Effect of Pre-Aging and Bake Aging on Hardening Properties of 6E21 Aluminum Alloy

The effects of pre-aging and baking aging on the hardening properties of Er and Zr microalloyed 6E21 aluminum alloy are studied by hardness test, tensile test at room temperature, SEM and TEM. It is found out that the optimal pre-aging scheme is heat treated at 140 ℃ for 20 min. Compared with the alloy without pre-aging treatment, the precipitated phase of the alloy pre-aged at 140 ℃ for 20 min changes significantly and the pre-β″ clusters are precipitated. The pre-aging treatment can reduce the susaturation of the matrix, reduce the precipitation kinetics and improve the hardening effects in the cause of natural aging following. Bake aging at 180 ℃ for 25 min can significantly promote the hardness of alloy, and pre-aging at 140 ℃ for 20 min can enhance the baking effects of the alloy. The yield and tensile strengths of the alloy pre-aged at 140 ℃ for 20 and baking aged at 180 ℃ for 25 min are 339 and 360 MPa, respectively, and the percentage elongation after facture is 11.1%, indicating the mechanical properties of the alloy are excellent.