Effect of hydrogen fluoride and magnesium oxide on AZ31 Mg alloy/carbon fiber-reinforced plastic composite by thermal laser joining technique

Although hydrofluoric acid (HF) surface treatment is known to enhance the joining of metals with polymers, there is limited information on its effect on the joining of AZ31 alloy and carbon-fiber-reinforced plastics (CFRPs) through laser-assisted metal and plastic direct joining (LAMP). This study uses the LAMP technique to produce AZ31-CFRP joints. The joining process involves as-received AZ31, HF-pretreated AZ31, and thermally oxidized HF-pretreated AZ31 alloy sheets. Furthermore, the bonding strength of joints prepared with thermally oxidized AZ31 alloy sheets is examined to ascertain the combined effect of HF treatment and thermal oxidation on bonding strength. The microstructures, surface chemical interactions, and mechanical performances of joints are investigated under tensile shear loading. Various factors, such as bubble formation, CFRP resin decomposition, and mechanical interlocking considerably affect joint strength. Additionally, surface chemical interactions between the active species on metal parts and the polar amide along with carbonyl groups of polymer play a significant role in improving joint strength. Joints prepared with surface-pretreated AZ31 alloy sheets show significant improvements in bonding strength.