Effects Of Cross Rolling and Calcium Additions on the Microstructure and Thermal Properties of AZ31 Magnesium Wrought Alloy during Hot Deformation

摘要

Magnesium is the lightest structural metal and magnesium alloys are therefore obvious candidates in weight critical applications. The hexagonal close-packed structure of magnesium results in poor room temperature formability. However, on heating, several magnesium alloys show superior forming properties, with the ability to deform to very high strains. In the current work, effects of cross rolling and 0.7% Ca additions during hot deformation on the microstructure and thermal properties of AZ31 magnesium wrought alloys were investigated. Grain refinement in AZ31 alloy containing initial coarse grains was successfully achieved by thermos-mechanical processing (TMP) by dynamic recrystallization. After hot rolling normal and bimodal grain-size distribution were observed in AZ31 and AZ31-0.7%Ca alloys respectively. SEM and EDX results confirmed that the number and size of β-Mg_(17)Al_(12) particles were increased due to the addition of small amount of calcium. Indeed, during hot deformation, the discontinuous precipitation of β-Mg_(17)Al_(12) phase strongly influences the microstructural changes. Dynamic recrystallization was favored in grains havingβ-Mg_(17)Al_(12) phase as close neighbor. DSC was also carried out to compare thermal properties of both AZ31 and AZ31-0.7%Ca alloys.