Bio-Inspired Functional Surface Fabricated by Electrically Assisted Micro-Embossing of AZ31 Magnesium Alloy

Abstract

Developing bio-inspired functional surfaces on engineering metals is of extreme importance, involving different industrial sectors, like automotive or aeronautics. In particular, micro-embossing is one of the efficient and large-scale processes for manufacturing bio-inspired textures on metallic surfaces. However, this process faces some problems, such as filling defects and die breakage due to size effect, which restrict this technology for some components. Electrically assisted micro-forming has demonstrated the ability of reducing size effects, improving formability and decreasing flow stress, making it a promising hybrid process to control the filling quality of micro-scale features. This research focuses on the use of different current densities to perform embossed micro-channels of 7 μm and sharklet patterns of 10 μm in textured bulk metallic glass dies. These dies are prepared by thermoplastic forming based on the compression of photolithographic silicon molds. The results show that large areas of bio-inspired textures could be fabricated on magnesium alloy when current densities higher than 6 A/mm2 (threshold) are used. The optimal surface quality scenario is obtained for a current density of 13 A/mm2. Additionally, filling depth and depth–width ratio nonlinearly increases when higher current densities are used, where the temperature is a key parameter to control, keeping it below the temperature of the glass transition to avoid melting or an early breakage of the die.

A Review on Micro/Nanoforming to Fabricate 3D Metallic Structures

“…Based on the electroplastic effect in EA microforming, we developed an EA microembossing apparatus for manufacturing typical bioinspired functional surfaces over magnesium alloy AZ31 using a BMG die, and the results indicated that EA microembossing can significantly improve the filling quality of Sharklet patterns. [ 160 ] Meanwhile, EA microforming methods have gradually been used to fabricate other 3D microparts. For example, Mai et al [ 161 ] fabricated microchannels on 316L‐stainless‐steel sheets using EA microembossing, and the results showed that the channels were deeper and the residual stress was smaller when assisted by electricity.…”

Investigation on micro-textured tappets from design and production to the application properties

“…6 For the production of such surface textures, micromanufacturing processes like laser ablation, micromachining, direct 3D printing, photochemical machining or microcoining can be used. 3 Each process faces specific challenges, which have to be taken into account when selecting the manufacturing strategy. In laser ablation, the spot size has to be quite small for the fabrication of microscopic surface textures.…”

“…7 Although direct 3D printing enables the production of complicated textures, the lead times are very high and the selection of materials is limited. 3 Photochemical machining is a costly process in which several process steps and equipment parts are required. 8 Unlike the previously described processes, microcoining provides a method to realize an efficient mass production of textured surfaces.…”

Numerical and Experimental Investigation of the Impact of the Electromagnetic Properties of the Die Materials in Electromagnetic Forming of Thin Sheet Metal

“…In contrast to the investigations related to the forming die, investigations regarding the workpiece show influences on the plastic material behavior by an electric current density (electroplastic effect-EPE) [18]. In this context, an increase in plasticity was shown for both long-term [19] and short-term [20] current duration time. This influence is attributed to the movement of free electrons, which lead to an increased (local) temperature of the workpiece due to the Joule heating caused by the electron movement [21].…”