Significance Aluminum alloys and aluminum matrix composites have been widely used in aerospace components such as fuselage skin materials, engines, fuel tanks, panels, brackets, and metal mirrors owing to their excellent physical and chemical properties such as good thermal conductivity, electrical conductivity, ductility, plasticity, corrosion resistance, and low density.

Traditional methods for fabricating aluminum components, such as casting and extrusion, require the use of tools or dies to produce the parts. However, aluminum alloys used in such processes suffer from low as-cast strength and require long production cycles. Furthermore, forming complex structures using these materials is difficult and the wastage of materials is high. Such limitations prevent aluminum alloys from meeting the requirements of high efficiency and fast manufacturing technology in aerospace industry and the flexibility to produce complex precise structures. Driven by this urgent demand, innovative developments have been made in the additive manufacturing (AM) processing of aluminum alloys and their composites.

Selective laser melting (SLM), a type of laser three-dimensional (3D) printing, is a layer-based AM technology used for manufacturing complex and customized structures from metal powders. The main advantages of this process over conventional manufacturing methods include highly flexible design, simple machining process, structural integration, high material utilization, and high mechanical properties of produced samples. SLM can be used to produce intricate parts that conventionally require a series of manufacturing processes. Moreover, this process can be cost-effective by reducing the costs of raw materials and time-effective by reducing the time required for design and manufacturing.

Although commercial applications of AM have increased rapidly, few materials have been deemed suitable for SLM so far. Aluminum alloys show good weldability; however, such materials are typically difficult to process in the field of laser 3D printing compared with titanium and nickel alloys. Thus, they have limited processing applicability. Moreover, their inherent high laser reflectivity, high thermal conductivity, easy oxidation, and low density cause problems in the formation process such as high liquid viscosity, balling defect, and poor powder fluidity. Moreover, fabricating aluminum matrix composites using SLM is even more difficult owing to the additional particles used in the process.

Recently, improvements in the technology and application of high-power fiber laser equipment as well as increasing research on aluminum alloys have led to numerous achievements in SLM aluminum alloys. However, because limited varieties of aluminum alloys and their composites, most SLM techniques are focused on Al-Si systems. Accordingly, most research must be conducted in this field to promote the wide application of SLM based on aluminum alloys and their composites.

Progress Herein, improvements in the performance of SLM aluminum alloys and their application in the aerospace field were summarized. First, methods for improving the mechanical properties of the alloys by optimizing the SLM parameters were introduced and the best parameter range was determined using single tracks and molten pool morphology (Figs. 6 and 7). Among the processing parameters, the effects of laser scan speed and power have been widely studied. Then, the post-treatments of heating and surface remelting of SLM aluminum alloy parts were detailed. The post-treatment processes were found to considerably improve the elongation of the sample (Fig. 8). In addition, the results of previous research on the properties of AM aluminum alloys and their composites with particles were summarized in detail (Table 2). In particular, some researchers have determined that the mechanical properties of aluminum alloys can be effectively improved by adding reinforcing particles (Figs. 9 and 10). Finally, research progress in the field of aerospace in terms of SLM aluminum components, such as metal mirrors, antenna brackets, and aircraft engines, was discussed (Figs. 11--15).

Conclusions and Prospects Rapid developments have been made recently in SLM technology. In particular, the SLM technology based on aluminum alloys has entered the practical stage, with the application of key components in the field of aerospace manufacturing. In addition, SLM based on these alloys and their composites is expected to transform from scientific research into production and manufacturing, showing broad application prospects. In the future, the SLM based on aluminum alloys and their composites in the aerospace field will continue to develop in the following directions. (1) The mechanical properties of SLM aluminum components can be improved through the reasonable optimization of preprocessing parameters, postprocessing, and surface treatment, as well as by adding reinforcements. (2) The use of these alloys and their composites in SLM can be further developed for various aerospace structural parts. (3) Further developments should be made in terms of SLM equipment with large sizes, multiple beams, intelligent digitalization, complex structure, and customization based on aluminum alloys.