Constructing a novel bi-lamellar microstructure in selective laser melted Ti-6Al-4V alloy via electropulsing for improvement of strength and corrosion resistance

Traditional heat treatments may cause deterioration in the yield strength and corrosion resistance of the selective laser-melted (SLM) Ti-6Al-4V alloy due to the coarsening of α lath and alloy element partitioning (AEP). However, electropulsing has been found to inhibit the growth of primary α and the process of AEP. It also introduces finer α′ lath in the transformed β region and generates a novel bi-lamellar microstructure. This microstructure has minimal element concentration difference between the primary α and transformed β. As a result, the transformed β region exhibits a higher content of Al element and finer α′ lath, leading to a higher overall yield strength (952 MPa) compared to the heat-treated sample (855 MPa). The novel microstructure induced by electropulsing enhances the polarization resistance, improves the stability and thickness of the passive film, and ultimately enhances the corrosion resistance. Additionally, this technology can be extended to other SLM α + β titanium alloys to simultaneously improve their mechanical properties and corrosion resistance.