Aluminum coating of twinning-induced plasticity plates via plasma-enhanced magnetron sputtering as a potential industrial technique

Abstract

Challenges are encountered in the use of the conventional hot-dip galvanization process to deposit a protective layer on the surface of twinning-induced plasticity (TWIP) steel due to the low wettability, which is caused by manganese oxidation on the surface of the steel. In a vacuum environment and after conducting etching on the surface to remove surface oxides, corrosion-resistant aluminum (Al) coatings were prepared on the surface of TWIP steel via the hot-wire plasma-enhanced magnetron sputtering (PEMS) technique under various target and wire discharge currents (Ihot-wires/Itarget). The substrate ion current density at −50 V was as high as 0.88 mA/cm2 under a high hot wire discharge current of 20 A and a low target current of 3 A (20 A/3 A), which was 4 times the ion current under Ihot-wires/Itarget of 5 A/3 A, respectively. According to an analysis of the coatings via pulsed radio frequency glow discharge optical emission spectroscopy, Al, Fe and Mn elements diffused at the interface between the coating and steel substrate. The diffusion layers on both sides of the interface resulted in the Al coating remaining well adhered to the surface of the TWIP steel after Rockwell indentation, scratch testing and Erichsen cupping tests. As the sacrificial and passivated anode, the self-corrosion potential of the dense Al coating increased from −0.770 V of the TWIP steel to −0.471 V, and the corrosion current decreased from 3.91 × 10−4 A/cm2 to 6.14 × 10−5 A/cm2. The dense coating remained undamaged after electrochemical corrosion. Additionally, the structure of the TWIP steel was not affected by the PEMS coating processes.