{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T08:27:10Z","timestamp":1786955230000,"version":"build-2736575974"},"reference-count":36,"publisher":"MDPI AG","issue":"16","license":[{"start":{"date-parts":[[2026,8,16]],"date-time":"2026-08-16T00:00:00Z","timestamp":1786838400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>The continuous joining of aluminum alloys to engineering thermoplastics has emerged as a promising manufacturing path for lightweight hybrid structures, yet the influence of polymers\u2019 mechanical behavior on friction stir joining remains poorly understood. This work investigates the role of melt rheology on the morphology, joining interface, and mechanical strength of dissimilar joints that combine AA6082-T6 with two engineering-grade thermoplastics, Noryl\u00ae GFN2 and SustaPEEK\u00ae. Two joining strategies were assessed under identical processing conditions: conventional friction stir joining (FSJ) and through-slot friction stir joining (TS-FSJ), the latter incorporating thin titanium strips intended to reduce heat transfer to the polymer. Joint morphology was assessed by optical and scanning electron microscopy, mechanical performance was evaluated through quasi-static tensile-shear testing, and the rheological behavior of both polymers was characterized by steady shear and oscillatory measurements. Conventional FSJ produced defect-free aluminum\u2013Noryl joints, with a mechanical strength of 111.3 \u00b1 8.4 kN\/m, whereas aluminum\u2013PEEK joints exhibited localized polymer overflow, poor surface finish and scattered strength performance of 116.7 \u00b1 77.2 kN\/m. Rheological measurements showed that PEEK exhibited higher melt viscosity and viscoelastic moduli, restricting polymer flow and promoting unstable interface formation. Although titanium inserts reduced heat transfer in TS-FSJ, their deformation reduced the effective joining area, resulting in lower tensile strength. Polymer rheology was identified as one of the key factors governing material flow, defect formation, process stability, and the joints\u2019 mechanical performance, emphasizing the importance of tailoring the processing parameters reflecting the rheological characteristics of each polymeric base material.<\/jats:p>","DOI":"10.3390\/polym18161993","type":"journal-article","created":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T08:05:41Z","timestamp":1786953941000},"page":"1993","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Friction Stir Joining of Structural Polymers and Aluminum Alloys\u2014A Direct Comparison of Mechanical Behavior and Rheological Effects on Dissimilar Metal\u2013Polymer Joints"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8165-5946","authenticated-orcid":false,"given":"Arm\u00e9nio N.","family":"Correia","sequence":"first","affiliation":[{"name":"LAETA, IDMEC, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"B\u00e1rbara","family":"Coelho","sequence":"additional","affiliation":[{"name":"Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5871-4936","authenticated-orcid":false,"given":"Catarina R.","family":"Leal","sequence":"additional","affiliation":[{"name":"Departamento de F\u00edsica, Instituto Superior de Engenharia de Lisboa, Instituto Polit\u00e9cnico de Lisboa, 1959-007 Lisboa, Portugal"},{"name":"Centro de F\u00edsica e Engenharia de Materiais Avan\u00e7ados, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"},{"name":"CENIMAT\/I3N, NOVA School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7871-6717","authenticated-orcid":false,"given":"Susete N.","family":"Fernandes","sequence":"additional","affiliation":[{"name":"CENIMAT\/I3N, NOVA School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal"},{"name":"Department of Materials Science, NOVA School of Science and Technology, 2829-516 Caparica, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Virg\u00ednia","family":"Infante","sequence":"additional","affiliation":[{"name":"LAETA, IDMEC, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4749-3036","authenticated-orcid":false,"given":"Pedro","family":"Vila\u00e7a","sequence":"additional","affiliation":[{"name":"Department of Energy and Mechanical Engineering, School of Engineering, Aalto University, 02150 Espoo, Finland"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Correia, A.N., Braga, D.F.O., Baptista, R., and Infante, V. 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