Influence of medium polyurethane coating on mechanical, wear, and corrosion performance of a galvanised steel sheet

Abstract

Colour-coated steel, also known as pre-coated steel or pre-painted steel, has become a material of choice across diverse industries due to its aesthetic allure and practical advantages. The present study delves into the coated low-carbon (∼ 0.04 wt%) steel's mechanical properties, abrasive wear behaviour, and electrochemical corrosion resistance. The excellent combination of tensile properties (340 MPa YS, 347 MPa UTS and 33 % total elongation) ensures structural integrity and load-bearing capacity. The robust polyurethane (PU) coating demonstrates good abrasion resistance through its lower Taber wear index (0.022). Nano-scratch tests further reinforce the coating's ability to withstand frictional forces, with minimal signs of observed wear. The results of electrochemical corrosion indicate that the coating provides exceptional protection against deterioration, even in harsh environments with 5 % NaCl solution for 600 h. Both OCP and Tafel plots illustrate lower corrosion rates in PU-coated steels owing to lower potential and inhibited reactions. The I_corr of the coated steel was 265 µA/cm², which is substantially lower than that of the uncoated steel of 1864 µA, indicating much lesser corrosion. The more positive E_corr (-637 mV) value for the coated steel also denotes better corrosion resistance coupled with robustness. Nyquist plots validate higher charge transfer resistance, which portrays the coating as a strong impediment against chloride. This significantly increases the lifespan of coated steel under extreme conditions. The corrosion tests confirmed long-term durability, with negligible rust or coating degradation signs. Hence, colour-coated steel emerges as a true champion, combining good mechanical properties, wear resistance, and corrosion protection.