Analysis of Residual Strain Profiles in Distorted Aluminum Engine Blocks by Neutron Diffraction 2013-01-0171

In recent years, light weight components have been an area of significant importance in automotive design. This has led to the replacement of steel and cast iron with aluminum alloys for many automotive components. For instance, Al-Si alloys have successfully replaced nodular and gray cast iron in the production of large automotive components such as engine blocks. However, excessive residual strain along the cylinder bores of these engine blocks may result in cylinder distortion during engine operation. Therefore, in this study, neutron diffraction was used to evaluate residual strain along the aluminum cylinder bridge and the gray cast iron liners of distorted and undistorted engine blocks. The strains were measured in the hoop, radial, and axial orientations. The results suggest that the residual strain along the aluminum cylinder bridge of the distorted engine block was tensile for all three measured components. Conversely, the undistorted engine block had compressive strains in the axial and radial orientations, while the hoop direction had tensile strain of lower magnitude. The gray iron liners, meanwhile, had compressive residual strain for both engine blocks. The variation in strain, specifically in the aluminum cylinder bridge, suggests that permanent dimensional distortion in the cylinders was triggered by tensile residual stress when exposed to service conditions.