Patent Application
20200032373
Aluminum alloys are strong, lightweight, easily formed, and easily machined. Accordingly, numerous products are made from aluminum alloys. Some aluminum alloys offer yet another advantage for consumer-product manufacture—namely, that the surface of the formed aluminum-alloy component may be further conditioned via the electrochemical process of anodization. Under suitable conditions, anodization of a formed aluminum-alloy component yields a smooth, wear-resistant, and visually appealing surface.
Examples are disclosed that relate to strengthened aluminum-alloy composite materials and associated methods of manufacture. One example provides an article comprising a bulk layer of an aluminum-alloy composite and a surface layer. The bulk layer includes an aggregate dispersed in an aluminum-alloy matrix, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less. The surface layer comprises an anodized form of the bulk layer.
Another example provides an article formed from an aluminum-alloy composite, the article comprising a bulk layer of the aluminum-alloy composite and a surface layer. The bulk layer includes an alumina-powder aggregate dispersed in an aluminum-alloy matrix, the alumina-powder aggregate having an average particle size of 20 microns or less. The surface layer comprises an anodized form of the bulk layer.
Another example provides a method of manufacture of an aluminum-alloy composite article, the method comprising melting an aluminum alloy; dispersing an aggregate in the melted aluminum alloy to form a dispersion, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix and having an average particle size of 100 microns or less; cooling the dispersion to below a solidification point of the dispersion to form an aluminum-alloy composite; extruding the aluminum-alloy composite to form an aluminum-alloy composite extrusion; and anodizing the aluminum-alloy composite extrusion.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.
This disclosure is presented by way of example and with reference to the drawing figures listed above. Components, process steps, and other elements that may be substantially the same in one or more of the figures are identified coordinately. It will be noted, however, that elements identified coordinately may also differ to some degree. It will be further noted that the figures are schematic and generally not drawn to scale. Rather, the various drawing scales, aspect ratios, and numbers of components shown in the figures may be purposely distorted to make certain features or relationships easier to see.
As noted above, high-strength, lightweight articles may be formed from various aluminum alloys. In some areas of manufacture, there is ever-increasing demand to further improve the strength-to-weight ratios of aluminum-alloy components. The demand is particularly evident in the manufacture of consumer-electronics. Laptop computers, tablet computers, and cell phones, for example, typically comprise a rigid shell or armature formed from an aluminum alloy. As the demand for display size in these devices continues to increase, it becomes necessary to engineer structural components from intrinsically stronger materials, in order to keep the weight of the devices within an acceptable range.
Table 1 shows the tensile strength of various aluminum alloys, along with certain other properties.
The 5xxx- and 6xxx-series aluminum alloys are popular choices for structural and enclosure components of consumer-electronics devices, due in part to their malleability, ductility, and ease of extrusion. For instance, the shell of a laptop computer may be cold formed from a thin, rolled sheet, or machined from an extrusion. A sheet of a 5xxx- or 6xxx-series aluminum alloy may be suitable for this application, when rolled to a thickness of 500 to 1000 microns (μm) or greater. When rolled thinner, however, the sheet may lack sufficient strength.
It will be noted, based on the Table above, that certain alloys of 7xxx-series aluminum may be significantly stronger than those of the 5xxx- or 6xxx-series, and may be used to make rolled sheets or extrusions of suitable strength, even when the thickness is 1 millimeter (mm) or lower. However, 7xxx-series aluminum may be disadvantageous for some consumer-product applications, as these alloys may be poor substrates for electrochemical anodization. In many instances, an anodized surface finish is desirable for structural components of a consumer-electronics device. Under suitable conditions, anodization of a formed aluminum-alloy component yields a smooth, wear-resistant, and visually appealing surface. However, anodization of a 7xxx-series aluminum article may cause numerous surface defects (cosmetic and otherwise), and may result in an overall low product yield.
Accordingly, examples are disclosed that relate to strengthened aluminum-alloy composites based on 5xxx- and 6xxx-series aluminum alloys, which may reliably provide substantially defect-free surfaces under electrochemical anodization conditions. As described in more detail below, a suitably strong, anodizable material may comprise an aluminum alloy composite in which a continuous alloy matrix is interrupted by a dispersion of small, materially hard particles, which are insoluble in the alloy. Without tying this disclosure herein to any particular theory, the strengthening effect may be somewhat analogous to the effect of precipitation hardening in conventional metallurgy, wherein the dispersion of insoluble particles limits the movement of dislocations within the alloy matrix, therefore strengthening the material. A disadvantage of precipitation hardening, relative to the approach here disclosed, is that if precipitates were to separate from the solid solution as large particles (due to slow cooling), the strengthening effect on the aluminum alloy may be limited. Similarly, if large precipitate particles fail to re-dissolve in the solid solution during solution treatment, the hardening effect may be minimal. On the other hand, if large precipitate particles did dissolve in the solid solution during solution treatment, but the holding time were too long, grain growth would be inevitable, which may result in lower strength and in discoloration after anodization.
At 20 of method 16, an aggregate is dispersed (i.e., substantially uniformly mixed) into the molten aluminum alloy to form a dispersion. In general, the aggregate selected for dispersion may be a solid which is unreactive in the melt. In some examples, the aggregate added to the molten aluminum alloy may comprise 1 to 20 percent by mass of the aluminum-alloy composite. Compositionally, the aggregate may include a carbide, nitride, or oxide in the form of a freely flowing powder. In more particular examples, the aggregate may include alumina powder of any suitable mesh size. The average particle size of the aggregate may be 100 microns (μm) or less, 20 μm or less, 10 μm or less, 5 μm or less, or 1 μm or less, for instance. The morphology of the aggregate particles is not particularly limited, but may include substantially spherical or oblong particles. In some implementations involving subsequent extrusion, particles with very high aspect ratios (e.g., elongate fibers) may be avoided.
At 22 of method 16, the dispersion is cooled to below its solidification point to form an aluminum-alloy composite. Cooling may be accomplished rapidly, in order to avoid or limit separation of the dispersed aggregate from the aluminum alloy matrix.
Subsequently, in method 16, the aluminum-alloy composite may be extruded or optionally rolled. If extrusion is selected, then at 24, an aluminum-alloy composite extrusion is formed. At 25, the aluminum-alloy composite extrusion may be machined, optionally, to the desired shape. If rolling is selected, then at 26, the aluminum-alloy composite may be rolled to form a sheet. At 28, the rolled sheet may be optionally formed, cut and/or machined into the desired shape. It will be noted that extrusion step 24 and rolling step 26 may be enacted independently of the other or in combination, and in general, each of steps 24 through 28 are optional. Typically, extruded aluminum can be made to near net shape in the extrusion direction, and then machined to a desired shape. Rolled aluminum sheet, by contrast, is typically formed to the desired shape, and may or may not be subject to subsequent machining.
At 30 of method 16, the aluminum-alloy article is anodized. The anodization process may include any suitable cleaning or chemical etching step (e.g., acid or base etching) followed by electrochemical oxidation in a suitable electrolyte solution—e.g., an aqueous sulfuric acid or suitable carboxylic acid solution.
Continuing in
Hardened aluminum-alloy articles as described above may be stronger than articles of equal thickness made from unhardened aluminum alloys. This advantage enables the manufacture of strong, lightweight products for a variety of applications. Moreover, the articles formed using the above methods may present an attractive, wear-resistant outer surface, which is desirable in various manufacturing areas.
Another example provides an article comprising a bulk layer of an aluminum-alloy composite, the aluminum-alloy composite including an aggregate dispersed in an aluminum-alloy matrix, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less; and a surface layer comprising an anodized form of the bulk layer.
In some implementations, the aluminum-alloy matrix includes a 5xxx-series aluminum alloy. In some implementations, the aluminum-alloy matrix includes a 6xxx-series aluminum alloy. In some implementations, the aggregate includes one or more of a carbide, nitride, or oxide. In some implementations, the aggregate includes alumina powder. In some implementations, the aggregate has an average particle size of 20 microns or less. In some implementations, the aggregate has an average particle size of 5 microns or less. In some implementations, the aggregate comprises 1 to 10 percent by mass of the aluminum-alloy composite. In some implementations, the surface layer is 1 micron or greater in thickness. In some implementations, the article is a body of a portable computing device.
Another example provides an article formed from an aluminum-alloy composite, comprising a bulk layer of the aluminum-alloy composite, the aluminum-alloy composite including an alumina-powder aggregate dispersed in an aluminum-alloy matrix, the alumina-powder aggregate having an average particle size of 20 microns or less; and a surface layer comprising an anodized form of the bulk layer.
In some implementations, the aluminum-alloy matrix includes a 5xxx-series aluminum alloy. In some implementations, the aluminum-alloy matrix includes a 6xxx-series aluminum alloy. In some implementations, the aggregate has an average particle size of 10 microns or less. In some implementations, the aggregate has an average particle size of 1 micron or less. In some implementations, the aggregate comprises 1 to 20 percent by mass of the aluminum-alloy composite.
Another example provides a method of manufacture of an aluminum-alloy composite article, the method comprising: melting an aluminum alloy; dispersing an aggregate in the melted aluminum alloy to form a dispersion, the aggregate being solid and unreactive in a melt of the aluminum-alloy matrix, and having an average particle size of 100 microns or less; cooling the dispersion to below a solidification point of the dispersion to form an aluminum-alloy composite; extruding the aluminum-alloy composite to form an aluminum-alloy composite extrusion; and anodizing the aluminum-alloy composite extrusion.
In some implementations, the method further comprises rolling the aluminum-alloy composite extrusion prior to anodizing. In some implementations, the aggregate includes alumina powder. In some implementations, the aggregate has an average particle size of 20 microns or less.
It will be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. As such, various acts illustrated and/or described may be performed in the sequence illustrated and/or described, in other sequences, in parallel, or omitted. Likewise, the order of the above-described processes may be changed.
The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.
