Effect of grain structure on the mechanical properties and in vitro corrosion behavior of additively manufactured pure Zn

Laser powder bed fusion (LPBF) has been previously used to produce customized medical implants from biodegradable Zn and its alloys. In this study, we investigated the effect of the grain structure on the mechanical properties and in vitro corrosion behavior of pure Zn samples, by varying the scanning speed and building direction during the LPBF process. Increasing the scanning speed from 300 to 700 mm/s resulted in finer grains, irregular grain morphology, and a weaker grain texture, which enhanced the strength and ductility. Vertically built LPBF Zn tensile samples had higher strength and ductility compared with horizontally built samples, indicating strong anisotropy of the mechanical properties. Electrochemical tests revealed that the in vitro corrosion behavior was not strongly correlated with the scanning speed. This was attributable to the random distribution of tiny pores on the surface of the LPBF samples, although immersion tests showed that the sample prepared with the highest scanning speed exhibited the highest corrosion rate. With increasing immersion time in Hank's solution, the Zn2+ concentrations of the samples produced with different scanning speeds increased, their pH stabilized, and the differences between the corrosion rates narrowed. The effects of the processing parameters on the final performance of the samples could be well explained by the grain structures. The findings of this study afford bases for selecting the processing parameters for optimizing the properties of LPBF-produced Zn parts for biodegradable applications.