When the Additively Manufactured Aluminum is mentioned general reference was given to an Aluminum part created by Selective Laser Melting which is the most common practice for 3D printing of metals and it is the case for Aluminum. SLM Aluminum parts due to the nature of the method (See 

“Additively Manufactured Aluminum Without a Corrosion Compromise” 

for more information) contains specific micro sections in a melt pool referred as i) Core ii) Melt Pool Borders iii) Heat Affected Zone (HAZ) and there are several effects on said sections of microstructure for the corrosion behavior of the part. SLM Aluminum contains a cellular microstructure made of Silicon rich cell walls and an alpha aluminum core. In normal conditions the corrosive attack tends to propagate towards Alpha-Aluminum and after cleaning a single cell stops the process meaning said cell wall prevents further corrosion. But the borders of the melt pools have been identified as a significant aspect in the corrosion of these materials among the many characteristics of the microstructural features of Additively Manufactured Al-Si alloys. Several investigations have revealed that Al cells in the melt pool boundaries are selectively corroded during corrosion tests. Although it is thought to be a hard process penetrating the cell walls with corrosion, some researchers find that the melt pool borders inhabit large corrosion lengths and are a driving force to overcome cell borders' challenges.

Representation of corrosion attack in a SLM Al-Si alloy with different melt pool sections identified, MBP: Melt Pool Borders HAZ: Heat Affected Zone


The unique microstructure of additively built Al-Si alloys is the product of extraordinarily fast cooling rates and thermal gradient direction. The directional distribution of heat gradients during the fusion and solidification of the material's distinct layers results in an innately anisotropic microstructure. The microscopic alpha-Aluminum cells enclosed by the Si network are rounded in the plane parallel to the building platform, but elongated in the plane perpendicular to the building platform. Furthermore, elongated laser tracks are easily identifiable in surfaces parallel to the construction platform (XY plane), but a scale-like characteristic of melt pool boundaries is frequently visible in surfaces perpendicular to the building platform (XZ plane). It is currently controversial how this anisotropy affects the corrosion behavior. Even though there are some theories conflicting each other and not yet a useful analogy has been made.


In general, the literature for metallic materials demonstrates that the higher the surface roughness, the higher the corrosion rate. Copper, nickel, aluminum, stainless steel, magnesium, and titanium alloys all showed this pattern. The effect of producing varying roughnesses on both localized and overall corrosion performance of the alloys was examined in all circumstances. Looking at the situation with a wettability angle, wettability impacts corrosion rate, and generally speaking, larger water contact angles result in lower corrosion rates. The contact angle decreases as the volume fraction of primary Si rises in Al-Si alloys between 7 and 50 percent. For samples roughened with 240 or 800 grit sandpaper, the water contact angle reduces from almost 80° to 65° as the weight percentage of silicon rises from 7% to 50% for the same degree of roughness and droplet size. It is also observed that an increasing contact angle is occurring with increasing surface roughness for Al-Si alloys.


Despite the fact that several studies have shown that the special conditions during 3D printing of Aluminum have a significant impact on the microstructure and corrosion behavior of these materials, few studies have been dedicated to investigating the impact of their special microstructure on corrosion protection mechanisms. These studies have been conducted so far to investigate the effect of microstructure, heat treatments, Si content, and flaws on the anodizing behavior of Al-Si alloys produced by selective laser melting. This anodization process of  Aluminum and aluminum alloys is conducted to increase the corrosion resistance of the part. There has not yet been a successful and consistent application of anodization made for SLM parts made with Al-Si alloy. Studies concluded that SLM-produced Al-Si alloys can be anodized. It was demonstrated, however, that the distinctive microstructure of SLM manufactured components has a considerable influence on the voltage-time response and the developed anodic oxide film. Furthermore, when compared to a cast alloy of the same chemical makeup, they demonstrated dramatically different anodizing behavior. The voltage-time response of the cast alloy exhibits the normal steady-state growth regime, but the AM material exhibits a continuous increase in voltage until a steady-state is attained. The moving oxide front will be hindered to a greater extent in additively manufactured Al-Si alloys due to the fine distribution and strong connectivity of the Si network, resulting in the production of a thinner oxide layer. Furthermore, the SLM alloy had a considerably lower oxide development rate than the cast alloy. This reduced oxide growth rate was attributable to Si oxidation consuming a greater percentage of the anodic charge in the SLM alloy. Furthermore, significant anisotropy was observed during galvanostatic anodizing of additively manufactured Al-Si samples. The voltage-time response curves of the anodized surface exhibited a varied response with different orientations. The voltage-time response of a surface parallel to the building platform (XY surface) is considered to have a larger steady-state potential value than a surface perpendicular to the building platform (XZ surface). This asymmetric anodizing behavior is independent of the alloy's Si concentration. The reason for said asymmetry is thought to be caused by differences in the size of aluminum cells on various planes, or simply by the density of melt pool boundaries encountered by the anodizing front.


With current studies showing a complicated process for complicated new microstructures inside the additively manufactured aluminum parts, currently, the industry does not have a reliable corrosion protection service available thus having to ship parts without any protection, so a compromise is made in the sector. But with the emerging technologies and recent developments in computer science, this problem can be solved. The Anodization of said additively manufactured parts is possible and can also be economically viable with the help of automated systems powered by an Artificial Intelligence network improving the parameter and solving the complicated adjustment problems encountered in the anodization process. Currently, in iyiMetal this solution is proven to be successful and shows a greater future promise for the industries using Al-Si alloys such as automotive, 

aviation, and aerospace. Especially in the automotive industry considering the emergence of the E.V market and with the pressure of Green Deal, Aluminum parts used in the sector are higher than ever and this anodization problem should be solved to design, manufacture and create parts that do not compromise on quality.

1-Martin, John H., et al. "3D printing of high-strength aluminium alloys." Nature 549.7672 (2017): 365-369.

2-Blakey-Milner, Byron, et al. "Metal additive manufacturing in aerospace: A review." Materials & Design 209 (2021): 110008.

3-Shakil, S. I., et al. "Additive manufactured versus cast AlSi10Mg alloy: Microstructure and micromechanics." Results in Materials 10 (2021): 100178.

4-Verkens, D. "Study of the anodizing behaviour of additive manufactured AlSi10Mg aluminium alloy." Vrije Universiteit Brussel (2016): 2017-10.

Corrosive Behavior of Additively Manufactured Aluminum

Additive Manufacturing (A.M) also known as 3D Printing has been one of the main focus of production techniques in many industries in the 21st century due to its high promise in various areas creating a multi-billion USD industry both in production and research & development. With the push of the sector and the ever-increasing interest of the industry, metal additive manufacturing technologies are increasing at a fast rate to fill the needs of many with the un-parallel capabilities that are not possible to fulfill with any other metal production method. The rapid pace of the worldwide development of this technology and its adaptation of commercially-availability is quite prominent.

The main principle of additive manufacturing is to create a part with the layer-by-layer approach. Creating a new layer on top of the existing one with a precise technique. Because of this layered nature, it is also referred to as Layered Manufacturing. This type of approach is significantly beneficial for creating complex structures which are much harder to produce using traditional methods. Although there are several types of achieving said Layered Manufacturing existing under the additive manufacturing roof, Selective Laser Melting (SLM) accounts for most of the industry with its on-point accuracy, melting a loose powder bed with high precision laser creating layers after layers.

The last decade shows highly promising improvement in the metal additive manufacturing market and it is valid to assume this increase in the market is a direct result of the increase and availability in the technology.

Considering the ongoing research efforts still in progress and the ever-reaching new goals in the quality side of the parts, it is not irrational to assume this increase in the market is not going to slow down any time soon.

The basic concept behind A.M - SLM production is boiled down into two main acts; deposition of the prepared metal in a powder form and scanning of the designated cross-sectional area with a high-energy laser to achieve precision local melting in the desired spots. Both of these processes involve delicate engineering for obtaining optimum performance. The powder is the building block of the process and the selection of the right powder is crucial. This selection and preparation are done according to the particle size, surface finish, and microstructural composition. It is also important to utilize optimum moisture and oxide levels which can affect the final property of the material.

The Scanning process of SLM can be divided into three parts starting with a single dimensional line, a scan track, created with said mechanism, a horizontal overlap of multiple scans tracks creating a layer, and the vertical overlap of the layers completing the 3D structure. Throughout this process important parameters fall under four distinct categories;

 Laser Power, Laser Size, Pulse Duration, Pulse Frequency

 Particle Size, Particle Shape and Distribution, Powder Bed Density, Layer Thickness, Material Properties.

Powder bed temperature, Powder Feeder Temperature, Temperature uniformity.


Materials that have high-reflective properties such as Aluminum consequently require higher power lasers in order to melt without a problem. Otherwise, the partial melting of the spot could lead to a distortion of the alloy.

With this many variables to account for in such a young technology, the constant improvement and optimization of the process are well expected and every new achievement consequently means high promise for the future of the technology.

Selecting an alloy suitable for the SLM production is considered to be similar to the alloy selection in the casting process and welding process. Although there are some similarities across the methods the difference is still quite significant. The most important and also the most unique difference in terms of SLM is the very high cooling rates subjected to the alloy that might cause all sorts of problems that need to be overcomed by selection of the right alloys.


Investigating a part produced with SLM with two main perspectives:

In terms of Additive manufacturing of Aluminum with SLM process overcoming said challenges with conventional 2xxx,5xxx,6xxx, and 7xxx alloys is not fully doable with industrial scales, and high cooling rates in SLM result in these alloys micro-crack resulting in parts that are unusable in terms of structural integrity. They simply aren’t considered successfully processable by SLM. But the unique properties observed in the Al-Si alloys exhibit advantageous ease in the production of 3D Printed Aluminum.


It is observed that with increasing Silicon content the

 of the molten metal decreases. Looking at the phase diagram of the Al-Si, increasing silicon content results in a lower melting temperature up until the eutectic point. This decrease in melting temperature providing a lower viscosity works very well in favor of the previously explained SLM mechanisms. One of the main reasons for encountering a malfunctioning product is that there is not enough time for the molten metal to fully encapsulate the melting pools resulting in defects leading to problems in the Structural integrity side of things.


But creating a low viscosity alloy with the help of added silicon provides a perfect fit for avoiding such problems because with the lack of resistance to flow (definition of low viscosity) the molten metal is enabled to move much quicker than other alloys and this provides plenty of time to encapsulate the melting pools properly avoiding the unwanted defects.

These benefits result in AlSi10Mg and AlSi12 alloys gaining the most attention with additive manufacturing of the Aluminum parts. The work and research being done for these Al-Si alloys massively surpass the other aluminum alloys.

To further increase the properties of SLM Aluminum alloys it is also necessary to provide a high temperature in the melt pools working towards further lowering the viscosity level.

These 3D printed Al-Si alloys are one of the main focuses in many industries such as automotive, aerospace, and aviation specifically with the parts that demand complex structural design.


Investigating the microstructural properties of the Al-Si alloy parts manufactured with the SLM process the solidification mechanism is observed as cellular-dendritic, to identify more broadly one should consider the proposition that the history of heat equals the microstructure. During the SLM process, the material is put through to thermal gradients that are very high and re-melted repeatedly due to both the penetrating power of the laser beam across the layers and the overlaps in the scan track. Cooling and solidification happen very rapidly, between 10^3 to 10^8 Kelvin per second, resulting in a fine microstructure made by metastable phases. This fine microstructure is opposite to the coarse microstructure observed in traditional casting

With a first glance three distinct sections of each melt pool manifests themselves as important in terms of temperature:

i) Core of the Melt pool providing a cellular pattern in a finer equiaxed structure. Referred to as “Fine Zones”.

ii) Melt pool boundary providing coarser cells that are elongated. Referred to as “Coarse Zones”.

Each section provides different properties and the amounts and locations of said sections are determined by various parameters such as the partial overlap ratios in the scan track creating re-melts and cooling rates subjected to the aluminum powder. Various combinations give a very wide range of properties in the final product allowing the possibility of tailoring in the production.

Aluminum in its natural form has a tendency to become corrosion resistant due to its nano-scale oxide layer formed on the surface. To further increase this beneficial property an electrolytic passivation process, anodizing is used for creating an even thicker oxide layer increasing the scale from nano to micro level.


Although it is quite a common and simple process to anodize some aluminum alloys, working with high silicon aluminum alloys which has a large place in additive manufacturing and casting part industries it is still not conveniently anodized for commercial use. Even though the addition of silicon into the metal allows it to become much more processable in terms of casting and additive manufacturing, the presence of silicon interferes with the anodizing process which eliminates a standard practice in traditional aluminum part production. An algorithm-based method created specifically to supervise the anodizing process of high silicon aluminum alloys is currently being developed in iyiMetal to overcome the shortcomings and allow the mass production of the said high silicon Aluminum alloy anodizing process. Creating this process on an industrial scale would enable a broad new range of possibilities in many industries such as Automotive, Aviation, and Aerospace that heavily use this type of high silicon aluminum alloy parts in their design. With the recent developments in artificial intelligence over the last decade, implementing this newly developed technique into coating technology is the basis of the process.


The said anodizing process is a life-extending coating mechanism aiming to increase the quality of the part for better performance. The absence of this vital coating process in the parts produces with additive manufacturing or SLM, implicates some serious performance deficiencies mostly in terms of quality of life and longevity of the part. Being able to anodize previously mentioned parts would create a path to a longer life, hustle-free user experience.

1-Verkens, D. "Study of the anodizing behaviour of additive manufactured AlSi10Mg aluminium alloy." Vrije Universiteit Brussel (2016): 2017-10.

3-Aboulkhair, Nesma T., et al. "3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting." Progress in materials science 106 (2019): 100578.

Additively Manufactured Aluminum Without a Corrosion Compromise

In the 19th century, by the discovery of the extraction of aluminum, has started a new era in engineering. Recent technological developments have opened a way to enhanced aluminum alloys. Consequently, aluminum alloys find a wide application area in the industry especially in transportation. Since aluminum provides  high corrosion resistance, has a high strength to weight ratio and low melting point, which ensures recyclability. Aluminum is the 3rd lightest metal in the earth crust, so its low theoretical density results in higher specific strength of aluminum than steel. Corrosion resistance in the ambient atmosphere is another engineering design parameter that encourages the use of aluminum, because of the passive oxide layer that composed itself. Even though there are numerous positive parameters listed for aluminum, none of the metals that are manufactured cannot be used as they are produced. One of the important treatments is done to make surface appearance better and improve the quality of the material to enhance corrosion resistance and surface quality, hardness and wear properties of the engineering materials, which is called surface treatment in the engineering terminology. Surface treatment of aluminum is divided into two distinct subgroups regarding their application method. second group of the surface treatment consists of passivation, powder coating, and anodising. Among surface treatments anodising is the most applicable and beneficial method, and in the recent research surface treatments will be compared and the reason for wide application of anodising will be argued.

Powder coating is a common technique for surface treatments of many materials, including aluminum. The mechanism of this process relies on applying the dry mixture of resin and pigment through an electrostatic gun to coat the material surface. Powder coating is an option for conventional painting since it offers more protection to the material and is relatively eco-friendly in contrast to the liquid painting. Even though powder coating is better than traditional coating, it is inadequate against anodization. The coating layer provided by powder coating cannot adhere to the surface as well as the oxide layer, which results in the peeling of the layer quickly. Since the coating layer cannot adhere as well as the oxide film to the material's surface, oxidizing agents have a higher chance of finding a way to leak in. Thus, even a small amount of water present within the coating and layer will result in corrosion to take place. That is called crevice corrosion, which can be considered the most dangerous corrosion type because observation of the propagation of corrosion is not possible. Moreover, it has been claimed that powder coating has no volatile organic compounds (VOCs') or is not harmful to the environment. But powder coating constituents involve within the VOCs' somewhat. According Karel Kellens et al. study, it is reported that by using the Europe ReCiPe H/A life cycle assessment method, the environmental impact of the powder coating was determined. Consequently, the ecological impact level was found to be the midpoint level. Midpoint level categories, as indicated in the study, are fossil depletion, climate change ecosystems, particulate matter formation, human toxicity, and climate change human health. (2015, p. 423) As a result, although powder coating is said to be eco-friendly, the byproducts of the process are not environmentally friendly.

Hexavalent Chromium Coating and Trivalent Chromium Passivation

In recent years, hexavalent chromium salts have been faced with strict regulations by Registration, Evaluation, Authorisation, and restriction of chemicals (REACH). REACH is a constitution that regulates and prevents the chemicals that threaten human life. According to REACH, hexavalent chromium is classified as carcinogenic and mutagenic, unlike trivalent chromium. The industrial use of hexavalent chromium was stopped on 21th of September 2017 by REACH because of its severe negative impact on the environment and human health. As WHO stated, hexavalent chromium is considered to be carcinogenic to lung, nasal, and sinus cancers. Since hexavalent chromium can easily pass the cell membranes by using sulfate transport systems, once the hexavalent chromium is absorbed by the cell membrane, the oxidation to tetravalent or pentavalent chromium might occur. These intermediate products can cause health abnormalities. Besides health problems, hexavalent chromium also causes environmental problems. Leakage of hexavalent chromium waste results in contamination of municipal water or underground water sources, which also threatens human life. The contamination of groundwater sources also affects the soils. Consequently, alternative technologies that prioritize human life are developed to manufacture hexavalent-free chromium coating products. However, in the aviation industry, hexavalent chromium coating is still used. On the basis, trivalent chromium plating is done following the same process routes, with slight operational change. When hexavalent and trivalent chromium products are compared, the drawback of trivalent coating is obvious. According to table 6.4.1A, which is given in the Toxics Use Reduction Institute University of Massachusetts Lowell work, many parameters are similar, but the maximum coating thickness that can be achieved by using trivalent coating is less than hexavalent coating. (2006. Chapter 6) Furthermore, it is concluded by Flink and Västerlund that the 6xxx series of aluminum coated by trivalent chromium has a lower contact angle in contrast to hexavalent chromium conversion, and while the hexavalent chromium coating is thick and compact, trivalent chromium coatings are found to be thin and do not have as high coverage as hexavalent coatings. (2016) Moreover, the amount of water used within the anodizing bath is higher than hexavalent and trivalent, which makes chromium baths less sustainable than anodizing process. From the overall analysis, it can be emphasized that using chromium compounds in the metal coating can be very detrimental to the environment and threaten human life by contaminating municipal water systems or polluting soil. Briefly, neither hexavalent chromium nor trivalent chromium coatings contribute to the green environment.

In the recent decade, concerns about global warming have increased. From the aluminum point of view, recycling and waste reusing have come up. Since aluminum alloys have broad application areas in the industries such as automotive, food packages, beverage cans, and aviation, secondary aluminum production gains importance. Besides, increasing the recycling rate of aluminum is not just correlated with the source of scrap. Primary production of aluminum is an energy-costly process and less environmentally friendly. As a result, secondary aluminum's economic and environmental contributions make it attractive. Recycling also helps to eliminate landfill occupation and reduces climate change issues for the industry. In Addition, anodized aluminum increases the aluminum scrap quality because no other elements must be removed. When extra layers are composed on the surface, they should be removed before the process; Thus, excess waste is created. Consequently, anodized aluminum enables easy recyclability, which can be realized with endless cycles without extra process parameters. When primary and secondary aluminum production is compared, as stated by Das et al., production from its ore requires 48 kWh of energy and 12 kg of carbon dioxide emission for each kilogram of metal produced. On the other hand, recycling aluminum only requires 2,8 kWh of energy and 0.6 kg of carbon dioxide emitted to the environment from each kilogram of metal produced. Therefore, energy consumption and emission of green gasses are reduced by approximately 95%. (2010, p. 22) As indicated in Aluminum Industry Vision, electrical energy that is consumed by aluminum can be considered as an "energy bank." (2001, p. 17). Compared with other materials such as steel and polymers, recycling aluminum and its alloys is effortless. Moreover, the quality that is obtained from recycled aluminum is higher. As steel scraps are recycled, the quality of steel is decreased; thus, obtaining a certain quality is challenging. When polymers are considered, the primary reason that causes global warming since they are non-degradable in nature. Furthermore, some types of polymers can never be recycled. Therefore, recycling aluminum is more feasible, energy savings are higher, and carbon dioxide emissions are lower, which makes the usage of aluminum reasonable. In brief, aluminum produced by conventional metallurgical extraction techniques embeds electrical energy into the material. In contrast to primary aluminum, aluminum manufactured from secondary resources contributes positively to the environment and energy usage.

In the end, in contrast to other surface finishes, anodization offers more precise solutions to recent environmental issues and improves surface quality by enhancing, which is composed natural oxide layer by aluminum itself. First of all, anodization plants complete the overall process without chemical loss. Pre-treatment step, which threatens the environment, does not involve anodizing; thus, significant recovery rates are obtained for wastewater formed during anodization. Moreover, after the surface treatment, harmful byproducts do not form, such as carbon dioxide, solvent emissions, or volatile organic compounds. AAC emphasizes that "anodizing is a water-based process and uses no volatile organic compounds (VOCs)." (n.d.) In anodizing usage of vehicle solvents, carrier resins, pigmentation, or halogenated hydrocarbons do not take place. However, the wastewater of anodization does not contain any hazardous waste and minerals produced. In Addition, aluminum-rich wastes are eco-friendly and valuable in some pollutant-removing processes. Another point is that anodizing takes advantage of the base metal to increase the thickness of the oxide layer, thereby creating a strong and corrosion-resistant coating achieved in the cleanest way. Also, anodizing improves the products' life and enhances the ability to recycle. Besides, the oxide layer after the anodizing contributes to mechanical properties such as wear resistance, hardness, and durability. Other positive help of anodizing is color stability, aesthetic looking, and cost-effectiveness. Among them, the most crucial contribution is offering health and safety. From the overall highlighted points, which are discussed with their proofs, it can be concluded that anodization is the most proper surface treatment technique for aluminum; as citizens living today, increasing the use of anodization should be one of the steps to be taken in order to leave a greener world for our children and young people to live in in the future.

[1]  Kellens, K., Paraskevas, D., Dewulf, W., & Duflou, J. R. (2015). Environmental comparison of metal coating processes. 

[2] University of Massachusetts Lowell. (2006). Five Chemicals Alternatives Assessment Study. Chapter 6. The Massachusetts Toxics Use Reduction Institute. pp. 294-350.

[3]  Västerlund, E., & Flink, R. (2016). Analysis and characterization of environmental friendly trivalent chromium passivation of aluminum alloys.

[4] Das, S. K., Green, J. A. S., & Kaufman, J. G. (2010). Aluminum recycling: economic and environmental benefits. 

[5] Aluminum Industry Vision. (2001). Sustainable Solutions for a Dynamic World. The Aluminum Association. p. 17.

[6]  Aluminum Anodizers Council. (n.d.). Anodizing and the Environment.

https://www.anodizing.org/page/anodizing-environmental-advantages