Semi-additive manufacturing of metal-polymer hybrid parts by direct material extrusion onto anodized and onto organosilicate-coated aluminum

Purpose Additive manufacturing of polymer-metal components increases the freedom of design and avoids expensive tooling. Few studies investigated the direct printing of thermoplastics onto metal parts, and geometrically coarse form fits have been used to achieve adhesion. The suitability of anodizing and organosilicate coating of metal surfaces – performant adhesion promoting layers in conventional production – has not been tested. This study aims to test the hypothesis that these treatments are suitable if convenient printing parameters are used. Design/methodology/approach Polymers are printed onto aluminum parts using fused-filament-fabrication (FFF). The effects of anodizing in phosphoric acid at low voltages and of organosilicate coating bearing epoxy functionality on the joint strength are evaluated. Sufficient FFF parameters of the first printed layer were identified with PLA and then transferred for printing with the PA, ABS and PETG. Findings Low interfacial pore content and thus high joint strength is achieved for excessively increased metal-surface temperatures and when subsequently ironing the first printed layer. The parameters print speed, layer height of the first layer, and nozzle temperature had negligible impact. For anodizing, joint strengths of 15.5 MPa, 8.7 MPa, 2.6 MPa and 2.5 MPa were determined for PLA, PA, ABS and PETG, respectively, whereas the organosilicate enabled joint strengths of 5.1 MPa, 9.2 MPa, 5.0 MPa and 4.4 MPa, respectively. Originality/value To the best of the authors’ knowledge, it is shown for the first time that anodizing and organosilicate coating enable moderate joint strengths between aluminum and typical FFF polymers. Besides adhesion promotion, a significant added value of these treatments is the possible integration of further functionalities into the manufactured components, such as protection against wear by anodizing and corrosion protection by the organosilicate coating.