Effect of laser micromachining crater-array–multi-grooves on the bonding strength and failure mode of aluminum alloy adhesive joints

Abstract

The strength of aluminium (Al) alloy adhesive joints is essential for aerospace, ship and automotive applications. This study proposes the two-step laser processing of crater-array–multi-groove (CAMG) to maximize the shear strength of adhesive joints for 7075-T6 aluminum alloys. Firstly, the effects of CAMG feature parameters (groove pattern, groove spacing L, and groove depth Gp) on the surface roughness (Sa), shear strength (τ), and microscale failure mode were studied. The failure mode and anchoring structure reveal the influence mechanism of CAMG feature parameters on τ. Then, the parameters are optimized to obtain the best combination that maximizes τ. Finally, the advantages of CAMG were demonstrated by comparing it with a reference specimen and analyzing the surface morphology, wettability, chemical properties, and anchorage structure. The results show that for CAMG the surface had high cleanliness, wettability, and chemical modifications. The multi-scale anchoring structure formed by the grooves, craters, and micropores on the surfaces with the adhesive was sufficiently strong to allow cohesive failure (CF) to occur throughout the bonding region, maximizing τ. When the groove pattern is parallel-groove, L ≤ 100 μm, and the number of scans is N = 2–5, CAMG maximizes τ (∼29.34 MPa). To increase efficiency and save energy, the optimal combination of parameters for laser processing CAMG is parallel-groove, L = 100 μm, and N = 2. Compared with laser processing multi-grooves, CAMG improved the processing efficiency by 3.5 % and reduced the laser energy by 35.2 %. The proposed method shows great advantages in improvement of bonding strength.