November 28, 2017

Composition of Alloy and Process Limitation

Composition of aluminum alloy make the process condition of anodizing is conditioning in order can get good performance of anodized alloy. Surface finish, prior processing, temper or heat treatment are influence to the quality of anodic coatings. The limitations imposed by each of these variables on various condition of aluminum alloy are as follows:

Chromic acid process should not use for anodize aluminum casting alloys containing more than 5% of Cu or more than 7.5% of total alloying elements, because this alloy can resulting of excessive pitting, and may burning. Sulfuric acid bath can be used for commercial alloys, while hard anodizing process is usually apply in limited alloys containing less than 5% Cu and 7% Si. Choice of alloys is important when the product should have maximum corrosion or abrassive resistance required. Alloys contain of copper and copper magnesium is able to produce hard, corrosion resistance coating.

Two kind of alloy can be anodized together in the same anodizing bath if the voltage requirement are identical, even simultaneous anodizing of two different alloy is not normal applied. This process can be more difficult for sulfuric acid process than chromic acid process.

Finished anodizing will form an anodic film, and often time formed surface irregularities that are emphasized more by chromic acid bath than by sulfuric acid bath. For this reason, suggest that sulfuric acid bath is use instead of chromic acid bath where optimum corrosion or abrasion resistant surfaces are required. Clad sheet should be handled with careful to prevent mechanical abrasion or exposure of the core material. Scratch on surface of aluminum make this magnifies exposed, with different color of anodized finished.

Anodizing grade must be specified for extruded products so that mill operations are controlled to minimize longitudinal die marks and other surface blemishes. Surface irregularities must be removed from forgings, and surface of forgings must be cleaned by a process that removes trapped and burned-in die lubricants.

Castings can be anodized provided their composition is within the process limits described under alloy composition. Uniform will appearance, however anodizing usually is undesirable for castings.

November 22, 2017

Special Anodizing Process

Special anodizing process is the condition of several anodizing process that is done from several process of by certain company or from proprietary information available to licencess only. Anodizing condition process that is proposed based on licence are Martin Hard Coat (MHC), Aluminate 225 and 226, Alcanodox Hardas, Sandford, Kalcolor and Lasser.

Hard anodizing process uses a sulfuric acid bath containing 10 to 20% of acid, with or without additives. Operating condition temperature of the bath range from 0 to 10 oC, and with current density range between 2 and 3.6 A/dm2. By adding some additives and modifier for power, hard anodizing can be operated at higher temperature than room temperature. But hard anodizing that operate in higher temperature than room temperature may result soft formation and more porous outer layer. The change of character result will reduce wear resistance coating significantly and tends to limit coating thickness. If without use of some additives or modified power, such as superimposed alternating current over direct current or pulsed current, excessive operating temperatures result in dissolution of coating and can burnt and damage the work.

Prefer process condition that are commonly use solution containing 120 to 160 g of sulfuric acid and 12 to 20 g of oxalic acid per 3.8 lt water. Operating temperature at 10 + 1 oC and use current density of 2.5 to 3.6 A/dm2, voltage is increase gradually from zero to 40 or 60 V. Time treatment about 25 minute will result anodizing thickness about 1 mil or 25 micron.

For special condition process that mensioned above will use some parameter limitation as on the table below:

Process NameBathTemperature, oCDuration, minVoltage, voltCurrent Density, A/dm3
Martin Hard Coat (MHC)15% sulfuric acid, 85% water- 4 to 045 (b)20 - 752.7
Aluminate12% sulfuric acid, 1% oxalic acid, water1020, 4010 - 752.8 (b)
AlcanodoxOxalic acid in water2 - 20(a)(a)(a)
Hardas6% Oxalic acid, 94% water4(a)60 DC plus AC overide2
SanfordSulfuric acid with organic additives0 - 15(a)15 - 150 DC1.2 - 1.5
Kalcolor7 - 15 % sulfosalicylic acid, 0.3-4 % sulfuric acid, water18 - 24---------1.5 - 4
Lasser0.75 % oxalic acid, 99.25 % water1 - 7to 20rising A 50 - 500V controlled
a: Lincence only
b: change from last edition

November 19, 2017

Benefit of Anodized Aluminum

Any part that formed from aluminum metal should be anodized because the properties of origin aluminum metal will improved and change into better properties. Even of many anodized product can make more stand to corrode or stand to scratch but anodizing to aluminum is purposed to certain purpose of anodizing. The below lists are some reason why people doing anodizing to aluminum, outlined on the below:
  1. Anodizing aluminum is purposed to increase corrosion resistance. Oxide film that formed on the surface of aluminum sheet can stand to corrode in atmospheric condition and salt water attack. So this oxide film can protect underlying metal by serving as barrier from attracting some corrosive agent. To make the oxide film can protect the aluminum sheet is treated the aluminum sheet after anodized into hot water with slightly acidified, or use dichromate solution, or nickel acetate solution.
  2. Other reason to anodize aluminum improve decorative appearance. All anodic coating have lustrous and relatively good abrasion resistance. The degree of lustrous of anodic coating depends on the condition of aluminum before anodizing. Dull etching will decrease luster, bright etching, chemical or electrolytic brightening and buffing will increase luster either diffuse or spectacular. For this kind of aluminum finished are use in structural and architectural application.
  3. Aluminum anodizing can increase abrasive resistance. From the experience product result the thickness of hard anodizing about 25 micron (1mm) to more than 100 micron (4 mm). This thickness is enough for many applications that involving rotating parts where abrasion resistance is required.
  4. Some anodizing process is purposed to increase paint adhesion. Alloy metal from aluminum can anodized to activate the surface of alloy metal. Aluminum base alloy materials that are painted for service in severe corrosive environment are anodized before painting.
  5. Other reason of anodizing of aluminum alloy is improve adhesive bonding. This kind material are used in aircraft structure of most modern aircraft. Anodizing use phosphoric acid or chromic acid can improve bond strength and durability.
  6. Anodizing process also can improve lubricity, by combination of polishing or honing of hard anodizing to smoother surface before applying a polytetrafluoroethylene coating.
  7. General purpose of anodizing product is purpose for aesthetic performance, can provide unique, decorative finished color. As already discussed of mechanism of coloring in anodizing process, that sealing of anodizing aluminum is together with coloring of oxide film on the surface of aluminum. Integral anodizing, depending on the alloy composition, is used to provide a range of stable earth-tone colors suitable for architectural applications.
  8. Anodizing process also purpose to provide electrical insulation. Aluminum oxide is a dielectric, that mean can’t conduct electric current until certain voltage. The breakdown voltage of anodic film varies from a few volts to several thousand volts. This depend on the alloy properties itself and on the natural and thickness of oxide film on the surface.
  9. Anodizing of metal also make subsequent plating. The porosity of certain anodic films enhances electroplating.
  10. Anodized surface of aluminum can detect of surface flaws. Chromic acid solution bath can be used as an inspection medium for detection of fine surface cracks. When object containing surface flaws is removed from anodizing bath, then washed and dried quickly, chromic acid entrapped in the flaws seeps out and stains in the anodized coating in around of the flaws.

November 18, 2017

Hard Anodizing Aluminum

Hard anodizing aluminum is similar to standard aluminum anodizing in that are controlled by electrochemical processes. The key difference is that hard coat anodizing provides a surface more wear resistant and has a smoother and harder surface than standard anodizing. Hard anodizing aluminum will result a uniform aluminum oxide layer on the surface that penetrate the material pores. Anodizing process condition for hard anodizing involved by submersing part in sulfuric acid solution at room temperature from 20 minutes two hours. The longer time submerged determines the thickness of coating. Aluminum oxide formed in the surface during hardcoat anodizing is more uniform, dense, and much harder than the natural oxidation.

The benefit of Hard Anodizing:

The benefit of hard coat anodizing have many, some reason to create hard coat for aluminum anodizing is as follows:

  • More corrosion resistance
  • Looking better than normal aluminum
  • Use as insulator because oxide film can’t conduct electric current
  • Increase wear resistance and abrasion resistance
  • More bright can use as reflector
  • Light weight
  • Flame resistance
  • No contaminate for example in use for medical instrument

Many Hard Anodizing Aluminum Application:

Some service company and repair company use hard coat anodizing process to serve their customer to give satisfaction to their customer and create credible company for their service.

Many application can use hard coat anodized, for example as below:

  • Automotive
  • Aviation & Aerospace (mostly all frame and the furniture use aluminum anodized)
  • Buildings & Architecture (for structure frame, windows and door)
  • Electronics (for casing of electronic)
  • Food Manufacturing / Preparation Equipment (canning and keeping material and product)
  • Home Furnishing
  • General Manufacturing
  • Marine Industry
  • Medical / Dental Equipment
  • Military / Law Enforcement
  • Sporting Goods

November 16, 2017

Anodizing Condition Process

Generally anodizing process is associated with aluminum metal, but similar process of anodizing can be applied to several kind of base metal like magnesium, titanium, and zinc. Anodizing aluminum can be accomplished in wide variety of electrolytes, employing varying operation condition including concentration and composition of electrolyte. Anodizing can be process in several kind of process, that is used different anodizing bath solution, such as chromic acid process, sulfuric acid process, and oxalic acid anodizing bath. As on the table condition process of anodizing, there are two kind of anodizing process condition. For conventional anodizing and commercial anodizing process.

Bath Solution % weight Temperature, oCDuration, minVoltage, voltCurrent Density, A/dm3
Sulfuric Acid Bath101815 - 3014 - 181 - 2
Aluminate sulfuric acid bath152110 - 6012 - 161.3
Oxydal Sulfuric Acid20183012 - 161 - 2
Anodal and anoxal20185012 - 160.3
Cromic acid bath340600 - 500.3

Chromic acid, Commercial5 - 10 4030 - 600 to increasing limit controlled by amperage0.5 - 1.0
Oxalic acid, Eloxal2 - 1020 - 8030 - 8020 - 800.5 - 30
Oxalic acid, Oxal2 - 1020 -8010 - 240 601.5
Oxalic acid, Ematal1.2 - 4050 - 7030 - 401203

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Composition of Alloy and Process Limitation

Composition of aluminum alloy make the process condition of anodizing is conditioning in order can get good performance of anodized all...