The Effect of Multiple Thermal Process on Microstructural Evolution and Mechanical Properties of Additive Manufactured Al/Steel Structure

Wire and arc additive manufacturing (WAAM) provides a convenient solution for the integrated design and manufacturing of Al/steel structures. The multiple thermal cycles inherent in WAAM can affect the Al/steel interface and ultimately the overall performance of the Al/steel structure. Herein, the evolution behavior of the Al/steel interface microstructure under different WAAM modes, number of thermal cycles, and interpass temperature is investigated. The results show that the process of heat accumulation plays an important role in the evolution of Al/steel interface. As the number of thermal cycles increases, the intermetallic compounds layer gradually transforms from the mainly τ₅-Al₈Fe₂Si phase to (Al, Si)₁₃(Fe, Cr)₄ phase. The rise of interpass temperature significantly aggravates the microstructural evolution process, but the final interface structure can be manipulated employing temperature control. When the interpass temperature is lower than 250 °C, the formation of the brittle Fe₂Al₅ phase is avoided. With the increase of thermal cycles, the shear strength of Al/steel additive specimens increases first, then decreases, and finally tends to be stable. The changes in shear strength are closely related to the interface microstructures.