The effects of laser radiation at 248 nm on the surface characteristics and joint properties of aluminum adherends
Procedures presently used to prepare surfaces of aluminum adherends for bonding with structural adhesives entail the use of corrosive solutions that are environmentally hazardous. As an alternative, we investigated whether eximer laser radiation can effectively be used to prepare the surfaces of aluminum adherends. The results indicate such a methodology to be very promising. Using a KrF laser, at a radiant intensity of 1.67 × 1013 W/m2/pulse, successive mm2 regions of aluminum coupons were irradiated for fixed numbers of pulses/region. This resulted in changes to the topographies and oxidation states of the surfaces. Symmetric lap shear joints from coupons so treated had considerably increased strains at fracture and 24% greater joint strengths as compared with controls. The results further indicate that fracture toughness can be increased above that of presently used procedures. The topographies of the treated and control surfaces were characterized using a new topographic characterizing system. An elastic model is presented that relates failure characteristics to experimentally-determined topographic parameters. The results suggest that different mechanisms for joint enhancement are operative.