ANALYSIS OF THE STRESS-FREE INTERPLANAR SPACING DURING SOLUTION HEAT TREATMENT OF 319 Al ALLOY ENGINE BLOCKS VIA IN-SITU NEUTRON DIFFRACTION

摘要

Aluminum alloy engine blocks have successfully replaced ferrous materials in order to maximize weight savings and improve vehicle fuel efficiency. However, the development of an optimal heat treatment process is required to improve engine block casting integrity and prevent potential problems such as in-service cylinder distortion. Optimization of heat treatment parameters requires an in-depth study to determine how residual stresses are relieved with time during solution heat treatment. In order to perform this analysis, however, in-situ neutron diffraction must first be carried out on stress-free samples of the same composition and processing history as the engine blocks to account for factors such as thermal expansion and changes in lattice parameter due to dissolution of secondary phases. The results from this study suggest that thermal expansion caused the largest change in do spacing, while prolonged exposure at the solutionizing temperature resulted in a relatively small contraction in do due to phase dissolution.