Experimental Studies on Friction Coefficient of Al 6061-T6 Alloy Contacts under Full Sliding

Abstract

Aim of the present research work is to study dry sliding coefficient of friction of aluminium to aluminium contacts in detail and to study evolution of coefficient of friction with change in normal load, sliding speed and temperature. Dry sliding experiments were conducted using pin on disk type tribometer. Specimens (both pin and disk) were fabricated using Al 6061-T6 alloy. The disk specimen has dimensions of 165 mm diameter and 8 mm thickness; the pin specimen dimensions are 30 mm length, 6 mm x 6 mm cross-section and 3 mm radius of curvature at cylindrical contact. Experiments were conducted with cylinder on flat contact configuration. Dry sliding experiments were conducted by applying normal loads of 1 kg, 1.5 kg and 2 kg; at different sliding speeds of 1.25 m/s, 2 m/s and 3 m/s; at different temperatures room temperature (31 ± 1 °C), 60 °C, 100 °C and 150 °C. The coefficient of friction at contact interface is influenced by both frictional heat generated and external temperature. The frictional heat at contact interface was estimated by measuring temperatures at 3 mm and 7 mm from contact interface of pin specimen during dry sliding experiments. One-dimensional inverse heat transfer model was developed using Finite Element Method and Beck’s algorithm to estimate the contact interface temperature. The inverse heat transfer model was validated by using ANSYS transient thermal analysis. Maximum bulk temperature at contact interface was observed for all the experimental conditions at room temperature. Temperature due to frictional heat at contact interface increased with increase in normal load and sliding speed. The maximum frictional heat of 100 °C was observed at 2 kg normal load and 3 m/s sliding speed condition. The frictional heat and external heat source temperatures are the reasons for formation of oxide layer at contact interface during sliding which ultimately changes the coefficient of friction of contact pair. Coefficient of fiction, after the first cycle of sliding, stabilized stage, unsteady state and steady state are reported elaborately in this study. The coefficient of friction and wear rate were more influenced by increase in normal load than by increase in sliding speed and temperature. Adhesive and abrasive wear mechanisms were observed in dry sliding of Al 6061-T6 alloy contacts from the microscopic analysis of worn contact surfaces. Under normal loads of 1 kg and 1.5 kg, Al 6061-T6 alloy showed better wear resistance at higher temperatures when compared to that at room temperature