Influence of Zn Addition on the Aging Precipitate Behavior and Mechanical Properties of Al-Cu-Li Alloy

In the present work, the effect of Zn on the aging precipitates and mechanical properties of Al-Cu-Li alloys was investigated by Vickers hardness, tensile tests, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results indicated that the addition of Zn reduced the activation energy of the T₁ phase and makes it easier to precipitate. The activation energy of the T₁ phase, which was 107.02 ± 1.8 KJ/mol, 94.33 ± 1.7 KJ/mol, 90.33 ± 1.7 KJ/mol and 90.28 ± 1.6 KJ/mol for 0Zn, 0.4Zn, 0.8Zn and 1.2Zn alloy, respectively. The area number density of the T₁ precipitate ranged from 97.0 ± 4.4 pcs/μm² to 118.2 ± 2.8 pcs/μm² as the Zn content increased from 0 to 1.2 wt.%. Consequently, the addition of Zn promoted the precipitation of the T₁ phase. Therefore, the peak hardness and tensile strength of the alloy also increased with the increase in the Zn content, and the hardness of the alloy with Zn content of 1.2 wt.% increased by 16.5 ± 1.4 HV; meanwhile, the ultimate tensile strength increased by 46.5 ± 2.5 MPa. Therefore, the area number density of precipitates increased and improved the strength of the Zn-containing alloy.