Aluminum alloy has the characteristics of low density, high specific strength and specific stiffness, good plasticity, excellent electrical conductivity, thermal conductivity and corrosion resistance. It is the first choice material to achieve lightweight structures and is used in aerospace, transportation, ships and other fields. It has broad application prospects and research value. The wide application of aluminum alloys has promoted the development of aluminum alloy manufacturing technology. Traditional aluminum alloy processing techniques mainly use smelting, casting and forging. However, with the continuous improvement of product technology and the continuous shortening of development cycles, it is difficult to manufacture complex precision structures. The aluminum alloy components also put forward new requirements, which not only require efficient and fast manufacturing technology, but also require rapid response capabilities that change with changes in equipment design, as well as flexible adaptability to the production and manufacturing of complex precision components. Based on the above situation, the use of 3D printing technology to manufacture aluminum alloy structural parts has become a hot spot in current research. 3D printing, also known as additive manufacturing, is a technology that uses CAD design data to accumulate materials layer by layer to manufacture physical parts. It is also used in aviation It is widely used in many industries such as aerospace, biomedicine and rail transportation. Additive manufacturing is characterized by rapid manufacturing of single parts or small batches. By building solid parts layer by layer, it increases design freedom and manufacturing flexibility, enables complex geometric customization of products, shortens market time, and eliminates traditional Size limitations.

Due to different working principles and heat source types, the current process methods for aluminum alloy additive manufacturing technology at home and abroad mainly include laser additive manufacturing (LAM), wire and arc additive manufacturing (WAAM) ), electron beam additive manufacturing (EBAM), ultrasonic additive manufacturing (UAM) and friction stir welding additive manufacturing (FSAM), this article focuses on these 5 A brief introduction to the different process characteristics is given.

1 Aluminum alloy laser additive manufacturing technology

Laser additive manufacturing technology uses laser as the heat source. This technology has the characteristics of high forming accuracy, few internal defects and excellent mechanical properties. When laser additive manufacturing of aluminum alloys, aluminum alloy powder is often used as raw material, which leads to the uncertainty of the powder gap and affects the density of the formed parts. Moreover, most aluminum alloys have high reflectivity to laser, making the laser The utilization rate is low and is currently limited to cast aluminum alloys or aluminum alloys with better weldability. According to the forming principle, aluminum alloy laser additive manufacturing technology is mainly divided into Laser Metal Direct Forming (LMDF) technology that feeds synchronous metal powder and Laser Selective Laser Melting (Selective Laser Melting, which is characterized by powder bed laying). SLM) technology.

2 Aluminum alloy arc additive manufacturing technology

Arc additive manufacturing technology is an additive manufacturing technology carried out through the layer-by-layer accumulation method of synchronous fuses. Due to the characteristics of the welding arc, it is mainly used to manufacture ultra-large and complex parts. It has high material utilization rate, low equipment cost, and is easy to form. The structure is large, but due to the large heat input, the surface quality and forming accuracy of the formed parts are very poor, requiring more subsequent processing. In the future, for aluminum alloy arc additive manufacturing technology, how to reduce heat input and improve forming accuracy and quality will be the focus of future research.

3 Aluminum alloy electron beam additive manufacturing technology

According to different filling materials, electron beam additive manufacturing technology is mainly divided into electron beam selective melting technology (Electron Beam Selective Melting, EBSM) and electron beam fuse additive manufacturing technology (Electron Beam Freeform Fabrication, EBFF).                    

EBSM technology uses electron beams as the heat source and metal powder as the forming material in a vacuum environment. It scans and heats at high speed, melts and superimposes layer by layer, and obtains metal parts. However, EBSM technology has high preparation costs for metal powder materials, is susceptible to contamination, and is difficult to use. It has shortcomings such as low efficiency, cumbersome cleaning work, and difficulty in manufacturing large-size parts.

EBFF technology, like other additive manufacturing technologies, uses high-energy electron beams to melt synchronously fed wires, and manufactures them in layers according to the specific processing path of the CAD model, stacking them layer by layer until a dense metal part is formed. This process has the characteristics of fast forming speed, good protection effect, high material utilization rate and high energy conversion rate.

4 Aluminum alloy ultrasonic additive manufacturing technology

Aluminum alloy ultrasonic additive manufacturing technology uses high-power ultrasonic energy and uses the heat generated by vibration and friction between aluminum alloy layers to promote the mutual diffusion of metal atoms between the interfaces and form a solid-state physical metallurgical bond, thereby achieving additive manufacturing. This technology has the following advantages:

(1) Solid-state forming, low temperature, low residual stress inside the material, and good structural stability.

(2) No welding slag, waste liquid, harmful gases and other pollutants are produced during the manufacturing process. Raw materials are easily available and the cost is low.

(3) It does not require a high-temperature environment, does not cause volatilization of alloy elements, and does not affect the performance of the connection.

(4) During the manufacturing process, the oxide film on the surface of the aluminum foil can be broken and removed by ultrasonic waves.

The preparation of gradient functional materials can be achieved.

There are still some shortcomings in aluminum alloy ultrasonic additive manufacturing technology. Due to the current limitations of ultrasonic power, only aluminum foil with a small thickness can be rapidly formed. In the future, the output power of ultrasonic transducers will need to be greatly increased to achieve large thickness and high strength metals. Additive manufacturing of sheet metal.

5 Aluminum alloy friction stir welding additive manufacturing technology

Friction stir welding additive manufacturing technology is a new type of additive manufacturing method developed based on friction stir welding. Aluminum alloy friction stir welding additive manufacturing is to insert a high-speed rotating stirring head into an aluminum alloy plate and then move it in a predetermined direction at a certain traveling speed. Frictional heat is generated at the contact area between the stirring head and the aluminum alloy plate to plasticize the aluminum alloy plate. The softened and plasticized metal fills the cavity behind the stirring needle under the rotation of the stirring head, forming a layer of additive area, and then continues to superimpose a layer of base material on top, and repeat the above operation according to the same path and additive spacing. The aluminum alloy formed parts produced by this technology have small microstructure changes in the heat-affected zone, low residual stress, are not easily deformed, do not need to remove oxide films, do not require protective gas, and are low in cost.

At present, aluminum alloy additive manufacturing technology has broad application prospects in military and civilian fields. Aluminum alloy additive manufacturing technology has significant advantages such as complex precision forming and lightweight design. The current main development trends are as follows:

(1) Develop new methods for aluminum alloy additive manufacturing and further explore the intrinsic relationship between "process-structure-property" in aluminum alloy additive manufacturing. Elucidate the stress formation mechanism of aluminum alloy additive manufacturing components, propose methods to effectively control the residual stress level and distribution of additive components, and provide guidance for the preparation of large and complex aluminum alloy additive manufacturing components.

(2) Reveal the physical metallurgical mechanism and phase transformation behavior of the micro-molten pool mass transfer, non-equilibrium solidification and cooling processes in aluminum alloy additive manufacturing, and achieve microstructural control of aluminum alloy additive manufacturing. Through a combination of experiments and numerical simulations, the temperature field distribution patterns of aluminum alloy additive manufacturing are controlled and predicted, and the additive thermal process is controlled.

(3) Further develop additive manufacturing + milling processing (precision machining) integrated equipment to improve the forming accuracy of aluminum alloy additive manufacturing components and achieve precision processing of aluminum alloy components. Through process optimization and equipment upgrading, the pore defects of aluminum alloy additive manufacturing components will be completely eliminated, the density will be increased, and the comprehensive mechanical properties will be improved.