Research Papers

Investigation and Optimization of Laser Welding of Ti-6Al-4 V Titanium Alloy Plates

[+] Author and Article Information
Fabrizia Caiazzo

e-mail: f.caiazzo@unisa.it

Vittorio Alfieri

e-mail: valfieri@unisa.it

Gaetano Corrado

e-mail: gcorrado@unisa.it

Francesco Cardaropoli

e-mail: fcardaro@unisa.it

Vincenzo Sergi

e-mail: sergi@unisa.it

Department of Industrial Engineering,
University of Salerno,
Fisciano, Salerno 84084, Italy

Manuscript received March 28, 2013; final manuscript received September 25, 2013; published online November 18, 2013. Assoc. Editor: Yung Shin.

J. Manuf. Sci. Eng 135(6), 061012 (Nov 18, 2013) (8 pages) Paper No: MANU-13-1111; doi: 10.1115/1.4025578 History: Received March 28, 2013; Revised September 25, 2013

Titanium alloys are employed in a wide range of applications, from aerospace to medicine. In particular, Ti-6Al-4 V is the most common, thanks to an excellent combination of low density, high specific strength, and corrosion resistance. Laser welding has been increasingly considered as an alternative to traditional techniques to join titanium alloys. An increase in penetration depth and a reduction of possible welding defects are indeed achieved; moreover, a smaller grain size in the fused zone (FZ) is benefited in comparison to either tungsten inert gas (TIG) or plasma arc welding, thus improving the tensile strength of the welded structures. This study was carried out on 3 mm thick Ti-6Al-4 V plates in square butt welding configuration. The novelty element of the investigation is the use of a disk-laser source, which allows a number of benefits thanks to better beam quality; furthermore, a proper device was developed for bead protection, as titanium is prone to oxidation when in fused state. A three-level factorial plan was arranged in face-centered cubic scheme. The regression models were found for a number of crucial responses and the corresponding surfaces were discussed; then a numerical optimization was carried out. The suggested condition was evaluated to compare the actual responses to the predicted values; X-ray inspections, Vickers micro hardness tests, and tensile tests were performed for the optimum.

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Fig. 1

Face-centered central composite design scheme

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Fig. 2

Bead characterization: geometric features (above) and imperfections (below)

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Fig. 4

Bead aspect of the specimen corresponding to the center point of the experimental plan

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Fig. 5

Cross-section micrograph of the specimen corresponding to the center point of the plan

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Fig. 6

Micrograph of the base metal

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Fig. 7

Micrograph of the heat affected zone for the specimen corresponding to the center point of the plan

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Fig. 8

Micrograph of the fused zone (center point of the plan)

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Fig. 9

Fused zone as a function of thermal input

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Fig. 10

Fused zone as a function of power

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Fig. 11

Fused zone as a function of welding speed

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Fig. 12

Bead profile with a focused (left) and defocused beam (right), all other parameters being equal

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Fig. 13

(a) Shape factor for a given speed of 20 mm/s and (b) shape factor for a given negative focus position of 3 mm

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Fig. 14

(a) Grain size for a given power of 2000 W and (b) grain size for a given speed of 20 mm/s

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Fig. 15

X-ray transmitted image of the bead as obtained in the suggested optimal welding condition

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Fig. 16

Vickers micro hardness trend in the cross-section

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Fig. 17

Fracture surfaces from tensile tests, top-side (left), back-side (right)




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