S. Y. Shim, D. H. Kim, T. H. Kim, S. G. Lim, i-Cube Center, Gyeongsang National University, Jinju, South Korea
The Al-Zn-Mg alloys have been improved by demand to reducing weight for vehicles including automobile, trains and aircraft structural parts. However, their high strength has led to reduce formability in extrusion process. The Thixo-extrusion is one of solutions to solve the problem. For obtaining thixo-extrusion reasonable feedstock, we have fabricated a semi-solid billet by the cooling plate method which is able to form spherical grains as flowing melts on copper plate. For observing Thixo-extrusion behaviors, we carried out extrusion at various semi-solid ranges of the billets. Comparing with a conventional extrusion, the results have showed that Thixo-extrusion process using feedstock fabricated by cooling plate could improve the formability as concerning extrusion pressure, extrusion ratio and ram speed. Furthermore, the EPMA analysis gave us that addition of 0.1wt% Sc contents effectively prevented coarsen grain during reheating process of semi-solid feedstock because of forming Al3Sc precipitations.
Summary: In this paper, we evaluated fabricating feedstock via cooling plate method and extrudability for Al-Zn-Mg-0.1wt%Sc aluminum alloy. The results can summarize that it is effective to add Sc during homogeneous heating process for preventing a coarse grain and that comparing with conventional extrusion, although there is no dramatic decrease, extrusion pressure was reduced 7.7% about 600MPa and surface crack was appeared in ram speed above 2mm/sec.
