Patent Description:
This section provides background information related to the present invention which is not necessarily prior art. This section provides a general summary of the invention and is not a comprehensive disclosure of its full scope or all of its features.

Direct bonding of incompatible dissimilar metals (e.g., Al/Fe, Ti/Fe, Mg/Fe, etc.) through either fusion-based approaches (e.g., arc or high energy beam) or solid-state methods (e.g. ultrasonic welding, conventional friction welding, and conventional friction stir welding) introduced brittle intermetallic compounds at the joint interface making the resultant welds inapplicable as safety-critical engineering structures. Conventional approaches have been focused on metallurgical means by influencing phase transformation kinetics and diffusion through reducing the processing peek temperatures and/or increasing the cooling rate during manufacturing. Unfortunately, these approaches only result in an incremental reduction in the size of intermetallic compounds at the joint interface. The problem remains unsolved. <CIT> (describing the preamble of claim <NUM>) discloses a joined body and a process for manufacturing the same.

According to a first aspect of the present invention, method of joining a first component and a second component according to claim <NUM> is defined. Further embodiments of the claimed invention are defined in the dependent claims.

The methods according to the present invention enable new, cost-effective ways of manufacturing stronger dissimilar metal structures minimizing the presence of detrimental intermetallic compounds.

The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present invention, which is defined by the appended claims.

According to the teachings of the present disclosure, as illustrated in <FIG>, methods of and systems for joining at least a first component <NUM> and a second component <NUM> are disclosed having a novel dissimilar metal interfacial microstructure control methodology. It should be understood, as illustrated herein (see <FIG> and <FIG>), that the present teachings are equally useful for joining more than two components, such as first component <NUM>, second component <NUM>, and a third component <NUM>.

The first component <NUM> is made of a dissimilar metal relative to the metal of the second component <NUM>. In this way, a quasi-liquid metal <NUM> and shear localization within the quasi-liquid metal <NUM> can be created and maintained at a dissimilar metal interface <NUM> disposed between the first component <NUM> and the second component <NUM>. This quasi-liquid metal <NUM> is created by rapid friction between the first component <NUM> and the second component <NUM>. Quasi-liquid metal herein can be defined as a metal in a liquid-like state at temperatures below the melting point of the metal. The quasi-liquid metal have a higher viscosity than the molten liquid metal.

With particular reference to <FIG>, a molecular dynamic (MD) simulation is provided illustrating formation of quasi-liquid metal <NUM> under rapid sliding (friction) condition according to the principles of the present teachings. <FIG> illustrates first component <NUM>, being made of aluminum alloy (Al), for example, being in physical contact with second component <NUM>, being made of steel (Fe), for example along the dissimilar metal interface <NUM>. Applying rapid frictional sliding between the first component <NUM> and the second component <NUM> is sufficient to generate a layer of quasi-liquid metal <NUM> and shear localization at the dissimilar metal interface <NUM> between the first component <NUM> and the second component <NUM>, as illustrated in <FIG>.

According to the present teachings, the formation of quasi-liquid metal <NUM> and the shear localization within the quasi-liquid metal <NUM> promotes alloy amorphization at the dissimilar metal interface <NUM>. A nanoscale amorphous layer <NUM> at dissimilar metal interface <NUM> has been produced successfully and repeatedly on bimetallic samples. As illustrated in <FIG>, a transition region between the first component <NUM> and the second component <NUM> is not an intermetallic compound, but rather a nanoscale amorphous metal or layer <NUM> with averaged thickness about <NUM> nanometers, in some embodiments.

As illustrated in <FIG>, detailed atomic probe tomography (ATP) examination reveals that a nanoscale amorphous layer <NUM> indeed forms and has a composition corresponding to a "Metallic Glass Former" composition. Such a metallic glass state composition could typically only be reached through rapid solidification in the range of <NUM><NUM> to <NUM><NUM> °C/s. However, according to the principles of the present teachings, we have found that through experimental joining trials the present teachings can achieve the desired composition with a cooling rate of less than <NUM><NUM> °C/s. This difference is caused by the formation of quasi-liquid metal <NUM> at the dissimilar metal interface <NUM> created by the methods of the present teachings.

The above findings lead to two categories of novel dissimilar manufacturing processes that can be employed to produce stronger dissimilar metal structures:.

Firstly, as indicated, an in-situ generated quasi-liquid metal <NUM> is achieved by rapid friction between the first component <NUM> and the second component <NUM>, being made of dissimilar metals, under certain contact pressure and relative velocity conditions resulting in a shear strain rate higher than the threshold shear strain rate. The threshold shear strain rate within the quasi-liquid metal <NUM> is at or above 1x10<NUM> s-<NUM>. The rapid friction needs to be terminated and the processing temperature needs to be reduced to temperatures lower than the crystallization temperature of the quasi-liquid metal <NUM> after sufficient quasi-liquid metal <NUM> has formed at the dissimilar metal interface <NUM> and before the occurrence of crystallization within the quasi-liquid metal <NUM>. The rapid friction needs to be terminated and the processing temperature needs to be reduced to temperatures lower than the crystallization temperature of the quasi-liquid metal <NUM> after sufficient quasi-liquid metal <NUM> has formed at the dissimilar metal interface <NUM> and before the occurrence of substantial crystallization within the quasi-liquid metal <NUM>. Occurence of substantial crystallization means <NUM>% of the quasi-liquid metal has crystallized.

Secondly, as indicated, in some embodiments, quasi-liquid metal <NUM> can be applied through the addition of metallic glasses (whose glass transition temperature (Tg) lower than <NUM>% of the lowest melting point of the metals to be welded) according to the following steps: (<NUM>) positioning metallic glasses at the dissimilar metal interface <NUM>, (<NUM>) heating the metallic glasses to a temperature above the transition Tg but below the lowest melting point of the metals involved, (<NUM>) applying a compressive pressure to generate thermoplastic deformation, and (<NUM>) reducing the welding temperature below the crystallization temperature of the quasi-liquid metal <NUM> before the occurrence of crystallization. In some embodiments, the welding temperature need to be reduced to below the crystallization temperature of the quasi-liquid metal <NUM> before the occurrence of substantial crystallization. In some embodiments, occurrence of substantial crystallization means <NUM>% of the quasi-liquid metal has crystallized.

As illustrated in <FIG>, in-situ generated quasi-liquid metal <NUM> is achieved by applying rapid friction, via applied pressure P and relative movement between the first component <NUM> and the second component <NUM>. The rapid friction between the first component <NUM> and the second component <NUM> needs to be sufficient to generate an interfacial pre-melting (i.e. to form a thin layer of quasi-liquid metal <NUM>) and shear localization within the quasi-liquid metal <NUM> at the dissimilar metal interface <NUM>. The rapid friction needs to be terminated and the processing temperature needs to be reduced to temperatures lower than the crystallization temperature of the quasi-liquid metal <NUM> after sufficient quasi-liquid metal <NUM> is formed at the dissimilar metal interface <NUM> and before the occurrence of substantial crystallization within the quasi-liquid metal <NUM>.

In some embodiments, a quasi-liquid metal <NUM>, being thicker than <NUM> at the dissimilar metal interface <NUM>, is sufficient. In some embodiments, a quasi-liquid metal <NUM>, being thicker than <NUM> at the dissimilar metal interface <NUM>, is sufficient.

In some embodiments, the relative movement between the first component <NUM> and the second component <NUM> needs to be terminated within <NUM>-<NUM> seconds once sufficient quasi-liquid metal <NUM> is formed. In some embodiments, the relative movement between the first component <NUM> and the second component <NUM> needs to be terminated within <NUM>-<NUM> seconds once sufficient quasi-liquid metal <NUM> is formed.

In some embodiments, the first component <NUM> and the second component <NUM> each have a surface <NUM>-the surface 20a of one component (a) is configured to be bonded to the surface 20b of the other component (b). In this way, the surface or surfaces <NUM> of each of the first component <NUM> and the second component <NUM> that are configured to be joined, welded, or assembled will be referred to as the faying surfaces <NUM>. The joining, welding, or assembling of the faying surfaces <NUM> of first component <NUM> and second component <NUM> is along the dissimilar metal interface <NUM>.

In some embodiments, contamination on the faying surface(s) <NUM> of the first component <NUM> and the second component <NUM> should be removed prior to joining, welding, or assembling for the purpose to improve the quality of the bond. In some embodiments, the surface contamination can be removed through grinding. In some embodiments, the surface contamination can be removed through organic solvent. In some embodiments, surface oxidation on the faying surface <NUM> can be removed or be reduced to a thickness less than <NUM> before the welding or assembling process. In some embodiments, the faying surface(s) <NUM> can be flat. In some embodiments, as illustrated in <FIG>, the faying surface <NUM> can be concave to form a shallow groove to enhance the rapid friction at the dissimilar material interface <NUM>. In some embodiments, the shape of the faying surface <NUM> of the first component <NUM> can be complementary to the faying surface of the second component <NUM>. In some embodiments, the shape of the faying surface <NUM> of the first component <NUM> can be different from the faying surface of the second component <NUM>.

In some embodiments, the faying surface <NUM> of the harder component (i.e. the first component <NUM> or the second component <NUM>) can have and/or be flattened to a roughness value of Ra < <NUM>. In some embodiments, the faying surface <NUM> of the harder component can have and/or be flattened to a roughness value of Ra < <NUM>. In some embodiments, the faying surface <NUM> of the harder component can have and/or be flattened to a roughness value of Ra < <NUM>.

With reference to <FIG>, in some embodiments, in-situ generated quasi-liquid metal <NUM> at dissimilar metal interface <NUM> can be achieved by inserting a rotating tool <NUM> through at least one of the first component <NUM> and the second component <NUM> to generate locally activated rapid friction at the dissimilar metal interface <NUM>. In some embodiments, rotating tool <NUM> can comprise any one of a number of cross-sectional shapes as described herein. In some embodiments, rotating tool <NUM> can comprise one or more shoulder portions <NUM> and one or more probe members <NUM> extending from the shoulder portion <NUM>. In some embodiments, as illustrated in <FIG>, the rotating tool <NUM> comprises two shoulder portions <NUM>. At least a portion of the probe member <NUM> physically contacting at least one of the first component <NUM> and the second component <NUM> to generate rapid friction at the dissimilar metal interface <NUM>.

In some embodiments, as illustrated in <FIG> and <FIG>, the shoulder portion(s) <NUM> and probe portion <NUM> can rotate independently and/or move independently in the axial direction. In some embodiments, the shoulder portion <NUM> and probe portion <NUM> can rotate independently. In some embodiments, only the probe member <NUM> rotates.

In some embodiments, the probe member <NUM> having at least one side surface <NUM> and at least one distal end surface <NUM>. In some embodiments, the at least one distal end surface <NUM> can be concave, convex, or flat, or various combinations thereof. In some embodiments, as illustrated in <FIG>, a cross sectional shape of the probe member <NUM> can be a circular, polygonal, or irregular.

According to the present invention, surface features increasing the surface roughness are added to the rotating tool <NUM>, such as to the probe member <NUM>, to enhance the rotational flow of material around rotating tool member <NUM> to enhance locally activated rapid friction between the dissimilar metals. In some embodiments, the probe member <NUM> can promote rotation of quasi-liquid metal around the probe member <NUM> and shoulder portion <NUM>, being larger in diameter compared to the probe member <NUM>, can act as a shoulder or barrier to inhibit or prevent flow of the quasi-liquid metal out of the processing zone.

In some embodiments, as illustrated in <FIG>, rotating tool <NUM> can comprise a positioning prop <NUM> extending from distal end surface <NUM> of the probe member <NUM>, from side surface <NUM>, or a combination thereof. In some embodiments, rotating tool <NUM> can comprise the positioning prop <NUM> extending from side surface <NUM> of the probe member <NUM>. In some embodiments, rotating tool <NUM> can comprise the positioning prop <NUM> extending from distal end surface <NUM> of the probe member <NUM>. In some embodiments, the positioning prop <NUM> is located at the center of distal end surface <NUM> of the probe member <NUM>. In some embodiments, the positioning prop <NUM> is deviate from center of distal end surface <NUM> of the probe member <NUM>. In some embodiments, a plurality of positioning props <NUM> is used.

In some embodiments, as illustrated in <FIG>, the positioning prop <NUM> can comprise one or more ring-like shaped members extending from side surface <NUM> of the probe member <NUM>. In some embodiments, the positioning prop <NUM> extends entirely around the probe member <NUM>. In some embodiments, the positioning prop <NUM> extends only a portion around the probe member <NUM>. In some embodiments, the positioning prop <NUM> is located at the center of the probe member <NUM> in the axial direction. In some embodiments, the positioning prop <NUM> can be used to produce butt joints. In some embodiments, multiple rings can be used as the positioning prop <NUM>. In some embodiments, an end surface of the positioning prop <NUM> is flat.

In some embodiments, positioning prop <NUM> is configured to provide a standoff distance from the dissimilar metal interface <NUM>. For example, in some embodiments, as illustrated in <FIG>, the probe member <NUM> of rotating tool <NUM> can be spaced apart from dissimilar metal interface <NUM> a standoff distance, h. Although this standoff distance h can be achieve in many way (as illustrated and described herein), one or more positioning prop <NUM> can extend from distal end surface <NUM> and have a length equal to standoff distance h such that positioning prop <NUM> can contact faying surface <NUM> of the second component <NUM> to ensure proper positioning of the probe member <NUM> of rotating tool <NUM>. In some embodiments, whether associated with positioning prop <NUM> or not, standoff distance h (and thus length of positioning prop <NUM>) can be about <NUM> to <NUM>. In some embodiments, the surface area of a distal end surface of positioning prop <NUM> can be about <NUM>% of the surface area of distal end surface <NUM> of the probe member <NUM>.

In some embodiments, the positioning prop <NUM> can tightly contact the faying surface <NUM> of the second component <NUM>. In some embodiments, the positioning prop <NUM> can slightly penetrate the faying surface <NUM> of the second component <NUM>. In some embodiments, the relative positioning between the positioning prop <NUM> and faying surface <NUM> is controlled by monitoring and controlling the counterforce applied on the positioning prop <NUM>.

In some embodiments, as illustrated in <FIG>, the end surface of the positioning prop <NUM> is parallel to the faying surface <NUM>. In some embodiments, the end surface of the positioning prop <NUM> is a regular shape. In some embodiments, the end surface of the positioning prop <NUM> is irregular shape. In some embodiments, the end surface of the positioning prop <NUM> is sharp.

In some embodiments, the positioning prop <NUM> of the probe member <NUM> and the probe member <NUM> are made from the same materials. In some embodiments, the positioning prop <NUM> of the probe member <NUM> and the probe member <NUM> are made from different materials. In some embodiments, the positioning prop <NUM> of the probe member <NUM> is made from harder and more wear resistant materials compared to the probe member <NUM>.

In some embodiments, the rotating tool <NUM> can be inserted through the component (<NUM>, <NUM>) that has a relatively lower melting point compared to the other component (<NUM>, <NUM>). In some embodiments, the rotating tool <NUM> traverses along the welding direction to produce a long butt or lap joint.

In some embodiments, interfacial amorphization through the addition of metallic glasses <NUM> (also known as amorphous metal) can be used to produce spot joints <NUM> (<FIG>). Amorphous metal can be inserted and then heated to temperatures above its glass transition temperature (Tg) and below the lowest melting points of all components involved through friction energy, induction energy, or other heating sources. Once the amorphous metal is heated to the targeted temperatures, the metallic glass exists as a highly viscous liquid metal and increases its fluidity. A compression pressure can be applied to deform the highly viscous quasi-liquid metal <NUM>.

In some embodiments, the processing temperature can be reduced below the crystallization temperature of the quasi-liquid metal <NUM> before substantial occurrence of crystallization within the quasi-liquid metal <NUM>. In some embodiment, substantial occurrence of crystallization means <NUM>% of the quasi-liquid metal has crystallized.

In some embodiments, the processing temperature can be reduced below the glass transition temperature of the quasi-liquid metal <NUM> before substantial occurrence of crystallization within the quasi-liquid metal <NUM>.

In some embodiment, glass transition temperature of the metallic glasses <NUM> is lower than <NUM>% of the lowest melting point of the components to be welded.

In some embodiments, interfacial amorphization through the addition of metallic glasses can be used to produce long lap joints or long butt joints.

In some embodiments, heating and compression can be locally applied through an integrated tool <NUM> (<FIG> and <FIG>). In some embodiments, heating and compression can be locally applied through separated tools <NUM>, <NUM> (<FIG>). In some embodiments, local heating and/or compression pressure can be applied in sequence from the beginning to the end of the weld.

A tool and method for producing weld between dissimilar material components can be achieved by:.

Claim 1:
A method of joining a first component (<NUM>) and a second component (<NUM>), the first component (<NUM>) and the second component (<NUM>) being made of dissimilar metals, the first component (<NUM>) having a lower melting temperature than the second component (<NUM>), the method being characterised by the following:
smoothing the faying surface (<NUM>) of the second component (<NUM>) to a roughness value of Ra < <NUM> and reducing surface oxidation of the second component (<NUM>) to a thickness less than <NUM> before joining;
inserting a rotating tool (<NUM>) having one shoulder portion (<NUM>) and one rotating probe portion (<NUM>) into the first component (<NUM>), the rotating probe portion (<NUM>) is spaced apart from a faying surface (<NUM>) of the second component (<NUM>) by a standoff distance of <NUM> to <NUM>; rotating the rotating tool (<NUM>) to generate rapid friction between the second component (<NUM>) and material of the first component (<NUM>) rotating around the one rotating probe portion (<NUM>) at the dissimilar metal interface (<NUM>), the friction being sufficient to generate a layer of quasi-liquid metal (<NUM>) and produces shear localization within the quasi-liquid metal (<NUM>) at a dissimilar metal interface (<NUM>) between the first component (<NUM>) and the second component (<NUM>), the quasi-liquid metal (<NUM>) being a metal in a liquid-like state at a temperature below the melting point of the first component (<NUM>) and the second component (<NUM>), the quasi-liquid metal (<NUM>) having a shear strain rate above 1x10<NUM> s-<NUM>;
wherein the rotating tool (<NUM>) comprises surface features for increasing the surface roughness to enhance the rotational flow of material around rotating tool member (<NUM>), and to enhance locally activated rapid friction between the dissimilar metals; and
terminating the application of rapid friction and reducing a processing temperature of the quasi-liquid metal (<NUM>) below a crystallization temperature of the quasi-liquid metal (<NUM>) within <NUM> to <NUM> seconds after generation of the quasi-liquid metal (<NUM>) and before <NUM>% of the quasi-liquid metal (<NUM>) has crystallized within the quasi-liquid metal (<NUM>) thereby joining the first component (<NUM>) and the second component (<NUM>) along a nanoscale amorphous layer (<NUM>).