Abstract:The influence of trace Zr on the quench sensitivity of 7055 type aluminum alloy was investigated by ambient tensile testing, optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The results showed that the addition of trace Zr increased the quench sensitivity for the strength of alloy, but decreased the quench sensitivity for elongation, especially when the Zr amount was not less than 0.1%. The recrystallization occurred in the Zr-containing alloy not only increased the amount of random high angle grain boundaries, but made Al3Zr dispersoids losing the coherency with the matrix. As a result, the nucleation sites increased for heterogeneous precipitation during slow quenching, and the quench sensitivity of strength increased. The reasons for the decreased quench sensitivity of elongation were mainly due to the inhibition of recrystallization and the grain refining effect by Zr adding.