Effect of laser processing microstructure on the bonding strength and failure mode of 7075-T6 aluminum alloy adhesive joints

The strength of adhesive joints of aluminum (Al) alloys can be enhanced by laser surface treatment. In this study, a nanosecond fiber laser was used to process crater array (CA), multi-groove (MG), and crater-array-multigroove (CA-MG) microstructures on 7075-T6 Al alloy substrates. The shear strength (a) was measured by a single-lap shear test. For the CA microstructure, how the pulse energy (E) and crater overlap rate (6) affect a was studied. For the MG and CA-MG microstructures, how E and the groove distance (H) affect a was studied. Also, the mechanism by which the characteristic parameters of each microstructure affect a was compared through the failure mode. The results show that when 6 = 30 %, the CA microstructure is the most conducive for improving the shear strength; however, regardless of the choice of E and 6, the CA microstructure leads to cohesive failure in part of the bonding region. The MG microstructure leads to cohesive failure in the entire bonding region only when H = 0; when H = 40 or 80 mu m, the region outside the grooves is prone to adhesive failure. Regardless of the choice of E and H, the CA-MG microstructure formed by two-step laser processing leads to cohesive failure in the entire bonding region. From the perspective of improving efficiency and saving energy, E = 880 mu J and 6 = 30 % should be selected for processing the CA microstructure and E = 176 mu J and H =80 mu m should be selected for processing the MG microstructure.

Automated summary

The study found that the CA microstructure is most conducive to improving shear strength, while the MG microstructure only leads to cohesive failure in the entire region when the groove distance is 0.