2008-2-13 17:23
Heifetz
金属表面工艺我不懂:( 我找了点质料，但，都是英文的。。。:@ 这种工艺有很多颜色。见图。。。
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Anodized aluminum
Aluminum alloys are anodized to increase corrosion resistance, to increase surface hardness, and to allow dyeing (coloring), improved lubrication, or improved adhesion.
When exposed to air at room temperature, or any another gas containing oxygen, pure aluminum self-passivates by forming a surface layer of amorphous aluminum oxide 2 to 3 nm thick which provides very effective protection against corrosion. Aluminum alloys typically form a thicker oxide layer, 5-15 nm thick, but tend to be more susceptible to corrosion. Aluminum alloy parts are anodized to greatly increase the thickness of this layer for corrosion resistance. Generally, corrosion resistance is significantly decreased by alloying elements or impurities such as copper, iron, and silicon.,[4] so 2000, 4000, and 6000-series alloys tend to be most susceptible. Most aluminum aircraft parts, architectural materials, and consumer products are anodized. Anodized aluminum can be found on mp3 players, flashlights, cookware, cameras, sporting goods, window frames, roofs, in electrolytic capacitors, and on many other products both for corrosion resistance and the ability to retain dye. Although anodizing only has moderate wear resistance, the deeper pores can better retain a lubricating film than a smooth surface would. For example, the cylinders of a modern BMW aluminum V8 cylinders have no loose liner: instead, the walls are hard anodized. This complicates a reboring operation (although not common, given the longevity of modern engines due to improved lubricants), as the hard coating must be restored if the block is rebored. (Earlier liner-free aluminum block designs use specific aluminum alloys, with softer components chemically etched away to expose the harder portions of the mixed crystal structure.)
Anodized coatings have a much lower thermal conductivity and coefficient of linear expansion than aluminum. As a result, the coating will crack if exposed to the "thermal stress" of a 60°C change from the anodizing temperature, or in general any temperature gradient caused by caused by a rapid change in ambient temperature, although aluminum is less susceptible to this, due to high thermal conductivity. The coating can crack, but it will not peel. The melting point of aluminum oxide is 2050°C, much higher than pure aluminum's 658°C.(This can make welding more difficult.) When aluminum is oxidized, it doubles in volume. So in a typical aluminum anodization process, the aluminum oxide grows down into the surface, and at the same time grows an equal distance out from the surface. So anodizing will increase the part dimensions on each surface by half of the oxide thickness. For example a coating that is (2 μm) thick, will increase the part dimensions by (1 μm) per surface. If the part is anodized on all sides, then all linear dimensions will increase by the oxide thickness.
Process
Before being anodized, wrought alloys are cleaned in either a hot soak cleaner or in a solvent bath and may be etched in sodium hydroxide (normally with added sodium gluconate), ammonium bifluoride or brightened in a mix of acids. Cast alloys are normally best just cleaned due to the presence of intermetallic substances unless they are a high purity alloy such as LM0.
The anodized aluminum layer is grown by passing a direct current through an electrolytic solution, with the aluminum object serving as the anode (the positive electrode). The current releases hydrogen at the cathode (the negative electrode) and oxygen at the surface of the aluminum anode, creating a build-up of aluminum oxide. Alternating current and pulsed current is also possible but rarely used. The voltage required by various solutions may range from 1 to 300 V DC, although most fall in the range of 15 to 21 V. Higher voltages are typically required for thicker coatings formed in sulfuric and organic acid. The anodizing current varies with the area of aluminum being anodized, and typically ranges from 0.3 to 3 amperes of current per square decimeter (15.5 square inches).
Aluminum anodizing is usually performed in an acid solution which slowly dissolves the aluminum oxide. The acid action is balanced with the oxidation rate to form a coating with microscopic pores, 10-150 nm in diameter.These pores are what allows the electrolyte solution and current to reach the aluminium substrate and continue growing the coating to greater thickness beyond what is produced by autopassivation.[6] However, these same pores will later permit air or water to reach the substrate and initiate corrosion if not sealed. They are often filled with colored dyes and/or corrosion inhibitors before sealing. Because the dye is only superficial, the underlying oxide may continue to provide corrosion protection even if minor wear and scratches may break through the dyed layer.
Conditions such as electrolyte concentration, acidity, solution temperature, and current must be controlled to allow the formation of a consistent oxide layer. Harder, thicker films tend to be produced by more dilute solutions at lower temperatures with higher voltages and currents. The film thickness can range from under 0.5 micrometres for bright decorative work up to 150 micrometers for architectural applications.
The most widely used anodizing specification, MIL-A-8625, defines three types of aluminum anodization. Type I is Chromic Acid Anodization, Type II is Sulphuric Acid Anodization and Type III is sulphuric acid hardcoat anodization. Other anodizing specifications include MIL-A-63576, AMS 2469, AMS 2470, AMS 2471, AMS 2472, AMS 2482, ASTM B580, ASTM D3933, ISO 10074 and BS 5599. AMS 2468 is obsolete. None of these specifications define a detailed process or chemistry, but rather a set of tests and quality assurance measures which the anodized product must meet. BS 1615 provides guidance in the selection of alloys for anodizing. For British defence work, a detailed chromic and sulfuric anodizing processes are described by DEF STAN 03-24/3 and DEF STAN 03-25/3 respectively.
[quote]原帖由 [i]macg4[/i] 于 2008-2-13 15:28 发表 [url=http://leica.org.cn/bbs/redirect.php?goto=findpost&pid=69950&ptid=5533][img]http://leica.org.cn/bbs/images/common/back.gif[/img][/url]
Heifetz：
镀黑是用得什么工艺？磷化吗？
手工真是没得说，高仿！:lol [/quote]
[[i] 本帖最后由 Heifetz 于 2008-2-13 17:53 编辑 [/i]]