Adhesion of AA5182 aluminum sheet to DLC and TiN coatings at 25 °C and 420 °C

A limiting aspect of aluminum hot forming process is the interaction between the hot tool and aluminum workpiece surfaces, which causes adhesion and accumulation of aluminum on the tool surfaces, resulting in a decrease in the surface quality of the finished products. In this study high temperature adhesion phenomena between AA5182 aluminum alloy and two types of coatings, namely DLC (non-hydrogenated) and TiN coatings deposited on AISI 52100 type steel were investigated. Experiments were conducted at 420 °C and consisted of measurements of i) strength of adhesive junctions formed and ii) coefficients of friction as a function of sliding distance. Aluminum samples were heated to 420 °C to simulate hot forming contact conditions but coated surfaces were held at lower temperature to prevent oxidation. The force necessary to break the adhesive junctions formed at 420 °C was the highest for the uncoated steel–Al pair and the lowest for the DLC–Al pair. The amount of material transferred to the contact surface of DLC was negligibly small after 2 × 103 mm of sliding and thus had no significant effect on the surface roughness whereas significant amounts of Al were transferred to TiN coating and uncoated steel.