Effect of structural parameters on the surface roughness and mechanical properties of Ti-6Al-4 V alloy thin-walled structure fabricated by selective laser melting

Ti-6Al-4 V alloy (Ti64) thin-walled parts with different structural parameters including placement mode, tilt angle (theta), length and thickness were fabricated by selective laser melting (SLM). The effects of structural parameters on the surface roughness and mechanical properties were investigated to provide guidance for optimizing SLM process of thin-walled structures. Firstly, surface roughness on downdip plane is larger than that on updip plane. The thin-walled parts perpendicular to the scraper and increasing theta are beneficial for reducing surface roughness. Secondly, pores size is concentration below 50 mu m, and the porosity is concentrated between 0.28% and 1.5%. The porosity shows a decreasing trend with increasing theta. Coarse columnar prior-beta-Ti grains are parallel to building direction (BD), which is not affected by theta. alpha-Ti/beta-Ti laths exhibit thickness less than 0.5 mu m inside prior-beta-Ti grains, and are refined with reducing thickness of the thin-walled parts. Finally, Ti64 thinwalled parts with different structure parameters exhibit relatively stable strength and plasticity, namely tensile strength of 1040-1130 MPa, yield strength of 1015-1145 MPa, and elongation of 7 similar to 8.5%. In summary, placement mode and theta exhibit more significant impact on the final properties of the thin-walled parts, namely, perpendicular to the scraper and increasing theta are beneficial for reducing surface roughness and porosity. While the structural parameters show no significant effect on the mechanical properties.