Abstract:The quenching sensitivity of AA7136 alloy was investigated by time-temperature-property (TTP) diagrams, and the heterogeneous precipitation behavior during isothermal holding was investigated using scanning electron microscopy, scanning transmission electron microscopy and high resolution transmission electron microscopy. Based on 99.5% TTP diagram, the nose temperature is determined to be about 346 °C with the transformation time of about 0.245 s. The precipitation of η (MgZn₂), T (Al₂Zn₃Mg₃), S (Al₂CuMg) or Cu-Zn-rich Y phases can be found depending on isothermal holding temperature and time, and it is described in a time-temperature-precipitation diagram. The size and area fraction of isothermal holding induced phase particles increase, which results in the decrease of hardness of samples after aging. The quantitative contribution to loss of hardness by grain boundaries/subgrain boundaries and dispersoids in the matrix is discussed based on the amount of heterogeneous precipitation related to them.

Key words: AA7136 alloy; quenching sensitivity; time-temperature-property diagrams; heterogeneous precipitation