Use of Multicomponent Phase Diagrams for Designing High Strength Casting Aluminum Alloys

Abstract

Principles of optimization of the phase constitution of a new group of aluminum alloys, i.e., sparingly alloyed high-strength casting nickalyns are considered. The Thermo-Calc software and experimental methods (LM, SEM, TEM, EPMA, etc.) were used for analyzing the phase constitution of the Al–Zn–Mg–Cu–Fe–Ni system as applied to high-strength (UTS>450 MPa) aluminum alloys based on (Al)+Al3Ni and (Al)+Al9FeNi eutectics. Both eutectics possess the fine structure but the latter is more expedient due to the lower content of nickel. Then the iron becomes an alloying component rather than a harmful impurity. It is shown that the addition of copper substantially complicates the phase constitution and strongly decreases the equilibrium solidus, which limits the possibility of carrying out the high temperature annealing. This can negatively affect the spheroidization of the Al3Ni and Al9FeNi phases. A set of calculated and experimental data is used to show the perspectives of replacement of the existing high-strength casting aluminum alloys based on Al–Cu system (AA201, 206, 224) by the sparingly alloyed low-copper weldable nickalyn Al6Zn0.5Ni.