Effect of double-step homogenization treatments on the microstructure and mechanical properties of Al–Cu–Li–Zr alloy

Abstract The Al3Zr particles formed in the Al–Cu–Li–Zr alloy during single and double-step homogenization treatments contributed to various microstructures and mechanical properties during the subsequent thermomechanical treatment. Compared with the single-step homogenization treatment (ST), the double-step homogenization treatment (DT) generated higher density and more uniform distribution of β′ (Al3Zr) phases, which makes the alloy retain more substructures and improve the initial strength of solid solution. With the ageing process, Al3Zr particles induced the T1 precipitation in grain interior and the width of PFZ get narrowed. Therefore, the strength and toughness of the DT sample improved in peak aged state compared with the ST sample. The peak hardness values of DT sample is 167.8HV, which is higher than that of ST sample with 153.1HV. Furthermore, the tensile strength and elongation of the DT sample at peak aged state (521 MPa, 556 MPa and 8.8%, respectively) are higher than those of the STA sample (492 MPa, 535 MPa and 6.7%, respectively), and the impact toughness of the DTA sample (13.2 J cm−2) is also higher than those of STA sample (9.1 J cm−2). Strength model showed that more uniform distribution of Al3Zr phases and substructures improve the initial strength of solid solution state, which increased by 16 MPa in the DT sample compared with the ST sample. The promotion of T1 precipitation inducing the strength increased by 18 MPa in the DT sample at the peak aged state compared with that of the ST sample. The increase of elongation and toughness contributed from the oriented grains with finer distribution and higher Schmid factor, less grain boundaries precipitates and narrower PFZ width.