RESUMO
Magnesium alloys are among the most promising materials for medical implants, and by preparing a superhydrophobic surface, the rate of corrosion can be effectively slowed down and durability be improved. However, the anticorrosion surfaces are inevitable to be damaged for the conventional micro-nanostructured superhydrophobic magnesium alloys, which highly limits their application prospects. This work proposes the development of a Terracotta Warrior pit superhydrophobic structure (TWPSS), consisting of a wall structure with a Terracotta Warrior-like pit and a lotus-like surface papillae structure within the wall. For the first time, top-down laser ablation of the pits to prepare the lotus-like surface papilla structure is used in conjunction with a bottom-up laser-guided melt stacking of the raised wall structure to achieve rapid fabrication of a TWPSS on a magnesium alloy surface. The Cassie-Baxter-based design of the wall structure spacing effectively protects the internal lotus-like surface papillae from damage and the disappearance of low surface energy material, and the results show that the superhydrophobic surfaces of magnesium alloys have excellent mechanical durability and repairability. In addition, it was found that the recast layer and laser melting stacked layers produced on the surface of the alloy during femtosecond laser processing refined the grain size of the magnesium alloy and effectively suppressed the corrosion rate. The combination of the superhydrophobic gas layer and the resulting grain refinement slowed down the corrosion of the magnesium alloy. Thus, the rapid preparation of TWPSS structures with mechanical durability and corrosion resistance by femtosecond lasers expands the clinical applications of superhydrophobic surface magnesium alloys in medical devices.
RESUMO
This study investigates the effect of twinning on the corrosion behavior of AZ31B magnesium alloy using solid solution heat treatment (SHT) and laser shock peening (LSP) techniques. The corrosion characteristics are assessed by scanning electron microscopy (SEM), scanning Kelvin probe force microscopy (SKPFM), zero resistance ammeter (ZRA), scanning vibrating electrode technique (SVET), and electrochemical tests. Results indicate that the twinning region in AZ31B magnesium alloy, enriched with { 10 1 ¯ 2 } tensile twins induced by laser shock, demonstrates increased corrosion susceptibility. This region exhibits higher electrochemical activity and an accelerated corrosion rate compared to the matrix region. Micro-galvanic coupling between the twinned and matrix regions promotes faster dissolution of the alloy. Additionally, the corrosion product film on the surface is extensively cracked and propagates to the matrix corrosion surface, confirming that { 10 1 ¯ 2 } tensile twins provide inadequate protection against corrosion in AZ31B alloy.
RESUMO
Different cathode materials have different surface chemical components and machining capacities, which may finally result in different machining quality and machining efficiency of workpieces. In this paper, in order to investigate the influence of cathode materials on the electrochemical machining of thin-walled workpiece made of 304 stainless steel, five cylindrical electrodes are used as the target working cathodes of electrochemical machining to conduct experiments and research, including 45# steel, 304 stainless steel, aluminum alloy 6061, brass H62, and tungsten steel YK15. The stray current corrosion, taper, and material removal rate were used as the criteria to evaluate the drilling quality of efficiency of a thin-walled workpiece made of 304 stainless steel. The research results show that from the perspectives of stray current corrosion and taper, aluminum alloy 6061 is an optimal tool cathode, which should be used in the electrochemical machining of thin-walled workpieces made of 304 stainless steel; on the aspect of material removal rate, the 45# steel, 304 stainless steel, and aluminum alloy 6061 present close material removal rates, all of which are higher than that of brass H62 and tungsten steel YK15. Based on comprehensive consideration of both machining quality and machining efficiency, the aluminum alloy 6061 is the best option as the cathode tool in the electrochemical machining of thin-walled workpieces made of 304 stainless steel.
RESUMO
Surface roughness is used to quantitatively evaluate the surface topography of the workpiece subjected to mechanical processing. The optimal machining parameters are critical to getting designed surface roughness. The effects of cutting speed, feed rate, and depth of cut on the areal surface roughness of AZ31B Mg alloys were investigated via experiments combined with regression analysis. An orthogonal design was adopted to process the dry turning experiment of the front end face of the AZ31B bar. The areal surface roughness Sa and Sz of the end face were measured with an interferometer and analyzed through direct analysis and variance analysis (ANOVA). Then, an empirical model was established to predict the value of Sa through multiple regression analysis. Finally, a verification experiment was carried out to confirm the optimal combination of parameters for the minimum Sa and Sz, as well as the availability of the regression model for predicting Sa. The results show that both Sa and Sz of the machined end face reduce with the decrease in feed rate. The minimum of Sa and Sz reaches to 0.577 and 5.480 µm, respectively, with the cutting speed of 85 m/min, the feed rate of 0.05 mm/rev, and a depth of cut of 0.3 mm. The feed rate, depth of cut, and cutting speed contribute the greatest, the second and the smallest to Sa, respectively. The linear regression model can predict Sa of AZ31B machined with dry face turning, since the cutting speed, feed rate and depth of cut can explain 97.5% of the variation of Sa.