Patent Application
20160326624
Devices such as mobile phones, tablets and portable (e.g. laptop or palm) computers are generally provided with a casing. This casing typically provides a number of functional features, for example protecting the device from damage.
Increasingly, consumers are also interested in the aesthetic properties of the casing. Furthermore, as devices such as mobile phones, tablets and portable computers are typically designed for hand held functionality, consumers also consider the weight of the device.
By way of non-limiting examples, device casings and processes of manufacturing such casings according to the present disclosure will be described with reference to the following drawings in which
The present disclosure describes a method of treating the surface of a metal substrate, for example the metal surface of a casing for a device. The method comprises forming a metal layer on the substrate using a thermal spray process followed by an electrochemical treatment to the metal layer to provide desired physical and aesthetic properties.
The use of thermal spray processes to apply a metal layer on the surface of the metal substrate can enhance the adhesion of the metal layer to the metal substrate when compared to application of metal oxides by thermal spray processes due to the relative smaller size of the metal to its oxide, therefore better filling of the pores of the metal substrate. This in turn can result in a more visually appealing product for highly porous metal substrates such as magnesium and its alloys, where multiple surface coatings can be required, resulting surfaces that are aesthetically undesirable, for example the coating looking cheap and “painted on”.
Furthermore, due to the substantially lower melting point of metals as compared to their oxides, energy requirements to perform the thermal spray process can be greatly reduced. The relatively lower melting point also makes thermal spray processes possible for highly reactive, light metals that can burn when exposed to high temperatures.
Referring to
For example, the metal substrate (150) may be magnesium or its alloys. Use of magnesium in industry is typically limited due to a number of undesirable properties such as its high reactivity, tendency towards being corroded, high-temperature creep properties and flammability. Certain magnesium alloys can also provide further undesirable properties, for example magnesium alloys including iron, nickel, copper and/or cobalt increase tendency for the corrosion of the magnesium in the alloy.
However, magnesium is a strong, light weight and low density metal. These are particularly desirable properties for casings of electronic devices. Furthermore, although magnesium can be significantly more expensive than other light metals, casting and other formation processes are easier, more economical and faster with magnesium than for other light metals, for example aluminium.
Although, as noted above, certain magnesium alloys produce undesirable properties; the addition of small amounts of aluminium, zinc and/or manganese can positively alter the physical properties of magnesium. For example, the addition of manganese can increase corrosion resistance, while the addition of aluminium and zinc promote precipitation hardening, resulting in an alloy with a strength-to-weight ratio comparable to those of certain aluminium alloys and alloy steels. However, as discussed above, working and shaping the magnesium alloy is easier, more economical and faster than these alloys of comparable strength-to-weight ratio.
As seen in
Thermal spray processes (120) are processes in which melted or heated materials are sprayed onto a surface. The feedstock may be heated by electrical (plasma or arc) or chemical (combustion flame) means.
Thermal spray processes can provide thick layers of the feedstock over a large area at high deposition rates as compared no other processes such as electroplating, physical and chemical vapour deposition. In thermal spray processes, the feedstock materials are fed in powder or wire form, heated to a molten or send-molten state and accelerated towards the substrate in the form of particles, the particles typically sized from 3-200 nm.
A propelling fluid source such as compressed air for delivering a propelling fluid to an arc point, propelling molten metal particle created at the arc point of the two wires on to the substrate. The arc point is the location at which the wires come into contact an electrically arc based on their opposing electrical currents. The molten metal particle are created at the arc point which is then transmitted to the surface by the propelling gas. A directional nozzle may also be included to more accurately direct the molten metal onto the metal substrate.
One example of a thermal spray process is wire arc spraying, an example of which is shown in
In order to transmit the molten metal particles (230) onto the substrate, a propellent is used, for example a gas stream (240) provided by a compressed gas source. A directional nozzle (250) may also be used to more accurately direct the molten metal particles (230) on to the metal substrate (150).
Other methods of thermal spray processes that may be used include plasma spraying, detonation spraying, flame spraying, high velocity oxy-fuel coating spraying (HVOF), warm spraying and cold spraying. The thickness of the metal layer formed by the thermal spray process may be in the order of 1-100 μm, and in particular 5-50 μm.
Feedstocks currently used for providing a metal finish to a substrate are typically metal oxides in order to provide certain physical and aesthetic properties to the substrate being treated. However, metal oxides have a significantly higher melting point when compared to their pure metals, for example aluminium has a melting point of around 660° C. whereas aluminium oxide (Al2O3) has a melting point of 2,072° C. As a result, significantly lower energy requirements are needed to produce molten metal required for thermal spray processes as compared to the energy requirements for metal oxides.
In addition, as a result of the lower temperatures of molten metals as compared to molten metal oxides, spray coating techniques using metals can be suitable for more reactive light metals such as magnesium which present a fire hazard and may burn when exposed to high temperatures.
Furthermore, the resulting metal layer applied by thermal spray processes better adheres to the porous metal substrate when compared to metal oxides applied by the same process due to the metal particles being smaller and therefore providing increased surface area of contact between the metal applied by the thermal spray process and the porous metal substrate.
As shown in
Properties of the electrochemically formed second layer or coating (170) such as porosity, hardness, colour, conductivity, wear resistance, corrosion resistance, thickness and adherence can be varied by varying the parameters of the electrochemical treatment. Such parameters include: the type of process used (e.g. anodizing, micro-arc oxidation or electrophoretic deposition); the chemical solution in which the treatment occurs (e.g. temperature and composition); the potential (e.g. pulse or continuous, direct current or alternating current, frequency, duration and voltage) and the processing time.
As shown in
It will be appreciated that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/013982 | 1/31/2014 | WO | 00 |
