Welding of Two Dissimilar Polymers UHMWPE and PP, Using Friction Stir Welding and Evaluation of Mechanical Properties

The joining using friction stir welding (FSW), of two dissimilar polymers: ultra-high molecular weight polyethylene (UHMWPE), and Polypropylene (PP), was undertaken in this work, under butt position of the experimental pieces. Initial tests presented poor welding results, associated with poor mechanical properties; nevertheless; the use of a self-designed and constructed fixed aluminum shoulder, together with the appropriate FSW parameters, which included: advance speed, rotation speed, approaching speed, preheating or no preheating, leads to results markedly improved. Mechanical properties were improved showing that tensile strength for dissimilar joints UHMWPE-PP attaint as high as 80% the welding efficiency of parent materials, and showing brittle fracture behavior for all tensile tests. Fracture surface examination was undertaken, together with the analysis of transition from laminar to turbulent flow during the FSW tests in order to assess the generalities of cause effect for the improvement of mechanical properties. Finally, the microhardness along the welded zones was obtained and the results were discussed in regard the testing parameters, the physical-mechanical properties of welded joints and the welding process parameters.