Ultrafast Precipitation Kinetics in an Ultrafine-Grained Al-Cu Alloy Used for Oil Drill Pipes

摘要

In the ultrafine-grained (UFG, <1 μm) Al-Cu alloys having very poor thermal stability, only intergranular equilibrium θ-Al_2Cu precipitates were found after aging treatment, which means that the precipitation was greatly accelerated even at room temperature and has directly transformed to equilibrium θ phases while bypassed the metastable phases GP zones, θ" and θ' as usually seen in representative precipitation transition sequence of coarse grained (CG, >10 m) Al-Cu alloy. It was found the precipitation kinetics of θ phases in the UFG Al-Cu alloy occurred at several orders of magnitude faster than that can be predicted by conventional grain boundary precipitation theory. Considering ultrafast solute diffusion at the UFG length-scale, a developed/modified precipitation kinetics model at the UFG length-scale has been established. It yields predictions in satisfied accordance with experimental aging precipitation process/parameters of UFG Al-Cu alloys.