Journal of Welding Science

In this project, joining Ti-6Al-4V and AISI 304 dissimilar plates by laser-spot-welding method has been studied. In this regard, Ti-6Al-4V and AISI 304 plates, with a thickness of 0.7 and 0.5 respectively, were lap-welded using an interlayer of 0.2 & 0.3 mm copper and silver (pure silver). The process was done by 400Watt pulsed laser (Nd:YAG) using oncentric spot welding with 4mm diameter circles as lap welding. Once the spots were created, they got studied and surveyed first by eye inspection, then by optic metallography inspection and finally, by tensile strength and SEM; of course, if cracks were not detected on joining. The results proved copper a better interlayer compared to silver: no joining occurred while using silver as an interlayer for 3 milliseconds, and replacing the upper metal didn’t change the outcome. The best joining result was observed when AISI 304 was placed above (near the laser), copper plate interlayer was used in 7 milliseconds, with 15 Hz frequency, 10.7 J heat input and 1.5 KW peak-power. This way, sheer strength equaled 160 MPa and micro hardness equaled 504 HV.

The aluminum alloys of Al1050 with thickness of one millimeter and Al3105 with thickness of half millimeter  were joined via ultrasonic spot welding (USW). To create a suitable welding, a vibrating horn (welding tool) fit to transducer and ultrasonic generator was designed using ANSYS software. Due to mechanical and thermal cycles during USW, both diffusion and mechanical mixing facilitated the formation of welded interfaces. The alloying element, Mn, in Al3105 diffused into Al1050 during USW, and diffusion behavior varied with selection of top sheet. The fracture mechanism during lap shear testing, i.e. debonding or pullout fracture, varied based on welding power, time and pressure of jack. The optimal point for the existing welding conditions was obtained. The best welding conditions were for 750 W at 2 and 3 seconds when the horn was held on the overlap of the sheets.  Also, in the tensile test, sheet rupture was performed around the welding spot (out of welding spot).