Study On Aging Treatments And Strengthening Mechanisms Of An Al-Cu-Mg-Ag Alloy

The effect of non-isothermal aging（NIA）treatment and the conventional isothermal（T6）aging treatment of an Al-5.06Cu-0.90Mg-0.60Ag alloy were investigated.The microstructural parameters and the kinetics of theΩprecipitate were studied quantitatively.The strengthening mechanisms were also studied using several models.The main conclusions are summarized as follows:（1）NIA treatment can modify the tensile properties of the studied alloy by setting proper heating rates.Both investigated NIA treatments（heating rates at 20℃/h and 40℃/h,herein refer to as NIA20 and NIA40）can modify the yield strength to 472 MPa and 484 MPa respectively,showing an enhancement of～8 and～20 MPa for yield strength compared with the optimal T6 treatment（165℃/14 h）.（2）The statistical results indicate that the number density and volume fraction ofΩprecipitates in the 165T6（165℃/14 h）alloy are the highest,followed by those in the NIA40,NIA20 and 200T6（200℃/2 h）alloys.By using the interfacial strengthening model,precipitates with a larger aspect ratio as well as a higher number density and volume fraction are deduced to be more favorable to the contribution of yield strength（YS）,namely the precipitates in the NIA40 treatment.（3）Al-Cu-Mg-Ag exhibits excellent thermal resistance.No significant change in both the microstructure and mechanical properties of the studied alloy can be found after prolonged aging to 250 hours at165℃.The coarsening kinetic of theΩprecipitate can be described by（）=0.15441..The variation in volume fraction can be predicted by the Kolmogorov-Johnson-Mehl-Avrami relationship,which is presented as1)（）=0.0151 1-0)（-0.0038.）.（4）The predictions of the YS increment from shearing mechanisms are satisfying forΩprecipitate.On the basis of the interfacial strengthening mechanism alone,the YS increment can be well predicted whenγ_i=0.230 J×m^-2.