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Comparison of commonly used metal materials for 3D printing: titanium alloy and aluminum alloy

Introduction
Metal is currently one of the most important materials in additive manufacturing processes, and its excellent performance is suitable for applications that require strict performance and strength requirements. In this article, we will focus on introducing the two main metals used in 3D printing: titanium and aluminum. These two materials are mainly used in processes such as laser powder bed fusion (L-PBF) or directed energy deposition (DED), and are generally in powder form. We will compare their similarities and differences in order to better understand their characteristics and applications, as well as the advantages they provide in the manufacturing process.
Production and characteristics of titanium and aluminum
Titanium: Titanium is a material that does not appear as a standalone element in nature and must be extracted from minerals such as rutile (TiO2) or ilmenite (FeTiO3). The extraction of pure titanium is a complex process that involves multiple steps. The widely used method for producing pure titanium * is the Kroll method, developed by American chemist William J. Kroll in 1940. This method uses chlorine gas (Cl2) to reduce titanium dioxide (TiO2) to produce titanium tetrachloride (TiCl4), which is then reduced with magnesium (Mg). Although the Kroll process is effective in producing pure titanium, it is a high cost process that requires a large amount of energy. In addition, the high reactivity of titanium makes it difficult to obtain as a pure metal, and samples with a purity of 99.9% are considered commercial pure titanium. Therefore, it is usually used in combination with other elements to form alloys.
Titanium has many properties and can be used in many fields. It is usually used in the form of alloys, but due to its high biocompatibility, pure extracted titanium is often used in the medical industry. Its main characteristics are high mechanical strength, low density, excellent corrosion resistance, and high rigidity.
There are several types of titanium alloys used for 3D printing:
Ti6Al-4V, Grade 5: * Important and * Common titanium alloys. Due to its high strength and durability, it is used in additive manufacturing. This alloy is composed of titanium, aluminum, and vanadium, and can withstand high temperatures and corrosive environments.
Ti6Al-4V, grade 23: Due to its biocompatibility, it is commonly used in medical implants and prostheses.
Ti Beta 21S: Stronger than traditional titanium alloys, and more resistant to oxidation and deformation. It is very suitable for orthopedic implants and aviation engine applications. Beta titanium is highly respected in orthodontics.
Cp Ti (pure titanium), grades 1 and 2: Due to the biocompatibility of titanium with the human body, this alloy has a wide range of applications in the medical industry.
TA15: An alloy made almost entirely of titanium, with the addition of aluminum and zirconium. The components made of this alloy are very sturdy and resistant to high temperatures, making them very suitable for manufacturing sturdy components for aircraft and engines. Compared to their strength, they are also very light.
Aluminum: Aluminum is a metal that provides a compromise between lightweight and strength. In addition to corrosion resistance, it can also be welded. Its pure state is very rare, so it is used in the form of an alloy that contains metals such as silicon and magnesium that can improve its physical and mechanical properties. To obtain pure aluminum, it is necessary to first use the Bayer method to obtain alumina from bauxite. The ore is washed and crushed, dissolved in caustic soda, and filtered to obtain pure aluminum hydroxide. Then heat to obtain alumina powder. Then, using the Hall Heroult process, aluminum oxide is electrolytically reduced to obtain pure aluminum.
As mentioned above, aluminum alloys are more common than pure aluminum and are used in many industrial applications. In addition, they also have excellent strength to weight ratio, as well as excellent fatigue and corrosion resistance. On the other hand, it also has recyclability, thermal conductivity, and conductivity, and low toxicity.
The main alloys used for aluminum 3D printing are as follows:
AlSi10Mg: This is a common alloy formed by silicon and magnesium. It can be used to manufacture sturdy and complex parts, as well as to manufacture casings, engine parts, and production tools.
Al2139: Strong aluminum alloy, due to its light weight, high strength, and chemical resistance, is very suitable for industries such as automobiles. It has been used by organizations such as the US Air Force, Mercedes Benz, and Airbus. The beauty of this material lies in its design specifically for additive manufacturing, with superior performance compared to many other alloys on the market.
Al 7000 series: This is a * powder alloy series with high tensile strength and low temperature resistance.
Al 6061&Al 7075: * Recently, 3D manufacturers have achieved good results using these two alloys. The tensile strength and hardness of 6061 are lower than 7075. On the other hand, 7075 has better impact resistance and smaller deformation than 6061 aluminum.
A201.1: It is part of the 200 series copper aluminum alloy and is known for its strong durability. However, they are difficult to cast. These alloys are recommended for applications where strength to weight ratio is crucial, such as transportation and aerospace.
What is the difference between the two?
In terms of strength to weight ratio, titanium is an ideal choice when high strength and durability are required, which is why it is used in medical components and even satellite components. On the other hand, although aluminum is not as sturdy as titanium, it is lighter and more affordable. In terms of thermal performance, aluminum is very suitable for applications that require high thermal conductivity. On the other hand, titanium is very suitable for applications in high-temperature environments, such as aviation engine components, due to its high melting point. Aluminum and titanium both have excellent corrosion resistance. However, titanium is more biocompatible than aluminum, which is why it is widely used in the medical field.
Material form and compatibility with 3D printing technology
Form
In most cases, titanium and aluminum appear in powder form, but they can also be provided in wire form, such as titanium or aluminum wire provided by Virtual Foundry or Nanoe. To use these metal 3D printing parts, it is necessary to first obtain alloy powder, which is mainly achieved using two technologies: plasma atomization or gas atomization. Plasma (ionized gas) atomization is a process that uses high temperature, energy, and heat sources, inert media (such as argon), and high-speed atomization of metals to produce high-quality wear-resistant powders. Gas atomization uses air, argon, or helium as gases to break the molten material flow, which is a very effective process widely used in the production of small spherical metal powders.
3D printing technology used
To use titanium in 3D printing, processes that can be used include laser powder bed melting (L-PBF), DED, and adhesive spraying (BJ). For processes related to aluminum, in addition to those already mentioned, there is another type that is cold spraying.
In L-PBF, the laser beam is used to heat the powder metal layer by layer to its melting point and construct the object. Titanium melts at very high temperatures (1600 ° C), so it is necessary to analyze the thermal and mechanical effects of the material before 3D printing. The melting temperature of aluminum is much lower (about 630 ° C), but aluminum has high reflectivity and thermal conductivity. Another interesting aspect of aluminum additive manufacturing is that it forms a natural oxide layer.
Regarding DED, it is very similar to the previous process, but the material here melts during nozzle deposition and can be used in powder or wire form for manufacturing. Usually, this technology leads to higher production speeds and lower unit volume costs.
In the BJ process, the material is in the form of unmelted powder, but in order to make the particles adhere to each other, multiple nozzles are used to print and spray the adhesive onto the layer at a specific location. After printing, sintering steps or other post-curing treatments are also required. When they leave the 3D printer, these components are very fragile and porous, requiring heat treatment to achieve their final mechanical properties.
In the cold spraying process, metal materials also exist in powder form, but since melting or fusion is not necessary in this case, cold spraying can avoid thermal deformation and does not require a protective atmosphere.
Post processing
In order to obtain * results, one or more post-processing steps must be taken. There is no specific difference in the post-treatment of titanium and aluminum, so the following steps are applicable to these two materials. Due to the frequent use of titanium and aluminum in applications that withstand mechanical stress, shot peening is very useful. Spray small metal or ceramic beads onto the surface of the part, causing controlled deformation of the surface layer of the part. This improves the adhesion of subsequent coatings and reduces the likelihood of cracks and fractures. Shot peening only removes the top layer of the material, which can improve the appearance of the parts, remove dirt and corrosion, and prepare the surface for subsequent coatings.
Another option is to combine metal printing with traditional manufacturing methods. CNC machining is a post-treatment process suitable for this purpose, as it ensures strict tolerances and the required surface finish. Especially with the use of DED technology, the surface of 3D printed components is very rough because the metal melts directly during the spraying process. Therefore, CNC machining is always required to obtain a smooth and clear surface.
Annealing is a heat treatment option that heats printed components to high temperatures and rapidly cools them to alter their microstructure, thereby improving the material's ductility or ability to deform under load before fracture. Usually, this process can achieve better mechanical performance and is mainly used for aluminum parts.
When aluminum and titanium are used in so-called indirect 3D printing processes such as FDM or powder bonding, sintering is also required. After the printing stage, the components must undergo a degreasing process to separate the polymer from the metal adhesive. Then heat the components in the sintering furnace to a specific temperature, just below the melting temperature, which will consolidate the final object. This results in a very low porosity of the component, as the cavity where the adhesive is located is compressed during this process, leading to part shrinkage.
Application
The aerospace industry has found that the use of titanium in additive manufacturing has great benefits. It is an ideal material for manufacturing aerospace components such as jet engines and gas turbines, as it can significantly reduce the weight of high stress structures. An example of the application of titanium in additive manufacturing is the collaboration between Boeing and Norsk Titanium to manufacture large structural components for the 787 Dreamplane. The technology used in this process is DED, which is reported to be 50 to 100 times faster than powder based systems and 25% to 50% less titanium than forging, potentially saving up to $3 million per aircraft.
Although titanium is currently being used for space exploration through 3D printing, the application of aluminum in industry has multiplied. For example, Boeing is using aluminum alloy coated with nanoparticles during the cooling phase to produce 3D printed components. This makes it possible to weld extremely sturdy aluminum alloys without cracking at high temperatures. The manufactured components are lighter, allowing the aircraft to effectively use fuel and fly longer distances with the same amount of fuel.
Although the high price of titanium in the automotive industry may hinder its widespread use, we may see an increase in its use in this field, especially in the luxury goods sector. Currently, 3D printing is used to manufacture components with a crucial weight/performance ratio. For example, Bugatti printed brake calipers for its titanium brake system using SLM technology in just 45 hours. It is reported that the result is 40% lighter than traditional milled aluminum brake calipers. Although lightweight, titanium components also ensure their elasticity and temperature resistance.
On the other hand, aluminum is more common in the automotive industry. Porsche uses 3D printing to manufacture high-performance aluminum pistons for its flagship 911 model GT2 RS. Using this technology, a 700 horsepower twin turbocharged engine can achieve up to 30 horsepower of power and improve efficiency. In addition, in 2020, Porsche produced an all aluminum 3D printed casing for electric transmissions, which passed all the company's quality and load tests.
*Titanium is a very attractive material in the medical industry due to its high strength, corrosion resistance, and biocompatibility, making it an ideal choice for orthopedic and dental implants. 3D printing allows for the creation of porous structures that mimic bone textures, which helps with rapid healing and growth of bones and tissues. TrabTech in Türkiye uses titanium to make trabecular implants, such as hip joints. Aluminum is not as common as titanium in the medical industry, but it can be used for orthopedic and dental applications.

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