The relationship between tensile properties and microstructural parameters are discussed. Grain size, degree of recrystallization, size and distribution of precipitates were varied by thermomechanical processing. Tensile tests were performed and the microstructures were characterized using transmission electron microscopy (TEM). Quantitative analysis was carried out to explain the yield strength in connection with the change in the microstructural parameters. The primary strengthening precipitates of the under aged alloy were δ′ (Al3Li) and S′ (Al2CuMg). The greater the warm rolling reduction ratio and the lower warm rolling temperature give a higher strength. Closely distributed fine S′ precipitates were effective in improving the yield strength. The increment in yield strength by S′ precipitation can be explained quantitatively by the Orowan's mechanism.
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