Sven Gall

Simulation of the Co-Extrusion of Hybrid Mg/Al Profiles

Extrusion of composite materials can offer big advantages. In this work the manufacturing of a hybrid metal profile in a single production step was investigated. A porthole die was used, thus producing profiles with extrusion seams. Along the seams a material mix up was visible. The extrusion process was simulated with the Finite Element Method to investigate the material flow in die and welding chamber in order to understand the cause for the defects at the seams.

Characterization of weld seam properties of extruded magnesium hollow profiles

Extrusions of hollow profiles with weld seams were conducted using the magnesium alloy ME21 applying various extrusion ratios. Subsequent analysis of the profiles’ microstructure was performed comparing weld free with weld seam containing material using (polarized) light optical microscopy (LOM). Additionally, the local texture and microstructure in the weld-free material as well as in the weld seam region has been examined with a scanning electron microscope coupled with electron backscatter diffraction technique (SEM-EBSD). The weld-free material and the weld seam are characterized by recrystallized microstructures, whereas few residual cast grains were identified. The local texture distinctively changes from the weld-free material to the weld seam. The texture of the weld-free material is comparable with the typical ME21 sheet texture. In the weld seam area, a pole density is found, which is distributed towards the transverse direction (TD) combined with a split and broadening of the pole density in the extrusion direction (ED). This texture influences the mechanical anisotropy due to the dependence of the activation of basal 〈a〉-slip and

Extrusion of Hollow Magnesium Profiles and Investigation of Extrusion Seams

\{ 10\bar{1}2\} \;\langle 10\bar{1}1\rangle

Analysis of the flow imbalance on the profile shape during the extrusion of thin magnesium sheets

{101¯2}⟨101¯1⟩-extension twinning on the loading direction in favorably oriented grains.

Changes of the texture and the mechanical properties of the extruded Mg alloy ME21 as a function of the process parameters

Due to the increasing demand of deep drawing applications for magnesium alloys in the future magnesium sheets with good mechanical and forming properties are required. These properties depend on the processing route of the sheet material. The deformation behavior of magnesium alloys is strongly influenced by the texture. Extruded magnesium sheets exhibit a different texture than rolled magnesium sheets. Therefore, the forming properties of the extruded magnesium sheets are supposed to be different compared to rolled sheets. Thin extrusion of the magnesium alloy AZ31 with a thickness of 1.5 and 2 mm were performed. Adjacent the extruded sheets were tested for their microstructure, texture and mechanical properties. The texture stability and evolution after the rolling of extruded magnesium sheets were investigated. Thus some of the 1.5 mm sheets were rolled to 1.0 mm and analyzed by OIM, X-Ray and mechanical testing. Concluding the results were compared to the properties of the just extruded 1.5 mm sheet and conventionally rolled sheet of 1 mm thickness.

Mechanical properties and forming behavior of extruded AZ31 and ME21 magnesium alloy sheets

The extrusion of hollow profiles with porthole dies is well known for aluminum alloys, but there is almost no data available regarding the formation and thus the quality of extrusion seams in magnesium hollow profiles. Therefore, extrusion experiments using magnesium alloys AZ31 and ME21 have been conducted with a porthole die which is designed in a way that the extrusion seams are located in the corners as well as in the middle of one of the profile surfaces. The profiles were analyzed for their microstructure with the focus on the extrusion seams compared to the seamless areas. These analyses were performed by OIM and SEM with EBSD. Furthermore, the mechanical properties of the extrusion seams were characterized by room temperature tensile tests in dependence of the extrusion direction. In order to optimize the extrusion of magnesium hollow profiles accompanying FE-simulations were carried out.

Hot working behavior of AZ31 and ME21 magnesium alloys

The rolling of magnesium sheets is carried out in a process consisting of multiple passes with low degree of deformation per pass. The low degree of formability of magnesium and its alloys makes it necessary to carry our rolling in multiple steps. Alternatively, it has been shown that the extrusion of flat and thin plates is feasible.

Hot working behavior of a WE54 magnesium alloy

The extrusion process facilitates the production of magnesium sheets featuring a very thin thickness as well as excellent surface properties by using a single process step only. However, the extrusion of the magnesium sheets applying not optimized process parameters, e.g. low billet temperature or/ and poorly deformable magnesium alloy, produce pronounced buckling and waving of the extruded sheets as well as a variation of accuracy in profile shape along the cross section. The present investigation focuses on the FEM-simulation of the extrusion of magnesium sheets in order to clarify the origin of the mentioned effects. The simulations identify the flow imbalance during extrusion as the main critical factor. Due to the flow imbalance after passing the die a large compression stress zone is formed causing the buckling and waving of the thin sheets. Furthermore, the simulations of the magnesium sheet extrusion reveal that the interaction of the material flow gradients along the width and along the thickness direction near the die orifice lead to the variation of the accuracy in profile shape.