Normal wear of the Al-Si matrix can be described by the ultra-mild-wear (UMW) regime. The UMW · regime can be broken down into thr

Normal wear of the Al-Si matrix can be described by the ultra-mild-wear (UMW) regime. The UMW regime can be broken down into three stages: ● Stage I: Silicon particles fracture and are embedded into the supporting aluminum matrix. ● Stage II: Increased wear occurs as exposed aluminum matrix is removed. ● Stage III: A smooth and stable surface supported by ultra-fine aluminum grains with a ZDDP and molybdenum (moly) rich tribofilm forms followed by a reduction in wear and friction. Along with proper lubrication, surface modification techniques must be applied to these components for use in an Al-Si engine.37 Depending on what type of piston is used, cast or forged, and its silicon content, extremely tight piston to cylinder clearances of 8 - 32 µm (0.0003-0.0012”) require durable piston skirt coatings that reduce friction and prevent wear. The process, originally referred to as “tining”, provides a thin coating on the piston skirt that provides a wear barrier between the aluminum piston and the aluminum bore. These coatings are critical to the long-term reliability of aluminum cylinder bores. Due to the abrasive nature of the Alusil or Lokasil sliding surface with its exposed silicon particles, when the piston skirt coating fails, galling caused by aluminum on aluminum contact will occur. This will result in cylinder and piston scoring and/or seizure, primarily on the thrust side of the piston skirt with localized wear starting at the bottom of the bore (BDC) moving upwards towards the mid-stroke region on the corresponding cylinder surface.38 When the UMW regime can no longer be supported, the severe wear regime begins the progression to catastrophic surface failure.39 An area without sufficient silicon exposure or with more than 40% of the primary silicon particles crushed40 will experience accelerated wear of the softer aluminum matrix that supports it, resulting in premature engine failure from scuffing and scoring.41 When silicon particles fracture and become dislodged from the Al-Si matrix, the aluminum substrate that supports the silicon particles becomes pitted, generating a large amount of wear debris, accounting for high wear rates and high total wear volume.42 Cold start conditions with insufficient lubrication and higher porosity from the aforementioned pitting of the aluminum matrix further reduce scuffing resistance.43 The coefficient of friction in the piston and liner system increases when surface finish roughness increases with highest areas of 37 Improved Engine Performance Via Use of Nickel Ceramic Composite Coatings (NCC Coat). K. Funatani, et al. Metal Matrix Composites (Sp-1010). SAE Technical Paper Series 940852. 1984. 38 Friction and Wear of Tribo-Elements in Power Producing Units For IC Engines - A Review. Roop Lal, et al. International Journal of Engineering Trends and Technology - Vol 14 no. 5 - August 2014. 39 Sliding wear behavior of eutectic Al-Si alloy under lubricated conditions: An investigation on the effect of ethanol (E85) addition. Victor Vimalrajan Francis. University of Windsor. 40 The new Porsche 944 4-cylinder aluminum engine. Paul Hensler. Porsche AG. SAE International. 41 Replacing the Cast Iron Liners for Aluminum Engine Cylinder Blocks: A Comparative Assessment of Potential Candidates. John Lenny Jr. 42 Wear of different material pairings for the cylinder liner - piston ring contact. Thomas Wopelka, et al. Industrial Lubrication and Tribology. DOI 10.1108/ILT-07-2017-0218. 43 Sliding wear behavior of eutectic Al-Si alloy under lubricated conditions: An investigation on the effect of ethanol (E85) addition. Victor Vimalrajan Francis. University of Windsor. LN Engineering Technical Library. Copyright ©2019 LN Engineering LLC