Effects of laser-weld joint opening size on fatigue strength of Ti-6Al-4V structures with several diameters

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Processo FAPESP: 06/58816-2

Processo FAPESP: 07/51306-1

P>This study was conducted to evaluate the fatigue strength of Ti-6Al-4V laser-welded joints with several diameters and joint openings. Sixty dumbbell rods were machined in Ti-6Al-4V alloy with central diameters of 1 center dot 5, 2 center dot 0 and 3 center dot 5 mm. The specimens were sectioned and then welded using two joint openings (0 center dot 0 and 0 center dot 6 mm). The combination of variables created six groups, which when added to the intact groups made a total of nine groups (n = 10). Laser welding was executed as follows: 360 V per 8 ms (1 center dot 5 and 2 center dot 0 mm) and 380 V per 9 ms (3 center dot 5 mm) with focus and frequency regulated to zero. The joints were finished, polished and submitted to radiographic examination to be analysed visually for the presence of porosity. The specimens were then subjected to a mechanical cyclic test, and the number of cycles until failure was recorded. The fracture surface was examined with a scanning electron microscope (SEM). The Kruskal-Wallis test and Dunn test (alpha = 0 center dot 05) indicated that the number of cycles required for fracture was lower for all specimens with joint openings of 0 center dot 6 mm, and for 3 center dot 5-mm-diameter specimens with joint openings of 0 center dot 0 mm. The Spearman correlation coefficient (alpha = 0 center dot 05) indicated that there was a negative correlation between the number of cycles and the presence of porosity. So, laser welding of Ti-6Al-4V structures with a thin diameter provides the best conditions for the juxtaposition of parts. Radiographic examination allows for the detection of internal voids in titanium joints.