Ceramic Coatings for Aluminum Engine Blocks

The trend toward lighter vehicles for improved performance has recently introduced the use of aluminum and plastic materials for vehicle bodies and drive trains. In particular, the aluminum alloy block for engine application is certain to reappear. The soft aluminum cylinder liner will require additional treatment before acceptance. Three possible approaches appear to solve the aluminum cylinder liner dilemma. These approaches are:

1. 1.
   Use of high silicon aluminum such as the 390 aluminum.
2. 2.
   Insert or cast steel liners into the aluminum engine block.
3. 3.
   Ceramic coat the low cost standard aluminum engine block.

Each has known advantages and disadvantages. It is the purpose of this paper to present the merits of Option 3, the ceramic coated aluminum cylinder bore from the standpoint of low weight, cost, and tribological effectiveness.

The advantages of approaches (1) and (2) are obvious. High temperature after treatment of the ceramic engine components is not required. Aluminum properties are such that one must carefully observe changes in physical properties of aluminum such as creep, aging, stress/strain and other important properties dependent upon temperature. Therefore, a ceramic coating possessing low curing temperature is highly desirable. A low temperature organo-metallic phosphate (OMP) coating developed recently for aluminum alloy substrates is expected to meet requirements of lowered cost and improved effectiveness for engine applications.

Engine tests were conducted to determine the effectiveness of this ceramic composite coating. The aluminum engine block of an 84mm x 70 mm (bore × stroke) single cylinder diesel engine was ceramic composite coated and laboratory rig tested. Preliminary engine test data reflects the improved cylinder liner coating over the steel or cast iron mating parts. A reduction in fuel consumption due to friction reduction, thermal insulation, and possible improvement in combustion have been demonstrated and observed in SAE Paper 910461⁽¹⁾. The thin coated cylinder liner and its advantage has been further discussed in previous literature SAE Paper #890143⁽⁴⁾.

The ceramic composite coating on aluminum has performed well. The coating can also be applied in the form of silicon nitride, other nitrides, or carbides onto aluminum, titanium or stainless steel substrates. Durability tests are currently underway to demonstrate the viability of these ceramic coated aluminum components for tribology and insulation of future engine components.