1. Introduction
2. Design of experiment in taguchi method
3. Materials and method
4. Results and discussion
4.1 Optimal Parameters Determination
Table 3
Table 4
Materials | Thermal conductivity (W/m•K) | Specific heat capacity (J/g•C) |
---|---|---|
Ti-6Al-4V | 6.7 | 0.5263 |
Ti-3Al-2.5V | 8.3 | 0.5250 |
Table 5
4.2 Verification by Experiments
4.3 Comparison of surface bead width and back bead width at a different heat input
4.4 Microstructure of Titanium Alloys at optimum conditions
4.5 Hardness
4.6 Tensile test
5. Conclusions
1) The bead geometry of titanium alloys is optimized by the Taguchi method. At optimal welding conditions, the bead width of Ti-6Al-4V is wider than the Ti-3Al- 2.5V due to the lower thermal conductivity and higher heat capacity of Ti-6Al-4V.
2) Welding current is the most influencing factor for Ti-6Al-4V, whereas welding speed is the most influencing factor for Ti-3Al-2.5V. This is confirmed as another reason for the wider bead width in Ti-6Al-4V. With increasing heat input, the difference in bead width between the two alloys becomes more prominent.
3) At optimal parameters, the weld zone of both Ti-6Al- 4V and Ti-3Al-2.5V consisted mainly of martensite structure. However, Ti-3Al-2.5V contains a small amount of retained β in the weld zone, which is not observed in Ti-6Al-4V weld metal.
4) During the tensile test of the welds, a fracture occurred in the base metal portion. Ti-6Al-4V shows higher tensile strength than Ti-3Al-2.5V as the base metal of Ti-6Al-4V contains a high amount of beta phase compared to Ti-3Al-2.5V.