Hot Extrusion And Electrochemical Etching Process Of Mg-Ca-Zn Alloys

Magnesium and magnesium alloys have been widely used in various applicationsincluding aerospace components, computer parts, automobile manufacturing etc. dueto their low density, high strength-weight ratio and good machinability. In this study，two alloys with some component of Ca and different Zn had been founded，and thealloy elements strengthening mechanism and mechanical properties were studied. Theresults indicated that Ca and Zn can refine the magnesium alloy, binary phase Mg₂Caand ternary phase Mg₆Ca₂Zn₃appeared in the microstructure of the alloys. And thetensile, compression and bending test showed that the tensile strength, compressionstrength and bending strength growed with the increased of Zn content.What’s more, the hot extrusion process of magnesium alloy is researched in thisstudy. The content was as follows: as-cast Mg-Ca-Zn alloy bars with60mmdiameters were extruded at583K with extrusion ratio16:1to obtain the alloy bar of15mm diameters, and studied the effect of hot extrusion on its microstructure andmechanical properties. The results showed that α-Mg appeared to be the fine stripband along the extrusion direction in this hot extrusion process, the second phaseMg₆Ca₂Zn₃is crowded broken and become dispersion distribution, the deformationorganization is not uniform via hot extrusion with fine microstructure in the edges andrough microstructure in the center. And the tensile strength, compression strength andbending strength of extrused alloy is higher than as-cast alloy’s.Magnesium and magnesium alloys are chemically active and easily corroded,and for which the electrochemical etching is a harder process. Based on these points,an electrochemical etching technique was investigated using the Mg-Ca-Zn alloy asanode, and silver as cathode for magnesium alloy patterning, a new electrolyte ofalkaline solution and technological parameter were obtained. The whole processincludes making patterns, adjusting reaction temperature and stirring speed in etchingand the etched samples were immersed in NH₄F solution to modify the etchedsurfaces.The results are as follows: horizontal etching is restrained and verticaletching is guaranteed via adjusting reaction temperature （30oC） and stirring speed （50r/s） in this new electrolyte solution. Further, the net structured magnesium fluoride layer evenly formed on the etched surface by the fluoride optimization treatmentwhich was confirmed to improve the corrosion resistance of magnesium alloysignificantly.