Investigation Of Affecting Factors On Microstructure Of Hot Extruded Mg-Al-Zn Alloys

With many advantages,including low specific gravity,high specific strength and specific rigidity,damping capacity,process,excellent thermal conductivity and electromagnetic shielding,and recyclability,magnesium alloys are considered as eco-structural metal material in the 21^st century and attract many researchers.The Mg-Al-Zn series magnesium alloys,such as AZ31 and AZ61,are popular in commercial application as wrought magnesium alloy for extrusion.AZ10 alloy was designed for high plasticity and fast extruding.It is well known that the microstructure on cross section of the extruded products is quite asymmetry,while the uniformity of alloy microstructure is essential for good mechanical properties,especially for high plasticity,so it makes sense to research the uniformity of the extruded microstructure of Mg-Al-Zn series magnesium alloys.In this paper,we used physical modeling extrusion technology and improved a set of thermal simulation squeeze experiment.It can simulate the actual industrial extrusion process. We do simulate extrusion experiment of the AZ series of magnesium alloy such as AZ10, AZ31,AZ61,AZ91.Result shows the difference of the Microstructure of the Edge and center. The edge of the Microstructure is uniform.but the center of the Microstructure is not,there are some structures like "island" from the edge to the center,which gradually increased.As the compression ratio increased,the white island of the Microstructure decreased and the Microstructure gradually becomes more uniform.With the increasing of Extrusion rate,the Microstructure did not change significantly.With the rise of Squeeze temperature, re-crystallization area ratio gradually increased,the size of grain is smaller.The Microstructure of products without homogenization before the extrusion have extrusion stripes and non-uniform,but the average grain size is smaller,micro-hardness is higher,there are a number of parallel stripes in the zone with the direction of extrusion 45°.The concentrations of stripe contains Al,Zn element is lower than the fine grain areas.With the increase of the elements in the alloy,grain gradually becomes smaller.The microstructure of AZ61 alloy with different compression deformation has three obvious regions,with the increase of deformation,the Microstructure was separated from the fine-grained gradually,it tends to be uniform.This paper will provide access and theoretical guidance to make extrusion products of magnesium alloy with quality and uniform.