## 3 Results  
### Mechanical Properties  
Figure 1a shows hardness curves of CR samples aged at 373 K, 403 K and 433 K. Before aging, the hardness of the CR samples was 174 V. It can be seen that during the aging process at 433 K, the hardness decreased continuously with the aging time. After aging for 1500 min, the hardness of the alloy decreased from 174 HV to approximately 102 HV, a decrease of approximately 41.38%. During the aging at 403 K, the hardness of the alloy decreased smoothly. After aging for 1500 min, the alloy hardness decreased from approximately 174 HV to approximately 122 HV, a decrease of approximately 29.89%. When aging at 373 K, the hardness value peaked twice. At the beginning of the aging process, the hardness of the alloy decreased and the first hardness peak, at 420 min, had a value of 171 HV. The hardness then decreased and gradually increased after fluctuating. The hardness of the samples reached a second peak (181 HV) after 1200 min of aging and then decreased. Tensile results are shown in Figure 1b. After PA treatment, the ultimate tensile strength (UTS), yield strength (YS) and elongation to failure (E\({}_{\mathrm{f}}\)) were 475 MPa, 350 MPa and 11.8%, respectively. Figure 1b shows that the UTS, YS and E\({}_{\mathrm{f}}\) of the CR samples were 571 MPa, 528 MPa and 4.2%, respectively. For the CR-373K (420 min) samples, the UTS and YS decreased to 544 MPa and 484 MPa, respectively, whereas the E\({}_{\mathrm{f}}\) increased to 5.4%. It is worth noting that the UTS, YS and E\({}_{\mathrm{i}}\) significantly increased to 614 MPa, 564 MPa and 8.7% for the CR-373K (1200 min) samples compared with the CR samples.  
Based on the engineering stress-strain curve in Figure 1b, measuring the plastic strain increments before and after the peak stress resulted in the uniform elongation (E\({}_{\mathrm{u}}\)) and local elongation (E\({}_{\mathrm{i}}\)) of the tensile specimen in Figure 2a. Figure 2a shows that the E\({}_{\mathrm{f}}\) value of the tensile specimen was mainly contributed by E\({}_{\mathrm{u}}\). In contrast, the E\({}_{\mathrm{i}}\) values contribute little. In general, the E\({}_{\mathrm{u}}\) value was employed to characterize the uniform deformation capability of a material, which could be determined using the Considere criterion \(\sigma=\left(\frac{\partial\sigma}{\partial\epsilon}\right)_{\dot{z}}\)[12] (where \(\sigma\) is the true stress and \(\epsilon\) is the true strain). As shown in Figure 2a, the CR samples had the lowest E\({}_{\mathrm{u}}\) value (3.3%). With prolonged aging, the E\({}_{\mathrm{u}}\) value increased gradually and the E\({}_{\mathrm{u}}\) value of the CR-373K (1200 min) samples was 7.4%. Moreover,the uniform deformation capability or \(\rm{E_{u}}\) value of materials was directly related to the work-hardening rate, which was determined by the formula \(\Theta=\frac{1}{\sigma}\big{(}\frac{\partial\sigma}{\partial\epsilon}\big{)}_{ \epsilon}\)[12]. When \(\Theta>0\), dislocations could be further stored during deformation and then work-hardening occurred. When \(\Theta<0\), deformation mainly occurred in a local area, which caused the alloy to enter the necking stage. Continued deformation broke the alloy. In the work-hardening rate curves of Figure 2b, the CR-373K sample had a higher \(\Theta\) than the CR sample. In the CR-373K (1200 min) samples, the \(\Theta\) value was still \(>\)0 when the true strain was \(>\)7% but the \(\Theta\) values of the CR samples at true strain \(>\)3.5% were \(<\)0.