Effects of uniaxial creep ageing on the mechanical properties and micro precipitates of Al-Li-S4 alloy

In the present work, effects of creep ageing (CA) on the mechanical properties and micro precipitates of Al-Li-S4 alloy was investigated. Compared with single stress-free ageing (SFA), experimental results show that CA has significantly improved the mechanical properties of Al-Li-S4 alloy, including hardness, strength and elongation. Meanwhile, the peak-ageing time was also prolonged under CA treatment. When specimens were continuously placed under an exterior stress of 240 MPa after CA treatment at 153 °C for 25 h, more T1(Al2CuLi) nano-precipitates developed and further contributed improvement in mechanical properties. It is mainly attributed to the exterior stress that promoted to form T1 nano-precipitates. Moreover, CA enabled to restrict both the coarsening of precipitates at grain boundaries and the formation of precipitation free zone. In addition, fractographic examination of SFA-treated and CA-treated Al-Li-S4 tensile specimens were carried out, respectively. Through controlling the formation process of fine T1 nano-precipitates during CA treatment, it can facilitate the development of novel microstructures in Al-Li-S4 alloys with certain promising mechanical properties.