Effect of Ni Addition on the Solidification Process and Microstructure of Al-12%Si-4%Cu-1.2%Mn-x%Ni Heat-Resistant Alloys

By Pandat^TM phase diagram calculations based on Equilibrium and Scheil Models and microstructure observation by optical microscope, XRD and SEM-EDS, the effect of Ni addition in Al-12%Si-4%Cu-1.2%Mn-x%Ni heat-resistant alloys (in wt%; x = 0, 0.8, 2.0, 2.4, 3.4) on solidification process and microstructure is discussed in this study. Microstructure observation are in good consistence with the prediction from phase diagram calculation, except for the constituent of Ni-rich phase. Ni addition considerably changes the solidification process, not only enlarging the crystallization temperature range of primary Al₁₅Mn₃Si₂ phase but also completely suppressing the two-phases eutectic reaction when Ni content is beyond 2 wt%. And it also results in an increase in the amount of primary Al₁₅Mn₃Si₂ phase, and makes its morphology change from coarse dendrites to slender rods. In Ni1 (x = 0.8) and Ni2 (x = 2.0) alloys, fish-skeleton δ-Al₃CuNi is found to be partially in coupled growth with blocky γ-Al₇Cu₄Ni phase, and in Ni3 (x = 2.4) and Ni4 (x = 3.4) alloy, new short-rod ε-Al₃Ni is formed.