Excellent Choice For Additive Manufacturing in The High-end Aerospace Field

Titanium and aluminum alloy performance and cost are the two eternal driving forces for the development of material technology, while lightweight, integration, and structural function integration are the common challenges of aircraft structural design, material application and manufacturing technology. In the past few decades, near-net forming technologies such as hot isostatic pressing, injection molding, and discharge plasma sintering have made great progress in the field of titanium alloys, but the bottleneck problems such as oxygen content and porosity have not been effectively solved, thus restricting their application in the manufacture of aviation titanium alloy structures.

From the perspective of scientific exploration and development, modern industry needs structural materials with high strength, fracture toughness and stiffness, while reducing weight as much as possible. Therefore, lightweight high-strength alloys such as titanium and aluminum and load-bearing heat-resistant alloys such as Ni-based superalloys have become the focus of new material research and development plans in various countries. In addition, these materials are also important application materials in laser additive manufacturing.

Advantages and differences between titanium alloy and aluminum alloy

Titanium alloy has high specific strength, specific stiffness and good corrosion resistance, which meets the design needs of aircraft with high maneuverability, high reliability and long life, and its application level has become an important symbol to measure the advanced degree of aircraft material selection.

Titanium alloys and aluminum alloys are widely used in aerospace, automotive, machinery manufacturing and other fields because of their excellent low density and structural strength. Especially in the aviation industry, they play a very important role and are the main structural materials of the aviation industry. Although titanium alloys are about two-thirds heavier than aluminum alloys, their inherent strength means that the required strength can be achieved in smaller quantities. Titanium alloy has become an important material to reduce fuel costs because of its strength and low density, and is widely used in aircraft jet engines and various types of spacecraft. Aluminum alloy is the most widely used and common automotive lightweight material at this stage, and its density is only one-third that of steel. Studies have shown that aluminum alloy can be used up to 540kg in the whole vehicle, so that the weight of the car will be reduced by 40%. The use of all-aluminum bodies in vehicles of brands such as Audi and Toyota is a good example.

Since both materials have high strength and low density, other factors must be considered when choosing an alloy.

In critical situations where high strength and low weight are required, every gram counts, but if higher strength components are needed, titanium is the best choice. Therefore, titanium alloys are used to make medical devices/implants, complex satellite components, fixtures and brackets.

In terms of cost, aluminum is the most cost-effective metal for machining or 3D printing; While titanium costs more, lightweight parts will bring huge benefits to the fuel saved by aircraft or spacecraft, while titanium alloy parts have a longer service life.

In terms of 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 parts.

Titanium's corrosion resistance and low reactivity make it the most biocompatible metal and is widely used in medical applications such as surgical instruments. Ti64 also resists salinity environments well and is often used in marine applications.

In the aerospace field, aluminum alloys and titanium alloys are widely used. Titanium alloy has the advantages of high strength and low density (only about 57% of steel), and its specific strength (strength/density) far exceeds that of other metal structural materials, and can produce parts with high unit strength, good rigidity and light weight. The starting parts, skeleton, skin, fasteners and landing gear in the aircraft are all made of titanium alloy. In addition, 3D printing technology reference to check the relevant materials found that aluminum alloy is suitable for working in an environment below 200 °C, Airbus A380 fuselage uses more than 1/3 of the aluminum, and C919 also uses a large number of conventional high-performance aluminum alloy materials. Aluminum alloy is used for aircraft skins, partitions, wing ribs and other parts.

Due to its high melting point and difficult processing properties, titanium alloys are one of the most expensive metal materials. However, the lightweight, high strength and high temperature resistance of Ti6Al4V titanium alloy make it a high-profile in the aerospace field. Its application range includes blades, discs, receivers and other parts working in the low temperature section of engine fans and compressors, and the working temperature range can reach 400-500 °C. In addition, it is used in the manufacture of fuselage and capsule components, rocket engine cases, and helicopter rotor propeller hubs. However, due to its poor conductivity, titanium is not ideal for electrical applications. Although the price of titanium alloy is relatively high, its high temperature resistance and corrosion resistance cannot be replaced by other light metals.

Aluminum-based alloys have excellent physical properties and mechanical properties such as low density, high specific strength, strong corrosion resistance and good formability, so they are widely used in industry. However, from the perspective of additive manufacturing molding process, the density of aluminum alloy is small, the powder fluidity is relatively poor, the uniformity of laying on SLM forming powder bed is poor, or the continuity of powder transportation in the LMD process is poor, so the precision and accuracy of the powder spreading/feeding system in laser additive manufacturing equipment are 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, because Al-Si alloy belongs to cast aluminum alloy, although it is prepared by optimized laser additive manufacturing process, its tensile strength is still difficult to exceed 400MPa, which limits its use in load-bearing components with higher service performance requirements in aerospace and other fields.

Modern aerospace components face a range of demanding requirements, including lightweight, high performance, high reliability and low cost. This complex structure is extremely difficult to design and manufacture. Through the innovation and development of laser additive manufacturing technology for typical aluminum, titanium and nickel-based components of aerospace, we can not only achieve lightweight and high performance in material selection, but also reflect the development trend of precision and net shape of additive manufacturing technology. With the integration of materials-structure-properties additive manufacturing, we can apply additive manufacturing technology to major engineering in the aerospace field.