Dynamic mechanical properties of a near-nano aluminum alloy processed by equal-channel-angular-extrusion

Microstructure of AA5056 Al-Mg alloy is refined drastically to nano-scale by the equal-channel-angular-extrusion(ECAE) process. Dynamic mechanical properties at room temperature in the ECAE processed 5056 Al-Mg alloy (5056-ECAE) are characterized by a modified Hopkinson-bar method. Yield stress (YS) in 5056-ECAE exhibits remarkably higher value than that of a fully annealed 5056 alloy(5056-O). Hall-Petch(H-P) relation of 5056 alloy is compared with those of a binary Al-Mg alloy and Aluminum. The slope of the H-P relation in the granular 5056 alloy is almost equal to that of a binary Al-Mg alloy with a similar content of magnesium, and larger than that of Aluminum. On the other hand, the slope of the sub-grained alloy exhibits lower value than that of the granular alloy. The result indicates that grains effectively refined by the ECAE process, however, the grain boundary strength of the sub-grained alloy is relatively lower than that of the granular alloy. The elongation-to-failure of 5056-ECAE exhibits a larger value than those of some fine-grained bulk aluminum alloys such as a mechanically alloyed aluminum. Fractography of 5056-ECAE revealed that this alloy was fractured with ductile dimples. The result supports the possibility that this alloy exhibits the high speed impact performance and capability for high-rate forming. (C) 1998 Acta Metallurgica Inc.