Ultrafine Grain Structure Processing in Al-Mg-Sc-Zr Alloy under Severe ABC Forging at Elevated Temperature

The effect of multidirectional (abc) forging (MDF) to the strain of about 8.5 at 325 degrees C (similar to 0.65 T-m) and 10(-2) s(-1) on the grain refinement of a 1570C Al-Mg-Sc-Zr alloy was investigated. The cast and homogenized alloy had an equiaxed microstructure with the grain size of similar to 25 mu m and nearly uniform distribution of nanosized (similar to 5-10 nm in diameter) coherent dispersoids Al-3(Sc, Zr). In the early MDF stages, new fine (sub) grains with low-and high-angle misorientations were preferably formed in grain interiors and near original grain boundaries, respectively. With increasing strain, the mean boundary misorientation gradually increased resulting in almost completely recrystallized structure with the grain size of similar to 1.3 mu m and the fraction of high-angle boundaries similar to 0.85. The strain dependency of microstructural parameters suggested that grain refinement occurred via continuous dynamic recrystallization. The role of disperse phases in the structural alloy behavior is discussed.