The Effect Of Zn On The Microstructure And Properties Of Mg-Al-Ca-Mn Magnesium Alloy

With the rapid development of science and technology,the problems of limited resources,environment sustainability,and energy are becoming increasingly serious.Additionally,the restrictions on lightweight industrial processing are also escalating.Magnesium and its alloys,which combine high specific strength,stiffness,and machinability,have attracted great attention as lightweight components that have often been used in the automobile industry over the past decades.Unfortunately,poor formability and low ductility at room temperature of magnesium alloys induced by the hexagonal close-packed(HCP)structure greatly restrict their industrial applications.The grain refinement plays a key role in enhancing the strength.Generally,two methods are used to refine grain in magnesium alloy,one is usage of plastic deformation,such as extrusion,rolling,and friction stir processing;the other one is alloying.The influence of Zn addition on the microstructure,mechanical properties and corrosion properties of Mg-1Al-0.3Ca-0.3Mn(wt%)alloy was investigated in this paper by metallographic observation,scanning electron microscopy,energy dispersive spectrometer and X-ray diffraction.The main conclusions are listed as follows:1.The as-extruded alloy exhibited incomplete dynamic recrystallization.Zn addition led to grain refinement when the Zn content was less than 0.4%,due to dynamic recrystallization during the extrusion process and the suppression of grain growth by solid solution atoms.The further addition of elemental Zn induced significant heat generation,leading to grain growth during the extrusion process.2.The addition of Zn also slightly influenced the texture of the as-extruded alloy,while Zn micro-alloying can slightly enhance the conventional basal texture.The tensile strength of the extruded alloy improved considerably with the addition of 0.2 wt% Zn.This dramatic improvement of the mechanical properties could be attributed mainly to the integrated effects of fine grain strengthening,solid solution strengthening,and work-hardening.In particular,the plasticity of the as-extruded alloy increased with increasing Zn content.3.During FSP,complete dynamic recrystallization(DRX)takes place in the coarse primary ?-Mg matrix and considerable grain refinement is achieved in Mg-1Al-0.3Ca-0.3Mn-0.6Zn alloy.Furthermore,the DRXed grain sizes increase with increase of the rotation speed from 1000 r/min to 1600 r/min,which is attributed to the integrated effect of strain rate and thermal input.After FSP,strong {0001} basal texture is formed,with the intensity ranging from 83.64 to 105.19.4.Compared to base metal,the elongation of Mg-1Al-0.3Ca-0.3Mn-0.6Zn alloy is significantly enhanced by ~158%,while ultimate tensile strength and yield strength are reduced.The variation of mechanical properties is mainly due to the grain refinement and strong {0001} basal texture achieved by FSP.5.According to immersion tests and electrochemical polarization tests,the addition of Zn element was beneficial to the corrosion resistance of as-extruded Mg-1Al-0.3Ca-0.3Mn alloys.Among these alloys,the as-extruded Mg-1Al-0.3Ca-0.3Mn alloys containing 0.2wt% Zn element exhibited the best corrosion resistance,which was contributed to the micro-galvanic corrosion and grain refinement.