Effects of pre-aging and natural aging on the clusters, strength and hemming performance of AA6014 alloys

摘要

In this study, the effects of pre-aging and natural aging on the clusters, strength and hemming performance of AA6014 Al-Mg-Si alloys with different Mg/Si ratios were investigated through three-dimensional atom probe (3DAP) in combination with tensile test and three-point bend test. Samples are subjected to natural aging (room temperature, -25 ℃) or pre-aging (elevated temperature, 75 ℃) treatments in order to generate different types of clusters. The number density, size and compositions of clusters are analyzed by 3DAP. The increased strength and deteriorated hemming performance are found in natural aged alloys, especially for Si-rich alloy. The hemmability is sensitive to the strength, and an increased strength leads to inferior hemmability. The formation of Mg_1Si_1 type cluster is encouraged during pre-aging treatment regardless of the alloy composition. Natural aging following directly water quenching promotes the formation of a large number density of small-sized Si-rich clusters in Si-rich alloy, whereas relatively low density of clusters with scattered Mg/Si ratios distribution in Mg-rich alloy. The concentration of the excess vacancies and the binding energy between vacancy and Mg and Si atoms plays an important role in the precipitation kinetics of cluster during different aging processes. Finally, the clusters and solid solution atoms statistics are utilized to predict the yield strength of the alloys in different aging conditions.