The Deformation Behavior and Microstructure Evolution of a Mn- and Cr-Containing Al-Mg-Si-Cu Alloy During Hot Compressio
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Due to the demand for further weight-savings in automobiles, 6000 series heat-treatable wrought Al-Mg-Si(-Cu) alloys are increasingly used in the automobile industry as they possess a combination of medium strength, favorable formability, excellent corrosion resistance, and lower costs. It has been recognized that the addition of copper can further improve the mechanical properties of these alloys, due to age hardening by an Al2Cu-type of precipitation. In addition to copper, manganese and chromium could also remain at a high level of supersaturation in the as-cast ingot of the Al alloys. Consequently, fine Mn- and/or
YI XU, HIROMI NAGAUMI, and YI HAN are with the Suzhou Research Institute for Non-ferrous Metals, No. 200 Shenxu Road, Suzhou Industrial Park, Suzhou, Jiangsu, 215026, People’s Republic of China. Contact e-mail: [email protected] GONGWANG ZHANG and TONGGUANG ZHAI are with the Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY, 40506. Contact e-mail: [email protected] Yi Xu and Gongwang Zhang have equally contributed to this research work. Manuscript submitted March 25, 2015. Article published online January 3, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
Cr-containing dispersoids could be formed in the alloys during homogenization following casting. These dispersoids with a high thermal stability could effectively retard the behaviors of recovery/recrystallization of the alloys, due to their strong pinning effects on the movement of dislocations and grain boundaries at elevated temperatures during or after plastic deformation.[1–3] This could improve the mechanical properties of the alloys, such as strength and fracture toughness. For an example, Jeniski et al.[1] studied the effect of Mn content on the formation of Mn-containing dispersoids and recrystallization in an AA6013 aluminum alloy. By increasing the Mn content, the volume fraction of dispersoids was increased, thereby enhancing the alloy’s resistance to recrystallization. Furthermore, the addition of these alloying elements could complicate the precipitation sequence during age hardening[4,5] and compromise the hot workability of Al alloys.[6] More balanced properties of these alloys could only be achieved by optimizing the thermomechanical fabrication conditions, which requires further understanding of microstructure evolution in the alloys during thermomechanical processing. In an alloy with high stacking fault energy, like most Al alloys, etc., dislocations could more readily rearrange themselves, leading to dislocation annihilation and the VOLUME 48A, MARCH 2017—1355
formation of subgrain boundaries during hot deformation, which is the so-called dynamic recovery. As a result, the conventional discontinuous dynamic recrystallization, consisting of nucleation and long-distance growth of new grains, does not commonly take place in commercial aluminum alloys except in high-purity aluminum and in aluminum alloys containing coarse particles.[7–9] However, continuous or geometric dynamic recryst
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