| Precipitation process, microstructural and hardness changes in 2090 and Cl alloy were investigated by optical observation, hardness test, transmission electron microscopy and STEM energy dispersive X-ray spectra mode. Hardness in Cl alloy was remarkably higher than that of an 2090 alloy. As result of TEM observation, δ`, α`, θ`/δ`, β`/δ` and T₁phases were precipitated on aging conditions in 2090 alloy, but GP zone, β`, θ`, S`, T and T₁phases were formed on aging conditions in the Cl alloy. And, θ` and T₁phases in the Cl alloy were finer than thoes of an 2090 alloy. This fine precipitates contributed to the increase in hardness. The precipitation process in Cl alloy was as follows: α`_(sss)＋β`→α`_(sss)＋β`＋GP zone→α``_(sss)＋β`＋θ`→α```_(sss)＋β`＋θ＋T₁＋S`＋T |
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