An overview of the polymer-to-metal direct-adhesion hybrid technologies for load-bearing automotive components

The work published in the open literature dealing with various polymer metal hybrid (PMH) approaches used to promote direct (adhesive-free) adhesion between metal and injection-molded thermoplastics is reviewed and critiqued. Different approaches are categorized as follows: (a) micro-scale polymer-to-metal mechanical interlocking; (b) in-coil or stamped-part pre-coating for enhanced adhesion; and (c) chemical modifications of the injection-molded thermoplastics for enhanced polymer-to-metal adhesion. For each of these approaches their suitability for use in load-bearing body-in-white (BIW) components is discussed. In particular, the compatibility of these approaches with the BIW manufacturing process chain (i.e. pre-coated metal component stamping, BIW construction via different joining technologies, BIW pre-treated and painting operations) is presented. It has been found that while considerable amount of research has been done in the PMH direct-adhesion area, many aspects of these technologies which are critical from the standpoint of their use in the BIW structural applications have not been addressed (or addressed properly). Among the PMH technologies identified, the one based on micro-scale mechanical inter locking between the injection-molded thermoplastic polymer and stamped-metal structural rib component appears to be most promising.