Effect of temperature on the frictional behaviour of an aluminium alloy sliding against steel during ball-on-disc tests

Ball-on-disc tests were carried out at elevated temperatures to determine the friction behaviour of the 7475 aluminium alloy against steel, resembling the material mating during hot extrusion. Friction coefficient was found to increase markedly with rising temperature, suggesting that the commonly accepted assumption of an unvaried friction coefficient in the FE simulation of the aluminium extrusion process involving temperature evolution is incorrect. A theoretical analysis showed that the high friction values measured during high-temperature ball-on-disc tests could be partly attributed to the increased plowing friction caused by the severe deformation of the aluminium alloy. The effect of temperature on the stress and strain distributions at the ball/disc interface was revealed by means of three-dimensional finite-element (3D FE) simulation. Increased deformation in the aluminium disc around the contact point with rising temperature was confirmed. The alterations of the strain state and stress state around the contact point were considered responsible for the generation of wear debris, the oscillations of friction coefficient along the wear track and the increase of friction coefficient with rising temperature.