Influences of impact energy on the densification and mechanical properties of powder metallurgical Fe–C–Cu preforms during a powder-forged process

Abstract

Accurate impact energy control is important for the success of the powder-forged (P/F) technique. This paper address how impact energy influences the densification and mechanical properties of powder metallurgical (P/M) preforms during a P/F process by combining finite element simulations and experiments. The simulated results coincide well with the experimental results. Results reveal that impact energy strongly influences the P/M preform densification by controlling their stress states and strain rate. The densification continuously proceeds throughout the P/F processing by the three steps of micro-pore compression, segmentation, and closure, while the densification uniformity gradually deteriorates in the earlier free upsetting step and then significantly improves in the later closed compressing step. The increased impact energy within the range below 56.3J/cm3 induces a higher strain rate, and thus facilitates the P/M preform densification notably. Inversely, the excessive impact energy not only has less influence on the densification but also creates exceptionally high forging pressure. The notably increased density improves the mechanical properties of the P/F forgings significantly; meanwhile, the concomitant work hardening changes their tensile fracture modes and slows down their ductility rising. In this study, the P/F Fe–C–Cu forgings prepared at the optimized impact energy of 56.3J/cm3 have a high and uniform density and good mechanical properties. This study can provide theoretical guidance for the rational process design of powder forging.