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Research on Deformation Law of Micro Gas Blow Bulging for Rolled Foil of AZ31Magnesium Alloy

Author: WangGang
Tutor: CuiLingJiang
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: gas blow micro-bulging deformation law size effect AZ31magnesiumalloy
CLC: TG306
Type: Master's thesis
Year: 2012
Downloads: 10
Quote: 0
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Abstract


With the ongoing miniaturization in products, there is a growing demand for thedevelopment of accurate forming process for mechanical micro-parts. Gas blow micro-bulging is an novel technology to manufacture very small metal parts, in particular forbulk production. In recent years, gas blow micro-bulging have become a hot spot in thefield of microforming. In this paper, a series of experiments were carried out to studythe deformation law of gas blow micro-bulging for AZ31B magnesium alloy rolled foil.The AZ31B magnesium alloy rolled foils with0.1mm in thichness of differentgrain size were acquired through the heat treatment process at the temperature of245℃.The model of grain growth was builded by the way of regression. The foils withdifferent thichness of uniform grain size were acquired through the heat treatmentprocess at the uniform heating temperature and different healing time,the grain size isapproximately2μm.The influence of the gas pressure, bulging temperature, initial grain size, foilthickness and diameter of die cavity on formability of gas blow micro-bulging(thebulging height) were investigated using hemisphere free bulging tests. The experimentalresults showed that the optimum bulging temperature is380℃, in the range of forminggas pressure, the bulging height of the hemisphere parts increased with the increase ofthe forming gas pressure, the biggest bulging height of682μm and height to diameterratio of0.718were obtained at380℃、4.2MPa within15min; Using the foils whichwas subject to the heat treatment at245℃were used to study the influence of the grainsize on formability of gas blow micro-bulging, when the grain size get smaller, theformability of the gas blow micro-bulging is better and the height of hemisphere parts ishigher; When the grain size keeps constant, the thinner the thickness of foils, the higherthe bulging height; When the hemisphere parts are in good condition, the height todiameter ratio increased with the increase of the diameter of die cavity.On the basis of above study, cylinder bulging tests were performed with combineddie The deepth of die internal cavity was adjustable with the adjustable memorandumsale. The perfect cylinder was acquired with combined die at380℃、4.2MPa. Theheight of the cylinder is510μm and the radius of bottom corner is150μm.The microstrure revolution law and the fracture mechanism in micro gas pressurebulging were discussed by observing the microstrure and fracture appearance using OMand SEM. It was found that the grain size gets smaller as the deformation degreeincreases due to the dynamic recrystallization occurring during gas blow micro-bulging.Recrystallization become more completely and the grain become more homogeneous as the deformation got bigger. However, the grain size at different sites appear a littledifference; When the bulging temperature was300℃,the fracture mechanism of thematerial is quasi-cleavage fracture; as the temperature rise to350℃, there is somedimple near the fracture, the mechanism translate into the ductile fracture, at400℃, thedimple gets bigger and the mechanism translate into the intercrystalline fracture.Hemisphere and cylinder bulging tests are performed to analyse the law of wallthickness distribution. The results show that when height to diameter ratio is constant,the wall thickness distribution of micro hemisphere pares are more homogeneous thanmacro parts, the wall thickness distribution of micro cylindric roof is also relativelyhomogeneous, which could be caused by strain gradient hardden.The experiment is performed under the theorical minimum bulging pressure to findthe size effect of micro-bulging. The results show that the hemisphere parts wereacquired under the theorical minimum forming pressure, which indicates that there isthe size effect related to mechanical properties. When the ratio of the foil thickness tothe diameter of dia cavity is constant, along with the increase of bulging diameter, theheight to diameter ratio is increased.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metal pressure processing > General issues > Pressure processing
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