DYNAMIC-MECHANICAL PROPERTIES OF A NEAR-NANO ALUMINUM-ALLOY PROCESSEDBY EQUAL-CHANNEL-ANGULAR-EXTRUSION

Microstructure of AA5056 Al-Mg alloy is refined drastically to nano-sc ale by the equal-channel-angular-extrusion(ECAE) process. Dynamic mech anical properties at room temperature in the ECAE processed 5056 Al-Mg alloy (5056-ECAE) are characterized by a modified Hopkinson-bar metho d. Yield stress (YS) in 5056-ECAE exhibits remarkably higher value tha n that of a fully annealed 5056 alloy(5056-O). Hall-Petch(H-P) relatio n of 5056 alloy is compared with those of a binary Al-Mg alloy and Alu minum. The slope of the H-P relation in the granular 5056 alloy is alm ost equal to that of a binary Al-Mg alloy with a similar content of ma gnesium, and larger than that of Aluminum. On the other hand, the slop e of the sub-grained alloy exhibits lower value than that of the granu lar 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 elonga tion-to-failure of 5056-ECAE exhibits a larger value than those of som e fine-grained bulk aluminum alloys such as a mechanically alloyed alu minum. Fractography of 5056-ECAE revealed that this alloy was fracture d with ductile dimples. The result supports the possibility that this alloy exhibits the high speed impact performance and capability for hi gh-rate forming. (C) 1998 Acta Metallurgica Inc.