Drillability of Magnesium-Based Fiber Metal Laminates Obtained via Hot Metal Pressing with Different Metal Surface Treatments

Abstract

The demand for lighter and more performant aerospace and automotive components has resulted in a substantial surge in a recent interest in parts made of Fiber Metal Laminates (FMLs). For such components, drilling operations are crucial for permitting subsequent assembly. However, drillability of fiber metal laminates is critical due to the heterogeneous thermal and mechanical properties of the metal and composite that form the laminate. In this framework, the current research work aims at understanding how drilling operations can be affected by different surface treatments carried out on AZ31B magnesium alloy sheets joined with Glass Fiber Reinforced Polyamide 6 (PA6-GFRP) via hot metal pressing to form the FML. To this end, the Mg/PA6-GFRP/Mg composites were first fabricated using AZ31B surfaces that were previously treated through sandblasting, annealing, and their combination. Dry drilling was then performed using twist and spur drill bits. The feed was also varied, using two levels. The thrust force, hole quality, delamination and fiber pull-out were considered to evaluate the FMLs drillability. Results showed that the magnesium alloy sheet treatment influenced the drillability, and that the drill bit had an effect too. In particular, sheets that were both sandblasted and annealed allowed the highest drillability avoiding delamination. The use of spur drill bits improved the drillability too, reducing the FML inflection under the drill bit load.