Improved creep aging response in Al-Cu alloy by applying pre-aging before pre-straining

The improvement of post-form properties without compromising creep formability has been a critical issue in creep age forming of aluminum alloy component. A pretreatment process incorporating artificial pre-aging at 165 °C for 6 h/12 h/24 h followed by pre-strain (3%–9%) has been developed. This method not only evidently improves the strength but also accelerates the creep deformation during creep aging of an Al-Cu alloy. A strength increase of 50 MPa with a slight decrease of ductility relative to the 9% pre-strained alloy is acquired in the alloy artificially pre-aged for 24 h regardless of the pre-strain level (3%–9%). Artificial aging for 24 h prior to 3% pre-strain enables an increase of creep strain by 30%. The creep strain in the alloy artificially pre-aged for 24 h and pre-strained by 6% is comparable to that in the alloy pre-strained by 9%. The strength and ductility in the alloy artificially pre-aged for 6 h/12 h and pre-strained by 3% are even slightly higher than those in the alloy purely pre-strained by 9%. The characterizations by transmission electron microscopy reveal that pre-aging at 165 °C could promote the accumulation of dislocations during pre-straining due to the pinning effect of pre-existing Guinier-Preston zones (GP zones)/θ″ phases and thus expedite the creep deformation in respect to the pure pre-straining treatment. The enhanced precipitation of θ′ phases at these pinned dislocations contributes to the improved strength after creep aging. The results demonstrate applying artificial pre-aging before pre-straining is an efficient strategy to elevate the creep aging response in Al alloys.