Effects of processing temperature on failure mechanisms of dissimilar aluminum-to-polymer joints produced by friction stir welding

Abstract

An engineering grade, glass fibre reinforced (GFR) polymer – Noryl™ Resin GFN2 - and an aluminum magnesium silicon alloy - AA6082-T6 - were joined by Friction Stir Welding (FSW) in overlap configuration. A systematic analysis was conducted on the effects of different process parameters, namely, vertical force, rotating speed and transverse speed, on processing temperature and mechanical performance, and how they relate with the failure mechanisms of the joints. The analysis encompassed the morphology of the joints’ interfaces and generated defects associated to the joining process. The quasi-static tensile tests resulted in average tensile strengths varying between 15.9 and 37.9 MPa, representing joints’ efficiencies ranging from 19.9% up to 47.4%. Both macro and micromechanical interlocking were found to be the main joining mechanisms, whilst chemical bonding played a secondary role. The development of interlocking features was found to be related with the processing temperature, and it should be comprised between the softening and melting temperature of the polymeric material. Processing temperature influences both the joints’ strength, and failure mechanisms, with low strength joints’ tending to exhibit interfacial failure, whereas high strength joints’ failure can be associated with the failure of the weakest base material close to the joint region. This research work validates the feasibility of dissimilar polymer-to-metal joining through FSW. To this end it was studied the failure mechanisms in the Aluminum and the GFR polymer which exhibit highly dissimilar physical and thermo-mechanical properties. The mechanical performance of these joints is limited by the weakest base material and is mainly governed by macro and micro-mechanical interlocking features, which relates to the failure mechanism. The relation between macro and micro-mechanical interlocking features, failure mechanism and joint strength is crucial towards maximization of the joints’ mechanical performance.