Mechanical properties and corrosion protection of DED-Arc additively manufactured high-strength low-alloy steel components coated with low-pressure cold spray

Abstract

The directed energy deposition-arc (DED-Arc) process, using high-strength low-alloy (HSLA) feedstock wire, presents a promising solution for fabricating large-scale steel connectors in civil engineering. Due to the use of carbon steel feedstock wire, corrosion protection of the 3D-printed components is necessary. Therefore, this study investigates low-pressure cold spray (LPCS) as a method for applying zinc-based coatings. Two sets of thin walls were 3D-printed: one set uncoated and one set coated with LPCS Zn + Al2O3 coating. This LPCS coating was successfully deposited on untreated and on grit-blasted DED-Arc surfaces. Coating thicknesses exceeding 300 µm as well as electrochemical polarisation analysis confirmed sufficient corrosion resistance of the coated as-built specimens. To evaluate the influence of the surface condition and the coating process on the mechanical behaviour, dog-bone tensile specimens were extracted from the walls, 3D-scanned, and subsequently mechanically tested. Structured-light scanning of the geometry revealed different scatter of the specimens’ thickness based on their orientation with respect to the build direction. Uniaxial quasi-static tensile tests, combined with a four-camera digital image correlation (DIC) system, were performed both on specimens with machined surfaces and with LPCS Zn + Al2O3 coating on the as-built surface. While the machined specimens exhibited nearly isotropic behaviour, the coated as-built specimens showed pronounced anisotropy with comparable mechanical properties to uncoated as-built specimens from literature when excluding the coating thickness from the load-bearing cross-section. The LPCS Zn + Al2O3 coating led to a reduction of the corrosion rate by two thirds compared to uncoated HSLA DED-Arc.