Microstructure and tensile properties of a continuous-cast Al-Li-Hf alloy

Bars of 37.5 mm diameter and length higher than 300 mm of an Al-(1.2 wt.%) Li-(0.8 wt.%) Hf alloy were produced by continuous casting in a caster machine. The density of the as-cast alloy was determined to be about 2.626 Mg/m ³. The microstructure and mechanical properties of the ingots were compared with those of a continuous cast aluminium ingot produced in the same machine. The yield and ultimate tensile strengths of the as-cast alloy were much higher than those of cast pure aluminum. The elongation of the former material was smaller than the latter material. The fracture surface of the as-cast alloy showed a ductile fracture mode. These tensile properties were also similar or superior to those of non-heat-treatable wrought aluminium alloys in the annealed condition. The optical micrographs of the as-cast alloy showed columnar grain, elongated in the cast direction, and formed from the outer surface to the centre of ingot. Finer equiaxed grains were formed in the central part of the ingot. The MEB and MET micrographs showed that the microstructure of the as-cast alloy consisted mainly of granular α (Al-rich phase) grains containing colonies of dendrites or cells. These were outlined by a layer of solute-rich interdendritic zones.