Patent Publication Number: US-2019193339-A1

Title: Laser-induced micro-anchor structural and passivation layer for metal-polymeric composite joining and methods for manufacturing thereof

Description:
INTRODUCTION 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     The present disclosure pertains to a metal-polymeric composite joint and methods of manufacturing the metal-polymeric composite joint. More specifically, the metal-polymeric composite joint may include a laser-induced micro-anchor structural and passivation layer. 
     Weight reduction for increased fuel economy in vehicles has spurred the use of various lightweight materials, such as aluminum and magnesium alloys as well as use of light-weight reinforced composite materials. While use of such lightweight materials can serve to reduce overall weight and generally improve fuel efficiency, issues can arise in manufacturing certain components. For example, molding large, complex parts from a reinforced composite material may be difficult or infeasible. It may therefore be desirable to join multiple smaller components. However, joining dissimilar materials, such as a metal and a reinforced polymeric composite, may present additional challenges such as low-strength joints or long cycle times in manufacturing. Accordingly, it would be desirable to develop a quick and robust method of joining metal and composite components. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In various aspects, the present disclosure provides a metal-polymeric composite joint. The metal-polymeric composite joint includes a first component and a second component. The first component includes a metal. The first component has a first surface including a plurality of micro-anchors. The second component includes a composite material including a polymer and a reinforcing fiber. The second component has a second surface that at least partially engages the first surface of the first component. A portion of the polymer of the second component occupies at least a portion of the micro-anchors of the first component to fix the second component to the first component. 
     In one aspect, the first surface further defines a plurality of crests and a plurality of troughs. The plurality of crests defines the plurality of micro-anchors. 
     In one aspect, the first surface further defines a plurality of elongate valleys and a plurality of elongate peaks. The elongate valleys are disposed between the elongate peaks. A portion of the crests and a portion of the troughs are disposed on each elongate valley. A portion of the crests and a portion of the troughs are disposed on each elongate peak. 
     In one aspect, the plurality of elongate valleys and the plurality of elongate peaks are disposed parallel to one another, and the metal-polymeric composite joint can withstand loads of greater than or equal to about 6 kN in a direction perpendicular to the elongate valleys and the elongate peaks. 
     In one aspect, the metal is selected from a group consisting of stainless steel, aluminum, and combinations thereof. 
     In one aspect, the metal includes aluminum. The first surface is at least partially coated in a passivation layer including aluminum oxide (Al 2 O 3 ). 
     In one aspect, the polymer is selected from the group consisting of a polycarbonate (PC), a high-density polyethylene (HDPE), polyoxymethylene (POM), a thermoplastic elastomer (TPE), acrylonitrile butadiene styrene (ABS), a thermoplastic olefin (TPO), a polyamide (PA, nylon), and combinations thereof. 
     In one aspect, the metal includes aluminum, the polymer includes polyamide (PA, nylon), and the reinforcing fiber includes a carbon fiber. 
     In one aspect, at least a portion of the micro-anchors include micro-apertures. Each micro-aperture has perimeter defining a connected shape. 
     In various other aspects, the present disclosure provides another metal-polymeric composite joint. The metal-polymeric composite joint includes a first component, a second component, and a passivation layer. The first component includes aluminum and has a first surface. The second component is fixed to the first component. The second component includes a composite including a polymer and a reinforcing fiber. The second component has a second surface that at least partially engages the first surface of the first component. The passivation layer is disposed on the first surface of the first component. The passivation layer engages the second surface of the second component. The passivation layer includes aluminum oxide (Al 2 O 3 ). The metal-polymeric composite joint has a lap shear strength of greater than or equal to about 6 kN after 5 years. 
     In one aspect, the passivation layer has an average atomic percent of oxygen of greater than or equal to about 10% at a depth of 500 nm measured from the first surface of the first component. 
     In yet other aspects, the present disclosure provides a method of joining dissimilar materials. The method includes directing a first laser beam toward a first surface of a first component to form a plurality of micro-anchors in the first surface. The first component includes a metal. The method also includes disposing the first component on a second component so that the first surface of the first component at least partially engages a second surface of the second component. The second component includes a composite including a polymer and a reinforcing fiber. The method also includes directing a heat source towards a third surface of the first component to cause a portion of the polymer to melt and occupy a portion of the micro-anchors. The third surface is disposed opposite the first surface. 
     In one aspect, the first component includes metal and directing the first laser beam toward the first surface of the first component is performed in the presence of oxygen to form an aluminum oxide (Al 2 O 3 ) layer on the first surface. 
     In one aspect, directing the heat source toward the third surface of the first component includes directing a second laser beam toward the third surface of the first component. The second laser beam is a continuous wave (CW) laser beam. 
     In one aspect, the second laser beam has a power of greater than or equal to about 500 W and less than or equal to about 2000 W. The second laser beam has a scan speed of greater than or equal to about 100 mm/s and less than or equal to about 2 m/s. The second laser beam has a spot size of greater than or equal to about 100 μm and less than or equal to about 500 μm. 
     In one aspect, directing the second laser beam toward the third surface of the first component includes moving the second laser beam with respect to the first component to create a first plurality of elongate valleys on the third surface. Each elongate valley is disposed substantially parallel to the other elongate valleys. A centerline each elongate valley is disposed greater than or equal to about 0.5 mm and less than or equal to about 5 mm from the centerline of each other elongate valley. 
     In one aspect, directing the second laser beam toward the third surface of the first component further includes moving the second laser beam with respect to the first component to create a second plurality of elongate valleys on the third surface. Each elongate valley of the second plurality of elongate valleys is disposed substantially parallel to the other elongate valleys of the second plurality of elongate valleys. A centerline each elongate valley of the second plurality of elongate valleys is disposed greater than or equal to about 0.5 mm and less than or equal to about 5 mm from the centerline of each other elongate valley of the second plurality of elongate valleys. The elongate valleys of the second plurality of elongate valleys are disposed between the elongate valleys of the first plurality of elongate valleys. 
     In one aspect, the first laser beam is a nanosecond pulsed laser beam having a pulse width of greater than or equal to about 9 ns and less than or equal to about 200 ns. The first laser beam has a pulse overlap of greater than or equal to about 0% and less than or equal to about 50%. The first laser beam has a repetition rate of greater than or equal to about 10 kHz and less than or equal to about 500 kHz. 
     In one aspect, the first laser beam has a scan power of greater than or equal to about 50 W and less than or equal to about 500 W. The first laser beam has a scan speed of greater than or equal to about 100 mm/s and less than or equal to about 10 m/s. The first laser beam has a spot size of greater than or equal to about 10 μm and less than or equal to about 100 μm. 
     In one aspect, the metal includes aluminum, the polymer includes polyamide (PA, nylon), and the reinforcing fiber includes carbon fiber. 
     Further areas of applicability will become apparent from the description provided herein. 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 disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIGS. 1A-1C  show a metal-polymeric composite joint according to certain aspects of the present disclosure.  FIG. 1A  is a side view of the metal-polymeric composite joint;  FIG. 1B  is a top view of the metal-polymeric composite joint;  FIG. 1C  is a sectional view of the metal-polymeric joint of  FIG. 1A  taken at line  1 C- 1 C of  FIG. 1B ; 
         FIGS. 2A-2E  are scanning electron microscopy (“SEM”) images of a laser-treated metal surface according to certain aspects of the present disclosure;  FIGS. 2A-2B  are top views of the laser-treated metal surface showing a plurality of peaks and a plurality of valleys;  FIG. 2C  is a side perspective view of the laser-treated metal surface showing a plurality of troughs, a plurality of crests, and a plurality of micro-anchors;  FIGS. 2D-2E  are top views of the laser-treated surface showing the plurality of troughs, the plurality of crests, and the plurality of micro-anchors; 
         FIG. 3  is an SEM image of a metal-polymeric composite joint including the laser-treated aluminum surface of  FIGS. 2A-2E ; 
         FIG. 4  is a schematic of a method of laser-treatment of a metal component according to certain aspects of the present disclosure; 
         FIG. 5  is a top view of the metal component of  FIG. 4  showing a laser pattern according to certain aspects of the present disclosure; 
         FIG. 6  is a schematic of a joining process for forming a metal-polymeric composite joint according to certain aspects of the present disclosure; 
         FIG. 7  is a top view of the metal-polymeric composite joint of  FIG. 6  showing a laser pattern according to certain aspects of the present disclosure; 
         FIG. 8  shows alternative laser patterns for a laser-treatment process according to certain aspects of the present disclosure.  FIG. 8  is a top view of a metal component showing a laser pattern for forming a joint having high lap shear strength in two directions; 
         FIGS. 9A-9B  show alternative laser patterns for a laser-treatment process according to certain aspects of the present disclosure.  FIG. 9A  is a top view of a metal component showing a laser pattern for forming a joint having 360° high lap shear strength;  FIG. 9B  is a sectional view of the metal component of  FIG. 9A  taken at line  9 B- 9 B of  FIG. 9A ; 
         FIG. 10  shows x-ray photoelectron spectroscopy (XPS) depth profiles of (i) an aluminum component without a laser-treated surface and (ii) an aluminum component having a laser-treated surface according to certain aspects of the present disclosure; 
         FIG. 11  is a top view of an aluminum-polymeric composite joint prior to corrosion testing of a metal-polymeric composite joint; 
         FIG. 12  is a top view of an aluminum-polymeric composite joint after 2.5 years of corrosion; 
         FIG. 13  is a graphical representation of lap shear strength as a function of time for metal-polymeric composite joints including: (i) an aluminum component without a laser-treated surface, (ii) an aluminum component having a laser-treated surface, and (iii) a stainless steel component having a laser-treated surface; and 
         FIG. 14  is a graphical representation of degradation of lap shear force as a function of time for the aluminum-polymeric composite joints of  FIG. 13 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of “consisting of” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment. 
     Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated. 
     When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures. 
     Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%. 
     In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges. 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     As discussed above, joining dissimilar materials, such as metals and polymeric composites, may present certain challenges. One possible method of joining a metal component and a polymeric composite component includes applying an adhesive to the joint and then curing the adhesive. However, adhesive joining of metals and polymeric composites poses challenges for mass production because of the relatively long cure time. For example, a duration of curing may be on the order of magnitude of hours. 
     Another possible method of joining a metal component and a polymeric composite component includes welding the joint (e.g., ultra-sonic welding, laser welding, etc.). However, welded metal and polymeric composite joints may have an undesirably low strength, because the materials are not readily chemically bonded to one another. 
     In various aspects, the present disclosure provides a high-strength metal-polymeric composite joint. The joint may include a metal component having a first surface that defines a plurality of micro-anchors or openings, which will be described further below. The first surface of the metal component may engage a second surface a reinforced polymeric composite component. A polymer of the polymeric composite component may occupy a space defined by the micro-anchors so that the polymer is disposed within and therefore intertwined with the micro-anchors to create a robust mechanical joint. The joint prepared according to certain aspects of the present disclosure may have a lap shear strength of greater than or equal to about 6 kN, optionally greater than or equal to about 7 kN, optionally greater than or equal to about 8 kN, optionally greater than or equal to about 9 kN, optionally greater than or equal to about 9.1 kN, optionally greater than or equal to about 9.2 kN, optionally greater than or equal to about 9.3 kN, and optionally greater than or equal to about 9.4 kN. 
     In various aspects, the present disclosure also provides corrosion-resistant metal-polymeric composite joint. The joint may include a passivation layer disposed between a metal component and a reinforced polymeric composite component. For example, when the metal component includes aluminum, the passivation layer may include aluminum oxide (Al 2 O 3 ). The passivation layer may be intentionally formed by heating the aluminum in the presence of oxygen. The passivation layer may reduce corrosion at the joint, thereby prolonging a life of the joint. After 2.5 years, the joint may have a lap shear strength of greater than or equal to about 6 kN, optionally greater than or equal to about 6.5 kN, optionally greater than or equal to about 7.0 kN, optionally greater than or equal to about 7.5 kN, and optionally greater than or equal to about 7.7 kN. After 5 years, the joint may have a lap shear strength of greater than or equal to about 6 kN, optionally greater than or equal to about 6.1 kN, optionally greater than or equal to about 6.2 kN, optionally greater than or equal to about 6.3 kN, optionally greater than or equal to about 6.4 kN, optionally greater than or equal to about 6.5 kN, optionally greater than or equal to about 6.6 kN, optionally greater than or equal to about 6.7 kN, optionally greater than or equal to about 6.8 kN, and optionally greater than or equal to about 6.9 kN. 
     Referring to  FIGS. 1A-1C , a metal-polymeric composite assembly  10  according to certain aspects of the present disclosure is provided. The metal-polymeric composite assembly  10  includes a metal component  12  (or first component) and a reinforced polymeric composite component  14  (or second component). The metal component  12  and the reinforced polymeric composite component  14  may overlap at a joining region  16 . More specifically, a first surface  18  of the metal component  12  and a second surface  20  of the reinforced polymeric composite component  14  may directly engage or contact one another at the joining region  16 . The metal component  12  and the reinforced polymeric composite component  14  may be fixed to one another in the joining region  16  to form a metal-polymeric composite joint  22 . The metal component  12  may include a third surface  24  disposed opposite the first surface  18 . The reinforced polymeric composite component  14  may include a fourth surface  26  disposed opposite the second surface  20 . 
     In certain variations, the metal component  12  may include aluminum, stainless steel (e.g., 316 stainless steel), or combinations thereof. The reinforced polymeric composite component  14  may include a polymer and a reinforcing material. The polymer may be a thermoplastic polymer. As non-limiting examples, the polymer may include a polycarbonate (PC), a high-density polyethylene (HDPE), acetal or polyoxymethylene (POM), a thermoplastic elastomer (TPE), acrylonitrile butadiene styrene (ABS), a thermoplastic olefin (TPO), a polyamide (PA, nylon), and combinations thereof. In certain variations, the reinforcing material may include a fiber such as carbon fiber (e.g., powdered fiber, short fiber, long fiber, or continuous fiber) or a glass fiber. 
     As best shown in  FIG. 1C , at least a portion of the first surface  18  of the metal component  12  may include a plurality of elongate peaks  28  and a plurality of elongate valleys  30 . The elongate peaks  28  and elongate valleys  30  may be present on the first surface  18  in the joining region  16 , or where the first surface  18  of the metal component  12  engages the second surface  20  of the reinforced polymeric composite component  14 . The plurality of elongate valleys  30  may be disposed between the plurality of elongate peaks  28  so that the elongate peaks  28  and the elongate valleys  30  alternate with one another in the joining region  16 . 
     Referring to  FIGS. 2A-2B , each elongate peak  28  may be disposed substantially parallel to each other elongate peak  28 . Similarly, each elongate valley  30  may be disposed substantially parallel to each other elongate valley  30 . The elongate valleys  30  may be substantially evenly disposed within the joining region  16  of the metal-polymeric composite assembly  10 . In other variations, the elongate valleys  30  may be unevenly spaced. For example, the elongate valleys  30  may be disposed in smaller subgroups (e.g., subgroups of five elongate valleys  30  in close proximity spaced apart from other subgroups) (not shown). 
     The elongate peaks  28  and elongate valleys  30  may extend parallel to a first axis  34 . The first axis  34  may be substantially perpendicular to a second axis  36 . The second axis  36  may correspond to a direction of applied force as indicated by the arrows  38 . The arrangement of the elongate peaks  28  and elongate valleys  30  may result in a lap shear strength of the joint  22  being greatest along the second axis  36  because of a mechanical interaction of the elongate peaks  28  and elongate valleys  30  of the first surface  18  with the second surface  20  as the force  38  is applied. 
     The elongate peaks  28  and elongate valleys  30  may be formed by laser treating the first surface  18  (referred to as a laser treatment or surface ablation process). The laser treatment may include directing a laser beam at the first surface  18  of the metal component  12 . As discussed in greater detail below, the laser beam moves relative to the metal component  12  to create the plurality of elongate valleys  30 . The elongate peaks  28  are defined on areas of the first surface  18  adjacent to the laser-created elongate valleys  30 . As the elongate valleys  30  are created by moving the laser beam over the first surface  18 , the laser beam heats the first surface  18 , thereby liquefying a portion of the metal at the first surface  18  of the metal component  12 . The laser beam may be a nanosecond pulsed laser. Thus, during a laser pulse, the laser beam may melt the metal. The liquefied metal may cool and solidify during a time between laser beam pulses. The relatively-short nanosecond pulse may lead to a dynamic heating and cooling process so that the molten metal solidifies before it can reach equilibrium and settle to form a smooth surface. Such a dynamic heating and cooling process may facilitate the formation of a specialized rough or irregular topography on the first surface  18  of the metal component  12 , as discussed further herein. 
     With reference to  FIGS. 2B-2E , the first surface  18  of the metal component  12  is shown. The first surface  18  includes a plurality of crests  50  and a plurality of troughs  52 . At least at least a portion of the crests  50  and at least a portion of the troughs  52  may be defined on each elongate peak  28 . At least a portion of the crests  50  and at least a portion of the troughs  52  may be defined on each elongate valley  30 . The crests  50  and troughs  52  are created as the metal of the metal component  12  rapidly melts and solidifies during the dynamic heating and cooling process. A pattern of crests  50  and troughs  52  may be irregular. Dimensions of the crests  50  and elongate troughs  50  may also be irregular. For example, crests  50  may differ from one another in size and shape. Troughs  52  may similarly differ from one another in size and shape. By way of non-limiting example, an average roughness of the first surface  18  may be greater than or equal to about 5 μm and less than or equal to about 20 μm. 
     At least a portion of the crests  50  may also include a plurality of micro-anchors  54 . The micro-anchors  54  may include invaginations, cavities, pores, hooks, and/or undercut regions that are formed during the cooling process. More specifically, the micro-anchors are formed after liquefied metal rises to define a crest  50  that then collapses back toward the first surface  18 . The lasers used in accordance with certain aspects of the present disclosure enable the formation of such micro-anchor structures by melting and then rapidly solidifying the metal to facilitate formation of such complex structures desirably having extensions that are at an angle (e.g., substantially perpendicular) to the metal surface so as to form undercuts or protrusions that serve as anchoring regions for polymer (as compared to merely creating surface roughness/asperities formed by typical roughening techniques). A portion of the micro-anchors  54  may be micro-apertures or micro-openings  56  having perimeters defining connected shapes, as best shown in  FIG. 2C . A micro-aperture or micro-opening  56  is formed when solid material (i.e., the metal) extends around an entire perimeter of the micro-aperture  56 . Thus, a perimeter of the micro-aperture  56  may be substantially free of gaps. The micro-anchors  54  may be irregular in size, shape, and distribution. In certain variations, the micro-anchors  54  may overlap one another. 
     The topography of the first surface  18 , including the crests  50 , the troughs  52 , and the micro-anchors  54 , may increase an area of the first surface  18  to facilitate intimate contact between the first surface  18  and a mating surface (e.g., the second surface  20  of the reinforced polymer composite component  14 ). Additionally, the micro-anchors  54  may enable a strong mechanical interlock with the mating surface. More particularly, as discussed in greater detail below, a material of the mating surface may engage the micro-anchors  54  to mechanically lock the metal component  12  to a mating component (e.g., the reinforced polymer composite component  14 ). 
     The metal-polymeric composite assembly  10  may be particularly prone to corrosion at the joint  22  when the reinforced polymeric composite component  14  includes a conductive material. For example, the use of carbon fiber as the reinforcing material makes the reinforced polymeric composite component  14  electrically conductive. Because carbon fibers are very inert or noble when compared to certain metals, such as aluminum, a metal component that is electrically connected to a carbon fiber composite may be particularly prone to galvanic corrosion. Thus, even when the joint  22  has a high initial strength, it may rapidly deteriorate and decrease in strength due to the galvanic corrosion. In various aspects, the present disclosure provides a corrosion-resistant joint having a passivation layer disposed between the metal component  12  and the reinforced polymeric composite component  14 . The passivation layer may act as a protective layer to prevent or reduce corrosion of the joint  22 . 
     The passivation layer may be formed during the laser-treatment that creates the elongate peaks  28  and valleys  30 . That is, the formation of the elongate peaks  28  and valleys  30  may be concurrent with the formation of the passivation layer. The laser treatment may be performed in the presence of oxygen to facilitate the formation of the passivation layer on the first surface  18  of the metal component  12 . Whether the passivation layer is formed at all may depend on the composition of the metal component  12  and whether oxygen is present during the laser treatment. A thickness of the passivation layer may depend on the temperature of the first surface  18  during the laser treatment. In one example, the metal component  12  includes aluminum and the laser beam is directed at the first surface  18  in the presence of oxygen (e.g., ambient atmosphere) to form a passivation layer that includes aluminum oxide (Al 2 O 3 ). Aluminum oxide (Al 2 O 3 ) is a stable, nonconductive dielectric that can be used as a coating to reduce corrosion at the joint  22 . 
     Referring to  FIG. 3 , an example of the joint  22  including the metal component  12  and the reinforced polymeric composite component  14  is shown. The metal component  12  may include aluminum. The reinforced polymeric composite component  14  may include a polymer material  60  and a plurality of reinforcing fibers  62 . The polymer may be polyamide (PA, nylon) and the reinforcing fiber may include carbon fibers. The first surface  18  may include the elongate peaks  28  and the elongate valleys  30 . The polymer  60  at the second surface  20  of the reinforced polymeric composite component  14  may be in intimate contact with the first surface  18  of the metal component  12 . Thus, in certain embodiments, the joint  22  may be free of any interfacial delamination. 
     The joint  22  between the metal component  12  and the reinforced polymeric composite component  14  may be formed by applying heat at the joining region  16  ( FIGS. 1A-1C ). More particularly, after the metal component  12  has been laser treated as described above, it may be at least partially disposed on the reinforced polymeric composite component  14  so that the first surface  18  (i.e., the laser-treated surface) of the metal component  12  directly engages the second surface  20  of the reinforced polymeric composite component  14 . A heat source, such as a laser beam, may be directed toward the third surface  24  of the metal component  12 . This process may create a plurality of elongate valleys or grooves similar to the elongate valleys  30  of the laser-treatment process. Due to the high conductivity of the metal, the heat may be transferred through the metal component  12  from the third surface  24  to toward the cooler first surface  18 . The heat at the first surface  18  may cause the polymer  60  at the adjacent second surface  20  to melt. The melted polymer  60  may flow around the crests  50 , into the troughs  52 , and through the micro-anchors  54 . The metal may have a higher melting temperature than the polymer, thus, the metal at the first surface  18  may remain in solid form while a portion of the polymer  60  (i.e., the polymer  60  near the second surface  20 ) melts to flow through the micro-anchors  54 . The polymer  60  may at least partially occupy at least a portion of the micro-anchors  54 . In certain variations, the polymer  60  may fully occupy at least a portion of the micro-anchors  54 . In certain variations, the polymer  60  may fully occupy all of the micro-anchors  54 . Although the heat source is described as a laser beam, one skilled in the art would appreciate that the joining region  16  may alternatively be exposed to a torch, induction heating, or ultrasonic welding, by way of non-limiting example. 
     The polymer  60  may cool and solidify when the application of heat ceases. The solidified polymer  60  may be intertwined with the metal of the metal component  12 . For example, the polymer  60  may occupy the micro-anchors  54  to form hooks or loops around the micro-anchors  54 . The polymer hooks or loops can mechanically interact with the micro-anchors  54  to form a strong joint. In certain variations, the joint  22  may behave like a hook-and-loop fastener; however, unlike a typical hook-and-loop fastener, the joint  22  is permanent so that the metal component  12  cannot be readily peeled away from the reinforced polymeric composite component  14 . 
     In various aspects, the present disclosure provides a method of manufacturing a metal-polymeric composite joint. The method may include laser-treating a first surface of a metal component. The laser treatment may create a plurality of micro-anchors, such as micro-apertures on the first surface. In certain variations, when the laser treatment is performed in the presence of oxygen, a passivation layer may be formed on the first surface. The laser treatment and formation of the passivation layer may be performed as a one-step process or concurrently. For example, when the metal component includes aluminum, the laser treatment may facilitate formation of an aluminum oxide (Al 2 O 3 ) passivation layer. The method may further include disposing a second surface of a polymeric composite component on the first surface of the metal component. Heat, such as from a laser, may be applied to a third surface of the metal component opposite the first surface to join the metal component to the polymeric composite component. More specifically, the heat may be transferred through the metal component, from the third surface to the first surface, to melt a polymer of the polymeric composite at the second surface. The melted polymer may flow through the micro-anchors and solidify to occupy the micro-anchors to form a high-strength metal-polymeric composite joint. The method may have a cycle time on the order of magnitude of seconds. In certain variations, the same laser equipment may be used for the laser treatment process as for the joining process. 
     Referring to  FIGS. 4-7 , a method of manufacturing a metal-polymeric composite assembly is shown. The method is described with reference to the metal-polymeric composite assembly  10  of  FIGS. 1A-3 . Referring now to  FIGS. 4-5 , the method includes laser-treating the first surface  18  of the metal component  12 . Laser-treating the first surface  18  includes directing a first laser beam  70  from a laser source  72  towards the first surface  18 . A first focal plane  74  of the first laser beam  70  is aligned at the first surface  18 . The first laser beam  70  may be focused toward the first surface  18  to achieve the highest laser fluence possible in light of the other laser-treatment parameters. 
     The first laser beam  70  may be a nanosecond pulsed laser beam. The first laser beam  70  may have a pulse width of greater than or equal to about 9 ns and less than or equal to about 200 ns, optionally greater than or equal to about 50 ns and less than or equal to about 200 ns, optionally greater than or equal to about 100 ns and less than or equal to about 200 ns, and optionally about 200 ns. The first laser beam  70  may have a pulse overlap of greater than or equal to about 0% and less than or equal to about 50%, optionally greater than or equal to about 5% and less than or equal to about 45%, optionally greater than or equal to about 10% and less than or equal to about 40%, and optionally about 35%. The first laser beam may have a repetition rate of greater than or equal to about 10 kHz and less than or equal to about 500 kHz, optionally greater than or equal to about 100 kHz and less than or equal to about 400 kHz, optionally greater than or equal to about 150 kHz and less than or equal to about 300 kHz, and optionally about 200 kHz. 
     The first laser beam  70  may move relative to the metal component  12  to create a first laser pattern  76 . For example, a laser head may move the first laser beam  70  while the metal component  12  remains stationary. In another example, the metal component  12  may be moved while the laser head remains stationary. The first laser pattern  76  may include a plurality of parallel lines  78  (resulting in the plurality of elongate valleys  30 ). In one example, the first laser beam  70  may be moved in a first direction  80 , from a first end  82  of the metal component  12  to a second end  84  of the metal component  12  to create a first line  78   a . The laser head may then return to the first end  82  and move in a second direction  86  substantially perpendicular to the first direction  80  to a starting position to create another line  78  adjacent to the first line  78   a . The process may be repeated to create the first laser pattern  76 . 
     The lines  78  of the first laser pattern  76  may be disposed substantially perpendicular to the second axis  36 , which is aligned with a direction of the applied force  38 . The first laser beam may create a spot size of greater than or equal to about 10 μm and less than or equal to about 100 μm, optionally greater than or equal to about 30 μm and less than or equal to about 80 μm, optionally greater than or equal to about 50 μm and less than or equal to about 70 μm, and optionally about 67 μm. A first distance between lines  39  may desirably be less than the spot size to ensure that the entire joining area  16  includes the crests  50 , the troughs  52 , and the micro-anchors  54 . For example, when the spot size is about 67 mm, the first distance  39  between the lines  78  may be greater than or equal to about 20 μm to less than or equal to about 60 μm, optionally greater than or equal to about 25 μm and less than or equal to about 50 μm, and optionally about 50 μm. The first laser beam  70  may have a scan speed of greater than or equal to about 100 mm/s and less than or equal to about 10 m/s, optionally greater than or equal to about 200 mm/s and less than or equal to about 2 m/s, optionally greater than or equal to about 300 mm/s and less than or equal to about 1 m/s, and optionally about 500 mm/s. The first laser beam  70  may have a scan power of greater than or equal to about 50 W and less than or equal to about 500 W, optionally greater than or equal to about 100 W and less than or equal to about 400 W, optionally greater than or equal to about 200 W and less than or equal to about 300 W, and optionally about 240 W. 
     After the first surface  18  of the metal component  12  is laser treated to create the topography including the elongate peaks  28  and elongate valleys  30  having the crests  50 , the troughs  52 , the micro-anchors  54 , and the micro-apertures ( FIGS. 2A-2E ), the metal component  12  may be joined to the reinforced polymeric composite component  14 . The joining may include applying heat to the third surface  24  of the metal component  12  while the first surface  18  of the metal component  12  is in contact with the second surface  20  of the reinforced polymeric composite component  14 . In certain variations, the heat source may be the laser source  72 . With reference to  FIGS. 6-7 , the metal component  12  may be disposed on top of the reinforced polymeric composite component  14 . The components  12 ,  14  may overlap partially (i.e., at the joining region  16 ) or fully (i.e., over an area larger than the joining region  16 ). The first surface  18  may be disposed toward the second surface  20 . The first surface  18  may directly engage or contact the second surface  20 . The components  12 ,  14  may both be disposed within clamps  100 . A force  102  may be applied at the clamps  100  to maintain contact between the components  12 ,  14 . 
     Joining the components  12 ,  14  may include directing a second laser beam  104  from the laser source  72  towards the third surface  24 . The second laser beam  104  may be a continuous wave (CW) laser beam. A second focal plane  106  of the second laser beam  104  may be aligned above the third surface  24 , as shown in  FIG. 6 , or below the third surface  24  (not shown). Thus, unlike the laser treatment of the first surface  18  shown and described in  FIGS. 4-5 , the second focal plane  106  is not aligned with the third surface  24 . Instead, the second laser beam  104  may be defocused at the third surface  24 . Defocusing the second laser beam  104  minimizes damage to the metal component  12  due to overheating and material vaporization. The second laser beam  104  may be defocused within a range of greater than or equal to about −3 mm to less than or equal to about +3 mm. 
     As discussed above, heat from the second laser beam  104  is transferred through the metal component  12  from the third surface  24  to the first surface  18  to heat the second surface  20  of the reinforced polymeric composite component  14 . A first melting temperature of the metal component  12  may be greater than a second melting temperature of the polymer  60  of the reinforced polymeric composite component  14 . For example, the metal component  12  may include aluminum having a melting temperature of about 660° C. and the reinforced polymeric composite component  14  may include nylon having a melting temperature of about 250° C. 
     A temperature of the first surface  18  of the metal component  12  may remain below the first melting temperature during the application of the second laser beam  104  so that the metal component  12  remains in a solid state near the joint  22 . The temperature of the metal component at the first surface  18  may remain substantially below the first melting temperature to prevent or minimize damage to the metal component  12 . A temperature of the reinforced polymeric composite component  14  at the second surface  20  may be greater than or equal to the second melting temperature so that a portion of the polymer of the reinforced polymeric composite component  14  melts and flows into the micro-anchors  54  ( FIGS. 2A-2E ). Thus, a temperature in the joining region  16  may be greater than the second melting temperature and less than the first melting temperature. For example, the temperature in the joining region  16  may be greater than or equal to about 300° C. and less than or equal to about 600° C. In some examples, a temperature of the third surface  24  of the metal component may be greater than the first melting temperature, resulting the third surface  24  being liquefied during the heating process. 
     The second laser beam  104  may move relative to the components  12 ,  14  to create a second laser pattern  110 . For example, the laser head may move the second laser beam  104  while the components  12 ,  14  remain stationary. In another example, the components  12 ,  14  may be moved while the laser head remains stationary. The second laser pattern  110  may include a plurality of parallel lines  112 . As discussed above, it may be desirable to avoid overheating the metal component  12 . Thus, the second laser pattern  110  may be different than the first laser pattern  76  of the laser treatment for the first surface  18  ( FIGS. 4-5 ). In one example, the second laser pattern  110  may include two or more subsets of lines  112 , such as a first subset  112   a , a second subset  112   b , a third subset  112   c , and so on. The laser head may move in the first direction  80  to create a first line of the first subset  112   a . The laser head may then move in the second direction  86  and then in the first direction  80  to create another line  112   a  in the same subset. A second distance  114  between lines of the same subset may be greater than or equal to about 0.5 mm and less than or equal to about 5 mm. After the second laser beam  104  has completed the first scan set (e.g., moved through all of the lines  112   a  of the first subset), it may move in a third direction  116  opposite the second direction  86  to begin a second scan set. After the second laser beam  104  has completed the second scan set (e.g., moved through all of the lines  112   b  of the second subset), it may move in the third direction  116  to begin a third scan set. The above process may be repeated until the second laser pattern  110  is complete. As shown in  FIG. 7 , ellipses  118  in the second laser pattern  110  represent additional scan groups (e.g., to create a fourth subset and a fifth subset). In certain variations, the lines  112  of the second laser pattern  110  may be evenly spaced apart from one another. It may be desirable that the lines  112  do not overlap or cross one another to avoid overheating. 
     Although the second laser pattern  110  is shown as substantially aligned with the first axis  34  and substantially perpendicular to the second axis  36 , alternative laser patterns are contemplated. Because the second laser beam  104  is used to heat the components  12 ,  14  rather than to form a particular topography, the orientation of the laser pattern may be varied. In one example, the laser pattern may be aligned with the second axis  36 . In another example, the laser pattern may not be aligned with either axis  34 ,  36 . A person skilled in the art would appreciate that any laser pattern that does not overheat and damage the metal component  12  may be employed. 
     The second laser beam may have a power of greater than or equal to about 500 W and less than or equal to about 2000 W, optionally greater than or equal to about 800 W and less than or equal to about 1800 W, optionally greater than or equal to about 1200 W and less than or equal to about 1500 W, and optionally about 1400 W. The second laser beam  104  may have a scan speed of greater than or equal to about 100 mm/s and less than or equal to about 2 m/s, optionally greater than or equal to about 300 mm/s and less than or equal to about 1.5 m/s, optionally greater than or equal to about 500 mm/s and less than or equal to about 1 m/s, and optionally about 750 mm/s. The second laser beam  104  may create a spot size of greater than or equal to about 100 μm and less than or equal to about 500 μm, optionally greater than or equal to about 120 μm and less than or equal to about 300 μm, optionally greater than or equal to about 150 μm and less than or equal to about 200 μm, and optionally about 180 μm. 
     Referring now to  FIGS. 8 and 9A-9B , alternative laser patterns for the laser surface treatment are shown.  FIG. 8  depicts a metal component  140  having a first surface  142 . A laser pattern  144  includes a first plurality of parallel lines  146  and a second plurality of parallel lines  148 . The lines of the first plurality of parallel lines  146  are substantially perpendicular to the lines of the second plurality of parallel lines  148 . Thus, when the metal component  140  is joined to a reinforced polymeric composite component, the resulting joint has a high lap shear strength in two directions. 
       FIG. 9A  depicts a metal component  160  having a first surface  162 . A laser pattern  164  includes a plurality of concentric circles  166 . Thus, when the metal component  160  is joined to a reinforced polymeric composite component, the resulting joint has a 360° high lap shear strength. In certain embodiments, the concentric circles  166  of the laser pattern  164  may yield grooves  168  having different depths. For example, grooves  168   a  near a center of the concentric circles  166  may be deeper than outermost grooves  168   b . The depth of a groove can be controlled by applying different laser power to create grooves having different depths (i.e., a higher power to create a deeper groove and a lower power to create a shallower groove) or applying different quantities of scans/passes for different grooves (i.e., more scans to create a deeper groove and fewer scans or a single scan to create a shallower groove). 
     Example 1—Passivation Layer 
     Referring now to  FIG. 10 , a first sample includes an aluminum component without a laser-treated surface. A second sample includes an aluminum component that has a laser-treated surface. X-ray photoelectron spectroscopy (XPS) is performed on the first and second samples to obtain depth profiles. An x-axis  180  represents depth measured in nanometers (nm) from a first surface (similar to the first surface  18 ) toward a third surface (similar to the third surface  24 ). A y-axis  182  represents an atomic percent of various components. 
     A first XPS depth profile  184  represents aluminum content in the first sample. A second XPS depth profile  186  represents oxygen content in the first sample. A third XPS depth profile  188  represents aluminum content in the second sample. A fourth XPS depth profile  190  represents oxygen content in the second sample. The atomic percentages shown for the first and second samples may not add up to 100% because XPS depth profiles of other components are omitted for readability (e.g., carbon, which is typically present in XPS depth profiles, is omitted). 
     A comparison of the second and fourth XPS depth profiles  186 ,  190  demonstrates that oxygen content is generally higher in the second sample, indicating the presence of an aluminum-oxide (Al 2 O 3 ) passivation layer. The oxygen content in the first sample is consistently lower than the oxygen content in the second sample. For example, a surface oxygen content (at a depth of 0 nm) of the second sample is greater than about 35%. At a depth of about 100 nm, the second sample oxygen content is greater than about 40%. At a depth of about 200 nm, the second sample oxygen content is greater than about 30%. At a depth of about 250 nm, the second sample oxygen content is greater than about 25%. At a depth of about 300 nm, the second sample oxygen content is greater than about 20%. At a depth of about 400 nm, the second sample oxygen content is greater than about 15%. At a depth of about 500 nm, the second sample oxygen content is greater than about 10%. 
     Example 2—Initial Lap Shear Strength and Degradation of Lap Shear Strength Over Time 
     With reference to  FIGS. 11-14 , a first sample includes a metal-polymeric composite assembly having an aluminum component without a laser-treated surface. A second sample  200  includes a metal-polymeric composite assembly having an aluminum component that has a laser-treated surface. A third sample includes a metal-polymeric composite assembly having a stainless steel (316 stainless steel) component that has a laser-treated surface. Each of the first, second, and third samples includes a carbon-fiber reinforced nylon (nylon 6) composite having greater than or equal to about 20% and less than or equal to about 40% carbon fiber by weight. 
     Lap shear testing is performed to determine the lap shear strength of each of the samples. Similar samples are aged to test for corrosion. Referring to  FIG. 13 , an x-axis  210  represents age in years. A y-axis  212  represents lap shear strength in kN. A first curve  214  corresponds to the first sample, a second curve  216  corresponds to the second sample  200 , and a third curve  218  corresponds to the third sample. 
     A typical strength requirement for automotive joints is 6 kN. A joint of the first sample is always less than 6 kN. Instead, the first sample has an initial lap shear strength of about 2.792 kN. The second and third samples both have initial lap shear strengths that exceed the 6 kN threshold. The second sample has an initial lap shear strength of about 9.415 kN. The third sample has an initial lap shear strength of about 7.382 kN. 
     Similar samples, which will also be referred to as first, second, and third samples (i.e., the first sample includes untreated aluminum, the second sample includes laser-treated aluminum, and the third sample includes laser-treated stainless steel), are aged to allow time for corrosion and tested at 2.5 years. The first sample corrodes over 2.5 years so that the joint is completely degraded at the 2.5 year mark. A joint of the second sample  200 , which is believed to have an aluminum oxide (Al 2 O 3 ) passivation layer disposed between the metal and the composite, remains intact after 2.5 years with a lap shear strength of about 7.760 kN. As shown in  FIG. 12 , after 2.5 years, a break  230  occurs in a reinforced polymeric composite component  232  of the first sample  200  after 2.5 years rather than at a joint  234 . The third sample has a lap shear strength of about 6.355 kN after 2.5 years. Thus, both of the second and third samples having the laser-treated metal component remain about the 6 kN threshold after 2.5 years. 
     Additional similar samples, which will also be referred to as first, second, and third samples (i.e., the first sample includes untreated aluminum, the second sample includes laser-treated aluminum, and the third sample includes laser-treated stainless steel), are aged to allow time for corrosion and tested at 5 years. Again, the first sample corrodes so that the joint is completely degraded at the 5 year mark. A joint of the second sample  200 , which is believed to have an aluminum oxide (Al 2 O 3 ) passivation layer disposed between the metal and the composite, remains intact after 5 years with a lap shear strength of about 6.958 kN. The third sample has a lap shear strength of about 6.485 kN after 5 years. Thus, both of the second and third samples having the laser-treated metal component remain about the 6 kN threshold after 5 years. 
     Referring to  FIG. 14 , a percentage degradation of lap shear strength of the first, second, and third samples over time is shown. An x-axis  240  represents time in years. A y-axis  242  represents percentage degradation of lap shear strength ((initial lap shear strength−current lap shear strength)/initial lap shear strength). A first curve  244  corresponds to the first sample, a second curve  246  corresponds to the second sample  246 , and a third curve  248  corresponds to the third sample. Degradation of the third sample, including stainless steel, is low when compared to the aluminum samples because stainless steel is not corrosive. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.