SungMin Joo

Bio: SungMin Joo is an academic researcher. The author has contributed to research in topics: Filler metal & Heat-affected zone. The author has an hindex of 1, co-authored 1 publications receiving 19 citations.

Joining of dissimilar AZ31B magnesium alloy and SS400 mild steel by hybrid gas tungsten arc friction stir welding

Abstract: The joining of dissimilar materials, magnesium alloy (AZ31B) and mild steel (SS400), was performed using a hybrid gas tungsten arc-friction stir welding (HGTAFSW) method that applied a preceding gas tungsten arc welding (GTAW) preheating heat source to a mild steel plate surface during friction stir welding (FSW). The mechanical and microstructural characteristics of the HGTAFS welds were evaluated and compared to those of FS welds to confirm the effect of the additional GTAW preheating heat source. The tensile strength of the HGTAFS welds was approximately 91% of that of the magnesium alloy base metal but higher than that of the FS welds. This was attributed to the enhanced material plastic flow and partial annealing effect in the magnesium alloy and mild steel materials by GTAW reheating of the mild steel side, which induced a significant increase in the elongation of the welds. The concentration profiles indicated that no intermetallic FeAl and FeAl3 compounds had formed according to the phase diagram, which led to a decrease in joint strength. Overall, the use of HGTAFSW by applying a GTAW preheating heat source to a mild steelplate surface resulted in a mechanically sounder and metallurgically defect-free welds compared to FSW.

Improvement of interfacial bonding strength in roll-bonded Mg/Al clad sheets through annealing and secondary rolling process

Abstract: The effect of annealing and secondary rolling process has been investigated in relation to evolution of interface microstructure as well as interfacial bonding mechanisms of roll-bonded two-ply Mg/Al clad sheets in this study. Two types of thin reaction layers, viz., γ (Mg17Al12) and β (Mg2Al3) phase layers, were observed to form along the Mg/Al interface, the thickness of which was found to increase with annealing time. The grains in the γ layer were grown coarsely in a columnar shape, as they grew continuously in coarse-grained Mg substrate alloy side. The thickness of the γ layer was found to reduce significantly after the secondary one-pass rolling. At the same time, the initially columnar γ grains became refined into equi-axed grains by recrystallization caused by large plastic deformation during the secondary rolling. The serrated flow observed in the reaction layers during a nano-indentation test in the γ layer disappeared completely without any sign of micro-cracks after the secondary rolling. This in turn implies that the γ layer, acted as an embrittlement site before the rolling, may not be brittle any longer after the rolling. The grain refinement and disappearance of columnar grains in the γ layer appear to greatly improve the interfacial bonding strength in these clad sheets. This secondary rolling process seems to provide a great advantage in terms of manufacturing, since the same rolling stand for roll-bonding process can also be used without any additional equipment.

Auxiliary energy assisted friction stir welding – status review

Abstract: The present article introduces the auxiliary energy assisted friction stir welding (FSW) processes purported to overcome the shortcomings of the conventional FSW process. The auxiliary energies used for this purpose are thermal energy from electric resistance heat, induction heat, laser, plasma, arc, etc. and mechanical energy in the form of ultrasonic vibration. The state-of-the-art, experimentation and progresses in these FSW variants are surveyed and compiled. The auxiliary energy assisted FSW processes exhibit great promise by having numerous advantages over the conventional FSW in terms improved process window, heat generation, material flow, reduced load on the tools and mechanical properties of joints. Such remarkable advantages would lead these processes to redefine many global technologies and markets in the twenty-first century. However, these variants are still in their preliminary stages of investigation, and more systematic investigations are necessary for their critical assessment. I...