Microstructure and Mechanical Properties of Novel Heat Resistant Cast Al-Cu-Yb(Gd)-Mg-Mn-Zr Alloys

The present study focused on the development of the novel heat resistant cast Al-Cu-Yb(Gd)-Mg-Mn-Zr alloys based on the prevue investigations. Microstructures and mechanical properties were investigated by optical, scanning and transmission electron microscopy, hardness measurements, and tensile and creep tests at room and elevated temperatures. Ytterbium in combination with Zr and Ti provide greater Al grain refining than gadolinium. The L12-Al3(Zr,Yb) or L12-Al3(Zr,Gd) and Al20Cu2Mn3 phase precipitates were nucleated during solution treatment. The average sizes of L12-Al3(Zr,Yb) and L12-Al3(Zr,Gd) are 28 ± 6 nm and 32 ± 4 nm, respectively. Al20Cu2Mn3 phase precipitates formed with a more coarse size of 100–200 nm. The highest hardening effect was achieved after 3 h of aging at 210 °C in both alloys due to S’(Al2CuMg) precipitates. The ultimate tensile strengths (UTS) of the AlCuYbMg and AlCuGdMg alloys at room temperature are 338 and 299 MPa, respectively. The UTS decreases to 220–272 MPa when increasing the temperature of the tensile test to 200–250 °C. The rupture stress at 250 °C for 100 h under stress is 111–113 MPa. The contribution from different structure parts in the yield strength was calculated. The main strengthening effects of 54–60 MPa and 138–153 MPa were achieved from L12 and S’ precipitates, respectively. The calculated values of yield strength (YS) are consistent with the experimental data. Novel AlCuYbMg and AlCuGdMg alloys are a potential option for castings for high temperature application.