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Study of Rolling and Welding Process on Mg-Gd-Y-Zr Magnesium Alloy

Author: QiXin
Tutor: YuanWuHua
School: Hunan University
Course: Materials Processing Engineering
Keywords: Mg-Gd-Y-Zr alloy rolling fiber laser beam welding mechanicalproperties microstructures
CLC: TG339
Type: Master's thesis
Year: 2013
Downloads: 26
Quote: 0
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Abstract


In recent years,the development of magnesium alloys with rare earth ha sgradually became a research hotspot in the field of magnesium alloy.The Mg-Gd-Y-Zralloys have extensive application prospects in the war and aerospace industriesbecause of their high room and elevated temperature strengths,creep resistance.Thispaper has investigated the Mg-10Gd-4.8Y-0.6Zr alloys,the strengththe and theplasticity of the as-cast alloys are poor，the effects of homogenizing,rolling,agingtreatment and fiber laser welding on the microstructures and properties of alloys wereinvestigated.The purpose of the present work is to provide reference for the furtherdevelopment,production and application of the alloys.The key findings are as follows:the microstructure of the as-cast state involves-Mg solid solution andMg24(GdY)5eutectic structures at grain boundaries and thin rod phases in thegrain.The tensile strengthe of the as-cast alloys is124MPa, and the elongation is2.9%.The eutectic organization completely dissolved and square block phases appeardafter homogenized at470℃for2h and525℃for16h.the tensile strengthe of the T4alloys is139MPa, and the elongation is6.5%.500℃is the proper rolling temperature,the grain size could be effectivelyrefined by the rolling process,cuboid-shaped phases and strip-shaped phases existafter rolled.A mass of twins exist after initial rolled, they can harmonize the plasticdeformation and cause twinning-induced DRX.The number of twins decrease with theincreasing of rolling reduction and the DRX mode turns into grain boundary bulgingmechanism.The tensile strengthe of the as-rolled alloys is300MPa, and the elongationis2.6%.the tensile strength can reach up to326MPa using the cross rolling.Alloys were ageinged after rolled. Aged alloys can achieve a peak tensilestrength of370MPa after200℃/22h treated.The rolled-T5alloy has excellentelevated temperature mechanical properties:the tensile strength at200,250,300,350℃are392,381,251,112MPa while the elongation at350℃can reach to107%.The as-rolled alloy sheets were joined by fiber laser beam welding. Welding jointwith excellent appearance could be acquired with suitable welding parameters.Thefusion zone organization is mainly composed of uniform equiaxed dendrites and a fewcolumnar grain with few obvious HAZ. Islandlike precipitated phases and finedispersed precipitated phases were observed on the grain boundary.The joint ultimatetensile strength reached304MPa with welding speed at50mm/s and laser power at 1000W, which is up to92%of the base material.The tensile fracture occurred in thefusion zone,the ductile fracture is the main fracture mode.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metal pressure processing > Rolling > Non-ferrous metal rolling
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