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In the present study, a novel method for mechanically interlocking the dissimilar alloys of A6061-T6 aluminum alloy and SS400 structural steel using friction-stir forming (FSF) is suggested. In this study, the aluminum alloy is placed on top of a steel sheet containing a screwed hole. The present study suggests that friction-stir spot forming (FSSF) can be used to form a mechanical interlock between the aluminum alloy and steel sheet. FSSF is conducted on top of the aluminum alloy, which produces sufficient heat to plasticize the aluminum alloy. This results in a flow of aluminum into the screw hole in the steel, due to the plastic deformation, thereby mechanically interlocking the aluminum with the steel. Moreover, with the proposed method, the authors present a new concept of an easily separable joining of dissimilar alloys. The mechanical properties of the developed interlock are investigated through tensile and hardness tests and microstructural observation.

In slow melt-blending and annealing of poly(methyl methacrylate) (PMMA) and carbon nanofibers (vapor grown carbon fibers, VGCFs) with very small amount of high density polyethylene (HDPE), the flexible HDPE chains adsorb onto the rough surface of the VGCF ends and behave like a glue between VGCFs. After 4 h annealing, the percolation threshold of VGCF is determined as 1.15 vol% from dynamic viscoelastic behavior of the PMMA/HDPE/VGCF composites at 200 °C. Applying the percolation theory for gel systems to the composites, the fractal dimension d f is found to be 1.8 -2.0, reflecting very effective connectivity of VGCFs facilitated by the selective adsorption of HDPE. The dimension d f is found to be smaller for the composite with smaller molecular weight of HDPE, while the threshold does not change. The addition of HDPE and annealing at 200 °C for 4 hours also lead to the prominent reduction in the critical concentration of VGCF to 0.71 vol% at the insulator-conductor transition (1×10 -7 S/m). When the VGCF content exceeds the viscoelastic threshold (1.15 vol%), the electrical conductivity of the composite approaches up to 10 S/m.