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How Does Anodizing Affect the Thickness of Aluminium?

How Does Anodizing Affect the Thickness of Aluminium?
How Does Anodizing Affect the Thickness of Aluminium?
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Anodizing is a very common process within the metalworking and chemical engineering industries, though it is mostly associated with the treatment of aluminum as it improves the physical characteristics of the metal. A very important thing that engineers and designers often ask is what the effect of anodizing is on the thickness of aluminum. Anodizing is a process that enhances the aesthetics and resistance of aluminum; however, it also comes at the expense of certain dimensions, which, in certain very precise applications, could greatly affect the objectives and the performance. In the following article, we contend with some of the technical issues concerning the dynamics of anodizing which specifically deals with the effects of anodizing on aluminum thinness and, subsequently, outline the reasons why this particular area matters to the industry. The readers will become more familiar with anodizing and acquire more practical skills concerning the process of improving aluminum and the designs that go with it.

What is the anodizing process, and how does it work?

Anodizing - What is it and How Does it Work? Complete Aluminium Anodizing Process Explained

Anodizing is a surface enhancement electrochemical process that serves to develop the naturally occurring oxide layer that is present in aluminum. In this process, the metal component is placed in a sulphuric acid bath, and anodic direct current is passed through. This enables the oxidation reaction on the surface of aluminum to occur, leading to the formation of the oxide layer, which is both durable and corrosion-resistant. These layers prevent electric conduction, but they can be painted and have greater electric and abrasion resistance. The anodizing process is increasingly finding application in aerospace, building, and construction, as well as handheld device industries as it aids in attaining the enhanced characteristics of aluminum.

Understanding the anodizing process

  1. Preparation: In preparation for anodizing, the aluminum substrate is properly cleaned and pre-treated to remove any contaminants so that a uniform oxide layer can be formed. Degreasing and etching techniques may be required.
  2. Anodizing: In this step, the aluminum is cleaned followed by progressing into a bath (usually) containing sulfuric acid. The selected electrolyte solution is then, along with electrical current addition, used to enhance the property layer of oxide on the surface.
  3. Sealing: A sealing process is adopted to coat the porous oxide layer thereby increasing its corrosion resistance and durability. Commonly used methods of sealing include hot water and chemical sealing.

Several steps involved in the anodizing process of aluminum aim to reinforce its structural properties, visual appeal and performance, this allows the aluminum surface to be used in demanding settings.

The role of Anodized thickness in aluminum treatment

The anodized thickness greatly influences the performance features of treated aluminum. These parameters, including corrosion and wear resistance, as well as dyeability, are correlated with the thickness of the anodized layer. Standard anodic oxide coatings range from 25 microns for industrial and heavy duty use, to as little as 5 microns for purely decorative use.

For example, fine internally-focused architectural and consumer products are given an anodized coating of 5-10 microns to ensure passable abrasion resistance while enhancing aesthetics. Separately, marine equipment and aerospace parts with increased operational anodized coatings of 20-25 microns are used, considering the unforgiving nature of the environments, which require increased durability and corrosion resistance. Research suggests that thicker anodized layers help the materials achieve a greater resistance to salt spray and its admixed UV radiation, which requires levels of corrosion damage on the materials.

Also, the thickness of the anodized layer is adjustable for different industry needs. For instance, hard anodizing Mil-A-8625 Type III usually requires coatings that are 25 – 50 microns thick, which are sufficiently hard and protect from wear while having low thermal and electrical conductivity. The improvement in technology made it possible to achieve better control of the uniformity and consistency of the anodized layer, increasing the reliability of industrial applications.

The accurate control and optimization of strength and thickness of the anodized layer is extremely important for satisfying an individual’s aesthetic sense, functional needs, and contact with the environment. Some manufacturers of aluminum components modify the anodizing process to achieve greater service life, reduce the need of maintenance, and increase the practicality and performance of the components.

Differences between type ii and type iii anodizing

Type II and Type III anodizing are two different techniques that serve the purpose of enhancing the properties of aluminum components. Below are the differences between Type II and Type III in terms of a detailed process, characteristics, and uses.

Anodizing Thickness 

  • Type II: Generally, the anodized layers produced are thinner, which range from 0.0002 to 0.001 inches (5 to 25 microns) based on the specific use.
  • Type III: commonly referred to as hard anodizing, it forms thicker layers, which are more defined, within the range of 0.002 to 0.003 inches (50 to 75 microns).

Hardness 

  • Type II: Decorates heavily used components and ranges with moderate hardness for the softer consumer goods and architecture components.
  • Type III: Exhibits superior hardness components exceeding 60 Rockwell C value which is ideal for industrial and military uses with high wear resistance.

Color Options 

  • Type II: Because the layer is thinner and allows more dye absorption, Type II supports a larger spectrum of colors.
  • Type III: Color selection is often limited to dark colors such black or grey because of the high density and thick anodized layer.

Wear Resistance 

  • Type II: Moderate wear resistance, which is appropriate for non-abrasive settings.
  • Type III: Strong wear resistance, which can endure abrasive and high friction conditions.

Corrosion Resistance

  • Fortunately, Type II can withstand mild levels of corrosion, such as those found indoors or outside in the Type II environment.
  • Type III exhibits a much more robust corrosion resistance and is ideal for multi climatic regions and extreme atmospheres, including marine and aerospace.

Operating Temperature

  • The process is conducted around room temperature of 20 degrees Celsius or 68 degrees Fahrenheit within Type  II.
  • Type III can be operated at much lower temperatures of -2 degrees Celsius to 0 degrees Celsius or 28 degrees Fahrenheit to 32 degrees Fahrenheit.

Application

  • In consumer products, electronics, and architecture, Type II is primarily employed for light protective coatings or seals, which create decorative designs and structures.
  • For tougher, high performance applications such as medical devices, military equipment, or aerospace, Type III is ideal as it can withstand heavy duty usage to automotive components.

Cost

  • Type II models are easier on the wallet as they encompass much simpler techniques and require fewer materials to implement.
  • Due to the higher amount of energy needed, Type III is much more expensive along with the higher length of time taken to process.

With this vast information, manufacturers can make the appropriate decision when choosing the appropriate anodizing type that is functional and aesthetic with the requirements.

Does anodizing affect the dimensions of the material?

Does anodizing affect the dimensions of the material?

How does anodized thickness influence original dimensions?

The process of anodizing involves applying a layer of coating on the surface of the material, which raises its final measurements. On average, about fifty percent of the anodized coating builds up, while the rest of it is absorbed into the substrate. That is, for instance, a 0.002-inch thick anodized coating will add around 0.001 inches to the surface of the material while also going 0.001 inches below the material’s surface. This dimensional change may be taken into account in a more accurate application so a proper fit is ensured.

Understanding penetration into the substrate

In situations where anodizing goes beyond the surface and into the substrate, a tough and oxidation-resistant oxide skin is formed, which fills in the pores of the material instead of resting upon it. This is particularly beneficial from the standpoint of the material and its operations. The amount of penetration is associated with the general thickness of the anodized layer because it is calculated that anodizing penetrates most of the substrate. This trait is prevalent in most candidates, so it should be noted for the tolerances where accurate measurement is concerned so that there is no maintenance problem separated from construction.

How does anodizing contribute to corrosion resistance?

How does anodizing contribute to corrosion resistance?

Role of aluminum oxide in protecting against corrosion

A hard and long-lasting layer of aluminum oxide is created during the anodizing process. It’s a protective or a barrier layer that prevents the harmful effects of environmental factors. This layer stops the transmission of oxygen and moisture, two of the main causes of corrosion of the aluminum substrate. Furthermore, the metal, specifically aluminum, in which anodized aluminum will be used, will already have an edge in withstanding corrosive elements because oxide resists chemical reactions. The result of this natural process is anodized aluminum which has the ability to endure extreme integrity challenges.

Comparing hard anodizing and regular anodizing for durability

The disparity between hard anodizing and regular anodizing lies primarily in the durability levels associated with each, which in varying degrees depend on the thickness and density of the anodic layer. Listed below is a comparison between the mentioned processes:

Anodic Layer Thickness

  • Hard Anodizing: Used for a greater range of applications as it provides more wear and abrasion resistance. the anodic layer is usually between 25 to 150 microns.
  • Regular Anodizing: Sufficient for decorative purposes or light-duty applications. The anodic layer is generally 5 to 25 microns, so it is not as thick and does not provide as much wear resistance.

Wear Resistance

  • Hard Anodizing: Ideal for industrial uses as aerospace, automobile, and heavy machinery. The construction of the layer is thick and high density which guarantees excellent abrasion resistance.
  • Regular Anodizing: more suitable for architectural designs or consumer goods, it provides moderate abrasion resistance while the durability is not as heavy-duty.

Hardness

  • Hard Anodizing: Provides a mechanical damage-resistant anodic coating with a hardness of 400 to 600 HV.
  • Regular Anodizing: Provides a general-use capable anodic coating with a hardness of 200 to 300 HV, which is less durable under extreme stress.

Corrosion Resistance:

  • Hard Anodizing: With a thicker dense oxide layer, aggressive sweating with chemicals or moisture can be mitigated thanks to the superior corrosion resistance.
  • Regular Anodizing: Corrosion resistance is available, yet it is not able to perform in extreme environments.

Aesthetic Appearance

  • Hard Anodizing: Due to the insufficient number of available color choices and the coating thickness requirement, it is not suitable for decorative finishes. Hence, it is typically associated with a darker appearance.
  • Regular Anodizing: More flexible in aesthetic applications as it provides a wider range of colors and finishes.

Applications

  • Hard Anodizing: Commonly employed in mechanical parts, aerospace components, medical apparatus, and other industries where high durability and wear resistance are essential.
  • Regular Anodizing: More suited for products like consumer electronics, architectural fixtures, and decorative products.

Cost and Processing Time

  • Hard Anodizing: Typically, requires more planning since the voltage vs. temperature needs to be kept under precise control. Thus, it is more expensive and time intensive.
  • Regular Anodizing: The processing requirements are less strict, making it cheaper and faster.

Such differences make it clear that the selection of either hard anodizing or ordinary anodizing depends on the degree of resistance and decoration needed for the work. Both methods are important for improving the life and usefulness of an aluminum part.

What factors determine the thickness of the coating?

What factors determine the thickness of the coating?

Impact of anodizing bath conditions on thickness

The parameters such as temperature, composition of the electrolyte solution, current density and the time duration of the anodizing bath influence the anodizing coating thickness, with some exaggeration, it can be said that the current density and time can be said to mildly correlate with the thickness of the anodizing coat. For example, changing bath temperature can impact the bath because there are higher-density coats that are thicker coats at lower temperatures. Other factors like phosphoric or sulfuric acid ion concentration influence the anodizing rate and the final coat thickness. To achieve the desired endpoint, the limit variables should be controlled fixturely.

Influence of alloy composition and substrate type

Similarly, the alloy’s composition, together with the type of substrate used, affects the properties of the anodized coating. The aluminum alloys respond differently to the anodizing process because of the alloying elements such as silicon, magnesium, copper, and zinc. For example, pure aluminum (like 1xxx series) tends to yield thicker and more uniform anodized coatings because of its extremely high purity. In contrast, alloys with higher copper content, like the 2xxx series, could yield non-uniform coatings or surface defects as copper instigates localized galvanic reactions during anodization.

Alloys rich in silicon, on the other hand, for example, the 4xxx series, tend to produce coatings of dull appearance and diminutive thickness, as silicon particles do not react during anodization. Magnesium alloys, like the 5xxx series, anodize easily and give tough coatings that withstand corrosion, which is why they are used where high corrosion resistance is needed. However, zinc-containing alloys, like the 7xxx series, cause more difficulties since the high zinc content can cause porosity and non-uniformity in the coating.

The preparation for the substrate surface is, without a doubt, influential. The oxide layer on the substrate undergoes changes as surface roughness or as surface impurities change. For example, polished or chemically cleaned surfaces tend to anodize more evenly in both thickness and visual inspection. One report suggests that using a 25-minute anodizing process with 20°C sulfuric acid results in 25-30 microns of coating for 99.5% pure aluminum substrates, while very high silicon alloys under similar conditions only attain 15-20 microns.

What might be equally important to consider is the precise composition of the alloy and the parameters for the substrate when deciding on the anodizing process. These variables have a direct impact on the coating performance, such as the hardness of the coated surface, its corrosion resistance, and even its aesthetic appeal. With the correct choice of alloys and pre-treatment processes, the results can be maximized for the intended use of the industry.

What are the applications and benefits of using hard anodize?

What are the applications and benefits of using hard anodize?

Applications of hard anodized aluminum in industry

Owing to its superior surface features, strength, and versatility, hard anodized aluminum is extensively employed in a range of industries. An outline of its uses is given below together with relevant examples and statistics.

Aerospace Industry

  • Hard anodizing is applied to hydraulic cylinders, landing gear components, and other structural supports for critical components to increase the components’ wear resistance and provide corrosion protection. For illustration, aluminum alloy 7075 with a 50-micron hard anodized coating exhibits an increase of 25% in fatigue strength in high pressure environments.

Automotive Sector

  • Pistons, brake cylinders, and suspension arms are some parts that are frequently hard anodized due to the mechanical and environmental stresses that they are subjected to. Anodized aluminum brake cylinders can have a service life of up to 30 % longer than that of untreated aluminum parts.

Electronics and Electrical Equipment

  • Aluminum enclosures are hard anodized for sensitive electronics components where protection against mechanical and thermal stress is required. These are common in delicate devices where EMI and abrasion need shielding. Tested anodized surfaces exhibited five times higher dielectric strength than uncoated metal.

Food Processing and Packaging 

  • Hard anodized coatings do serve the dual purpose of cleanliness and acid or alkaline resistance in cookware, as well as on conveyors and storage vessels. Take, for example, the study that has been done on the anodized aluminum non-stick cookware that these tools can endure 10,000 abrasion cycles.

Marine Industry 

  • Aluminum Parts used in ship fittings and offshore structures are likely to be immersed in saline environments. These parts can be hard anodized to add corrosion resistance. Some studies show an improvement of up to 50% in the service life of anodized aluminum parts over uncoated aluminum.

Medical Devices 

  • Hard anodizing is used on most medical instruments and components to achieve biocompatibility as well as resistive properties to autoclave sterilization. It has been reported that surgical tools that have hard anodized coatings have functional integrity after a thousand sterilization cycles.

Machinery and Industrial Equipment 

  • Some components including gears, rollers, and the bodies of valves are anodized so that maintenance requirements are reduced and wear resistance is increased in heavy-duty applications. It was observed that industrial rollers that were subjected to a 25-micron hard anodized coating gained 40% more operational durability.

Each of these applications utilizes the superior hardness, corrosion resistance, and insulating properties of hard anodized aluminum, which makes it essential for industrial high-performance solutions.

How hardness and fatigue strength are enhanced

The improvement of hardness and fatigue strength of hard anodized aluminum is due to the formation of a dense, smooth oxide layer on the surface of the material during the anodizing process. This layer is mostly made up of aluminum oxide (Al2O3), which is harder than sapphires and has a hardness range from 400 to 600 HV, depending on the particular process conditions like temperature and electrolyte composition.

The sealing of microcracks combined with the decrease of stress concentrators present on the surface due to the anodizing process helps to considerably increase the fatigue strength by preventing fatigue failure that is usually caused by untreated materials. Research shows that the fatigue strength of aluminum alloys with hard anodization is able to increase by 25% at most. The anodized layer’s uniformity and thickness are important with regard to failure. Coatings of thickness between 25 and 50 microns are commonly used for applications with high requirements of fatigue resistance because these thicknesses provide a sufficiently protective surface and don’t add too much strain.

The use of sealing methods including hot water and nickel acetate sealing improves the wear resistance and lowers the oxide layer’s porosity. This increases the load bearing capacity and service life in high stress conditions. There is also progress in the field of pulse anodizing which, in addition to everything else, will advance the hardness and fatigue-resistant characteristics by producing more dense and less contaminated oxide layers.

Such evolutions allow anodized aluminum to endure greater mechanical stress and operational life in crucial areas such as aerospace components. In such critical areas, the performance of materials and reliability is sometimes very essential.

Frequently Asked Questions (FAQs)

Q: What is the most common thickness for an anodized aluminum layer?

A: Depending on the type of anodizing applied, one can expect the anodized layer to be between 5 micrometers and 100 micrometers. Chromic types of anodizing usually lead to thinner coatings, whereas hard anodizing will produce thicker coatings.

Q: What changes does anodizing apply to the already existing aluminum surface materials?

A: The surface of aluminum expands due to oxidation, forming an anodized layer. This layer constitutes both the surface and the region beneath it. Roughly two-thirds of the coating grows into the substrate while the rest increases above the surface.

Q: Which measurement controls do surface engineering professionals employ to quantify the anodized coating thickness?

A: The unit of measurement for anodized coating thickness is typically defined in micrometers (µm). Surface engineers prefer using the SI system. For example, in imperial units, the term ‘mil’ (one 1/1000 inch) is popular. Descriptions of coatings can often include 25µm thick or 1 mil thick quotations as well.

Q: What is the effect of anodizing on the dimensions of aluminum components?

A: The dimensions of aluminium components experience a minimal increase due to anodizing. For instance, external diameters will grow by roughly 2 times the thickness of the coating. A coating thickness of 25 microns will increase the diameter by approximately 50 microns.

Q: How thick are the coatings that chromic anodizing and hard anodizing produce when compared with each other?

A: The coating produced with chromic acid chromic anodizing is generally thinner than 5 µm. In comparison, hard anodising has the ability to produce much more thick coatings greater than 100 micron which increases durability and wear resistance.

Q: What other parts of the anodizing process influence the overall thickness of an aluminum part?

A: The thickness of an anodised aluminium part is increased by the outward growth of the part, which in most instances is one third; thus, the overall thickness of the component is increased by the amount of coating done. In this example, if the coating thickness is 30 microns, then the increase in the total thickness of the part shall be approximately 10 microns.

Q: What considerations are needed when detailing the anodized coating thickness for aluminum components?

A: Anodized coating thickness must consider the purpose of the application, wear resistance, color tolerance, and other dimensional restrictions that may exist. It is necessary to work together with specialists in surface engineering to determine the coating thickness that is appropriate for the task at hand.

Q: In what ways can the anodizing thickness affect the process of further treatment, such as with primers?

A: The thickness of the anodized layer affects the relationship between the surfaces and the adhesion, as well as the quality of the primer. Thicker anodized coatings may need extra processes or primers offering anodized features to improve the area of the anodized coating where the primer is to be placed.

Reference Sources

1. Impact of Voltage Anodizing and Added Tobacco Extracts to the Structure of Porous Anodic Aluminum Oxide (PAAO) Layer

  • Graduate: Mustofa Akhmad Zein Eko et al
  • Date of Publication: January 15, 2024
  • Abstract: This research aims to analyze the effects of anodizing voltage and the addition of tobacco extract to the structure of PAAO. Studies have found that when the anodization voltage was increased, there was a corresponding decrease in pore diameter and an increase in the thickness of the anodic layer. The thickness of the anodic PAAO layer also increased steadily with the increase of both anodization voltage and concentration of tobacco extract, thereby establishing clearly that these factors affect the characteristics of the anodized layer.
  • Approach: To complete these tasks, samples were examined using a Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) to determine the impact of voltages and additive concentration changes on the morphology of anodic layers(Mustofa et al., 2024, pp. 51–64).

2. Effect of phosphate concentration on the efficiency of anodizing process and hardness of aluminum surface in 16% sulfuric acid solution

  • Authors: Robby Sudarman et al.
  • Publication Date: May 31, 2024
  • Summary: This research studies the effect of phosphate concentration on the anodizing process, the oxide layer thickness and the surface hardness of aluminum. The results revealed that the phosphate concentration greatly increases the oxide layer thickness and hardness which indicates that there is an increase in the anodized layer on the surface of aluminum.
  • Methodology: The authors vary the concentration of phosphate and determine the oxide layer thickness and oxide hardness using standard methods such as mass gain and hardness testing (Sudarman et al., 2024).

3. Characterization of Oxide Layer Resulting from Anodizing Aluminum with Variable Immersion Time

  • Authors: Andika Wisnujati, Ferriawan Yudhanto
  • Publication Date: August 15, 2023
  • Summary: This research studied the hardness and thickness of the anodized oxide layer on aluminum with respect to the immersion time. The findings confirmed the hypothesis that longer immersion times resulted in thicker anodized oxide layers which showed that anodizing adds thickness to the aluminum surface.
  • Methodology: The study included increasing the immersion times during the anodizing process and then measuring the oxide layer thickness and hardness using Vickers hardness and coating thickness gauges(Wisnujati & Yudhanto, 2023).

4. Aluminium

5. Anodizing

6. Alloy

 
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Greetings, readers! I’m Liang Ting, the author of this blog. Specializing in CNC machining services for twenty years now, I am more than capable of meeting your needs when it comes to machining parts. If you need any help at all, don’t hesitate to get in touch with me. Whatever kind of solutions you’re looking for, I’m confident that we can find them together!

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