Mechanical properties and fracture behavior of an Al-Mg-Sc-Zr alloy at ambient and subzero temperatures

The tensile properties and fracture behavior of an Al-6%Mg-0.2%Sc-0.08%Zr (by wt%) alloy was examined at temperatures ranging from 77 to 293 K under as-cast conditions and after extensive hot rolling. It was found that in the temperature range 223-293 K this alloy exhibits the Portevin-Le Chatelier (PLC) effect, corresponding to a positive temperature dependence of the yield stress (YS). At T<223 K, the YS and ultimate tensile strength (UTS) tend to gradually increase with decreasing temperature. In the rolled alloy, the ductility increases with decreasing temperature over the entire temperature interval, while the as-cast alloy exhibits a ductile to -brittle transition (DBT) at ∼182 K. The hot rolled material exhibits ductile fracture over the entire temperature interval while the as-cast material shows a brittle intergranular fracture at 77 K and a dimple-type ductile mode of transgranular fracture at 293 K. It was found that hot rolling highly enhanced the mechanical properties of this material at cryogenic temperatures and the hot rolled alloy can be considered an advanced material for liquefied natural gas (LNG) structures. The foundations of the mechanical behavior of the Al-Mg-Sc-Zr alloy at cryogenic temperatures are discussed.