Evolution of Residual Stress and Lattice Strain Due to Precipitate Growth in AA7075

Precipitation strengthening in aluminum alloys results in slight, but significant lattice distortions that contribute to the impediment of dislocation motion, thereby increasing alloy strength. Precipitate evolution is well-established for AA7075; elements in solid solution concentrate at Guinier-Preston (GP) zones before transforming to MgZn2 (), T-phase, and/or S-phase particles. Less is known about the residual stresses that can arise from the resulting lattice distortions during precipitate evolution. Capturing the coupled relationship of precipitate formation and residual stress evolution during heat treatment is particularly useful when attempting to model heat treatment processes. In the present study, a series of heat treatments were carried out on solution annealed AA7075 ranging from 100oC to 250oC. Residual stress, lattice strain, and precipitate morphology and precipitate phase fraction were characterized using x-ray diffraction and transmission electron microscopy. Results illustrate the relationship between strain induced in the FCC matrix and precipitate size and volume fraction.