Progress The development of laser additive manufacturing technology has expanded the variety of heterogeneous metal connections, enabling performance customization according to the demands of various application scenarios, such as in the aerospace, medical, automotive, and petrochemical industries (Table 1). In the aerospace field, heterogeneous metals like Cu/Ni, Fe-based, and Ti-based alloys can be utilized for manufacturing power components and load-bearing structural components (Figs.1‒3) to meet the requirements of work in extreme environments. However, traditional laser additive manufacturing equipment poses several limitations in the preparation of heterogeneous metals (Table 2). For example, it faces challenges in achieving precise powder delivery and deposition, as well as limitations in the connection of heterogeneous composition within layers. Therefore, improvements are required in powder delivery, blending, and processing devices (Figs.4‒5). Additionally, the integration of additive manufacturing methods (Fig.6) can enhance the forming efficiency and quality of heterogeneous metals. For heterogeneous metal components, interface quality is of utmost importance and is primarily determined by the physicochemical properties of heterogeneous alloys and processing parameters (Fig.7). The complex physicochemical differences among heterogeneous metals, such as differences in thermal expansion coefficients, melting points, density, surface tension, elastic modulus, and mismatched crystal structures, along with variations in their response to laser processing, can lead to a range of macroscopic and microscopic defects. These defects include voids, cracks, harmful phases (brittle intermetallic compounds, oxide inclusions), and residual stresses, which significantly impact the interface quality and forming effectiveness. To avoid defects during the manufacturing process, it is critical to enhance the bonding quality between heterogeneous metals, optimize connection methods (Fig.8), and control process parameters (Fig.9). This involves achieving reliable connections between materials with disparate properties using gradient layers/intermediate layers and adjusting the laser parameters to match the bonding process of heterogeneous metals. Furthermore, employing online monitoring (Fig.10) and intelligent prediction methods (Fig. 11) during the manufacturing process can enable efficient process control, thus reducing trial-and-error costs and significantly improving the efficiency of heterogeneous metal connections. Simultaneously, pre-processing (Fig.12) and post-processing (Fig.13) can optimize the organization and performance of heterogeneous metal interfaces, improving the quality of the formed components.
Conclusions and Prospects Heterogeneous metal laser additive manufacturing technology has significant advantages in realizing functional integration and reliable manufacturing of complex components. This paper provides a comprehensive overview of the material systems, relevant applications, equipment development, and process optimization in the field of laser additive manufacturing of heterogeneous metals. The article discusses restrictive issues encountered during the additive manufacturing of heterogeneous metals, including limitations in manufacturing equipment, material incompatibility, and mismatched process parameters. It also summarizes and outlines the corresponding solutions, encompassing optimized connection strategies and processing parameters, the use of monitoring and prediction methods, as well as efficient pre-processing and post-processing techniques. Despite facing several challenges, the continuous development of related equipment and processes suggests that this technology will better serve industries such as aerospace in the future.
Major advances in materials science and manufacturing technology are being driven by fields such as aerospace, which are placing increasingly stringent requirements for the construction of complex, reliable, and high-performance components intended for extreme service conditions. For example, engine components must possess both high heat resistance and excellent thermal conductivity, while structural component aim with a combination of lightweight design and high strength. These intricate performance demands have spurred the development of heterogeneous metal integration, wherein different materials with complementary properties are integrated into a single component through optimized design and manufacturing process control. This approach aims to break through the performance limits of traditional single-material components and broaden their application scenarios. The effective connection between heterogeneous metals has always been a major challenge in the engineering field. Because of the inherent differences in the physicochemical properties of various metals, achieving a high-strength and reliable interface bonding through traditional welding or mechanical connection methods is often challenging. This difficulty is particularly pronounced when dealing with complex interface shapes or gradient functional areas. However, laser additive manufacturing technology, owing to its high forming precision and controllability, has provided a novel pathway for heterogeneous metal manufacturing. This technology significantly enhances the freedom of material design and shaping, enabling reliable connections between heterogeneous metals. Laser additive technology primarily includes laser powder bed fusion (LPBF) and laser directed energy deposition (LDED). These technologies can respectively meet the manufacturing needs of complex or large heterogeneous aerospace components. LPBF produces parts with a high degree of surface finish and intricate structures by preforming layers of dissimilar powders and selectively melting them layer by layer. In contrast, LDED uses lasers to deposit powder or wire materials onto a substrate and provides high flexibility and freedom in manufacturing. However, the maturity of both LPBF and LDED technologies is not yet sufficiently high, and they face various issues in practical applications. Therefore, it is imperative to systematically summarize and discuss existing research to facilitate the rapid development of this field.
