Optimizing Tribology Property Of Pistion Skirt Materials By Fine Particle Bombardment

With the global energy and environment problems getting more serious, the requirements on the internal combustion engine have been promoting, such as improving fuel economy, enhancing mechanical efficiency and reducing emission. The piston-cylinder is the key friction pair in the internal combustion engine. Complex and serious running condition between the piston and cylinder lead to exceptionally higher wear or scuffing, which is the major contributor to the failure of automotive engines. Under thrust load, piston skirt is one of the most prone to wear or scuff part in the internal combustion engine. Improvements in the tribological performance of piston skirt can generate the following benefits:reduced fuel consumption, increased engine power output, reduced harmful exhaust emissions, extended the service life of engines.Surface treatment of fine particle bombarding and Sn powder impact plating were conducted on two piston skirt materials. Roughness, surface hardness, hardened layer, surface texture, plating layer and microstructure of the modified layer were tested. Contact and mixed or boundary lubricated condition was simulated. Scuffing tests were processed on MM-200 friction and wear apparatus. The tribological performance of the piston skirt materials treated by different surface modified processes were evaluated through the analysis of friction coefficient, scuffing load, and wear morphology. The results show that:(1) Fine particle bombarding (FPB) can reduce the roughness, increase the surface hardness, refine the grain size and achieve a dimple-like textured surface on specimens. Sn powder impact plating (PIP) can form Sn2O3 coating, reduce roughness without changing the origin surface texture on specimens. Parameters of shot peening have great effect on the modified layer property.(2) The results of scuffing tests show that FPB, PIP and FPB+PIP compound treatments all can optimize the tribological properties of the two piston skirt material. The compound treatment reveals the best performance. In FPB treatment, peening parameters have great effect on specimen tribological performance. Al-SP0.2 and Fe-SP0.6 is the best treatment for the aluminum alloy and ductile iron, respectively.(3) After FPB and PIP surface treatment, lower roughness can improve lubrication environment leading to a reduction in friction coefficient. Higher surface hardness can reduce the wear damage and increase scuffing resistance by increase surface strength. Dimple-like textured can optimize the tribological properties by getting a better wettability and storing lubricating oil and wear debris.Fine grain layer near the surface can reduce the adhesive wear by inhibiting crack initiation and propagation.