Nanosecond laser ablation for improving the strength of CFRTP and aluminum alloy adhesively bonded joints

The improvement of adhesively bonded joints of aluminum alloy and carbon fiber reinforced thermoplastic composites (CFRTP) was achieved by nanosecond laser ablation. Surface morphology, roughness and wettability of CFRTP ablated were studied. Chemical compositions were determined by FTIR and oS. Tensile-shear tests were performed, and fractured surfaces were analyzed to determine the failure mode. The digital image correlation (DIC) technique was used to observe the micro-scale full-field strain. The durability of joints in extreme conditions was also evaluated. As the laser power increased, the resin was removed, and underlying fibers were exposed, increasing the surface roughness and contact area. This improved the strength of bonded joints. The highest strength of joints was 14.3 MPa when the laser power was 24.5 W, which was approximately 2.2 times of joints without ablation. However, excessive heat input would destroy the CFRTP decreasing the strength. The wettability of CFRTP after ablation was worse due to rough surfaces and fewer polar chemical bonds. Four failure modes were confirmed, and cohesive failure was obtained when the strength of joints was the highest. DIC results revealed the rougher surface after laser ablation could decrease the strain. High residual strength after hygrothermal aging was maintained due to good interface bonding.

Automated summary

The study improved adhesively bonded joints of aluminum alloy and carbon fiber reinforced thermoplastic composites (CFRTP) through nanosecond laser ablation. Increasing laser power removed resin and exposed fibers, enhancing surface roughness and contact area to boost joint strength. However, excessive heat input could damage the material and reduce strength, while ablation worsened surface wettability.