Effect of overlap percentage on morphology, microstructure, and mechanical properties during multilayer multi-pass friction rolling additive manufacturing

Solid-state metal additive manufacturing technology leads to efficient and rapid production of large, complex metal components. Friction Rolling Additive Manufacturing (FRAM) has successfully overcome the limitations of the width of formed parts and facilitates the manufacture high-performance large metal components. However, research on deposition strategies for thick-section-formed parts is yet to be conducted. This study reports the successful fabrication of multilayer multi-pass samples with different overlap percentages (OPs) (0 %, 12.5 %, 25 %, 37.5 %, 50 %, 62.5 %, and 75 %) and the effects of OP on sample morphology, microstructure, and mechanical properties. The results indicate that with gradually increasing OP, the effective deposition width narrows, mixing degree of plasticized material in overlap zone (OZ) improves, and forming morphology of samples progressively deteriorates. The height of OZ increases from 0.7 mm to 2.4 mm, with a maximum height difference of approximately 0.85 mm between the OZs and non-OZs. The height and slope of the grooves at the edges of the OZ gradually decrease. Simultaneously, the as-deposited (AD) 25 % OZ was observed to have small and uniform grains with sizes of about 5.82-7.44 mu m. The grain size and LAGBs of the post-deposited heattreated (PDHT) OZ center increased to 8.4 mu m and 52 %, respectively. The mechanical properties of the AD and the PDHT of the 25 % overlap sample were optimal. The maximum tensile strength and elongation of the PDHT25 % overlap sample in the Y- and Z-direction were 265 MPa, 15.8 %, and 242.3 MPa, 14.8 %, respectively. Thus, 25 % OP (OZ width of 3 mm) effectively balances the morphology, efficiency, and performance of the sample, providing an optimal multilayer, multi-pass deposition strategy for the future deposition of thick sections of large, complex metal components using FRAM.