Investigation of joining mechanism of electrical-assist friction stir joining between polyethylene (PE) and 316 stainless steel

In this study, the Polyethylene (PE) polymer and 316 stainless steel textiles lap welded by the electrical-assist friction stir joining (EA-FSJ) technique. Effects of stirring action of tool and electrical current heat on joining mechanism between PE sheets and 316 stainless steel are investigated. A scanning electron microscope (SEM) was used to investigate of internal material flow. To study the bonding mechanism in joint line, Fourier-transform infrared spectroscopy (FT-IR) and energy-dispersive X-ray spectroscopy (EDS) techniques were employed. Differential scanning calorimetry (DSC) was used to analyze of PE structure after welding. The results show that the joining mechanism in this joint consists of chemical bonding and mechanical locking between 316 stainless steel and PE. The presence of extra heat by electrical current decreased the strength of steel during the welding process and consequently increased chemical bonding and mechanical joining. The final joint flexural and tensile strength were increased by 9 and 10%, respectively, comparing PE raw sheet. The electrical heat increases the PE softening front of the tool and decreases joint thinning after the welding procedure. The mixing between PE and 316 stainless steel fragments increases the stir zone hardness near 84 ShoreD.