Impact of travel speed on the microstructure and mechanical properties of adjustable-gap bobbin-tool friction stir welded Al–Mg joints

The butt welds of 4-mm thick 5A06 aluminum alloy plates were produced by adjustable-gap bobbin-tool friction stir travel with travel speeds of 200, 300, and 400 mm/min in this study.The microstructure was studied using optical microscopy and electron backscatter diffraction(EBSD).Tensile tests and microhardness measurements were performed to identify the effect of the travel speed on the joint mechanical properties.Sound joints were obtained at 200 mm/min while voids were present at different positions of the joints as the travel speed increased.The EBSD results show that the grain size, high angle grain boundaries, and density of geometrically necessary dislocations in different regions of the joint vary depending on the recovery and recrystallization behavior.Specific attention was given to the relationship between the local microstructure and mechanical properties.Microhardness measurements show that the average hardness of the stir zone(SZ) was greater than that of the base material, which was only affected slightly by the travel speed.The tensile strength of the joint decreased with increasing travel speed and the maximal strength efficiency reached 99%.

A N-CoSe/CoSe_(2)-C@Cu hierarchical architecture as a current collector-integrated anode for potassium-ion batteries

The highly reversible insertion/extraction of large-radius K^+into electrode materials remains a tough goal,especially for con version-type materials.Herein,we design a current collector-integrated electrode(N-CoSe/CoSe_(2)-C@Cu) as an advanced anode for potassium-ion battery(PIBs).The conductive CoSe/CoSe_(2) heterojunction with rich Se vacancy defects,conductive sp^2 N-doped carbon layer,and the elastic copper foil matrix can greatly accelerate the electron transfer and enhance the structural stability.Consequently,the well-designed N-CoSe/CoSe_(2)-C@Cu current collector-integrated electrode displays enhanced potassium storage performance with regard to a high capacity(325.1 mAh·g^(-1) at 0.1 A·g^(-1) after 200cycles),an exceptional rate capability(223.5 mAh·g^(-1) at2000 mA·g^(-1)),and an extraordinary long-term cycle stability(a capacity fading of only 0.019% per cycle over1200 cycles at 2000 mA·g^(-1)).Impressively,ex situ scanning electron microscopy(SEM) characterizations prove that the elastic structure of copper foil is merged into the cleverly designed N-CoSe/CoSe_(2)-C@Cu heterostructure,which buffers the deformation of structure and volume and greatly promotes the cycle life during the potassium/depotassium process.