Joining light metals with polymer composites through metal overcasting

This work investigates a unique technique to join aluminum (Al) and magnesium (Mg) alloys to carbon fiber reinforced polymer (CFRP) composites without the use of adhesives or mechanical fasteners. The joints were made using an overcasting technique where the molten alloys were cast around the polymer composites using high pressure die casting method. Rapid cooling during casting allowed the composite to be embedded inside the cast metal without causing any gross damage to the former even though the molten metal temperature exceeded the melting point of the composite matrix by several 100’s of deg. C. The metal/composite interface was examined using optical and scanning electron microscopy and x-ray imaging, and the joint strength was examined through tensile testing. Although evidence of polymer melting was visible in the x-ray images and through microscopy, this melting was limited to the CFRP surface only while the bulk of the embedded section of the composite coupons retained their overall shape and integrity. Preliminary tension tests on Al/CFRP composites showed strength degradation of the CFRP and it failed a few mm outside the joint. This strength degradation in the CFRP suggests that the overcasting process needs further optimization to minimize thermal excursion in the CFRP section outside the joint. Nevertheless, the overcasting process shows great promise as a unique joining technique with application in fabricating light-weight structures for automotive and transportation industries.