Advanced manufacturing of fiber metal laminates: A review of fabrication strategies, interfacial control, and future outlook

Fiber metal laminates (FMLs) routinely outperform monolithic alloys in fatigue and conventional composites in impact, yet nominally identical FMLs made in different laboratories often differ substantially in interlaminar shear strength. The cause is almost always interfacial, and earlier reviews have treated fabrication route, surface preparation and cure cycle as separate topics. We treat the three as a single coupled system and ask which fabrication-interface pairs are compatible. Six families of surface treatment (degreasing, mechanical, chemical, coupling-agent, electrochemical and dry) and four fabrication routes are compared on cycle time, void content, lap-shear bond strength, hot/wet retention and industrial scalability. Three patterns emerge from the synthesis. The cycle-time/void envelope is dominated by autoclave-cured prepreg (180-420 min, void <1%) and by resin transfer moulding and hot-press routes at lower capital cost, while hand layup without post-cure consolidation sits off the envelope at 4-6% voids. Chromate-free surface treatments retain 52-84% of dry bond strength after 1000 h at 70 °C and 85% RH, whereas phosphoric acid anodising with a sol-gel primer retains 85-94%; the gap ranges from 1 to 42 percentage points depending on the chromate-free family chosen. Fabrication and interface treatment appear to interact, and modest nanofiller additions raise bond strength along the existing envelope rather than displacing it. The review is framed as a candidate hypothesis rather than a settled finding, and motivates further work on long-duration durability of chromate substitutes, field validation of natural-fibre FMLs, and recyclable thermoset interfaces.