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.

In this paper, homogenization heat treatment and laser shock peening (LSP) processes were successfully carried out regulate the microstructure (grain size, residual stress, and element distribution, etc.) of the AZ31B magnesium alloy substrate surface. Based on the regulated AZ31B magnesium alloy substrate surface, it further explored and analyzed the mechanism and influence pattern of the coupling distribution of grain size and residual stress on the intergranular corrosion susceptibility of the substrate surface. Scanning electron microscopy (SEM) was used to observe the surface morphology, scanning Kelvin probe force microscopy (SKPFM) to observe the surface potential, zero resistance ammeter (ZRA) and scanning vibrating electrode technique (SVET) to measure the galvanic current on the surface, and electrochemical tests were conducted to evaluate its surface corrosion behavior. The experimental results showed that in the residual tensile stress region (large grain region), tensile stress expanded the cracks on both sides of the grain boundaries, allowing corrosive media to penetrate deeper into the material. Under tensile stress, corrosion cavities expanded along grain boundaries and potentially connected to other areas via intragranular microcracks, highlighting the pronounced initiation of corrosion cavities. In areas with residual compressive stress (fine grain regions), the corrosion reaction rate at the grain boundaries decreased, and the initiation of corrosion cavities was delayed or slowed down, resulting in a more uniform corrosion surface. The coupling effect of grain size and residual stress exhibited an inhibitory effect on the initiation of corrosion cavities and corrosion susceptibility at the grain boundaries. Overall, this paper provides an important reference for further understanding and controlling the corrosion resistance of AZ31B magnesium alloy.

Electrochemical discharge machining (ECDM) is an emerging special processing technology for non-conductive hard and brittle materials, but it may encounter the problem of tool wear due to its process characteristics, which affects the processing accuracy. In this study, in the non-machining state, the tungsten carbide spiral cathode with a diameter of 400 μm was selected to analyze the influencing mechanism of the process parameters on tool wear, and a suitable voltage range for the processing was obtained. The influence of the cathode’s loss behavior on the film formation time and the average current of spark discharge was discussed based on the current signal. The results show that the tool wear mainly appears from the bottom to the end and edge tip of the protrusion. Loss is mainly in the form of local material melting or gasification at high temperature. In addition, the loss may shorten the film formation time, but the effect on the average current of spark discharge is small.

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.