Pre-threaded hole friction stir spot welding of AA2219/PP-C30S sheets

This paper examines the use of pre-fabricated interlocking arms/threading in enhancing the strength of friction stir spot welded hybrid joints of AA2219/PP-C30S polypropylene polymer by varying parameter combination. The process involves the fabrication of a pre-threaded hole on the Al alloy prior to the joining process, and the threading/crest-pitch profile aids mechanical interlocking. The peak temperature, crest-pitch interlocked profiles, microstructural and mechanical properties of the joints were examined. The results show that an increase in the tool rotational speed increases the thickness of the reaction layer (between the Al and the polymer substrates), the shear-tensile load (268–540 N), and the cross-tensile load (171–321 N) of the hybrid AA2219/PP-C30S joint. A rise in rotational speed reduces the volume of the unfilled zone while the formation of interfacial crack/discontinuity is promoted. Adhesive bonding impedes the formation of discontinuity/crack at the interface of the Al alloy and the reaction layer. The fracture of the joint is controlled by the volume of the unfilled zone, adhesively bonded region, and crest-pitch interlocked region.