-Si master alloys at a temperature in the range of 800 to 1000°C to obtain a melt of Al-Fe-N-Si in the following composition ranges.

Fe = 8 to 10 wt%, N=0.8 to 1.0 wt%, Si=0.8 to 1.7 wt% and balance Al, (ϋ) degassing the said melt (iϋ) adding magnesium or magnesium bearing master alloys in the range of 0.05 - 1.0 wt% to the degassed melt, (iv) pouring the resultant melt in a die to obtain a casting followed by cooling (v) heating the casting obtained to a temperature in the range of 350 to 500°C (vi) hot rolling/extrusion of the homogenized casting in the temperature range of 250 to 500°C.

In another embodiment of the invention the degassing of the melt is effected by adding flux or argon gas.

In still another embodiment of the invention the magnesium used is pure magnesium of 99.8% purity. In an embodiment of the invention the pure aluminium used is of 99.6% purity.

In yet another embodiment of the invention the magnesium used is magnesium bearing master alloys selected from the group consisting of Al-Mg, F₃-Si-Mg and Ni-Mg master alloys. In another embodiment of the invention the magnesium bearing master alloys used is selected from Al- 10-20% Mg, Fe-Si-9-20% Mg and Ni-10-20% Mg. Detailed description of the invention

The process of present invention makes use of melting and alloying in a furnace. Casting are made in die casting or in permanent mould for ensuring a cooling rate 10-50°C/s, which is common in foundry practices. The microstructure of the cast materials reveals ten- armed star shaped particles with composition similar to A1₃F₃ with some amount of V and Si along with other interdendritic Al-Fe-silicide phases. These star shaped particles act as notches, which are deleterious to the toughness of the materials. Moreover, the chunky star shaped particles prevent proper feeding of the casting which results in microporosity in castings. Thus, the mechanical properties of the samples deteriorate to a greater extent.

The present invention aims to modify/block primary intermetallic phases as well as interdendritic suicide phases by treating the melt with elemental magnesium or magnesium bearing master alloys to get a structure containing uniform distribution of intermetallic phases. The uniform distribution of primary and interdendritic phases are obtained with addition of magnesium or magnesium bearing master alloys because morphology of the interface changes, thus resulting in the creation of more nuclei. It also breaks dendrite of the primary particles leading to structural change and fine particles.

The following examples are given by way of illustration and should not be construed to limit the scope of invention. Example 1

2 kg of Al-8.0% Fe-0.8% V=0.9% Si alloy was melted in a clay bonded graphite crucible in electric resistance furnace. The alloy was modified with 0.5% pure magnesium. The materials taken were metallic silicon 18 gm, ferro-vanadium 25 gin, aluminium - 30%, iron master alloy 510gm. 0.5% pure magnesium (10 gm) was used to modify the alloy. After melting the melt was kept at a temperature of 860°C for complete dissolution of solute elements. Degassing treatment was done by pure argon followed by magnesium treatment at temperature of 850°C. The melt was poured in metallic mould of 30 mm diameter. The specimen so obtained was evaluated for microstructure and mechanical properties. The microstructure was uniform distribution of primary and interdendritic phases in aluminium matrix. The mechanical properties were reported in Table- 1.

Table 1: Mechanical properties of unmodified and modified alloys

Example 2

2 k.g of Al-8.0% Fe-0.8% V-0.9% Si alloy was melted in clay bonded graphite crucible in electric resistance furnace. The melt was modified with 1.0% of aluminum 20% magnesium master alloy 20 gm of master alloy was taken. The microstructure obtained by this modification was more uniform distribution of primary and interdendritic phase. The particle size distribution was liner than pure magnesium treatment. The mechanical properties were shown in Table- 1. The alloys were further hot rolled at a temperature of 350°C and deformation was 75%. The mechanical properties was shown in Table-2

Table 2: Mechanical Properties of hot worked alloys, hot rolled at 350°C, reduction

75%

Example 3

3 kg of aluminum 08.3% iron -0.8% vanadium -0.9% silicon alloy was melted in a clay bonded graphite crucible in electric resistance furnace. The alloy was modified with 1.0% of nickel - 20% magnesium. The materials taken were silicon 30 gm, ferro-vanadium 38 gm, aluminium - 30% iron master alloy 780 gm, nickel magnesium 30 gm. After degassing the melt the alloy was modified. Prior to modification the master alloy was preheated to 250°C. The microstructure obtained by modification was more uniform distribution or primary and interdentic phase. The particle size distribution was finer than pure magnesium treatment. The mechanical properties were shown in Table- 1. The alloys were further hot rolled at a temperature of 350°C and deformation was 75%. The mechanical properties are shown in Table -2.

By the process of present invention a cast high strength and high wear resistant Al-Fe- N-Si alloy having uniforms distribution of primary phases in the form of cuboidal, hexagonal, rectangular shape and refined interdendritic phase has been achieved. The properties of the alloy produced by the process of present invention are comparable to those obtained known process. The mechanical properties also improved considerably after hot working as shown in Table 1 and 2 above. The main advantages of present invention are:

1. The steps involved for making the alloy are simple economic and takes much shorter time than the existing process of rapid solidification route. 2. Costly equipment for making powders/ribbons are avoided in the process of present invention.

3. Cooling rate required is much lesser than the existing of rapid solidification.

4. The process of present invention has achieved distribution of refined primary intermetallic and interdendritic suicide phases. 5. The cast and mechanically worked products produced by the present invention exhibit comparable mechanical properties to those produced by rapid solidification processing route. 6. The cost of production of the present invention is much cheaper than the existing process of rapid solidification route.

Claims

We claim:

1. A process for the production of high strength and high wear resistant Al-Fe-N-Si alloy which comprises fx) melting pure aluminum, Al-Fe-N, Al-Si master alloys at a temperature in the range of 800 to 1000°C to obtain a melt of Al-Fe-N-Si in the following composition ranges.

Fe = 8 to 10 wt%, N=0.8 to 1.0 wt%, Si=0.8 to 1.7 wt% and balance Al, (ii) degassing the said melt

(iii) adding magnesium or magnesium bearing master alloys in the range of 0.05 - 1.0 wt% to the degassed melt.

(iv) pouring the resultant melt in a die to obtain a casting followed by cooling (v) heating the casting obtained to a temperature in the range of 350 to 500°C (vi) hot rolling/extrusion of the homogenized casting in the temperature range of 250 to 500°C.

2. A process as claimed in claim 1 wherein the pure aluminium used is of 99.6% purity.

3. A process as claimed in claim 1 wherein the degassing of the melt is effected by adding flux or argon gas.

4. A process as claimed in claim 1 wherein the magnesium used is pure magnesium of 99.8% purity.

5. A process as claimed in claim 1 wherein the magnesium used is magnesium bearing master alloys selected from the group consisting of Al-Mg, F₃-Si-Mg and Νi-Mg master alloys.

6. A process as claimed in claim 5 wherein the magnesium bearing master alloys used is selected from Al-10-20% Mg, Fe-Si-9-20% Mg and Νi- 10-20% Mg.