Moisture-induced defects produced by direct laser joining of AA7075 aluminum and PEEK

The present investigation aims to determine how polymer moisture and volatile compounds influence the mechanical behavior of hybrid metal-polymer joints made by Laser-Assisted Joining. Experimental laser joining tests were performed on AA7075 aluminum alloy and Polyetheretherketone (PEEK). Some polymer samples were pre-treated through drying to remove the moisture stored in the PEEK before joining. Laser spot joints were produced with dried and as-received samples at different heating times. Different characterization techniques were adopted to determine the influence of moisture on the performance of the joints. Single lap shear tests were performed to assess the mechanical behavior of the joints. Fracture surface analysis was carried out through Optical Microscopy to determine the influence of the moisture content on the mechanical behavior. The results indicated a significant influence of moisture on the mechanical behavior of the joints. This led to the formation and coalescence of voids at the metal-polymer interface that affected the mechanical behavior of the joints. Dried samples were characterized by higher shear force (up to 33 %) and higher toughness (up to 130 %) compared to as-received samples.