Linking Solidification Dynamics And Intermetallic Evolution To The Machinability Of A Multicomponent Al-Cu-Ni-Ta Alloy

Abstract

The present work investigates the coupled effects of thermal solidification parameters and microstructural evolution on the machinability of a Al-33%Cu-1%Ni-1.2%Ta weight, solidified under transient upward directional solidification. Solidification kinetics, macro and microstructural characterization, and quantitative analysis of secondary dendritic arm spacing (λ₂), eutectic lamellar spacing, and complex intermetallic morphologies were conducted along the length of the ingot. A consistent pathway was identified for the evolution of intermetallics containing Ta and Ni, showing position-dependent transformations from Al₃Ta and Al₂to Ni₃Ta/Ta(,Al)₂ with Al₇₄Ni rims. Machinability tests revealed shear temperatures of up to approximately 44 °C at a distance of 40 mm from the cold. Oscillating heating rates were observed in the columnar-equiaxial transition zone (CET). The maximum flank wear reached 0.071 mm, which is well below the ISO 3685 limit, while the surface roughness decreased from 0.27 μm near cold to 0.17 μm in the equiaxial region. Chip morphology has evolved from predominantly arc-shaped near cold to mixed arc/needle types in the CET and equiaxial zones. Multivariate regression identified liquidus isotherm velocity (V_L) as the most influential variable on machinability responses, followed by cooling rate (T_R), while λ₂ and specific intermetallic fractions played secondary roles. This is the first demonstration that the coupled solidification path of quaternary Al-Ni-Ta alloys governs position-dependent machinability. These findings provide new insights for tooling design, process optimization, and the sustainable use of complex aluminum alloys in advanced manufacturing.