Research On Fabricating AZ61Magnesium Alloy Sheets With Extrusion Composite Rolling Process

As a lightweight metal structural material, magnesium alloy has attracted more and more attention because of its low density, high specific strength, excellent shock resistance, electromagnetic shielding and other unique performances. The thick magnesium alloy plate with traditional cast rolling deformation process performed a low processing efficiency and a strong base panel texture. This paper employed a new approach of the extrusion composite rolling technology to research the deformation of the thick electromagnetic continuous casting AZ61wrought magnesium alloy plates. It compared the effect of the new approach with the cast rolling process on the microstructure and mechanical properties of the sheets. And it also explored the influence of rolling temperature on the new approach.The introduction of electromagnetic fields in the continuous casting process make AZ61cast microstructure refinement, broken the coarse mesh distributed β-Mg17Al12eutectic phase at the grain boundaries and making it be fine and dispersed. And it improved the surface quality of the magnesium alloy ingots. Compared with the normal casting, the ultimate tensile strength of the electromagnetic casting AZ61magnesium alloy ingot increased by25%of181Mpa, and the elongation had45%enhanced of7.4%.There will be a large number of twins in the early deformation of cast rolling sheets. Afterwards, the grain refinement mechanism is the twin dynamic recrystallization. The grains organization is incomplete dynamic recrystallization with75%deformation and the mechanical properties is σb=300MPa, σ0.2=235Mpa and δ=8.0%.In the early deformation period, dynamic recrystallization occurred around the fine grains in the extrusion of the extrusion composite rolling process. And then, the local shear zones produced by the rotation dynamic recrystallization bring the grain refinement to improve the plasticity. The average grain size of three different rolling deformations is less than the cast rolling.Mechanical properties of the60%rolling deformation sheets were equivalent to the cast rolling. The ultimate tensile strength, yield strength and elongation of75%and80%rolling deformation sheets were315MPa,283MPa,12.0%,325MPa,306Mpa and10.3%. Compared with the cast rolling process, they were increased by5%,20.4%,50%,8.3%,30.2%, and28.7%respectively. The maximum pole density of {0002} base panel texture of the sheets with extrusion composite rolling is lower than that of the cast rolling sheets under the same deformation.There are two reasons inducing the crack sources lead to the45°diagonal crack on the sheet side rolled at lower temperatures. First, the crack sources generate on the junction of the twin and grain boundaries because of large stress concentration. The other is the disorder of the deformation degree between the grains.As the rolling temperature increased, the cracks tendency reduced, the microstructure gradually turned into slightly coarse and equiaxed grains from a large number of twins because of fully dynamic recrystallization. The ultimate tensile strength and yield strength of the sheet decreased and a gradual increase in plasticity at the same time. And the fracture mechanism turned to mixed fracture from the typical quasi-cleavage fracture. The optimized rolling temperature of extrusion composite rolling process is400℃.It was studied that high-performance sheets can be manufactured under a small rolling deformation with extrusion composite rolling process, and the mechanical properties of them are equivalent to or even higher than the high rolling deformation sheets with traditional cast rolling process. Consequently, this new approach decreased the failure trends with a large rolling deformation and improved the processing efficiency of the magnesium sheets.