## 1 Introduction  
Carbon fiber-reinforced plastic (CFRP) is an attractive material candidate for weight reduction due to its high strength-to-weight ratio compared to metals. It is especially promising for the automotive industry since toughening environmental regulations and high fuel prices have demanded reduced carbon emissions and improved fuel efficiency [1; 2; 3]. However, the lack of reliable and productive means for joining dissimilar materials has limited the use of CFRPs. Only a handful of methods for joining CFRP and other metals have been used such as chemical binders and a few mechanical means. The toxic chemicals comprising the binders pose serious environmental and health problems and the relatively long processing time accompanied by the need for temporary fixtures has made chemical joining process inefficient [1]. The mechanical joining methods usually require careful alignment of the holes between the parts to be joined, and this poses a challenge for automation. In addition, the added weight of rivets, bolts, and screws increases the overall weight, which defeats the purpose of using lightweight CFRPs [1]. Furthermore, at the end of the lifecycle of the products, the presence of both chemical binders and mechanical joints makes recycling costly, which can be a significant environmental issue in the near future. Therefore, there is a high demand for new joining technologies such as fusion welding. Fusion welding is nearly impossible for thermoset CFRPs since they burn under the intense heat of the welding process. Thermoplastic CFRPs, on the other hand, allow fusion welding and thus can be a good alternative for increasing the production efficiency [4; 5; 6; 7]. ThermoplasticCFRP has been known to exhibit lower strength and lower heat resistance compared to its thermoset counterpart, but the recent advancement of thermoplastics has removed most of its weaknesses [8]. Many prior studies have investigated the application of laser fusion welding between CFRP and metals [4; 5; 6; 7]. [PERSON] et al. [4; 5] showed that tight bonding between the polymer matrix and the metal surface could be achieved by generating bubbles in the molten zone of the CFRP matrix. Expanding pressure caused by the bubbles pushes the molten polymer flow onto the metal surface structures. Surface pre-treatments prior to the joining process have been demonstrated as an effective method to enhance dissimilar joining strength [6; 7]. [PERSON] and [PERSON] investigated the feasibility of mechanical clinching for CFRP-aluminum joining and found that a high jointing strength of 2.5 kN can be achieved. [PERSON] et al. [9] showed that the pre-treatment of aluminum with the laser Surfi-Sculpt process could improve the shear strength of dissimilar joints to a large extent and discussed the bonding and the failure mechanisms of the dissimilar joints. The same group also investigated the effect of surface grafting on the laser joining strength of CFRP and aluminum alloy [10]. The results showed that the shear strength of the joint could be enhanced up to 600% using optimized UV grafting parameters, and new bonds including Al-C and Al-O-C could be the reason for such high joining strength improvement [11]. In this study, we investigate the influence of pre-inscribed laser surface patterning, via nanosecond pulse laser, on the laser fusion-bonding strength of carbon fiber-reinforced polyetheretherketone (CFR-PEEK) and zinc-coated steel (so-called galvan annealed steel). The materials are chosen since PEEK is considered as one of the most promising candidates for replacing PA6 or PA66 for a thermoplastic polymer matrix for carbon fiber composites due to its high thermal resistance, mechanical strength, and moisture resistance, and zinc-coated steel has been increasingly adopted in the automotive industry for improved corrosion resistance [8]. Optimization of the processing parameters, including laser power, focal position, pitch, number of passes, and clamping pressure was done prior to introducing the pre-inscribed laser patterns.