Effect of Thermal Impact Failure on Aluminum Alloy Piston Crown

Dileep. M, R. K. Mandloi

Piston, failure, aluminum alloy, thermal, microstructure.

An analytical study of the thermal impact failure on a diesel engine piston has been performed in order to determine and analyze the possible causes of the failure. The piston is subjected to preliminary inspection, microstructure analysis and then hardness testing. Visual examination revealed the impact made by piston with valve head and the subsequent welding of the broken valve portion with the piston crown. It is observed to be caused by improper operating conditions. SEM and EDS analysis performed on the piston specimen revealed the presence of high alloy content and various intermetallics that precipitated in the Al-Si alloy material during combustion process. These particles are attributed for the high hardness and brittleness of the piston surface which thereby resulted in its fracture upon the impact. The weak boundaries between the intermetallics easily enable fatigue crack growth up to failure. Results from the microhardness test performed on the specimens validate the increase in hardness on the crown than on skirt. The analysis of obtained data and observations suggests that piston would have failed by fatigue even if the valve operated properly.