Surface modification of magnesium alloys using triazine dithiols

Polymer plating of 6-dihexylamino-1,3,5-triazine-2,4-dithiol monosodium (DHN), 6-diallylamino-1,3,5-triazine-2,4-dithiol monosodium (DAN), and 6-mercapto-1,3,5-triazine-2,4-dithiol (TTN) groups at 10 °C in 1 mol/dm3 NaOH aqueous solution on the magnesium alloy AZ91D yielded poly(6-dihexylamino-1,3,5-triazine-2,4-disulfide) (PDH), poly(6-diallylamino-1,3,5-triazine-2,4-disulfide) (PDA), and poly(6-mercapto-1,3,5-triazine-2,4-disulfide) (PTT), respectively. PDH-plated magnesium alloys showed excellent corrosion resistance in air containing moisture and in corrosive water because PDH films have very low critical surface tension, are composed of ordered and closely packed layer structure like the LB-films, and have high crystallinity. An increase in film thickness of the PDH films suppressed the corrosion rate of the magnesium alloys and increased the induction period to initiate the corrosion. PTT-plated magnesium alloys showed outstanding adhesion to poly(phenylene sulfide) (PPS) compounds during injection molding in 140 °C. This is because PTT films have highly active points, such as SS bonds, and show excellent strength. PTT-film thickness in the range of 20 to 80 nm provided high tensile shear strength for the direct adhesion of PPS to PTT-plated magnesium alloys. PDA-plated magnesium alloys exhibited excellent adhesion to ethylene-propylene-diene terpolymer (EPDM) in a peroxide curing system and with acrylic rubber (ACM) under a triazine thiol curing system, although the peel strength was found to depend on film thickness.