PBT–anodized aluminum alloy direct joining: Characteristic injection speed dependence of injected polymer replicated into nanostructures

Roughened metal pieces and polymer can be joined via typical injection molding. We formed nanopores on the aluminum alloy surface by anodization and joined the alloy with polybutylene terephthalate. Tensile tests indicated the anodized metal and polymer joined with a shear strength of over 20 MPa. STEM-EDS analysis showed the polymer was replicated into the nanopores. We revealed the injection speed and joint strength have a negative correlation, which may result from the breaking of the nanopores. Additionally, measurement results for the polymer temperature indicated the local thermal decomposition could weaken the joint, especially in nanostructures. The joint strength dependence on the injection speed in anodic pores was similar to that of the NMT method. However, the characteristic correlation between the pack pressure and joint strength at high injection speeds has not been found for other surface treatments. These results provide insight into the behavior of injected polymers in nanostructures.