Effect of electrical pulse treatment on the microstructural and mechanical responses of heterogeneous linear friction welded TC17/TC4 dissimilar joint

Abstract

The heterogeneous microstructure of TC17/TC4 joint manufactured by linear friction welding will reduce the mechanical properties compared with the base metals, of which the strength and ductility are hard to be improved simultaneously by traditional aging heat treatment (AHT), seriously limiting the application of LFW in the manufacturing of TC17/TC4 blisks. To this end, the present work proposes to use electric pulse treatment (EPT) to enhance the strength and ductility of the joint simultaneously by improving its microstructure. The results show that EPT effectively improves the plasticity of the joint compared with AHT. The tensile properties of aging treated joint are similar to that of the as welded joint, which present a strength around ∼805 MPa and an elongation around ∼13%. When the joint was electric pulse treated at 550 °C and 630 °C for 1 h, the elongation increases to 15.8% and 16.3%, which is an increase of 21.5% and 34.7% compared to the corresponding heat-treated joint. The microstructural response under AHT is the aging precipitation behavior of lamellar α affected by welding process. Whereas, the microstructural response under electric pulse treatment is driven by local Joule heating effect and the electron wind effect. After EPT, the basket-weave distribution of α-lamellae on TC17 side enhances ductility while maintaining strength and the spheroidized α phase on TC4 side reduces the microstructural gradient and prevents stress concentration at locations of microstructural discontinuities, thereby improving ductility. This study offers valuable insights for improving the strength and ductility of LFW TC17/TC4 blisks and advancing the application of LFW in aeroengine components.