A novel friction and rolling based solid-state additive manufacturing method: Microstructure and mechanical properties evaluation

Fusion-based metal additive manufacturing (AM) processes are becoming progressively mature in some material systems. However, the printing of high strength aluminum alloy remains a considerable challenge due to its unavoidable solidification defects. In this study, a novel solid-state additive manufacturing process, being referred to as Friction and Rolling based Additive Manufacturing (FRAM), was developed to print AA6061. The method developed here achieved heat generation and continuous material addition simultaneously, using a modified horizontal CNC machine. The results indicate that fully dense microstructure with defect-free and refined grain was successfully obtained using the FRAM method. The adjacent layers have achieved good bonding without melting because the material at the top surface of the previous layer experience a secondary friction, which can enhance the interface metallurgical bonding and eliminate the potential interface defects. The grain size of the deposited material was significantly reduced compared to that of feeding material because of dynamic recrystallization caused by severe plastic deformation. This also led to the significant increase in elongation of the deposited material. The deposited material showed ductile fracture in both horizontal and vertical directions. The proposed process has the potential to print other non-weldable engineering alloys that are sensitive to solidification defects.