Effect of Atmospheric Pressure Plasma Treatment on the Lap-Shear Strength of Adhesive-Bonded Sheet Molding Compound Joints

Atmospheric pressure plasma treatment(APPT)technology was used herein to treat sheet molding compound(SMC)substrates to increase the lap-shear strength of adhesive-bondedSMCjoints.Further,the mechanisms behind the lap-shear strength improvements in APPT-treated adhesive-bonded SMC joints were explored.A maximum lap-shear strength about three times that of the as-received SMC joints was achieved when the APPT distance was set to 20 mm.The surface roughness,which exhibited little benefit to the lap-shear strength,was determined to not be the primary reason for the increase in lap-shear strength.Specifically,X-ray photoelectron spectra revealed that an increased amount of O-containing groups(i.e.,C–O–H,C–O–C,H–O–C=O or R–O–C=O)following APPT contributed to the improved lap-shear strength.In addition,the surface free energy increased significantly after APPT,which improved the lap-shear strength of the adhesive-bonded SMC joints.Compared to the change of surface morphology,the changes in both the surface chemical property and surface free energy played larger roles in increasing the lap-shear strength of APPT-treated SMC joints.

Study on the Weld-Bonding Process Optimization and Mechanical Performance of Aluminum Alloy Joints

The 5754 aluminum alloy has been widely used in the automotive industry to reduce the weight of vehicles.The weld-bonding(WB)process comprising resistance spot welding and adhesive bonding processes effectively improves the mechanical properties of joints.However,it is still a great challenge in the WB process to obtain high-quality and defect-free nuggets of aluminum alloys.In this study,the parameters of the WB process are optimized and the mechanism of generation of defects during WB is analyzed.The results show that the welding parameters have a significant effect on the nugget sizes,among which the welding current plays the most important role.The residual adhesive can easily cause defects during welding,e.g.,expulsion and porosity in the nugget.This can be effectively avoided by optimizing the welding parameters.In addition,the gas in the joints is effectively reduced by adding an appropriate preheating pulse prior to welding,thus lowering the damage degree of the adhesive layer.As a result,welded joints with better weld nugget quality and more stable mechanical properties are obtained.