Approaches to the design of the new high-strength casting aluminum alloys of 7xxx series with high iron content

摘要

The most high-strength aluminum alloys based on the Al - Zn - Mg - (Cu) system have a significant tendency to form hot cracks during solidification. Additional alloying of 7xxx series alloys with the eutectic forming elements (Fe and Ni) that are slightly soluble in an (Al) solid solution was proposed in order to reduce the hot cracking tendency. In this case, the iron becomes an alloying element, rather than an harmful impurity. Since the appearance of primary crystals of the iron- and nickel-bearing phases is unacceptable, the boundaries of primary crystallization of (Al), AlgFeNi, Al_3Ni and AI_3Fe phases (the liquidus projection) were computed using Thermo-Calc software. In accordance with the results of thermodynamic calculations of the multicomponent Al - Zn - Mg - Cu -Fe - Ni phase diagram, the new sparingly alloyed alloy ATs6N0.5Zh (Al - 6.3% Zn - 2.1 % Mg - 0.2% Cu - 0.4% Fe - 0.6% Ni) based on the (Al) + AlgFeNi eutectic was selected. The results of the fracture surface analysis of the castings after ageing show the mode of fracture is the dimple rupture. Traces of intergrain fracture typical for high-alloyed alloys of the 7xxx series without eutectic inclusions are not observed. Defect-free experimental samples with high mechanical properties (σ_r ~ 500 MPa, σ_(0.2) ~ 450 MPa, 5 ~ 4.7%) using liquid forging were obtained from the ATs6N0.5Zh alloy.