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AISI-4140H steel has been used as articulated piston crown material in heavy-duty engines. With the driving force for reducing manufacturing cost, microalloyed steel (MAS) was identified as a low-cost material to replace 4140H steel. In order to determine the feasibility of using MAS to replace 4140H steel, a test program was initiated to fully evaluate the material properties of MAS and to compare them to those of the baseline 4140H steel. The physical and mechanical properties of both materials from room temperature to 550°C were evaluated. The effect of long term thermal exposure on the material properties was also studied. Some engine tests were also conducted to evaluate the performance of the articulated pistons made with both materials. The inherently lower strength of MAS as compared to 4140H steel, requires a total re-design of the piston for the utilization of MAS as a low-cost replacement material for 4140H steel.

Diesel engine operation under high load conditions (>45 hp/cyl) may result in piston “debond” in which the Ni-resist ring carrier separates from the aluminum piston matrix leading to destruction of the piston. Historically, engine loads have increased to achieve higher power densities which together with more stringent emissions requirements have resulted in greatly increased stress levels in the piston. The higher stresses have resulted in debond failure. The design of the ring carrier will affect debond failure. Deformation of the ring carrier will initiate debond at the back of the insert at the junction with the piston matrix. The ring carrier cross-section must be made robust enough through proper design to achieve expected reliability. Another factor influencing ring carrier retention is the quality of the AlFin bond layer. Casting defects which arise from the AlFin bonding process, degrade the strength of the joint leading to failure.

In the design of aluminum (Al) cooling system components for heavy duty diesel engines, coolant flow velocities are critical to the durability of the parts. The geometries of the individual component parts used in the system must be designed to minimize turbulence which will affect the rate and type of corrosion. In addition, flow passages must be “sized” to maintain coolant velocities below a critical value. In high velocity flow, a combination of the mechanical damage produced by the impingement of a liquid on a metal surface and the inherent corrodibility of the metal may result in erosion-corrosion and impingement attack. Aluminum alloys are very prone to this type of corrosion damage because of the low inherent hardness of the material as compared to other alloy systems. The development of aluminum cooling system parts for a new 15 liter diesel engine was undertaken to lower weight and make a more compact design for the engine profile.