Abstract: Mercury Marine has recently developed a new aluminum-silicon alloy for use in a lower-unit gear case for a high power marine motor. A successful trial batch of the new, light weight gear casing was cast. The company is now in the process of tuning the production technologies using highly innovative techniques to mitigate the residual stress evolution in the casting and further enhance the microstructure of the alloy. This work presents metallography and residual strain studies of a machined and non-machined as-cast and T5 heat-treated gear case to determine the effect of heat treatment on the alloy’s microstructure and stress. A previous study conducted by the authors characterized the size, distribution, and volume fraction of the primary phases and measured the secondary dendrite arm spacing (SDAS) using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses. The microstructural analysis indicated that heat treatment did not significantly affect the alloy’s microstructure. In addition, residual stress profiles for non-machined as-cast and T5 heat-treated gear cases were characterized. This study presents the results of residual strain measurements that were performed using in-situ neutron diffraction (ND) techniques at the Canadian Nuclear Laboratory (CNL) in Chalk River, Ontario. The ND results indicate that heat treatment was successful in alleviating approximately 50% of the maximum residual strain in both the machined and non-machined gear cases.
Authors: J. Stroh and D. Sediako
Keywords: aluminum-silicon alloys, powertrain application, strain characterization, residual stress, neutron diffraction