Effect of a dual-rate ageing treatment on the tensile properties of a commercial 6060 Al alloy

摘要

A 6060 Al alloy has been age hardened through different ageing cycles with the aim to improve its mechanical properties and to increase industrial productivity. The following ageing cycles have been applied: a standard cycle, a dual step cycle and a dual rate ageing (DRA) cycle. The standard ageing cycle consists of a rapid heating (as fast as possible) to the final temperature. In the dual step cycle, the alloy is heated up to an intermediate temperature, held at that temperature for 1 h and then slowly heated (20 K/h) to the final temperature. Dual rate ageing, instead, comprises a first fast heating up to an intermediate temperature followed by a second heating carried out at different rates (20 K/h or 30 K/h) up to the final temperature. Tensile tests were carried out on samples aged for different times. A significant improvement in mechanical properties - σ_(y0,2) and UTS - has been observed when using the dual step and DRA cycles. The best age hardening was ascribed to the fine precipitation of coherent Mg_5Si_6 particles, revealed by TEM observations. The number and size of the precipitates, which are related to the ageing stage, influence also the strain hardening and the fracture behavior of the alloy.