Composition design and mechanical properties of B4C/Al-Zn-Mg-Cu functionally graded materials prepared by laser additive manufacturing

In this study, three types of three-layer functionally graded materials (FGMs) were designed by mainting the average content of the reinforcement constant and changing the span of the composition. The B4C particle-reinforced Al-matrix FGMs and a homogeneous composite (HC) with the same average composition were prepared using the laser additive manufacturing technique. The FGMs had a higher average secondary-phase content and grain size than the HC. Large (black) and reticulated (white) secondary phases corresponding to B4C phase, T phase, and MgZn2 were observed in the as-deposited FGM samples. The content of the secondary phase in the middle layer was generally low. The bottom layer, which was in direct contact with the substrate, exhibited the smallest grain size. The hardness and wear resistance significantly improved owing to the high B4C content in the top layer. The flexural behaviors of each layer of the FGM in different directions were systematically studied. The plasticity of the single-layer material decreased with increase in the B4C content. When the bottom layer had a high B4C content, the flexural ability significantly reduced. Among all the samples, G2 with 8% B4C particle content in the top layer exhibited the best comprehensive mechanical properties. The hardness value, wear rate of the top layer, maximum bending stress, and maximum bending strain of the FGM were 177.5 HV, 0.367 × 10−3mm3/(N·m), 585.6 MPa, and 7.36%, respectively. This study can provide a reference value for the future design and development of wear-resistant gradient materials for aerospace applications.