• 한국주조공학회지
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• 제31권6호
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• pp.347-353
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• 2011

There is thixo-extrusion to form high strength aluminum alloy. But, it is a problem that grains become grain coarsening during reheating process because the alloy was exposed at high temperature. In order to solve grain growth during reheating process, calcium was added in Al-Zn-Mg alloys. Primary a grain sizes of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca were measured with image analyzer after reheating. Measured primary a grain sizes were applied to LSW(Lifshitz-Slyozov and Wagner) equation to check the effect of Ca on grain coarsening. Coarsening rate constant K values of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca alloys were $371\;mm^3s^{-1}$, $247\;mm^3s^{-1}$, $198\;mm^3s^{-1}$ and $166 mm^3s^{-1}$, respectively. As increasing calcium content, K value decreased which means grains are refined. Also, grains of calcium addition were more spherical than that of calcium free.

• Journal of Advanced Marine Engineering and Technology
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• 제33권1호
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• pp.104-111
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• 2009

This paper shows the behaviors of macro- and micro-structures and mechanical properties for specimen's welding region welded by FSW. according to welding conditions with 5mm thickness aluminum 5083O alloy plate. It apparently results in defect-free weld zone in case traverse speed was changed to 32 mm/min under conditions of anti-clockwise direction and tool rotation speed such as 800 and 1250 rpm with tool's pin diameter of 5 ${\Phi}mm$ and shoulder diameter of 20 ${\Phi}mm$, pin length of 4.5 mm and tilting angle of $2^{\circ}$. The ultimate stress of ${\sigma}_T=331$ MPa and the yield point of 147 MPa are obtained at the condition of the travel speed of 32 mm/min with the tool rotation speed of 1250 rpm. There is neither voids nor cracks on bended surface of $180^{\circ}$ after bending test. The improvement of toughness after impact test was found. The lower rotating and traverse speed became, the higher were yield point, maximum stress and elongation(%) with the stresses and the elongation(%) versus the traverse speed diagram. Vickers hardness for cross section of welding zone were also presented. The typical macro-structures such as dynamically recrystallized zone, thermo-mechanically affected zone and heat affected zone and the micro-structures of the transverse cross-section were also showed. However, the author found out that the region of 6mm far away from shoulder circumference was affected by friction heat comprehensively, that is, hardness softened and that part of micro-structures were re-solid-solution or recrystallized, the author also knew that there is no mechanically deformation on heat affected zone but there are the flow of plastic deformation of $45^{\circ}$ direction on thermo-mechanically affected zone and the segregation of Al-Mg on nugget. The solid solution wt(%) of parent material as compared against of friction stir welded zone was comprehensively changed.