Effect of heat treatment on microstructure and mechanical properties of ZL270LF aluminum alloy

The effects of different heat treatment processes on the microstructure and mechanical properties of ZL270LF aluminum alloy were studied by metallographic microscope (OM), scanning electron microscope (SEM), backscattered electron diffraction (EBSD), transmission electron microscope (TEM), micro-Vickers hardness, and tensile test. The results show that the hardness, ultimate tensile strength, yield strength, and elongation of ZL270LF aluminum alloy increase from 102 HV, 286 MPa, 173.6 MPa, and 2.3% before heat treatment to 136 HV, 433.4 MPa, 261.9 MPa, and 12.4% after solution at 540 °C for 6 h and aging at 160 °C for 10 h, increasing by 33.3%, 51.4%, 50.8%, and 439.1%, respectively. The average grain size increases from 127.6 µm before heat treatment to 142.9 µm after heat treatment, but the grain size distribution is more uniform. Meanwhile, the CuAl 2 phase in ZL270LF aluminum alloy changes into a discontinuous short rod-like distribution from distributing in a network at the grain boundary before heat treatment. Furthermore, La and Ti elements in ZL270LF aluminum alloy are distributed on or near the surface of the second phase particles such as CuAl 2 , which is one of the main reasons for the improvement of mechanical properties of the alloy during heat treatment.