Electron Microscope Observation of Duralumin

The aging behavior of duralumin (17S) and its difference from those of Al-Cu and Al-Mg2Si alloys were investigated by means of a transmission electron microscope, tensile test, and hardness measurement. It was found that the aging process in duralumin up to the maximum hardness was almost the same as that in binary Al-4% Cu alloy, and subsequently occurred an aging process similar to that in Al-Mg2Si alloys. The distribution of precipitates were much finely dispersed than those in the corresponding Al-4% Cu alloy. The finer dispersion of the precipitates were found to cause the maximum hardness of duralumin in high temperature aging.Manganese, which is known to remove unfavorable effects of iron in this alloy, was found to form spherical particles of Al-Mn-Fe compound even in as-quenched state, and it was also found that precipitates were preferentially formed on these particles. The presence of these compound particles had no effects on essential process of aging, but it seemed to be favorable for grain refining. Aging at room temperature caused no change on structure when observed under an electron microscope. However, it allowed moving dislocations to yield irregular forms, which suggest that very fine and dense G. P. zones contributed to yield considerable hardening in room temperature aging.