Abstract:The quench sensitivity of 6063 alloy was investigated via constructing time-temperature-property (TTP) curves by interrupted quenching technique and transmission electron microscopy (TEM) analysis. The results show that the quench sensitivity of 6063 alloy is lower than that of 6061 or 6082 alloy, and the critical temperature ranges from 300 to 410 °C with the nose temperature of about 360 °C. From TEM analysis, heterogeneous precipitate β-Mg₂Si is prior to nucleate on the (Al_xFe_ySi_z) dispersoids in the critical temperature range, and grows up most rapidly at the nose temperature of 360 °C. The heterogeneous precipitation leads to a low concentration of solute, which consequently reduces the amount of the strengthening phase β'' after aging. In the large-scale industrial production of 6063 alloy, the cooling rate during quenching should be enhanced as high as possible in the quenching sensitive temperature range (410-300 °C) to suppress the heterogeneous precipitation to get optimal mechanical properties, and it should be slowed down properly from the solution temperature to 410 °C and below 300 °C to reduce the residual stress.

Key words: 6063 aluminum alloy; quench sensitivity; hardness; time-temperature-property curve; strengthening phase; heterogeneous precipitation; residual stress