Effect of Mn substitution on Cr in the Al-Cu-Er-Mg-Zr-Fe-Si-Ti cast alloy

The microstructure, phase composition, precipitates evaluation, casting, and mechanical properties of the novel cast Al-4Cu-2.1Er-1Mg-0.2Zr-0.2Cr-0.15Fe-0.15Si-0.1Ti alloy were analyzed using by optical microscope, scanning and transmission electron microscopes, differential scanning calorimetry, thermodynamic calculations, hot cracking and mechanical properties measurements. The positive effect of Cr as a substitution of Mn on plasticity and precipitation strengthening was demonstrated. The 0.2Zr, 0.2Cr and 0.1 Ti as a grain refiners provide a fine grain size of 25 mu m in the as-cast state due to primary Al75-80Cu10-12Er3-4Cr7 phase particles formation as a nucleation centers of Al. The hot cracking index (HCI) of the AlCuErMgCr alloy was 12-14 mm which is similar with HCI of the cast Al-Si-Cu-Mg alloys. The good casting properties in the AlCuErMgCr alloy achieved due to a fine grain structure and narrow solidification range. The contribution of the Al-3(Zr,Er) (40 nm), Al45Cr7 (6 nm), and S'(theta') (100/5 nm) precipitates is 38.5 MPa, 140.4 MPa, and 198.9 MPa and the calculated contribution from dislocation and precipitates is 262.3 MPa. The ultimate tensile strength (UTS) and elongation (El.) of the AlCuErMgCr alloy are 372 MPa and 6% which is higher in 16.6% and 150%, respectively, than in the Mn-containing alloy. Novel alloy has an excellent combination of yield strength (YS) and plasticity at 20-250 degrees C. The YS and El. are 301 MPa and 6% and 225-250 MPa and 4.6-11.5% at 20 and 200-250 degrees C, respectively. The rupture strength at 250 degrees C after 100 h (sigma(250)(100)) is 106 MPa. Mechanical and casting properties of the novel alloy are superior to the properties of commercial 201.0 (Al-Cu-Mn-Mg-Ag-Ti) alloy.