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One of the key coating layers that inhibits corrosion on modern automobiles is the pretreatment film. This layer, which is typically a tri-cationic zinc phosphate material, provides both corrosion protection and enhanced paint adhesion to the base metal. Recent tightening of environmental regulations has made the use of this coating more difficult. In response to these pressures, pretreatment suppliers have been developing a new generation of metal pretreatments based on zirconium oxide. Characterization of these new materials is challenging as the zirconium oxide-based coatings are over ten times thinner than the current zinc phosphate coatings. Methods that are currently employed for studying zinc phosphate films such as coating weight determination by weighing, and scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS) are not sensitive enough to fully characterize these materials.

Automatic transmissions equipped with Modulated Torque Converter Clutches (MTCC) require an effective combination of automatic transmission fluid (ATF) - friction material in order to maintain frictional integrity. However, in this study, thermal analysis has shown that ATFs can interact chemically with a friction material used in the MTCC under service conditions, potentially affecting the frictional characteristics. A technique was developed to evaluate friction material degradation. The results of this study showed that the friction material my be chemically altered by static aging in certain ATFs at elevated temperatures. The statically aged friction material samples exhibited thermal analysis signatures which were similar to identical material degraded during dynamometer and fleet vehicle tests. These vehicle tests resulted in deterioration in friction characteristics and experienced shudder.

An automatic transmission planetary gear fatigue test is used to screen lubricant performance of various automatic transmission fluids. The key use of this test is to assess the ability of a lubricant to extend or limit planetary gear system fatigue life. We study the fatigue behavior in this test and find the major failure modes are tooth macropitting, and macropitting-related tooth fracture of the sun and planetary gears (short and long pinion gears). Micropitting appears to be responsible for these gear failure modes. Macropitting is also seen on the shafts and needle rollers of the bearings. Gear tooth fracture appears to have originated from the surface as a secondary failure mode following macropitting. Bearing macropitting is initiated by geometric stress concentration. Bending fatigue failure on the sun and planetary gears also occurs but it is not a micropitting-initiated failure mode.

Engine oils contain additives that provide wear protection to prolong engine life. In a previous study using direct acting mechanical bucket valve train components, we found that aged oil provided better wear protection and friction reduction under certain circumstances. To understand this effect further, friction and wear performance of fresh and laboratory-aged oils with 0.1% phosphorus was studied with ball-on-flat and cylinder-on-flat rigs. Test durations were chosen according to the electrical contact resistance (ECR) values observed between the contacting surfaces. Anti-wear films were characterized primarily by UV and visible Raman spectroscopy, and results were corroborated by Auger electron and infrared spectroscopies. The greatest compositional differences occurred between films formed by fresh and aged oils. The degree of ECR response or the length of oil aging generally did not affect the type of component observed in the films.

The tribological characteristics of three different coated steel plates are compared to a bare steel plate. Coatings included a Ag/Mo coating, and two tungsten disulfide-based coatings. These materials are being considered as alternatives to bare steel and cast iron in automotive engine or powertrain components such as engine cylinders, bearings, and gears. In order to understand their tribological behavior, these coatings have been characterized in terms of surface coating properties, wear resistance, and lubricant interaction between the coating and the additive package in a test grease. Cameron-Plint test results show that the plates coated with Ag/Mo, and both tungsten disulfide-based materials all have lower friction and better wear resistance compared with the bare steel plate. Tungsten disulfide and Ag/Mo-coated plates appear to interact with grease additives. In some cases these specimens formed antiwear films.

The pretreatment of aluminum sheet material in preparation for further paint application can be challenging due to the presence of a thick oxide layer. The composition of the oxide layer is primarily aluminum oxide, but it may also contain magnesium that is typically dispersed unevenly throughout the oxide layer. Zinc-phosphate systems remove much of the oxide layer on aluminum, but questions remain on the extent of removal of the oxide layer by zirconium oxide-based pretreatments and how these oxide layers may affect the zirconium oxide-based pretreatment deposition on aluminum. Several methods have been used to characterize the coating of zirconium oxide-based pretreatments on aluminum. Scanning electron microscopy at very high magnification reveals a coating on aluminum that is significantly different in morphology than the same coating chemistry on steel substrates.