Study On Dual Rotary Fretting Wear Of 7075 Aluminum Alloy

According to the direction of relative motions, fretting can be defined as four basic modes under a contact configuration of ball-on-flat:i.e. tangential, radial, rotational and torsional fretting. At present, the researches focus on the tangential fretting mode. Dual rotary fretting is combined with torsional and rotational fretting. It usually occurred in many rotary components, but little research focuses on it up to now. Study on dual rotary fretting not only enriches the fundamental theory of fretting, but also has important guidance to palliate fretting damages in industry.Based on a rotary device with low speed and high precision and a six dimensional sensor, a dual rotary fretting tester has been developed to simulate the case of dual rotary fretting in this study under a contact of ball-on-flat. The dual rotary fretting tests for 7075 aluminum alloy against GCr15 steel ball have been carried out under different tilt angles, angular displacement amplitudes and number of cycles. Dynamic analyses in combination with the microscope examinations through optical microscope (OM), scanning electrical microscope (SEM), energy dispersive spectroscope (EDX) and profilometer, have been performed to study the running and damage mechanisms of dual rotary fretting in detail. The difference between 7075 aluminum alloy and LZ50 steel was discussed in dynamic curves, friction coefficients, friction dissipated energy and running condition fretting maps and so on. The similarities and differences of torsional fretting, rotational fretting and dual rotary fretting were also discussed. The conclusions have obtained as follows:1. The friction force vs. angular displacement amplitude curves (Ft-θcurves) could be used to characterize the kinetic characteristics of dual rotary fretting. According to a great deal test results, three types of Ft-θcurves could be obtained, i.e. linear, elliptic and parallelogram.2. Running condition fretting map (RCFM) of 7075 aluminum alloy was established, where the mixed fretting regime and the slip regime of 7075 aluminum alloy shift to the direction of lower angular displacement with the increase of tilt angle.3. The friction coefficients and friction dissipated energy of 7075 aluminum alloy were strongly dependent upon the tilt angle, angular displacement amplitude and number of cycles. 4. The running behaviors of 7075 aluminum alloy and LZ50 steel were quite different, i.e. the dual rotary fretting wear was strongly dependent upon the material properties.5. The wear volume of 7075 aluminum alloy was increased with increase of tilt angle at same angular displacement amplitude. The wear volume of torsional fretting was lowest but was highest of rotational fretting.6. It was found that the dual rotary fretting wear was highly dependent upon the tilt angle, angular displacement amplitudes and number of cycles. The damage features are outlined as follows:a) In the partial slip regime, the wear scar was asymmetric appeared in shape of annularity, and its center was sticking with free damage; and the micro-slip occurred at the outer ring of contact boundary zone, which corresponding with slight wear. The wear mechanisms mainly were slight oxidative wear and abrasive wear. In this regime, fretting white layer has been formed without cracks.b) In the mixed fretting regime, the sticking zone gradually shrank with the increase of the number of cycles, while the contact state transformed from the partial slip to the gross slip. The asymmetry of wear scar was enhanced accordingly. The wear occurred in the micro-slip region, and the wear mechanisms mainly were abrasive wear, oxidative wear and delamination. on the cross-section, some titled cracks propagated to the base alloy were observed.c) In the slip regime, the wear occurred at the whole contact zone, and the damage was severer with a great deal of wear debris. The distribution of wear debris was dependent upon the tilt angle. The wear mechanisms mainly were abrasive wear, oxidative wear and delamination in the slip regime. No tilted crack can be observed on the cross-section, which indicated that the wear held the superiority.