Process parameters effect on high-temperature friction and galling characteristics of AA7075 sheets

During hot forming of high-strength 7xxx series alloy, friction and galling often occur on the contact surface, degrade product surfaces quality, and affect severely by the process parameters, especially by load and speed. In the present paper, the effect of process parameters, namely applied load and sliding speed, on high-temperature friction and galling performance of AA7075 sheets has been determined using linear sliding tests at 350°C in simulated hot forming. The microscopic observations, i.e., scanning electron microscopy (SEM) and three-dimensional confocal scanning optical microscopy, were utilized to analyze hard phase distribution of the alloy as well as surface and sub-surface of the posttest specimens. A friction model was proposed to describe the friction mechanism. The results show that wear rate gradually decreased with increasing load and speed, attributing to the formed compacted oxide layer on the worn surface, which inhibited the rate of further attrition. Besides, for all test conditions, adhesion dominated the wear mechanism, and the compacted layer was damaged more serious due to more initiation of micro-cracks between hard phase and matrix and higher contact interface temperature at higher load and speed, thus the extent of adhesion is grievous resulting in a higher wear loss.