Metal fusion bonding – Process – Diffusion type
Reexamination Certificate
1999-11-09
2001-07-10
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Diffusion type
C228S178000, C228S233200
Reexamination Certificate
active
06257481
ABSTRACT:
The present invention relates to metal bonding and, in particular to the formation of bonds using a new variant of transient liquid phase (TLP) diffusion bonding.
TLP diffusion bonding is performed by bringing together, generally under pressure, surfaces of a metal to be bonded, with an interlayer of a material disposed in between the surfaces, and heating the area of contact. Typically, the interlayer material between the metal substrates forms a liquid layer at the bond line during joining and subsequently solidifies isothermally as a consequence of interdiffusion with the metal substrates, this all taking place principally at the bonding temperature.
It is desirable that the mechanical properties, e.g. shear strength, of a bond are comparable to those of the parent material, but this is difficult to achieve for many materials. For example, the presence of a tenacious and chemically stable layer of aluminium oxide on the surface of aluminium based alloys and composites has prevented the production of reliable bonds in these materials by conventional TLP diffusion bonding. Although the formation of the liquid phase in conventional TLP diffusion bonding leads to disruption of the oxide layer, some of the oxide particles may agglomerate in the bond line, so causing joint weakness.
The problem is increased by the random distribution of oxide particles in a joint with a planar interface, which causes inconsistency in the mechanical strengths of the bonds.
According to the present invention there is provided a method of bonding two pieces of metal having a foil or layer of another metal, either of lower melting point or such that it forms a liquid layer at or near to the bonding temperature, disposed therebetween, the method comprising steps of:
bringing the pieces into contact;
applying pressure across the area of contact;
heating the area of contact; and
providing a predetermined temperature gradient across the area of contact.
Preferably the temperature gradient is such that a bond of sinusoidal profile is formed.
The method may be of benefit in joining many metals and their alloys, and metal matrix composites, by TLP diffusion bonding, including aluminium and its alloys, nickel and its alloys.
The method of bonding of the present invention may also comprise a step of applying a coating to one or more of the contact surfaces. This coating may be applied by sputtering, electrodeposition or other similar approaches.
As an example, when the material is Al—Mg—Si alloy 6082 a suitable temperature gradient is 10° C./mm, a suitable joint temperature is 545° C., a suitable pressure to apply to the joint is 1 MPa and a suitable coating is copper at a thickness of 1.5 &mgr;m.
Also according to the present invention there is provided an apparatus for bonding two pieces of metal having a layer of another metal, either of lower melting point or such that it forms a liquid layer at or near to the bonding temperature, disposed therebetween, the apparatus comprising:
means for bringing the two pieces into contact;
means for applying pressure to the area of contact;
means for heating the area of contact; and
means for providing a predetermined temperature gradient across the area of contact.
REFERENCES:
patent: 3678570 (1972-07-01), Paulonis
patent: 4026677 (1977-05-01), Galasso et al.
patent: 4225322 (1980-09-01), Knemeyer
patent: 5234152 (1993-08-01), Glaeser
patent: 5322740 (1994-06-01), Ghosh
patent: 5372298 (1994-12-01), Glaeser
patent: 5664723 (1997-09-01), Sastri
Shirzadi-Ghoshouni Amir Abbas
Wallach Eric Robert
Cambridge University Technical Services Limited
Dunn Tom
Pittman Zidia
Sughrue Mion Zinn Macpeak & Seas, PLLC
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