Microstructural characteristics and deformation of magnesium alloy AZ31 produced by continuous variable cross-section direct extrusion

Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.

Fabrication of a biomimetic controllable adhesive surface by ultraprecision multistep and layered scribing and casting molding

Wedge-shaped microstructures have the ability to reproduce the excellent adhesive properties of geckos’feet because of their unique anisotropic structure.In particular,the controllability of the wedge-shaped microstructures on adhesion is beneficial to the undisturbed grasp or the capture of space targets.However,the problem currently remains of how to process it efficiently and with high quality.Here a strategy called ultraprecision multistep and layered scribing is proposed for the manufacture of the biomimetic controllable adhesive surface.The results show that the metal master mold prepared based on the manufacturing strategy has not only good surface topography but also high reliability and durability.Furthermore,the controllable adhesive surface of 1.96 cm2,fabricated by the proposed manufacturing strategy,has a normal adhesion of 1.012 N,and the corresponding shear friction and adhesion coefficient are 3.105 N and 4.82,respectively.Additionally,the controllable adhesive surface has been shown to be approximately superhydrophobic and also to possess the properties of controllable adhesion and dynamic adhesion.Also,after 250 adhesion-detachment cycles,the normal adhesion and shear friction only decrease by 5%and 3%,respectively.The research realizes an environmentally friendly and efficient method by which to manufacture a durable metal mold for fabricating a biomimetic controllable adhesive surface,laying a foundation for its effective application in the adherence of space-floating targets.