Cavitation Erosion of a Water-Cooled Aluminum Alloy 6061-T6 Combustion Chamber

Equipment in which an assembly of in-line cylindrical components rotated in water at 1040 rpm displayed excessive vibration after less than one hour of operation. The malfunction was traced to an aluminum alloy 6061-T6 combustion chamber that was part of the rotating assembly. Analysis (visual inspection, 100x/500x/800x micrographic examination, spectrographic analysis, and hardness testing) supported the conclusions that, as a result of improper heat treatment, the combustion-chamber material was too soft for successful use in this application. Misalignment of the combustion chamber and one or both of the mating parts resulted in eccentric rotation and the excessive vibration that caused malfunction of the assembly. Irregularities in the housing around the combustion chamber and temperature variation relating to the combustion pattern in the chamber were considered to be possible contributing factors to localization of the cavitation erosion. Recommendations included adopting inspection procedures to ensure that the specified properties of aluminum alloy 6061-T6 were obtained and that the combustion chamber and adjacent components were aligned within specified tolerances. In a similar situation, consideration should also be given to raising the pressure in the coolant in order to suppress the formation of cavitation bubbles.