Effects of Microstructure on Hot Cracking Behavior in Al–Zn–Mg–Cu Alloys

Abstract

An apparatus was developed to cast simulated ingot butts under conditions representative of solidification in commercial-scale DC ingots. The development of the as-cast microstructures of two distinct Al–Zn–Mg–Cu alloys were compared in an effort to determine the reasons for disparate hot-cracking behavior. Metallographic analysis was performed which generated an extensive collection of BSE and EDX map images which were processed using an automated image analysis technique. It was found that solidification rate, zinc and magnesium concentration, as well as silicon and iron concentrations affect the quantity, scale, and constitution of the eutectic structures and porosity. The disparate cracking behavior between the alloys examined was described and explained by the difference in each alloy’s ability to accommodate the strain resulting from solidification.