BACKGROUND

Micro-Arc Oxidation (MAO) is an electrochemical surface treatment process for metals (including alloys), to generate oxide coatings (such as a MAO Layer of ceramic material) on surfaces of the metals. The MAO layer can have good insulation properties, high hardness, wear resistance and corrosion resistance.

However, the MAO layer formed on a metal surface can generate cracks. The presence of cracks can sometimes destroy the entire MAO layer, which may lead to the peeling of the MAO layer from the surface of the metal substrate, and influence the protective function of the MAO layer on the metal substrate. For example, adopting a structure of a metal substrate - MAO layer as a housing of a mobile phone can result in peeling of coating material that is coated on the MAO layer on the surface of the housing because of the cracks. Especially, the peeling phenomenon can be more visible at the edges and corners of the housing, and thus may detract from the appearance of the mobile phone.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present disclosure, reference should be made to the Detailed Description below, in conjunction with the following drawings in which like reference numerals refer to corresponding parts throughout the figures.

Figure 1 is a flow diagram showing a method of treating the surface of a metal according to an example of the present disclosure;

Figure 2A illustrates an exemplary structure of an indented structure of a metal substrate in the present disclosure;

Figure 2B illustrates an exemplary structure of an indented structure of a metal substrate in the present disclosure;

Figure 2C illustrates an exemplary structure of an indented structure of a metal substrate in the present disclosure; Figure 2D illustrates an exemplary structure of an indented structure of a metal substrate in the present disclosure;

Figure 2E illustrates an exemplary structure of an indented structure of a metal substrate in the present disclosure;

Figure 2F illustrates an exemplary structure of an indented structure of a metal substrate in the present disclosure;

Figure 2G illustrates an exemplary structure of an indented structure of a metal substrate in the present disclosure;

Figure 3 is an exemplary diagram showing a housing made via die casting, thixomolding and forging according to an example of the present disclosure;

Figure 4 is an exemplary diagram showing a process of laser engraving in the present disclosure;

Figure 5 is an exemplary diagram showing a pattern formed of the indented structure on the surface of the metal substrate in the present disclosure;

Figure 6 is an exemplary diagram showing a surface structure of the metal substrate according to the present disclosure;

Figure 7 is an exemplary diagram showing a structure including a topcoat formed on the surface of the metal substrate in the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to examples, which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. Also, the figures are illustrations of an example, in which components or procedures shown in the figures are not necessarily essential for implementing the present disclosure. In other instances, well-known methods, procedures, and components have not been described in detail so as not to unnecessarily obscure aspects of the examples. As shown in Figure 1, an example of the present disclosure provides a method of oxidation treatment on metal surface. The method includes the following procedures.

At block 1, an indented structure is formed on a surface of a metal substrate.

At block 2, micro-arc oxidation is performed on the surface of the metal substrate having the indented structure, to form a MAO layer that covers the surface of the metal substrate.

Compared with a conventional metal substrate with a plain surface, the metal substrate with the indented structure on one of its surfaces may provide better adhesion for the MAO layer, and greater resistance to cracking.

Specifically, the indented structure can be a continuous or non-continuous repeated concave or convex structure on the surface of a metal substrate. In an example, the width of the concave or convex structure can be more than 1 um (micrometer), and the depth of the concave or convex structure can be less than five eighth of the thickness of the metal substrate. The cross-section of the concave or convex structure may exhibit an island geometric structure of triangular, square, circular arc or trapezoid shapes.

As shown in Figure 2A, the indented structure 2 is a geometric structure whose cross section exhibits multiple continuous islands on the metal substrate 1. In an example, the island structure is a structure with continuous triangles, of which the cross section exhibits continuous concave or convex structures of multiple continuous triangles, wherein the width of each triangle is more than 1 um, and the depth of each triangle is less than the five eighths of the thickness of the metal substrate.

In an example shown in Figure 2B, the indented structure 2 is the geometric structure whose cross section exhibits multiple continuous islands on the metal substrate 1, wherein the island structure is a structure of continuous squares. In Figure 2B, the cross section of the island structure exhibits continuous concave or convex structures of multiple continuous squares, wherein the width of each square is more than 1 um, and the depth of each square is less than the five eighths of the thickness of the metal substrate.

In an example shown in Figure 2C, the indented structure 2 is an island geometric structure whose cross section exhibits multiple continuous islands on the metal substrate 1, the island structure is the structure of continuous circular arcs, the cross section thereof exhibits continuous concave structures of multiple continuous circular arc, wherein the width of each circular arc is more than 1 um, and the depth of each circular arcs is less than the five eighths of the thickness of the metal substrate.

In an example shown in Figure 2D, the indented structure 2 is the geometric structure whose cross section exhibits multiple continuous islands on the metal substrate 1, the island structure is the structure of continuous right trapezoid, the cross section thereof exhibits continuous concave structures of multiple right trapezoid, wherein the width of each right trapezoid is more than 1 um, and the depth of each right trapezoid is less than the five eighths of the thickness of the metal substrate.

In an example shown in Figure 2E, the indented structure 2 is the geometric structure whose cross section exhibits multiple continuous trapezoids on the metal substrate 1, the cross section exhibits continuous concave or convex design structures of multiple continuous trapezoid, wherein the width of each trapezoid is more than 1 um, and the depth of each trapezoid is less than the five eighths of the thickness of the metal substrate.

In an example shown in Figure 2F, the indented structure 2 is the geometric structure whose cross section exhibits multiple continuous islands on the metal substrate 1, the island structure is the structure in which one side is rectilinear and the other side is circular arc, the cross section thereof exhibits multiple continuous concave structures in which one side is rectilinear and the other side is continuous circular arc, wherein the width of the structure is more than 1 um, and the depth of the structure is less than the five eighths of the thickness of the metal substrate.

In an example shown in Figure 2G, the indented structure 2 is the geometric structure whose cross section exhibits multiple continuous islands on the metal substrate 1, the island structure is the continuous structure in which both sides are circular arc and the top edge is rectilinear, the cross section thereof exhibits multiple continuous concave structures in which both sides are circular arc and the top edge is rectilinear, wherein the width of the structure is more than 1 um, and the depth of the structure is less than the five eighths of the thickness of the metal substrate. In an example, the metal substrate 1 can be made of one of aluminum, titanium, magnesium, lithium, niobium, zinc and iron, or is the alloy of at least two thereof. In the present disclosure, the above indented structure, i.e., continuous or non-continuous concave or convex structures, or continuous or non-continuous island structures can be formed by the surface of the metal substrate through die casting, thixomolding, Computer Numerical Control (CNC), chemical etching, laser engraving and forging, for instance.

As shown Figure 3, die casting, thixomolding and forging press metal substrate 1 using cavity 10, there is a press back which is complementary to the indented structure 2 on metal substrate 1 on the cavity 10, the required shape of the indented structure 2 is formed on the surface of the metal substrate 1 by pressing the metal substrate 1 through press back.

Also as shown in Figure 4, laser engraving engraves the surface of the metal substrate 1 using a laser etching machine, so as to remove the material on the surface of the metal substrate and form the required shape of the indented structure 2 on the surface of the metal substrate 1.

Chemical etching coats photoresist on the surface of metal substrate 1, develops the photoresist using a photoetching machine to form patterned photoresist, and etches the surface of metal substrate 1 using chemical reagent to form the required indented structure 2, finally remove the residual photoresist on the surface of metal substrate 1 by the method such as washing.

The above indented structure can be used to design the surface geometry of a metal substrate. As shown in figure 5, the distribution of the above indented structure is designed as the required pattern on the metal substrate 1. After the MAO which is conducted subsequently and forming topcoat, the ink or resin material used by the topcoat permeates into the gaps of the indented structure, which enhances the adhesive strength of the ink or resin material, and makes it difficult to grind off the pattern. The designed pattern can comprises the designed pattern on the surfaces of various products, such as the pattern of a trademark, company Logo and arabesquitic pattern etc.

The process of MAO in block 2 can be conducted by any suitable method, for example, placing the metal substrate whose surface comprises the indented structure of block 1 in an electrolyte, producing ceramic membrane layer, i.e. MAO layer, which is mainly composed of the metal oxide of the metal substrate on the surface of the metal substrate by instantaneous high temperature and high pressure generated by arc discharge on the surface of a metal substrate through the combination of the electrolyte and corresponding process parameters.

Take the example shown in figure 2B as an example, as shown in figure 6, the surface structure of the metal substrate forms the surface structure of the metal provided by the present disclosure after block 2, the structure comprises metal substrate 1 and MAO layer 3 formed on the surface of the metal substrate 1 by micro-arc oxidating, indented structure 2 is formed on the surface of the metal substrate 1, and the MAO layer 3 is on the indented structure 2. More specifically, the MAO layer 3 covers the surface of the indented structure 2 of the entire the metal substrate 1 comprising the side surface that debosses into the metal substrate 1; comparing with the outside surface formed just by the micro-arc oxidating of block 2 other than block 1, the outside surface of MAO layer 3 formed in such a way has increased surface area, and the degree of roughness thereof is also increased. The stress of MAO layer 3 former thereupon can be eliminated between the concave or convex features of the indented structure 2, and further reduce the stress of the MAO layer 3 formed by MAO of the surface of the metal substrate 1. This can effectively reduce the generation of cracks in the formed MAO layer 3. The use thereof in the treatment of the housing of a product, such as mobile phones, can effectively reduce the cracks and painting peel off phenomenon of the coating material of a product housing.

When the above method is applied to the surface treatment of a product, a topcoat is formed on the formed MAO layer after finishing the Micro-Arc oxidation on the surface of the metal substrate (block 2). The topcoat can be formed by electrophoretic deposition, spray coating, in mold decoration, nano-imprint lithography, ink transfer or inkjet printing and other methods. The material of the topcoat can comprise a polymeric coating, an inorganic coating or a hybrid coating. The main function of the topcoat is aesthetic, but the topcoat also provides certain protective to the housing of a product. As shown in Figure 7, the material of topcoat 4 can be formed on the MAO layer 3, such as ink, resin etc. and can enter the concave part 21 of the indented structure 2, increasing the contact areas between topcoat 4 and MAO layer 3, and enhancing the adhesion of topcoat 4, which further effectively prevents the topcoat 4 from peeling off. The above method of oxidation treatment of a metal surface and structure of a metal surface can be applied to the housing of a device such as an electronic device or a computing device including tablet, laptop, mobile phone, smart phone, MP3 and MP4 player, or the like.

There has been described a method of oxidation treatment of a metal surface and the structure of a metal surface. As an indented structure is formed on the surface of a metal substrate, the stress of the MAO layer can be reduced between the concave or convex features of the indented structure, which can reduce the stress of the MAO layer formed by Micro-Arc rupture on the surface of the metal substrate, and can effectively prevent or reduce the generation of cracks in the formed MAO layer. In addition, the indented structure can be formed as a patterned layout on the surface of the metal substrate, the patterned layout of the indented structure can be designed according to an aethestic design, such as a company logo, trademark and/or specific design graphic for instance, which can further enhance the adhesion of the design feature finally formed on the metal surface and make it difficult for the design feature to peel off. Moreover, when a subsequent coating process is conducted on an MAO layer where the indented structure is formed using ink or resin material for instance, the adhesion of topcoat is enhanced, which further prevents the topcoat from peeling off.

The foregoing description, for purposes of explanation, has been described with reference to specific examples. However, the illustrative discussions above are not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The examples were chosen and described in order to best explain the principles of the present disclosure and its practical applications, to thereby enable others skilled in the art to best utilize the present disclosure and various examples with various modifications as are suited to the particular use contemplated.