Process-structure-property relationship of laser-joined thermoplastic metal hybrids

During the last years, several studies have been conducted to improve the laser-based heat conduction joining of thermoplastic metal hybrids. Most scientists tried to improve the joint quality by a prior surface enlargement of the metal in order to achieve a strong mechanical interlocking. Only a few authors investigated hybrids which consist of merely cleaned and not additionally enlarged metallic specimens. For merely cleaned specimens, Katayama et al. postulated the bubble theory which suggests that small bubbles near the metallic interface are very important for strong joints. The bubble formation leads to a high pressure between thermoplastic and metal so that the thermoplastic melt wets the metallic surface and an anchor effect occurs. Investigations by the author confirm the anchor effect theory, but the bubble theory itself cannot be verified since strong joints can be realized without the formation of bubbles. On the contrary, it seems rather advisable to avoid bubbles because they indicate a thermal decomposition of the plastic. However, there is still no sufficient description of the relationship between process parameters, joint morphology, and resulting joint strength. The main objective of this paper is to point out the process-structure-property relationship of laser-based joined thermoplastic metal hybrids.