Titanium and Aluminum Alloys: Excellent Options for Additive Manufacturing in the High-End Aerospace Sector

Advantages and differences of titanium and aluminum
Aluminum and titanium alloys, due to their excellent low density and structural strength, are used in a large number of applications in aerospace, automotive, and machine building, whether using 3D printing or CNC machining, and are especially important in the aerospace industry, where they are the primary structural materials.
Titanium and aluminum are both light, but there is still a difference between the two. Although titanium is about two-thirds heavier than aluminum, its inherent strength means that a much smaller amount can be used to achieve the required strength. Titanium alloys are widely used in aircraft jet engines and all types of spacecraft, where its strength and low density reduce fuel costs. Aluminum alloy, with a density of only one-third that of steel, is the most widely used and common material for automotive lightweighting at this stage; there have been studies showing that aluminum alloy can be used for up to 540kg in a complete vehicle, in which case the car will lose 40% of its weight, and the all-aluminum bodies of Audi, Toyota, and other branded vehicles are a good example of this.

Since both materials have high strength and low density, other factors of difference must be considered when deciding which alloy to use.
Strength/Weight: In critical situations, every gram of a part counts, but if a higher strength component is needed, titanium is the best choice. Because of this, titanium alloys are used in the fabrication of medical devices/implants, complex satellite components, fixtures and braces, and more.
Cost: Aluminum is the most cost-effective metal to use for machining or 3D printing; titanium costs more but can still drive a leap in value. The fuel savings for an airplane or spacecraft from lighter parts will pay huge dividends, while titanium parts last longer.
Thermal properties: Aluminum alloys have high thermal conductivity and are often used to make radiators; for high-temperature applications, titanium's high melting point makes it even more suitable, and aero-engines contain a large number of titanium alloy components.
Corrosion resistance: Both aluminum and titanium have excellent corrosion resistance.
Titanium's corrosion resistance and low reactivity make it the most biocompatible metal, and it is widely used in medical (e.g., surgical instrumentation.) Ti64 also resists salt environments well and is often used in marine applications.

Aluminum alloys and titanium alloys are both very common in aerospace applications. Titanium alloy has high strength, low density (only about 57% of steel), and the specific strength (strength/density) is much greater than other metal structural materials, which can produce parts with high unit strength, good rigidity and light weight. Aircraft engine components, skeleton, skin, fasteners and landing gear can be used titanium alloys. 3D printing technology reference to check the information found that aluminum alloy is suitable for working in the environment below 200 ℃, Airbus A380 fuselage with aluminum accounted for more than 1/3, C919 also used a large number of conventional high-performance aluminum alloy materials. Aluminum alloys can be used for aircraft skins, spacer frames, wing ribs, and so on.

Titanium Additive Manufacturing and the Aerospace Industry
As noted in the Global Aerospace & Defense Industry Outlook 2019 published by Deloitte, as the aerospace and defense industry continues to grow, so will the demand for production. And, when designing for aerospace and defense applications, material selection is critical. For components that leave the ground, reducing the number of components and weight is critical. In these areas, every 1g of weight reduction brings significant benefits.

Titanium has an extremely high melting point of over 1,600°C and is typically difficult to machine, which is the main reason why it is more expensive than other metals.Ti6Al4V is the most widely used titanium alloy, and is not only lightweight, but also has high strength and temperature resistance, which have made it a popular material in aerospace applications. Common applications include parts such as blades, disks, and magazines used in the manufacture of engine fans and low-temperature sections of pressurized airplanes operating in the 400-500°C temperature range, as well as in the manufacture of fuselage and capsule assemblies, rocket motor cases, and helicopter rotor blade hubs. However, despite its high resistance to high temperatures and corrosion, titanium has poor electrical conductivity, making it a poor choice for electrical applications. Titanium alloys are also more expensive compared to other lightweight metals such as aluminum.

The use of additive manufacturing technology is conducive to reducing processing costs, reducing the waste of raw materials, and has significant economic advantages. Titanium-based alloys are also the most systematic and mature alloy system for additive manufacturing research. Additively manufactured titanium alloy components have been used as load-bearing structures in the aviation field. According to the investigation of 3D printing technology reference, the American Aero Met Company began to test manufacture titanium alloy sub-bearing structure test parts for Boeing F/A-18E/F shipboard joint fighter/attack aircraft in small batch in 2001, and took the lead in realizing the application of LMD titanium alloy sub-bearing structure parts on F/A-18 verification aircraft in 2002. Beijing University of Aeronautics and Astronautics breakthrough in titanium alloy laser additive manufacturing key technologies, alloy comprehensive mechanical properties are significantly more than forgings, the development of large-scale main bearing titanium alloy frame and other components, has been realized in the aircraft installation applications. Northwestern Polytechnical University used laser additive manufacturing technology for COMAC to manufacture the C919 aircraft central wing rib on the lower edge of the strip samples, the size of 3,000mm × 350mm × 450mm, the quality of 196kg.

Aluminum Additive Manufacturing and the Aerospace Industry
Aluminum-based alloys with low density, high specific strength, high corrosion resistance, good formability, good physical properties and mechanical properties are the most widely used class of non-ferrous structural materials in industry. For laser additive manufacturing, aluminum-based materials are typically difficult to process materials, which is determined by its special physical properties (low density, low laser absorption, high thermal conductivity and easy oxidation, etc.). From the perspective of additive manufacturing forming process, the density of aluminum alloy is small, the powder fluidity is relatively poor, the uniformity of laying on the SLM forming powder bed is poor or the continuity of powder transport in the LMD process is poor, so the precision and accuracy of the laying/feeding system in the laser additive manufacturing equipment are required to be high.
At present, the aluminum alloys used in additive manufacturing are mainly Al-Si alloys, of which AlSi10Mg and AlSi12 with good fluidity have been widely studied. However, due to the material nature of Al-Si alloy casting aluminum alloy, although the optimized laser additive manufacturing process is used for the preparation, the tensile strength is difficult to break through 400MPa, which limits its use in aerospace and other fields of service performance requirements of higher load-bearing components.

 In order to further obtain higher mechanical properties, many domestic and foreign enterprises and universities have accelerated the pace of research and development in recent years, and a large number of high-strength aluminum alloys dedicated to additive manufacturing have been listed. Airbus for aviation aluminum alloy parts additive manufacturing needs, the development of the world's first additive manufacturing of high-strength aluminum alloy powder materials Scalmalloy, room temperature tensile strength of 520MPa, has been applied to the A320 aircraft cabin structure parts of the additive manufacturing; the United States Hughes Research Laboratories (HRL) development of high-strength aluminum alloy for 3D printing 7A77.60L strength of more than 600Mpa, becoming the first forging for additive manufacturing. More than 600Mpa, becoming the first forging equivalent high-strength aluminum alloy can be used for additive manufacturing, NASA Marshall Space Flight Center has begun to apply this material to the production of large-scale aerospace parts; 3D printing technology reference has also reported that the domestic CVRI design and development of a new type of 3D printing of special high-strength aluminum alloy, breaking through the Airbus patent limitations, the tensile strength of the stable More than 560MPa, significantly better than Airbus Scalmalloy® aluminum alloy powder printing performance, can meet the domestic rail transportation equipment and aerospace and other high-end manufacturing parts 3D printing needs, and the domestic aerospace sector has begun the high-strength aluminum alloy additive manufacturing applications.