Aluminum and Titanium: Excellent Choices for Aerospace Additive Manufacturing

Based on the perspective of cutting-edge scientific exploration and development, Science once published an article pointing out that modern industry requires structural materials to have high strength, fracture toughness, and stiffness, and at the same time reduce weight as much as possible. In this case, light-weight high-strength alloys represented by aluminum and titanium, and load-bearing heat-resistant alloys represented by Ni-based superalloys have become one of the key materials developed in the research and development plans of new materials in various countries, and are also in the process of laser additive manufacturing. Important applied material.

Advantages and differences between titanium and aluminum

Aluminum alloy and titanium alloy, due to their excellent low density and structural strength, are widely used in aerospace, automobile, machinery manufacturing, and other fields, whether using 3D printing or CNC processing, especially in the aviation industry. It is the main structural material of the aviation industry.

Both titanium and aluminum are light, but there are still differences between the two. Although titanium is about two-thirds heavier than aluminum, its inherent strength means that the required strength can be achieved using less. Titanium alloys are widely used in aircraft jet engines and various types of spacecraft, and their strength and low density can reduce fuel costs. The density of aluminum alloy is only one-third of that of steel, and it is the most widely used and common lightweight material for automobiles at this stage. Studies have shown that aluminum alloys can be used in a vehicle up to 540kg. With a 40% reduction in weight, the all-aluminum body of Audi, Toyota, and other brand vehicles is a good example.

Material properties of aluminum and titanium

Since both materials have high strength and low density, other differences 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 part is required, titanium is the best choice. For this reason, titanium alloys are used in the manufacture of medical devices/implants, complex satellite assemblies, fixtures, and stents, among others.

Cost: Aluminium is the most cost-effective metal for machining or 3D printing; titanium is expensive but can still drive a leap in value. The fuel savings of lightweight parts for an aircraft or spacecraft will be huge, while titanium parts will 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 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 applications such as surgical instruments. Ti64 also resists salty environments well and is often used in marine applications.

Aluminum alloys and titanium alloys are very common in aerospace applications. Titanium alloy has high strength and low density (only about 57% of steel), and its specific strength (strength/density) is much greater than that of other metal structural materials. It can produce parts with high unit strength, good rigidity, and lightweight. Titanium alloys can be used in aircraft engine components, skeletons, skins, fasteners, and landing gear. 3D printing technology reference data found that aluminum alloys are suitable for working in an environment below 200 ° C. The aluminum material used in the Airbus A380 body accounts for more than 1/3, and the C919 also uses a large number of conventional high-performance aluminum alloy materials. Aircraft skins, bulkheads, ribs, etc. can be made of aluminum alloys.

Titanium Additive Manufacturing and the Aerospace Industry

As the 2019 Global Aerospace and Defense Industry Outlook published by Deloitte points out, as the aerospace and defense industry continues to grow, so will production demand. And, when designing for aerospace and defense applications, material selection is critical. For off-the-ground components, reducing component count and weight is key. In these areas, every 1g of weight loss can bring great benefits.

Titanium has an extremely high melting point, over 1600°C, and is also typically a difficult-to-machine material, which is the main reason why it is more expensive than other metals. Ti6Al4V is currently the most widely used titanium alloy material. It is not only light in weight, but also has high strength and high-temperature resistance. These characteristics make it very popular in the aerospace field. Common applications include the manufacture of blades, discs, casings, and other parts for the low-temperature section of engine fans and compressors, with an operating temperature range of 400-500°C; also used in the manufacture of airframe and capsule components, rocket engine cases and helicopters Rotor hubs, etc. However, despite its high temperature and corrosion resistance, titanium has poor electrical conductivity, making it a poor choice for electrical applications. Titanium is also more expensive compared to other lightweight metals such as aluminum.

Uses of Titanium in the Aerospace Industry

The use of additive manufacturing technology is conducive to reducing processing costs and waste of raw materials, which has significant economic advantages. Titanium-based alloys are also the most systematic and mature alloy systems for additive manufacturing research. Additively manufactured titanium alloy components have been used as load-bearing structures in the aerospace field. According to the survey of 3D printing technology references, Aero Met Company of the United States began to produce titanium alloy sub-load-bearing structural test pieces for Boeing F/A-18E/F carrier-based combined fighter/attack aircraft in small batches in 2001 and took the lead in realizing LMD titanium alloy in 2002. The application of secondary load-bearing structural parts on the F/A-18 verification machine. Beijing University of Aeronautics and Astronautics has made breakthroughs in the key technology of laser additive manufacturing of titanium alloys. The comprehensive mechanical properties of the alloys significantly exceed those of forgings. The large-scale main bearing titanium alloy frames and other components developed have been installed and applied on aircraft. Northwestern Polytechnical University used laser additive manufacturing technology to manufacture the upper and lower edge strip samples of the central wing rib of the C919 aircraft for COMAC, with a size of 3000mm×350mm×450mm and a mass of 196kg.

Aluminum-based alloys have low density, high specific strength, strong corrosion resistance, good formability, and good physical and mechanical properties. They are the most widely used non-ferrous metal structural materials in the industry. For laser additive manufacturing, aluminum-based materials are typically difficult-to-machine materials, which are determined by their special physical properties (low density, low laser absorptivity, high thermal conductivity, easy oxidation, etc.). From the point of view of the additive manufacturing forming process, the density of aluminum alloy is relatively small, the powder fluidity is relatively poor, the uniformity of laying on the SLM forming powder bed is poor, or the continuity of powder transportation in the LMD process is poor. Therefore, the precision and accuracy of the powder spreading/powder feeding system in the laser additive manufacturing equipment are relatively high.

At present, the aluminum alloys used in additive manufacturing are mainly Al-Si alloys, among which AlSi10Mg and AlSi12 with good fluidity have been widely studied. However, due to the material nature of the Al-Si alloy cast aluminum alloy, although it is prepared by an optimized laser additive manufacturing process, the tensile strength is difficult to exceed 400MPa, which limits its service performance in aerospace and other fields. Use on high load-bearing members.

The amount of aluminum alloy used in aircraft is as high as 20%

In order to further obtain higher mechanical properties, many companies and universities at home and abroad 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 has developed Scalmalloy, the world's first high-strength aluminum alloy powder material for additive manufacturing, with a tensile strength of 520MPa at room temperature, which has been applied to the additive manufacturing of A320 aircraft cabin structural parts. The strength of the high-strength 7A77.60L aluminum alloy for 3D printing developed by the Hughes Research Laboratory (HRL) in the United States exceeds 600Mpa, making it the first forged equivalent high-strength aluminum alloy that can be used for additive manufacturing. NASA Marshall Space Flight Center has begun to This material is used in the production of large-scale aerospace parts; 3D printing technology reference has also reported a new type of high-strength aluminum alloy designed and developed by the domestic CRRC Industry Research Institute for 3D printing, which breaks through the patent restrictions of Airbus. The stability exceeds 560MPa, which is significantly better than the printing performance of Airbus Scalmalloy® aluminum alloy powder, which can meet the needs of 3D printing of high-end manufacturing parts such as domestic rail transit equipment and aerospace. material manufacturing applications.

Modern aerospace components need to meet a series of demanding requirements such as lightweight, high performance, high reliability, and low cost, and the structure of components is more complex and more difficult to design and manufacture. Innovating and developing key technologies for laser additive manufacturing of aluminum, titanium, and nickel-based components in aerospace, not only reflects the development direction of lightweight and high performance in material selection but also highlights the precision of additive manufacturing technology itself. , The development trend of net shape can realize the integrated additive manufacturing of material-structure-performance and the major engineering application of additive manufacturing technology in aerospace.