Experimental investigation of temperature field, defects, and mechanical strength in dissimilar laser bonding of Ti6Al4V and polyethylene terephthalate

Laser welding is one of the most common technologies with various applications in different industries. In this paper, laser joining of the Ti6Al4V alloy and polyethylene terephthalate (PET) as a means of two common materials is discussed. According to the experimental results, the focal length is a very important parameter in this dissimilar laser welding, and because of the low melting point of PET, it is not possible to create welding at low focal lengths. Furthermore, changing the welding parameters such as welding speed and pulse duration changes the temperature field of the molten pool and its surrounding points, as well as the number, distribution, and the shape deformation of the bubbles formed in PET, which plays an important role in welding quality and mechanical strength. The number of bubbles clearly has a significant influence on the surface contact area and the resultant shear load test values. Generally, reducing the surface contact area between PET and the Ti6Al4V alloy evidently reduces the tensile shear load of the joints. The shear load of the joints has had about 40% variation upon changing the focal length. Additionally, the shear load changed only about 10% by changing the pulse duration from 6 to 10 ms. Seemingly, changing the energy density through a variation of focal length has had a higher influence of about 30% than the incident time of laser beam through increasing the pulse duration. Apart from selecting different laser parameters, the measured temperature in ranges between 100 and 120 °C can produce acceptable joints with lower defects.