Evaluation of the Enhanced Constrained Rod Casting Test for Hot Tearing of 7xxx Aluminum Alloys

The enhanced constrained rod casting (ECRC) test has been validated mainly on narrow-freezing-range alloys such as A206 and A380, and its repeatability and interpretation for wide-freezing-range 7xxx Al–Zn–Mg–Cu alloys remain largely unreported. Here, four cast 7xxx alloys containing 0.081–0.232 wt.% Fe were used as a case series, with three independent ECRC trials per composition. Crack widths, fracture locations, contraction load and temperature were cross-examined against JMatPro–Kou calculations, backscattered-electron/energy-dispersive spectroscopy (BSE/EDS) quantification and elastic–viscoplastic numerical simulations. Fracture locations were highly repeatable—the column-end junctions of the short rods A and B fractured in all twelve castings (100%)—whereas the long-rod (C, D) fractures were dispersed. The all-rod hot-tearing susceptibility (HTS) gave means of 67.1 ± 6.7, 74.1 ± 3.8, 68.3 ± 7.9 and 62.7 ± 19.0 for the Base, #1, #2 and #3 alloys; the between-alloy differences were smaller than the casting-to-casting variability and not statistically significant (p = 0.730). The peak contraction load was far more repeatable and ranked alloy #1 highest (87.2 ± 3.2 N, p = 0.077), as did the Kou index of the measured compositions, whereas a Fe-only scan produced nearly invariant indices—showing that the differences originate from the multicomponent solidification path, not from Fe alone. The simulation reproduced the longest late-mushy-stage residence and highest accumulated plastic strain at the A/B junctions, matching the 100% fracture frequency; rods C and D solidified first at mid-length, cutting off feeding and making their response geometry-dominated. The ECRC test is thus applicable to 7xxx alloys provided that short-rod and long-rod responses are interpreted separately, and that fracture-location statistics and the load signal—rather than the crack-width score—are used as the evaluation metrics.