Laser surface pre-treatment of aluminum for hybrid joints with glass fiber reinforced thermoplastics

Lightweight construction is a major trend in the automotive industry. The connection of fiber reinforced plastics with aluminum is consequently seen as a promising prospect. In this regard, thermal joining is one potential joining technology for bonding of such hybrid joints. Yet a pretreatment of the aluminum surface is necessary to create a load bearing metal-plastic joint. Recent research has shown that a laser surface pretreatment provides high joint strengths. However, there is a variety of laser sources and possible surface topographies with typical structure sizes ranging from macroscopic to nanoscopic profiles. Within this work, two different laser induced structures were generated on aluminum sheets which were subsequently joined to glass fiber reinforced thermoplastics. One of the two laser structures was created with a continuous wave laser using a modified remote ablation cutting process. The other structure was manufactured by a pulsed laser source with a pulse width in the nanosecond-range. The two laser processes were compared with a conventional abrasive blasting process and they were characterized in terms of surface topography and chemical composition of the surface. Furthermore, the achievable joint strength for joining with glass fiber reinforced thermoplastics was investigated. It is shown that the properties of the thermoplastic as well as the surface topography and chemical composition of the metal strongly influence the resulting joint strength.