Development Of Technology And Tooling Of Continuous Extrusion Forming Process For Magnesium And Zinc Alloys

The technology and tooling of continuous extrusion forming (CONFORM) formagnesium and zinc alloys were studied. According to plastic deformation mechanismof magnesium and zinc alloys and the studies of deformation partition on CONFORM,a suitable continuous deformation of magnesium and zinc alloys extrusion tooling wasdeveloped based on the existing soft aluminum continuous extrusion equipment. Theslot seal on the original block was redesigned by removing the groove designed tankseal, expanding θ2area, increasing the deformation process of alloys extrusiondeformation, making magnesium and zinc alloys extrusion process produces a lot ofheat to activate additional slip deformation of the surface, and improving plasticdeformation more quickly. The results showed that the modified tooling could productAZ31magnesium and ZnAl15zinc alloys fabricated products with no peeling, mixedsizes, uneven surface and other irregular phenomena. The samples in the presentexperiment which have good surface qualities were prepared by the modifiedaluminum continuous extrusion machine. It demonstrated the possibility of continuousextrusion forming of AZ31magnesium and ZnAl15zinc alloys. Microstructures,fracture surfaces of the tension specimens and crystal orientation of conventionalextrusion and continuous extrusion forming process were observed respectively byoptional microscopy, scanning electron microscope (SEM) and X-ray diffractometry(XRD), and mechanical properties of materials were tested by uniaxial tension tests.The results show that continuous extrusion forming process has not only improved thedegree of the structure homogeneity of materials, but also refined its grains. Crystalorientation was changed because the role of twinning, which cause crystal grainrotation. Furthermore, with more homogeneous, finer-grained microstructure exists inthe as-extruded AZ31magnesium and ZnAl15zinc alloys by CONFORM processwhich can stand much strain before failure, the ductility was enhanced. But the texturesoftening induced by the changing crystal orientation of basal plane which has a moreprofound effect on the tensile properties than the hardening caused by the refining ofgrain size during CONFORM process decrease tensile strength at room temperature,which displays an abnormal Hall-Petch relationship. The fracture mechanisms of theAZ31magnesium alloy prepared by CONFORM process change from the mixture ofductile and brittle to the full dimpled rupture compared with the conventional extrusion.