Characteristics of the Friction Between Aluminium and Steel at Elevated Temperatures During Ball-on-Disc Tests

Abstract

Appropriate specification of the frictional boundary condition for the finite-element (FE) simulation of metal-forming processes is of great importance to the trustworthiness of the results. The research reported in this communication aimed at understanding the interfacial contact between aluminium and steel at elevated temperatures and determining friction coefficients at this material mating. A series of high-temperature ball-on-disc tests were carried out with the AA7475 aluminium alloy as the material of disc and the hardened H11 steel as the material of ball. A mathematical model developed in the preceding research was employed to account for the evolution of the contact interface during ball-on-disc tests. Friction coefficients at different temperatures and over a number of laps were determined. The shear friction stresses and mean contact pressures along with the progress of the tests at 350-500°C were calculated. It was found that the friction coefficients obtained from ball-on-disc tests alone were insufficient to represent the frictional interaction between deforming aluminium and steel at elevated temperatures. The evolution of the contact interface with increasing sliding distance must be taken into consideration and the friction behaviour can be reasonably characterized by using friction stress.

Identification of a friction model for the bearing channel of hot aluminium extrusion dies by using ball-on-disc tests

“…Therefore, in order to reproduce the friction conditions in the bearing channel, it is vital to choose a friction testing technique being able to remove the surface oxides. Obviously, short sliding distance ball-on-disc test is one of the best friction testing techniques over the other ones, because during the ball-ondisc tests, severe plastic deformation occurs at the ball / disc interface [19,20,23], especially during the run-in period. Short sliding distance ball-on-disc test is highly suitable for the study of the friction between fresh metals, which emulates the contact condition in the bearing channel or welding chamber of the extrusion dies.…”

“…The plowing and shear friction have to be discriminated by means of FEM simulations [15,16] or theoretical analysis [19,28], and only the shear component of apparent friction representing the real friction between the two mating materials should be used in the FE simulations of metal forming operations as boundary conditions [15,16]. However, when the material combination of soft pin and 10 hard disc is used, the friction coefficients obtained from the tests are mainly attributed to the shearing (adhesive) friction.…”

“…The hardened H11 steel was selected as the mating material, which was the same material as that of extrusion dies. The tests were carried out under a constant normal load of 6 N at 350, 400, 450 and 500°C [19]. In order to achieve a high contact pressure between the mating materials, short sliding distance (1, 5 and 10 laps of sliding) ball-ondisc tests were employed to represent the friction condition in the bearing channel of hot aluminium extrusion process.…”

“…Although more efforts have been made previously to simulate the extrudate/bearing interactions by using tribological tests [19,20] …”

“…The tribological test is a sensible technique to understand the physical fundamentals of the friction under hot aluminium extrusion conditions. In the past, tribological tests (pin/ballon-disc tests) have been employed to identify the friction coefficients for metal cutting 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 5 process [19][20][21][22]. Recently, the first attempt to determine the friction coefficient for hot aluminium extrusion process by using ball/pin-on-disc tests has been conducted [23,24].…”