21 THINGS YOU NEED TO KNOW ABOUT ANODIZING ALUMINUMTDB Machining
21 THINGS YOU NEED TO KNOW ABOUT ANODIZING ALUMINUM
The process of anodizing is a popular and valuable procedure. It gives aluminum a long-lasting and lustrous exterior, making it more durable for use in multiple industries. Aluminum retains its original properties and gains an authentic appearance when treated in the anodize process.
The metal becomes corrosion-resistant and is preferred for use in multiple household and industrial applications including cookware and automobile sectors. can also be anodized if done using the right techniques and equipment. Sunrise Metal is a proud manufacturer of anodized aluminum and offers multiple finishing processes at the best costs in the market.
Anodized Al is an enhanced form of aluminum that has a better visual appearance and long-lasting anti-corrosive properties. It is an electrochemical process that strengthens the thickness of the oxide layer that is naturally found on the metals. Aluminum alloy contains a natural layer of aluminum oxide on its surface.
The natural layer of oxide present on aluminum is thin, uneven, and has low resistance to corrosion, which is why it is highly suited for the anodized process. This process turns that oxide layer into a much even and uniform layer with increased corrosive resistance and durability. Other nonferrous metals such as titanium, zinc, and magnesium can also undergo the anodizing process, but aluminum is most frequently used due to its reliability and other properties.
This is also an extremely durable procedure which not only polishes the appearance of the metal for various uses but also shields its surface from being scratched. it gives it unique visual effects, for example, thick anodized coatings that can absorb colors or transparent layers which reflect light.
Anodized aluminum has a reputation for being the most widely used and valuable material in the production of thousands of industrial and household products. The process does not take away the natural look of aluminum, despite its long-lasting impacts on its properties.
The first step is the proper cleaning of the aluminum metal, after which it is thoroughly rinsed. The aluminum is then placed into a soak of an electrolytic solution, primarily made up of sulfuric or chromic acid. An electrolyte solution is an electrically charged liquid with several positive and negative ions that pass the charge throughout the medium.
Al acts as an anode when a positive charge is applied to it while the suspending plates in the solution act as a cathode when a negative charge is passed through them. By doing so, an electric circuit is established in the electrolytic solution that moves the current from positive to the negative charge. In anodize, when the current passes, the positive ions move towards the negatively charged plates.
At the same time, oxygen ions from the electrolyte acid get separated and attach to the piece of Al (anode), immersed in the electrolytic solution. The attachment of oxygen ions on Al forms the thick aluminum oxide layer, which is responsible for its enhanced properties, such as high durability, better appearance, and high resistance.
The anodizing of aluminum or of any other metal can be modified by making changes in the nature of the electrolyte, the temperature of the setting, the voltage used for passing current, and the composition of the electrolytic solution.
There are several different types of aluminum anodizing process, based on their distinct advantages and the electrolytic acid used. The common types are Sulfuric acid, Chromic acid, and Hard anodizing.
It is the most commonly used type, and it produces a thick anodized layer of aluminum oxide. The porous nature of sulphuric acid forms a transparent layer, which is best for adding color to the metals. Sulphuric acid anodizing is cheaper than other types, in terms of power usage, time, and chemicals used for anodizing. Military weapons, computer components, and hardware are the main applications of this type.
Chromic acid anodizing forms a thin anodized layer on aluminum, unlike sulphuric acid. Despite anodizing a thin oxide layer, chromic acid provides similar corrosion protection to the metal as other types. The chromic anodize layer appears greyish in color, which limits it to be dyed only black, different colors cannot be applied on chromic anodized metal. Chromic acid anodizing is suitable for aerospace components and machines.
Hard anodizing, uses sulfuric acid as well but produces a thicker and denser layer on aluminum which works best for coloration. Due to its durable anodized coating, this type is suitable for the metallic parts that are to be used in harsh environments with high chances of corrosion and scratches. Works best for gears, shields, and hinges.
Yes, there is a barrier layer present in the anodizing procedure. The barrier layer protects the aluminum to undergo any further chemical reaction after the oxide layer has been formed.
After the current shifts, the positive and negative ions to their specific target in the electrolytic solution, the electrochemical process forces the aluminum to open up the pores on its surface. The pores on the surface of aluminum allow the additional positive ions to escape from aluminum. The negatively charged oxygen ions attach with the surface, and the barrier layer is formed, which stops the chemical reactions on that surface.
As the procedure progresses, those pores start to dig down in a perfect geometric p
attern. When the current keeps coming to the electrolytic solution, pores continue to wear down the substrate, which forms hollow structures in it. For different types of anodize, a certain level of penetration is achieved after which the surface is sealed simply by rinsing it with water. If no addition of color is required, then the process can be ceased here.
The barrier layer formation shows that aluminum anodizing is a highly controlled process. It is essential to note that the anodized layer is wholly integrated into the substrate; for non-hard anodizing, the penetration can be as deep as 10 microns.
Aluminum anodized can be done using a couple of different chemicals; the most common ones include sulfuric acid or oxalic acid and chromic acid. The less frequently used chemicals for the process are boric-sulfuric acid mix and phosphoric acid.
Most of the anodized aluminum are done using sulfuric acid as an electrolyte. It is highly suited for this process because sulfuric acid tends to form a thick oxide layer on aluminum in the process. The thickness of the barrier layer by sulfuric acid is due to 67% penetration in the aluminum substrate, which is not achieved with any other chemical.
When a thin anodized coating is required on the surface, chromic acid is preferred for anodizing. Chromic acid anodizing does not change the dimensions of the parts due to the thin layer. The chromic acid is obtained from chromite which is a highly oxidizing substance. Despite being light, chromic acid anodized aluminum has good adhesion and corrosive resistance.
The boric-sulfuric acid mix is used as an alternative to chromic acid, with several benefits. It is environmental-friendly, has fewer worker safety concerns, and less hazardous for health. Aerospace industries make the most use out to this kind of anodizing.
Phosphoric acid anodizing is used where excellent durability and exposure to adverse conditions are the main focus.
The answer to this question rotates around the different requirements of customers. The four main factors that help us understand the cost-efficiency of anodizing aluminum are:
Al Anodizing is cost-effective when a specific thickness of the coating is not required for your product. Although if you include special thickness instructions, such as lower or higher limits, this will be expensive. The narrower layer requires a higher cost, whereas extra thickness can also be costly due to the longer time for coating.
The cost of anodized aluminum, when compared to the PVDF paints, is higher. For a genuine copper, zinc or bronze look, anodize the parts is more expensive than painting them, but It is preferred over paints because of the more authentic look. When compared to the metals that anodized aluminum replaces, the cost does not seem so higher.
The anodized aluminum has much higher corrosive resistance and durability than standard aluminum or any other metal. For this reason, the cost of maintenance is almost none because anodized aluminum does not peel or chip, and it lasts longer. So, in the long term, it is a cost-effective process.
Sometimes a large scale, customers need additional processing and modifications for the anodizing process. The additional functions need more time, power, labor, and chemicals, which increase the overall anodizing cost.
Anodized is famous for its pigmentation, there are different ways through which color is added to the anodized aluminum, the two major methods are:
For the past decade, this method has been used to produce beautiful colors for anodized aluminum parts. The process of coloring starts after the metal has been anodized, the anodized Al is immersed in another bath of solution containing metallic salts. There are pores in the anodized aluminum, when the current is applied, the metallic salts start to fill in the base of the pores on the coating.
The final pigmentation and the tone on the aluminum depend on the metallic salts used, for instance, copper salts (Cu) give reddish color. The electrolytic coloring method is widely used because the final result is resistant to ultraviolet rays and has long-lasting effects, as the salts deposit in the pores.
This coloring method can be used to obtain an extensive range of colors. The freshly anodized Al part is placed in a liquid solution of organic or inorganic dyes. The porous layer of aluminum absorbs the dye, after which the surface is bubbled in water to stop any further reaction. The dip coloring method has more color choices but the end result is not ultraviolet resistant and fades quickly over time.
Anodized aluminum has a distinct metallic look, regardless of the color it has. The anodized coating of aluminum oxide is a radiant crystalline structure that improves the natural metallic appearance of the aluminum. The anodized aluminum gets its metallic look because of two important phenomena.
When the aluminum is anodized and colored, a rough surface is left behind due to the electrochemical engraving of the ions in the aluminum. Deeper pores make the coating more metallic looking and the color more durable.
Secondly, the three-dimensional crystalline structure of aluminum oxide refracts and reflects the natural light in a unique manner. When the light falls on the anodized aluminum, it interacts differently with the colored and uncolored metal parts. So, the light that reaches back to your eye is of different wavelengths as they interact with dissimilar surfaces. This unique style of reflection of light gives anodized aluminum its significant metallic appearance, which can never be achieved with painted Al.
When the paint is applied to the aluminum, it does not reproduce the natural metallic feel of the aluminum because of its one-dimensional structure. The metallic look is in paint coating but not in anodized coloring. Apart from the metallic look, painted aluminum does not even feel metallic when you touch it. Whereas, anodized aluminum with or without coloring gives a smooth metallic look and feel.
In comparison with the standard aluminum, anodized aluminum offers several benefits, such as:
Anodized aluminum coatings can have distinct visual effects; the light layers reflect light while the dark and deeper anodized layers absorb light. The anodized colors and finishes still maintain the metallic appearance of the aluminum. Unlike standard aluminum, IT can be dyed to achieve a wide range of coloration and gloss alternatives.
The anodized aluminum has better protection against ultraviolet rays as compared to the standard aluminum. It does not peel, chip, or corrode and is easily recycled, and the life span is extremely long. The finish of anodized Al can effortlessly be restored to its original look, by rinsing or cleaning it with water.
The anodizing process is not at all harmful for human health because it is a modification of a naturally occurring oxidation process. It does not decompose, has excellent stability, and is non-toxic to use. Although anodize is a chemical process, it produces no hazardous by-products.
Neither standard aluminum nor anodized aluminum can corrode, but anodized aluminum offers comparatively better resistance. The typical aluminum can rust in harsh conditions like constant moisture, air, and the presence of other elements. But anodized aluminum is rarely going to corrode with a thicker aluminum oxide layer on its surface.
Anodized aluminum improves corrosi
ve resistance and many other properties of aluminum by forming a thick oxide layer on its surface. Regardless of these enhanced properties, anodized aluminum occasionally becomes discolored. There a several causes of the discoloration of the anodized aluminum, for example:
In many industrial applications, welding is required after the aluminum has been anodized. The heat from the welding tends to make the aluminum discolored. Other than that, choosing the wrong alloy for welding wire can also damage the pigmentation of the aluminum.
Another likely cause of the discoloration of anodized aluminum is weathering bloom. In contact with the acidic environment, the coating of aluminum oxide becomes irregular, if the anodized aluminum was not sealed properly. Discoloration also occurs due to prolonged contact with an alkaline or acidic chemical, and it is often irreversible. The discoloration may not be visible for an extended period, and when it becomes visible, the damage is enough to replace the part.
Another possible reason for the discoloration in anodized aluminum is the anodizing process itself. Some factors are to be observed and monitored carefully in the anodizing process. Improper anodize is caused by wrong temperature and low voltage, etc., and forms a soft oxide layer. The soft oxide layer cracks and flakes quickly with exposure to the environment and the color fades away.
is a method widely used to obtain any shape with good physical properties. Unfortunately, the qualities that make die cast alloys famous economically also make them less fit for anodizing. It is a process that requires the substance to have no impurities so that the anodized coating is smooth and uniform.
In the case of die casting parts, their primary element is silicon which makes them less suited for anodizing due to lesser resistance and thickness. These silicon particles in hinder the anodic coating formation during the interaction with the cathode electrolyte. The silicon and other particles in the die casting alloy, therefore, form voids in the anodized coating, hence compromising the thickness and aesthetics.
For anodize, it becomes difficult to get a transparent anodic film. The reason is that the silicon content of the die casting parts makes the anodized layer grey to black, the anodic layer becomes speckled, and it would not dye into the colors of your choice.
For better anodize, die casting parts with minimum porosity and more machining are the right choice. Moreover, die casting alloy 360 and 380 can be anodized effectively, but the quality of die casting parts is crucial for magnificent anodizing results.
The sealing of anodized aluminum is the most crucial process in achieving the desired durability and the enhanced functionality of aluminum. Anodized aluminum is sealed using various methods, namely high temperature, mid-temperature, and cold or room temperature sealing.
The anodized aluminum is sealed using hot deionized water in a tank with metallic salts, with or without additives. The seal is achieved when the coating is boiled in unionized water at a high temperatures. The hydration causes the pores of the aluminum surface to swell and become sealed. This sealing method is a bit expensive because the temperature has to be maintained as high as 200 ºF.
Sealing in mid-temperature is more useful because it can be done in less time and at temperatures around 20-30 degrees Fahrenheit, which is much lower than the hot water seal. This method is cost-effective and consumes a lesser amount of energy, but it becomes analytically challenging to monitor.
This procedure has an advantage over the other approaches of sealing, because of the least energy cost and consumption. In the cold sealing method, a nickel-fluoride chemical is used to close the pores on the surface. The cold process, along with sealing of pores, improves the adhesion and bonding of the anodized aluminum. If the highest quality seal is needed, the cold or room temperature sealing method is the best choice.
The difference between the anodized and hard anodized can be known by observing the following factors:
One of the most visible differences between anodized and hard anodized is the thickness. Hard anodized has a thicker layer of oxide than the anodized, making it more resistant to rust. The reason is that hard anodized is done at low temperatures and higher current density. The surface of hard-anodized is smoother and more uniform than anodizing.
Hard anodized at its best thickness, has the hardness of up to 70C Rockwell, which is stiffer than a . Anodized, on the other hand, offers less abrasive protection than hard-anodized. Standard anodizing is done using chromic or sulfuric acid as electrolytes, but in a hard process, sulfuric acid along with added organic acids are used.
For standard anodize, the pores of the coating have to be closed by using different methods to stop the further reaction. But in the case of hard anodizing, the thickness is so durable and wear-resistant that no sealing is required.
Standard anodized is mostly applicable in the aerospace, automobile, and architecture industries. Whereas, for heavy-duty applications, such as hydraulics and cookware, hard-anodized is used. It is best for cookware, because of the super-smooth surface and the high heat-resistance.
It is a process to increase the corrosive resistance and surface thickness of metals. Aluminum is the common metal that undergoes the anodize process, other than that, titanium, magnesium, and zinc can also be anodized.
The primary purpose of titanium anodizing is to create a wide variety of colors for this metal, without using paints and dyes. That involves a finishing process that modifies the oxide layer on titanium so that the light reflects on it differently. This way, titanium has various possibilities of shades without using pigments. Anodized titanium has a long history of its usage in the aerospace industry.
Apart from plating, magnesium can also be anodized to enhance its mechanical properties. For anodizing magnesium, an alkali rich aqueous bath is used, a direct current is passed through the bath containing the substrate, which forms the coating on the surface. To increase the surface properties, extra elements can be added to the aqueous solution.
Anodized zinc does not give as beneficial results as aluminum or titanium because the anodized surface of zinc consists of phosphates and chromates along with the oxides. Although the zinc anodize process gives the high resistant anodic film, the cost and the procedure make it not generally used. Unlike aluminum, for zinc, a high temperature is required to achieve desired outcomes.
Over the past couple of decades, has become overly famous for its industrial applications, and it is now a significant business. China has some of the best manufacturers that offer for industrial purposes. Sunrise Metal is one such company that has been providing for over 10 years.
We offer services for a number of industries like plating, , and finishing, etc. We are a leading , extruded, and anodized aluminum products and processing components. As a certified company, we offer anodized aluminum procedures, finishes, and colors to serve clients’ choice. Our services include hard coat anodize as well as color anodizing, with the specialized process and other services such as plating and finishing.
Aluminum anodize forms an oxide coating on aluminum’s surface which is very hard. The anodized aluminum is exclusively abrasive-resistant and known for their durability. Compared to non-anodized aluminum, it does not peel, flake or chalk.
Aluminum oxide is from the Corundum family of gemstones, and it is second to diamond in terms of stiffness. The oxide layer passes the pencil hardness tests, which means the coating is highly durable.
When a tiny crack appears on the anodic layer of aluminum, the anodized film tries to heal itself by forming a protective layer. It stops the damage from crawling all the way down to its base. Unlike organic coatings on the aluminum or paints, anodized coatings are relatively permanent as they grow out of the bottom of the substance.
Despite being permanent, anodized coatings in some cases do wear off. They can be damaged through exposure to extreme weather and washing them with acid. Different types of anodize have a different response to the wear and tear, but they can be worn off.
The anodized film is delicate and brittle; prolonged temperature changes may develop tiny cracks in it. These cracks do not lead directly to wear of anodized film, but if you hit it or use force, tiny bits fall off the coating. Then this, later on, is what we call as the damage in the anodized aluminum coating.
Anodized aluminum offers different applications to many industries, including:
The primary necessity of this industry is substances that are lightweight and durable, and anodized aluminum has both of these qualities. Anodized aluminum has all the properties the aerospace industry needs, which include; corrosion resistance, low density, resistance to flaking, and harsh conditions. Even NASA uses anodized aluminum to make a wide variety of space equipment such as handrails and binds.
: Hundreds of useful electronic products are being made with anodized aluminum which provides excellent temperature resistance. Some examples of applications of anodized aluminum in electronics include; telephones, gaming systems, computers, and solar panels.
: The anodized aluminum coating makes it ideal for the food and packaging industries. Anodized aluminum is waterproof, can be cleaned easily, does not flake or peel, and it is resistant to fungus. Typical applications in food and packaging industries are in the manufacturing of; cookers, pans, kitchen equipment, bakeware, grills, and ice makers.
The anti-fungus and anti-corrosive properties of anodized aluminum make it exceptionally well suited for dental and medical equipment. Those equipment are often seen in the emergency rooms, operating rooms, and doctor offices. Medical and dental instruments need repeated sterilization, which is why anodized aluminum works best as it can be recycled repeatedly without becoming flaked or rusty.
Yes, you can powder coat anodized aluminum.
Powder coating is a finishing method that uses dry, free-flowing powder to a metal substrate to give it a tougher and more resistant varnish. The powder coating process is almost identical to the painting process; the only difference is the dry powder.
Anodized aluminum works perfect for abrasive resistance, but the anodized coating is fragile, any scratch or wear might lead to corrosion, in the longer term. The powder coating gives extra durability, a protective layer, and a wide variety of colors to the anodized aluminum. The powder sticks to the aluminum substrate through electrostatic charging of the powder, curing the surface.
Anodized aluminum is suitable for powder coating because it does not involve pre-cleaning or surface preparation, which is needed for raw metal parts. It is possible that for a particular color, more than one coat of powder might be required.
While most anodized aluminum parts can be powder coated, some anodized surfaces do not work sound with powder coating. The common reason is the application of inorganic dyes or paints on the surface of anodized aluminum.
To avoid incompatibility, a wet adhesion test is run through the anodized surface; if the test comes out positive, the anodized aluminum parts are right for powder coating. In case of negative results, you need an effective pretreatment process.
Anodizing is an electrochemical process that provides extra protection, durability, and a decorative look to the naturally existing oxide layer. Powder coating is a method that uses dry free-flowing as a coating to increase the toughness and resistance of metals.
These are the significant differences between powder-coated aluminum and anodized aluminum:
In anodized aluminum, the substrate is immersed in a bath with an electrolytic solution, and the oxide layer is formed when current passes through it.
Powder coating on aluminum or any other metal is done by spraying electrostatically charged powder on the metal parts.
The anodize process is more expensive than the powder coating.
The anodized aluminum once damaged is difficult to repair, but the powder-coated aluminum can be recoated and cured using heat.
It offers up to 30 color combinations, but there is a more significant color variation in the process. Whereas, color variations in powder coating are not possible, but the range of colors available is up to 100.
Powder-coated aluminum has a shorter life span than anodized aluminum due to the wear and tear and the moisture in the weather.
Powder-coated aluminum is most commonly used in the appliance industry for washer tops, air conditioner cabinets, heaters, side panels, and refrigerators.
Primary uses of anodized aluminum are in aerospace, furniture, food, and vehicle industries.
The most crucial point to remember is to thoroughly clean the aluminum surface by washing and drying before painting it. One of the properties of the anodized aluminum film is extreme adhesion. It proves highly beneficial for the painter because the pores in the anodized surface of aluminum are excellent at soaking in any liquid.
The painting procedure starts with the in-depth scrubbing of the aluminum parts. It is done to stop the porous anodized film from soaking in any contaminants present on aluminum, such as oil or air particles.
Once the aluminum is cleaned and completely dry, etching primer is poured over the surface without leaving behind any spot. The expected time for the primer to dry up is two hours. In some cases, the primer forms unnecessary bumps and grooves on the aluminum surface that have to be removed, before going to the next step. The sandpaper can be used to get rid of the bumps carefully; sandpaper does not damage the anodized layer.
In the last step, paint is applied to the aluminum surface. Oil-based
paint is preferred, to make better use of the adhesion of anodized aluminum. Depending on the shade of color, you decide any additional coats of paint. For instance, for blue, black, or darker colors, you may need three or more than three coats to get the best finishing.
Yes, the anodize process raises several environmental concerns. However, these are managed by using state-of-the-art equipment at Sunrise Metal and by complying with international ISO standards of safety.
Most of the process takes place with a sulfuric bath, which produces two by-products; aluminum hydroxide and degraded sulfuric acid. The Environmental Protection Agency (EPA) has classified aluminum hydroxide as hazardous. Wastewater containing aluminum hydroxide can not be effectively dumped into the municipal water treatment system. Aluminum hydroxide is a compound that takes oxygen and hydrogen from the sulfuric acid and the aluminum from the anodized part. Therefore, special measures are taken by quality assurance managers at Sunrise to make sure the disposal process is completed safely.
Degraded sulfuric acid mixed up in water has acute toxic effects on marine life, and its corrosive nature badly harms the plants and animals. The fumes of residual sulfuric acid can cause serious health issues when exposed to them for a long time. EPA has set firm rules and standards for the maximum acceptance of aluminum concentration in the waste upon dumping. According to the EPA, degraded sulfuric acid has to be nullified to a pH value of around 6 to 8.
Apart from the electrolyte tank by-products, other wastes are generated in the anodizing process as well. The materials used in the pre-cleaning of the aluminum such as solvents and industrial cleaners must also be thoroughly disposed of before exposing them to the natural environment. Sealing agents and the dyes used in the different processes related to anodizing also have adverse impacts on the environment, if not properly disposed of.
Sunrise Metal is a leading manufacturer of aluminum production, offering premium quality anodizing services for 10+ years. Modern plants have been set up to handle low volume projects and give them full-scale production runs. From production to surface coating, we use the right alloys and production methods to make sure your industrial needs are met successfully.
We offer aluminum anodizing services as part of our comprehensive 1-stop solution to industrial needs. Additional services offered by Sunrise include aluminum die casting, tooling, rapid prototyping, CNC machining, and a wide range of surface finishing.
Anodizing services are offered as two main services:
- Anodizing of aluminum die casting parts. The common aluminum die casting alloys are ADC12, A380, etc.
- Anodizing of Pure CNC machining parts. The popular machined alloys are Al6061, Al6063, etc.
All customers are able to benefit from the following facilities offered by Sunrise:
- Availability of both hard and standard anodizing services to help you make the right choice.
- Detailed metal finishing and inspection services offered to the automobile, medical, household, and other sectors.
- Option to choose from a range of anodizing colors to suit customized orders.
- State-of-the-art equipment that makes it possible to get the best results, detailed designs, and superb finishes.
- A seasoned team of anodizing specialists caters to your customized anodizing projects.
- Great service and premium quality production and design, in compliance with relevant international ISO standards.
- Catering to both low volume and high-volume anodizing aluminum services
If you want to know more about aluminum anodize, you may also check the . If you are ready to find an aluminum anodizing supplier now, you definitely can for your aluminum machining and anodizing demand.