Novel Control Factor for Tensile Strength and Solidification Cracking in Partially Solidified Al–Mn–Cu Alloy Based on Campbell’s Model with Fe-Rich Intermetallic Compounds

In this study, the effect of the Fe-rich intermetallic compound phases (IMC) on the solidification cracking susceptibility (Hot Tearing Susceptibility, HTS) of the Al–Mn–Cu alloy and the associated controlling factors were investigated. Using the Al–1.15Mn–1.0Cu–0.5Si–0.08Ti–0.016B–0.15Fe and Al–1.15Mn–1.0Cu–0.5Si–0.08Ti–0.016B–0.4Fe alloys, the HTS and mechanical properties in the partially solidified state were experimentally obtained. As a result, the HTS decreased with the increasing Fe contents. In addition, the tensile strength of the alloys in the partially solidified state (σ_max) increased with the increasing Fe contents. The fraction of solid cohesion considering the Fe-rich IMC phase (f_{sc IMC}) based on the Campbell’s model (f_{sc Campbell}) is proposed as the controlling factor of σ_max. The f_{sc Campbell}, which simulates the two-phases model of the α-Al and liquid phases, did not consistently demonstrate the dependence of σ_max on f_{sc Campbell} for the two alloys (σ_max = f(f_{sc Campbell})). However, when employing the f_{sc IMC}, which incorporates the Fe-rich IMC phase in a three-phases model, a consistent correlation is observed between f_{sc IMC} and σ_max for the two alloys (σ_max = f(f_{sc IMC})). Therefore, it is suggested that the controlling factor influencing the change in σ_max with the Fe content should be the f_{sc IMC}. Additionally, the bonding of primary α-Al phase together with Fe-rich IMC phase that is crystallized at the grain boundary will increase σ_max, contributing to the reduction of HTS.