1.2 mm thick DP1180 advanced ultra-high-strength steel were successfully friction stir spot welded (FSSWed) with additional water cooling. No hook defect and obvious keyhole were observed in the spot joints when using a specially designed WC-Co tool. Softening of the heataffected zone was substantially suppressed and the lap shear strength of the joints was obviously enhanced via water cooling. The enhanced strength of water-cooled joints was attributed to the grain refinement, the formation of the untempered martensite and the effective restraint of tool softening underwater. Accordingly, the maximum lap shear strength of 17.9 kN was obtained for the water-cooled joint. This study provides a novel strategy to enhance the strength of the FSSW joints for high-strength steels.

Observation of terminal atom effect in molecule NH 2 -Cn-NO 2 placed between gold electrodes with end atom sulfur and hydrogen studied using Hartree-Fock theory method. The conductance in molecule exponentially decreases with increases in the number of carbon connectors. Observed that the coupling between the molecule and the two electrodes and the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the molecule dominate the transport property of the current.