Method for molding aluminum and aluminum alloy powder

Abstract

A powder molding method of aluminum and aluminum alloy includes: preparing a feedstock by kneading aluminum powder, aluminum alloy powder, or aluminum composite powder containing a reinforcing material with a thermoplastic organic binder; molding the feedstock to a product having a complex shape via powder injection molding, compression molding, or extrusion molding; and then producing a high-density sintered body having relative density of at least 96% by performing debinding and sintering in a single heating process under an argon gas atmosphere.

Description

TECHNICAL FIELD[0001]The present invention relates to a precision part manufacturing technology, whereby a product having a complex and precise shape is manufactured to a near net shape via a powder molding method, such as powder injection molding, warm compression molding, warm powder extrusion, or the like by using metal powder of aluminum or aluminum alloy as a raw material.[0002]Further, the present invention relates to a precision part manufacturing technology, whereby a precision part is manufactured by a composite material, in which aluminum or aluminum alloy is reinforced with a ceramic or another inorganic reinforcing material.BACKGROUND ART[0003]Various precise shape manufacturing technologies are available as powder molding processes, such as powder injection molding, warm compression molding, warm powder extrusion, etc., whereby a complex shape is formed by using a feedstock including a powder material and a sufficient amount of an organic binder. In particular, as alrea...

AI Technical Summary

Benefits of technology

[0032]According to the present invention, a powder injection molding technology is provided, the powder injection molding technology being applicable to aluminum and aluminum alloys having many advantages as an industrial material, such as low density, high thermal conductivity and electrical conductivity, good corrosion and weathering resistance, and natural color, and in addition, having excellent mechanical properties owing to a high precipitation hardening effect depending on alloying.

[0033]In other words, according to a powder molding method of the present invention, a method of manufacturing a molded body having a complex shape from aluminum or aluminum alloy powder, and manufacturing a high-density sintered body having relative density of 96% or higher through following debinding and sintering processes is provided.

[0034]In addition, since debinding and sintering processes according to the present invention are performed in a single step in a same furnace using a single heating schedule, a separate additional facility, such as a solvent extraction system or a supercritical fluid extraction system for debinding is not required, the number of processes is reduced and accompanying energy consumption is reduced, and labor costs are reduced, and accordingly, overall production costs are reduced for economic effect.

[0035]Since aluminum or an aluminum alloy manufactured according to a powder molding method of the present invention does not necessarily include a sintering aid alloying element having a low melting point, such as tin having low solubility in aluminum, a sintered body having enhanced mechanical properties may be produced.

[0036]As such, a powder molding method according to the present invention is applicable not only to pure aluminum, but also to almost all commercial aluminum alloys including precipitation-hardenable aluminum alloys, such as Al—Cu—Mg—(Mn) series (AA 2xxx series), Al—Mg—Si series (AA6xxx series), and Al—Zn—Mg—(Cu) series (AA7xxx-series) alloys, and thus the powder molding method according to the present invention may have a significant industrial effect in production of precision parts required for various purposes.

[0037]In addition, an aluminum-matrix composite part may be manufactured by reinforcing an aluminum or aluminum alloy base with one or more materials selected from a group consisting of carbides such as SiC, B4C, TiC and WC, nitrides such as Si3N4, AlN, TiN, c-BN and h-BN, oxides such as Al2O3, SiO2, Y2O3, fly ash, and ZrO2, sulfides including MoS2, borides including TiB2, hard cobalt alloys including T-800, powder, powder, short fiber, or whisker of a refractory metals such as W and Mo, polycarbon, graphite, carbon nanotube, graphene and diamond.

Problems solved by technology

However, a powder injection molding technology has not yet been used industrially for aluminum and aluminum alloys.

The reason why the powder injection molding method is not industrially used for aluminum or aluminum alloys mainly is that it is difficult to manufacture a high-density sintered body.

Accordingly, due to the presence of such an oxide film that acts as an obstacle to material transfer between the adjacent particles in contact for densification, aluminum has been recognized as a material that is not suitable for the powder injection molding method.

However, the nitridation reaction may cause a big problem when a nitrogen gas is used as an atmospheric gas during a sintering process of a powder molded body according to the present invention, which is made of fine metal powder having a large specific surface area and a high reactivity, and having porosity of 50% to 10% after debinding.

That is, since the surface of aluminum powder is exposed to the nitrogen gas even before the onset of a sintering reaction between particles during debinding and further heating for a sintering, an aluminum nitride starts to form, and thus atomic migration across the interface between adjacent aluminum powders being in contact is inhibited, inter-particle bonding and densification during the sintering process are interfered.

Another reason why powder injection molding of aluminum is difficult compared to other metals is that a melting point of aluminum or a solidus temperature at which an aluminum alloy is liquefied and starts to melt is remarkably low compared to other metals, such as iron, stainless steel, nickel, copper, cobalt, titanium, etc., or alloys thereof.

Another problem to be solved during debinding and sintering of an aluminum molded body containing a large amount of an organic binder is formation of aluminum carbide (Al4C3) through a reaction between decomposed product of the organic binder and aluminum.

The aluminum carbide is brittle and is undesirable since it reacts with moisture by a reaction of Al4C3+6H2O=2Al2O3+3CH4.

As described above, various methods have been proposed for powder injection molding of aluminum and alloy thereof, but a method of precisely producing a complex-shaped product while properly realizing mechanical properties of aluminum alloys has not been provided yet.

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