Posted on: Aug 2, 2018, | By Mandy, WayKen Project Manager
There are many kinds of surface finishing methods for physical prototype, such as powder coating, anodizing, electroplating, and passivation and so on. Here we are introducing the common aluminum anodizing. If you are designing this surface finishing for your physical prototype, welcome to share ideals with each other.
The process of forming alumina thin film on the surface of aluminum or aluminum alloy by electrolysis is called anodic oxidation treatment of aluminum and aluminum alloy.
After anodizing, aluminum surfaces can produce several microns -- hundreds of microns of oxide film.
2.Benefits of Anodizing
(1) Enhance the hardness: pure aluminum anodizing hardness is higher than the hardness of aluminum alloy anodizing. Usually, its size and hardness of aluminum alloy composition, anodizing electrolyte of technical conditions. The anodizing is not only high hardness, and good wear resistance. Especially the surface layer of porous anodizing has the ability of adsorption lubricant, also can further improve the surface wear resistance.
(2) To improve the corrosion resistance: this is due to the chemical stability of anodizing is higher. After the test, the anodizing of pure aluminum is better than the corrosion resistance of anodic anodizing of aluminum alloy membrane. This is because the composition of alloy inclusions or metal compounds cannot be anodizing or be dissolved, and make the space discrete or produce anodizing, which greatly reduced the corrosion resistance of oxide film. So, generally after anodic oxidation membrane must be closed to deal with, to improve its corrosion resistance.
(3) Enhanced adsorption capacity: the anodizing of aluminum and aluminum alloy is a porous structure with strong adsorption capacity, so filling the hole with various pigments, lubricants and resins can further improve the protection, insulation, wear resistance and decorative properties of aluminum products.
(4) Good insulation performance: aluminum and aluminum alloy anodizing have no metal conductive nature, and become a good insulation material.
(5) Color Stability. Exterior anodic coatings provide good stability to ultraviolet rays, do not chip or peel, and are easily repeatable.
3.Application of Anodizing Aluminum Physical Prototype
Due to benefits of anodizing, aluminum anodizing has various commercial uses and different consumer applications in various industries.
(1) Strong & wear-resistant properties are very necessary for application in aviation and automobile fields.
(2) Aluminum oxide products are also a good choice for building exterior structures, greatly reducing the influence of weather.
(3) Deposition of magnetic metals or magnetic alloys by electrolytic coloring, which is magnetic can be used for data storage or other magnetic recording. Many of the components used in everyday and industrial electronics have also been improved through this valuable process.
(4) From satellites orbiting the earth to the smallest electrical and decorative items in our homes, the potential of anodic alumina products from satellites protected in earth orbit is limitless. This durable treatment improves the strength and beauty of aluminum extrusion products, making them easy to maintain and to extend life under any conditions, both indoors and in elements.
(5) Color Stability. Exterior anodic coatings provide good stability to ultraviolet rays, do not chip or peel, and are easily repeatable.0
4.Design Considerations of Anodizing Aluminum Physical Prototype
The appearance quality of anodic oxide film will be affected by the difference of aluminum composition and the content of impurities.
When the composition of aluminum alloy is certain, the main factor that affects the appearance quality is harmful impurities, such as copper, silicon, chromium, iron, zinc, manganese and other metal elements.
(1) Aluminum material selection
The lower the content of these metals in aluminum, the better the brightness of the clean light after anodic oxidation. If the condition is contrast, the result will be worse. The transparency, smoothness and brightness of the oxide film of various brands of high purity aluminum and pure aluminum gradually deteriorate with the increase of impurity content.
Aluminum alloys also have an effect on anodized. Remember, alloys like copper don't anodize, so high copper alloys like AL7075 or AL2024 have distinct colors. In general, the 6061, 3000 and 5000 series alloys will be reasonably consistent. Due to the high copper content, the black color will not be dark, so the yellow color will appear in the clear anodic oxidation process.
Someone may want to know can steel and/or stainless steel be anodized. The answer is steel and stainless steel can't be anodized; because the process baths used to anodize aluminum would attack and dissolve steel parts. Also it need to be completely stripped of any steel, otherwise the steel would not make it through the process.
(2) About the Angle
The processed parts avoid sharp corners, burrs, and other sharp, angular areas because anodized takes a long time and is an exothermic process. The corners of parts are often the places where the current is concentrated, so these parts are most likely to cause local overheating of parts, causing parts to be burned. Therefore, it is a good design suggestion to change all the angles of aluminum and aluminum alloy into chamfered angles.
(3) Dimensions and Machining Tolerance
For aluminum parts or assembly parts that require hard oxidation, a certain amount of machining allowance should be reserved in advance and the clamping part should be specified. Since the thickness of hard oxide film will change the size of parts, it is necessary to predict the possible thickness and size tolerance of oxide film in advance when machining, and then determine the actual size of parts before anodizing and more stringent tolerance standards. But in general, the size of the parts increases by about half the thickness of the anodized film（The maximum anodized film thickness is about 250 microns）.
(4) Threads, holes and masking
Anodized is the process of coating build-up, which is a factor to affecting tolerance. For example, thread holes, precision needle holes, and parts that need to be assembled are common in drawings. The most common solution to this problem is to avoid these design vulnerabilities as much as possible. If it is Type II anodizing, the above problems will be better improved, but if it is used to process small screw parts with Type III anodizing, the above problems should be paid attention to.
Above is a brief introduction to guide for anodizing aluminum physical prototype, which we hope will be helpful to your next project.