Patent Application
20160256948
The field of this application generally relates to solder joints of metals and alloys that form a passive oxide film and a method of forming the same.
Non-Ferrous metals and alloys, such as aluminum and titanium and their alloys, are excellent structural materials due to their light weight and high strength. Additionally, they offer superior corrosion resistance as compared with ferrous alloys. The superior corrosion resistance of these alloys typically is attributed to the passive oxide film that is formed instantaneously when the metal or alloy is exposed to the atmosphere.
However, this very attribute results in a drawback, rendering these metals and alloys unsuitable for forming joints using processes such as soldering. Since the passive oxide is instantly reformed after cleaning and the solder does not bond well with these oxides, currently the industry has to resort to techniques such as inert gas welding, fluxed soldering and brazing to successfully form joints with solder the solder material.
It is advantageous to form a joint between the metals and alloys that form passive oxides and solder material without the need for a flux, costly surface treatments or complicated equipment as required in inert gas welding for mitigating the formation of the passive oxide film. Such a technique may be used for providing economical means for joining an aluminum or aluminum alloy to a metallic or ceramic part. Examples of applications that can benefit from such a joint are, but not limited to, soldering of aluminum heat-exchanger fins to EV invertors and joining aluminum parts to steel parts of intake manifolds.
In an aspect, a solder joint includes, a first metal part; a second metal part; and solder material disposed between the first and second metal parts; such that the solder material forms a joint with the first and second metal parts; and the solder material has a plurality of abrasive particles disposed therein.
In some embodiments, the first metal part is made from a metal capable of forming a passive oxide layer on the surface.
In any of the above embodiments, the second metal part is made from a metal capable of forming a passive oxide layer on the surface.
In any of the above embodiments, the metal is an aluminum alloy.
In any of the above embodiments, the metal is a titanium alloy.
In any of the above embodiments, the solder material is selected from a group containing tin-lead-based solder alloys and lead-free tin-based solder alloys. In any of the above embodiments, wherein the solder material is brass.
In any of the above embodiments, the solder material is group consisting of silver and silver-based alloys.
In any of the above embodiments, the abrasive particle is selected from a group consisting of alumina, sand, calcite, emery, novaculite, pumic, rouge, garnet, sandstone, Tripoli, powdered feldspar, staurolite, carborundum, SiC, SiN, ceramic aluminum oxide, ceramic iron oxide, zirconia alumina, boron carbide, cubic boron nitride, diamond, and mixtures thereof.
In any of the above embodiments, the abrasive has an average particle size greater than 0.1 μm, or greater than 0.3 μm, or greater than 0.5 μm, or greater than 0.8 μm, or greater than 1 μm, or greater than 3.0 μm, or greater than 5.0 μm, or greater than 10.0 μm, or greater than 15.0 μm.
In any of the above embodiments, the abrasive particles are distributed preferentially at the interface of the solder material and the metal parts.
In any of the above embodiments, the abrasive particles are distributed throughout the solder material.
In any of the above embodiments, the solder joint has an ultimate tensile strength greater than 30 MPa.
In an aspect, a method of making a solder joint including, contacting a solder material with abrasive particles; locating the solder material and the abrasive particles between first and second metal parts to form a layered structure; applying a compressive force on the layered structure; applying ultrasonic vibration for a predetermined time to the layered structure to remove the passive oxide layer of the metal part; and applying heat to the layered structure to cause the solder material to melt and flow between the metal parts and form a bond with the metal parts.
In some of embodiments, the method of contacting of the solder material with the abrasive particles includes depositing the particles on the surface of the solder material by sedimentation of the abrasive particles from a slurry of the abrasive particles.
In some of embodiments, the method of contacting of the solder material with the abrasive particles includes coating a sheet of the solder material with the abrasive slurry.
In some of embodiments, the method of contacting of the solder material with the abrasive particles includes mixing the solder material particles with the abrasive particles.
In any of the above embodiments, the ultrasonic vibration has a frequency of greater than 15 kHz.
In any of the above embodiments, the compressive force is applied normal to the plane separating the metal parts.
In any of the above embodiments, the compressive force is greater than 15 MPa.
In any of the above embodiments, the applied heat raises the temperature of the solder material above 100° C. In some of the above the above embodiments, wherein, the applied heat raises the temperature of the solder material above 150° C.
The following figures are provided for the purpose of illustration only and are not intended to be limiting.
A flux-less solder joint that facilitates a joint between two metal parts, wherein abrasive particles are disposed in the solder material, is described.
In one or more embodiments, the metal parts are selected from metals and alloys that form passive oxide layers on the surface due to oxidation in presence of atmospheric oxygen. In one or more embodiments, the metal parts are aluminum or aluminum alloys. In some embodiments, the metal parts are titanium or titanium alloys.
There is no fundamental restriction on the type and chemical composition of the solder material that can be used according to one or more embodiments. The use of solder materials with a low melting temperature is contemplated since it makes the metal parts less prone to oxidation, as discussed below, and minimizes the overheating of parts being joint which minimizes the residual stress in the resultant solder joint. it is proposed. In some embodiments the solder material is a tin-lead or lead-free tin-based solder alloy. In some other embodiments, the solder material is brass. In some embodiments, the solder material is silver or a silver-based alloy. Other materials such as metals, including those used for brazing, may also be compatible to the ultrasonic abrasive surface activation method.
There is no fundamental restriction on the type and chemical composition of the abrasive material that can be used according to one or more embodiments. In some embodiments the abrasive material disposed in the solder material of the joint is selected from alumina, sand, calcite, emery, novaculite, pumic, rouge, garnet, sandstone, tripoli, powdered feldspar, staurolite, carborundum, SiC, SiN, ceramic aluminum oxide, ceramic iron oxide, zirconia alumina, boron carbide, cubic boron nitride, diamond, and mixtures thereof. In some embodiments, the average particle size, characterized by the d50 particle size distribution, is greater than 0.1 μm. In some embodiments, the average particle size of the abrasive is greater than 0.3 μm, or greater than 0.5 μm, or greater than 0.8 μm, or greater than 1 μm, or greater than 3.0 μm, or greater than 5.0 μm, or greater than 10 .0 μm, or greater than 15.0 μm. Particle size ranges bounded by any of the values identified hereinabove are also contemplated, e.g., 0.1 μm-15.0 μm, or 0.1 μm-10 .0 μm or 0.5 μm-5.0 μm, etc.
In some embodiments, the abrasive particles are disposed randomly throughout the solder material of the joint. In some embodiments, the abrasive particles are disposed in the vicinity of the interface between the metal part and the solder material.
In some embodiments, the metal or alloy-solder material interface is free of an passive oxide layer, thereby facilitating a direct contact of the metal or alloy part with the solder material. It is this direct contact, in the absence of the oxide layer, that is attributed to the superior bond strength and results in the high ultimate tensile strengths for the joint.
In another aspect, a method of making a solder joint is described. In some embodiments the method includes contacting the solder material with the abrasive particles; placing the solder material and the abrasive particles between the first and second metal parts to form a layered structure; applying a compressive force on the layered structure; applying ultrasonic vibration for a predetermined time to the layered structure to remove the passive oxide layer of the metal part; and applying heat to the layered structure to cause the solder material to melt and flow between the metal parts and form a bond with the metal parts.
In some other embodiments, contacting the abrasive particles with the solder material includes applying the abrasive particles on the solder material by techniques such as suspension sedimentation, aerosol techniques, and physical and chemical vapor deposition. In some other embodiments, the abrasive particles may be placed on the metal part surface, after which the solder layer is placed in between the parts.
In some embodiments, the contacting of the abrasive particles with the solder material includes preparation of a slurry of the abrasive. In some embodiments the abrasive slurry is made by dispersing the abrasive particles of the desired particle size in a solvent such as ethanol. This is schematically shown in
In some other embodiments, the surface of the solder sheet is coated with the abrasive slurry to dispose the abrasive on the surface of the solder sheet. The coating may be performed by any of the conventional application methods, such a, but not limited to, dip coating, roll coating, draw down, spraying and brushing on.
In some other embodiments, the abrasive particles are mixed with the solder material and this mixtures is disposed between the metal parts to be joint. In some embodiments, the mixture of the solder particles and the abrasive may be compacted to form a sheet prior to being disposed between the metal parts or may be disposed as a mixture of particles of abrasive and solder material. Without being bound by theory, the concentration of the abrasive particles in the solder material should be high enough to have sufficient number of abrasive particles disposed on the surface of the compacted solder sheet such that they are available to remove the passive oxide layer as described later in this document.
In some embodiments, the solder material with the abrasive particles disposed on one surface is placed between the metal parts that are to be joined with the abrasive particles disposed on the side of the solder sheet that is to form contact with the metal part which forms a passive oxide layer. This is schematically shown in
A compressive force is applied on the layered structure 305 along with an ultrasonic vibration for a predetermined amount of time. The compressive force can be applied by any of the conventional methods known to one skilled in the art. In some embodiments, the part is compressed in a hydraulic press. In some other embodiments the part is compressed by application of weight. In some embodiments the compressive force applied is greater than 15 MPa; or greater than 20 MPa; or greater than 40 MPa. Pressure ranges bounded by any of the values identified hereinabove are also contemplated, e.g., 15 MPa-40 MPa, or 15 MPa-20 MPa or 20 MPa-40 MPa, etc.
In some embodiments the vibration source is an ultrasonic welding machine a STAPLA Condor® ultrasonic welding unit is used for ultrasonic consolidation. A schematic of the ultrasonic welding machine is shown in
In some embodiments, the frequency of vibration used is 15 kHz, or 20 kHz, or 30 kHz, or 35 kHz, or 40 kHz, or 45 kHz, or 50 kHz, or 60 kHz. Frequency ranges bounded by any of the values identified hereinabove are also contemplated, e.g., or 15 kHz-60 kHz, or 20 kHz-60 kHz, or 15 kHz-40 kHz, or 20 kHz-40 kHz, or 20 kHz-30 kHz. In some embodiments, the amplitude of vibration used is less than 100 μm, or less than 80 μm, or less than 60 μm, or less than 40 μm, or less than 20 μm, or less than 3 μm. Amplitude ranges bounded by any of the values identified hereinabove are also contemplated, e.g., or 3 μm-100 μm, or 3 μm-80 μm, or 3 μm-60 μm, or 20 μm-80 μm, or 40 μm-100 μm. The duration the vibration is applied is 1 second. Other frequencies, amplitudes and time durations, not specified here, may be selected as long as the ultrasonic activation is sufficient to abrade the passive oxide layer that is present on the metal or alloy part.
Without being bound by theory, the process of surface initiation causes the passive oxide layer on the metal parts to be abraded and removed. Since the passive oxide is instantly reformed after cleaning and the solder does not bond well with these oxides the bond strength is significantly impaired. However, due to the compressive force being exerted on the layered structure 305, the interface is devoid of oxygen and fresh passive oxide cannot be formed back in accordance with the current disclosure. Thus, providing a clean, oxide free surface on interface 306 of metal part 303 to which the solder material can adequately bond in the subsequent heating step.
Once the vibration is stopped, the layered structure 305 is heated by heating the nickel foil through a hot plate 307. This is schematically depicted in
In some embodiments, the UPC setup also includes a hot plate which facilitate operation at elevated temperatures. In some embodiments, two cartridge heaters 401 such as, TUTCO, 9.5 mm diameter, 51 mm length, 400 W; and a K-type thermocouple probes 402, such as, OMEGA Model SP-GP-K-6, are inserted in the stainless steel heater plate below the die holder 403. This is shown schematically in
The process used for making the Al-solder joint shown in
A compressive force is applied on the layered structure 905 along with an ultrasonic vibration for a predetermined amount of time. The compressive force can be applied by any of the conventional methods known to one skilled in the art. In some embodiments, the part is compressed in a hydraulic press. In some other embodiments the part is compressed by application of weight. In some embodiments the compressive force applied is greater than 15 MPa; or greater than 20 MPa; or greater than 40 MPa.
In some embodiments the vibration source is an ultrasonic welding machine. In some embodiments the frequency and amplitude of the vibration applied is 20 kHz and 9 μm, respectively. In some embodiments, the frequency of vibration used is 15 kHz, or 20 kHz, or 30 kHz, or 35 kHz, or 40 kHz, or 45 kHz, or 50 kHz, or 60 kHz. Frequency ranges bounded by any of the values identified hereinabove are also contemplated, e.g., or 15 kHz-60 kHz, or 20 kHz-60 kHz, or 15 kHz-40 kHz, or 20 kHz-40 kHz, or 20 kHz-30 kHz. In some embodiments, the amplitude of vibration used is less than 100 μm, or less than 80 μm, or less than 60 μm, or less than 40 μm, or less than 20 μm, or less than 3 μm. Amplitude ranges bounded by any of the values identified hereinabove are also contemplated, e.g., or 3 μm-100 μm, or 3 μm-80 μm, or 3 μm-60 μm, or 20 μm-80 μm, or 40 μm-100 μm. The duration the vibration is applied is 1 second. Other frequencies, amplitudes and time durations, not specified here, may be selected as long as the ultrasonic activation is sufficient to abrade the passive oxide layer that is present on the metal or alloy part.
Without being bound by theory, the process of surface initiation causes the passive oxide layer on the metal parts to be abraded and removed. Since the passive oxide is instantly reformed after cleaning and the solder does not bond well with these oxides the bond strength is significantly impaired. However, due to the compressive force being exerted on the layered structure 905, the interface is devoid of oxygen and fresh passive oxide cannot be formed back in accordance with the current disclosure. Thus, providing a clean, oxide free surface on interface 906a and 906b of metal part 903 and 904 to which the solder material can adequately bond in the subsequent heating step.
Once the vibration is stopped, the layered structure 905 is heated through a hot plate 607. This is schematically depicted in
This application claims the benefit of the earlier filing date of U.S. Patent Application No. 61/894,122, filed on Oct. 22, 2013, the contents of which are incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US14/61537 | 10/21/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61894122 | Oct 2013 | US |
