No abstract

In this study, the microstructure and mechanical property of Al/Cu clad material fabricated by differential speed rolling at room temperature were evaluated. Al and Cu plates were prepared and mechanically cladded at a differential speed ratio of 2:1 between the upper and lower rolls. Post- heat-treatment was carried out after the mechanical cladding at 400 °C for 60 min to induce the formation of intermetallic compound layers at the bonded interface of Al/Cu. As a result, differential speed rolling afforded a soundly cladded interface without any defects such as voids and cracks. In addition, intermetallic compound layers such as Al4Cu9 and Al2Cu were formed at the mechanically bonded interface during post-heat-treatment for 60 min, which led to an increase in Vickers microhardness value more than 30% relative to the base material. Therefore, we systematically explained the relationship between formation of intermetallic compounds and mechanical property of Al/Cu clad materials in this study.

In this study, the formation mechanism of the stress-induced α ′′ martensitic phase in the deformation twinning (DT) band of metastable β-type Ti-27Nb-0.5Ge (at.%) alloy under tension was investigated. A preferential nucleation site for the stress-induced α ′′ martensitic transformation is inside a DT band with high dislocation density. The α ′′ martensitic phase developed in the DT band with increasing applied plastic strain. The α ′′ martensitic phase subsequently grew to intersect other DT bands, forming secondary DT bands themselves in the parent β grains.

We evaluated the developed microstructures and mechanical properties of a severely plastically deformed Ni-30Cr alloy. Normal rolling and differential speed rolling were used as deformation processes, and the thicknesses of the specimens were reduced to 68 % of the original thickness after holding at 700 o C for 10 min and annealing at 700 o C for 40 min to obtain a fully recrystallized microstructure. Electron backscattering diffraction was used to analyze the characteristic distribution of the grain boundaries on the deformed and annealed specimens. Differential speed rolling was more effective for refining grains in comparison with normal rolling. The grain size was refined from 33 mm in the initial material to 8.1 mm with normal rolling and 5.5 mm with differential speed rolling. The more refined grain in the differential-speed-rolled material directly resulted in increases in the yield and tensile strengths by 68 % and 9.0 %, respectively, compared to normal rolling. We systematically explain the relationship between the grain refinement and mechanical properties through a plastically deformed Ni-30Cr alloy based on the development of a deformation texture. The results of our study show that the DSR process is very effective when used to enhance the mechanical properties of a material through grain refinement.

This study was carried out to evaluate the development of microstructures and mechanical properties on friction welded dissimilar materials with a light weight. For this work, Al6063 and Duralumin alloys with a shape of rod were selected as experimental materials, and friction welding was performed under conditions with a rotation speed of 2,000 RPM, a friction load of 12 kgf/cm2 and an upset force of 25 kgf/cm2, respectively. After welding, the microstructural analysis such as the grain boundary characteristic distributions and the formation of intermetallic compounds was analyzed by electron back-scattering diffraction method and transmission electron microscopy, respectively. In addition, the evaluation of mechanical properties on welded materials was conducted by Vickers microhardness and tensile test. As a result, applying the friction welding led to the significant grain refinement from 50 μm in base material to 2 μm in welded zone, respectively. In case of mechanical properties, Vickers micro-hardness and tensile strength of the welded material occupied 81% and 96% in fraction relative to the base material, respectively, which was attributable to the formation and growth of intermetallic compounds during the welding.