Influence of aluminum surface pre-treatments on the bonding mechanisms and mechanical performance of metal-composite single-lap joints

Durability of Metal-Composite Friction Spot Joints under Environmental Conditions

“…Although, the PAA specimen did not show any significant changes on the fracture surface (Figure 11c), humidity diffusion was expected to take place faster than with the other surface pre-treatments, as was also explained by the moisture uptake. The PAA-P specimen also showed very similar features to the specimen before aging (refer to [30]), such as the primer remaining attached to the composite, as indicated by the white arrows in Figure 11d. Figure 12a shows the fracture surface of the SB specimen on the aluminum side of the joint.…”

“…In the second part of the paper, the mechanical performance of the joints under outdoor weathering conditions is briefly addressed. It should also be noted that the influence of different surface pre-treatments on the bonding mechanism and mechanical performance of the FSp joints was discussed thoroughly in [30]. Briefly, SB and PAA treatment led to a rough aluminum surface, increasing the micromechanical interlocking between aluminum and the molten polymer.…”

“…In contrast to the SB and CC specimens, the PAA-P pre-treated joints showed a reduction in the lap shear strength in the first six months, while retaining their residual strength on the same level afterwards. PAA-P pre-treatment led to strong chemical carbon-carbon bonds between CF-PPS and aluminum [6,30]. It seems that moisture does not have a great influence on such chemical bonds, and the joint retained more than 80% of its initial strength.…”

“…Four surface pre-treatments were selected; these were sandblasting (SB), stand-alone conversion coating (CC), phosphoric acid anodizing (PAA), and PAA with a subsequent application of primer (PAA-P). Although SB + CC gave a slightly higher lap shear strength than stand-alone CC in dry conditions [6,30], the CC specimen was selected for the aging experiments, in order to understand the behavior of chemical pre-treatment under environmental conditions. For a detailed explanation of each surface pre-treatment, refer to [6,30].…”

“…Since molten PPS wet and fill such crevices, moisture cannot penetrate easily or rapidly into the interface between the aluminum and PPS, which in turn reduces the degradation kinetic of the joints. Furthermore, the chemical bonding between the aluminum and PPS, in the cases of CC and PAA-P pre-treatments [30], reduces the moisture path into the joints. In all three cases, the moisture diffusion was not completely inhibited, but the diffusion kinetic was significantly reduced.…”