Heatsinks play a vital role in mechanical and electronic devices. Acting as passive heat exchangers, they transmit heat to a fluid medium (mainly air) from hot components. They are often made through the aluminum extrusion procedure, after that high-quality aluminum heatsinks are mostly work completed with anodized finish. This is done because anodization comes with a lot of advantages. But, first it is time to discuss what anodization is and how it works.
What is Anodization Procedure?
Anodization is an electrochemical method. Unlike powder coating or painting, nothing is applied to the surface of the aluminum. On the contrary, anodization turns the naturally present oxide layer (to protect it from corrosion) on the metal’s surface thick. This leads to improved corrosion resistance.
Characteristics of Anodization
- Resistance to corrosion (the acetic salt spray test of ISO 9227 expects that anodized aluminum will not show pitting after twenty-four hours)
- Electrical insulation (breakdown voltage changes from little to some hundred volts, as per the alloy, the thickness and nature of the film)
- High emissivity
- Superficial hardness
- Good appearance due to colors
Anodizing procedure has 5 main steps.
Acidic and alkaline cleaners are utilised to get rid of any residual dirt or grease on the surface. Then, the sodium hydroxide is used to etch the surface for removing slight surface imperfections. In this phase, a thin metal layer is taken off for creating a matte or dull finish. Next, this surface is made bright to an almost mirror finish by using a concentrated mixture of nitric and phosphoric acids to chemically smoothen the surface of the metal. Now, the surface can be anodized by letting electrical current pass through an acid electrolyte bath, which has the metal immersed in it. The thickness of the coating and characteristics of the surface are tightly regulated to meet the specifications of the end product.
Different ways contribute to coloring. When it comes to the technically advanced quality of color, the 2-step electrolytic coloring procedure is the aptest. The anodized part is put inside a bath, which has an inorganic salt metal. Then, the application of current, deposits the salt in the pores' base. The color that results from this depends on the metal that has been used, the dye intensity of the organic dyes and the processing conditions. Inorganic salt baths usually include cobalt, tin, copper and nickel.
Advantages of Anodized Aluminum Heatsinks
Finish Changeability – Interchanging of aluminum components is easy by swapping the material finish of one for another. This process often does not need any process change or tooling to be done. By changing the material finishes, it is possible to alter the performance of the reflector and appearance when required. You can use various versions of the reflector for varying optical situations like different distribution requirements or light sources.
Finish Variety – Anodized aluminum has over 50 variants of finishes (excluding colors or textures). The options include diffuse finishes, highly specular finishes and even asymmetrical choices to assist in overcoming particular issues related to design. Here, it must be kept in mind that all aluminum materials are capable of getting color anodized, i.e., colored dyes can be added to the aluminum extrusions. The porous layer of oxide is filled with dye that gets locked in and stands up to fading. Colors, such as green, blue, black and others are used to dye anodized heat sinks. The real effect of the color caters only to visual aspects and has nothing to do with transferring heat. Irrespective of the hue, heat transfer will not be impacted. At this point, take note that powder coating or painting should not be applied on heat sinks as these coatings act as insulators and impact heat transfer negatively.
Surface Emissivity - Anodized aluminum has improved surface emissivity (It is the ratio of the energy radiated from a surface’s materials to that radiated from an ideal emitter, called blackbody, at the same wavelength and temperature and under the same viewing conditions. It is a dimensionless number between 0, for an ideal reflector and 1, for an ideal emitter). The rise in emissivity makes a high difference in passive and small heat sinks. In case your heat sink is large, the enhanced radiation transfer of heat makes little difference. If the heat sink is active, the noticeable difference is minimum.
Tooling – No Tooling – Most aluminum reflectors can be manufactured without hard tooling, thereby, decreasing the total costs related to the production of parts. There are, however, a few exceptions to this.
Enduring Temperature and Dissipating Heat – When it comes to tolerating cold and heat, aluminum-based materials are known to be useful. A few coatings and layers on certain versions are temperature restricted. But, the higher temperatures at which the reflective features start failing are in the range of 510°C/950°F range. Keep in mind here that aluminum is an excellent conductor of heat and dissipates it with efficiency. In fact, it is the most common heat sink material in use.
Duration and Cleanability – Anodized aluminum has a long and useful life cycle. Aluminum can stand cold, UV, salt spray and heat. Cleaning this form of aluminum is quite convenient. You can use easily available products of cleaning for the purpose and resort to traditional methods of cleaning. You may find aluminum reflective finishes that last for over 25 years.
Prototypes and Production Start-up Expenses – Most of the aluminum reflectors allow prototyping and production as short-term components without hard tooling. Production can occur without tooling or commence a transition to a more economical procedure, as per the quantities needed. This allows you the choice to run lower production quantities without extra costs.
Completely Recyclable - Aluminum does not produce smoke or burn, caters to building codes for preventing smoke and fire and is 100% recyclable.
Strength - The reflectors that are made from aluminum are astonishingly strong at holding the optical shape and ensuring performance over a huge variety of environmental conditions.
As visible from the above list, anodized aluminum heat sinks display several benefits.