Effect Of Hot Plastic Deformation On Microstructure And Properties Of Magnesium Alloy

Electromagnetic continuous cast(EMC) has many advantages such as:smooth ingot surface,compact,homogeneous and higher casting velocity.Magnesium alloys are the lightest metallic structural materials and they are very attractive in automobile and aerospace industries. The EMC magnesium alloy crystal has much finer and more uniform than normal casted billet. In this paper,hot plastic deformation process of the EMC AZ31 and AZ61 alloy has been studied.And the microstructure,mechanical properties and fracture morphology has been researched before and after deformation.The results as follows:(1) As-forged AZ31 alloy has much refined grains and composition is more uniform, homogeneous and the material is more densified.The hardness of deformed AZ31 alloy was significantly improved.The hardness of as-forged alloy changed forging-direction once and twice is 55 and 63,which were respectively enhanced by 22%and 40%,compared with that of as-cast samples.The fracture morphology has changed,intergranular fracture at high forging temperature,while transgranular fracture at room forging temperature.(2) Rolled AZ31 alloy has fine grains and small uniform microstructure with no obvious deformation direction.There are a large number of deformation twins in grains,trending into the rolling direction.As-rolled AZ31 alloy has better mechanical properties than that of as-casted.The samples of 45°direction to rolling direction have the best mechanical properties, and its yield strength,tensile strength and elongation are respectively reached 194MPa, 383MPa and 27.7%.The fracture surface demonstrates that the rolled AZ31 alloy has characteristic of ductile fracture.(3) The hot extruded experiment results demonstrate that the extrusion processing gives rise to a strong basal texture.The grains are significantly refined and the average grain size of the localized fine grain area is 2μm.Compared with the EMC ingots,as-extruded specimens have much finer grain size and more uniform microstructure.The mechanical properties of the deformed AZ31 were improved after hot-extrusion.The yield strength,ultimate tensile strength and the reduction in cross-sectional area increased obviously with the increasing of extrusion ratio.When the extrusion ratio was 25,the yield strength,ultimate tensile strength and the reduction in cross-sectional area of as-extruded AZ31 alloy were 259MPa,357MPa and 30.5%, which were respectively enhanced by 86.33%,64.52%and 67.40%,compared with those of as-cast samples.With the increase of extrusion ratio,the grain refining effect was more significant and the microstructure was more uniform.The fracture surfaces demonstrate that the fracture mode changes from ductile-brittle fracture to ductile fracture after extrusion.(4) Yada model in MSC.superform was used to simulate the real extrusion deformation of AZ31 alloy.With the increase of extrusion ratio,the grain refining effect was more significant and the microstructure was more uniform,which consistent with the actual experimental results.