Research On Micro-embossing Process In Ultrafine-grained AZ31 Mg Alloy

Fabricating micro-channel by embossing represent the advantages of good stability,relatively low cost and suitable for mass production,while the grain size effect on micro-channel forming process significantly.The dimensional accuracy of the micro-channel cannot be guaranteed using course-grained materials.Ultrafine-grained material prepared by severe plastic deformation with higher strength and formability is an ideal material for micro-components.In this thesis,high pressure torsion is used to produce ultra-fine grained(UFG)AZ31 magnesium alloy of different grain size,obtain its micro-hardness,micro-structure and test its tensile performance.Observe the fracture of the micro-tensile specimen and the surface of the V-groove micro-channel,simulate the embossing process by Deform.Obtain the hardness distribution of AZ31 magnesium alloy samples of different number of turns,analyze the micro-tensile curve and its micro-structure.Analyze how the width of the V-groove and forming temperature effect the filling process.Also,an experiment of detecting the best forming parameters of U-groove UFG AZ31 micro-channel array are performed.At last,at the optimal temperature and force,micro-channel array of as-received,1/4T,1T,5T,10 T with the width of 50?m,100 ?m,150 ?m,200 ?m are embossed respectively.The study found that with the increase of the number of turns of HPT,the hardness significantly improved compared to the original specimen,and become uniform across the direction of the diameter,which significantly refined the grain size.The grain size tends to be uniform over the entire sample.The specimen processed by HPT for 10 turns gains the biggest elongation rate 400%,when the strain rate is 1.0×10-4s-1,at temperature 423 K.The cross-sectional area of ??the fractured sample increase with the increase of the number of turns of HPT and decreases with the increase of temperature but the fracture morphology did not change significantly.The sample processed by HPT has fine grain size and low yield stress,so the filling performance has been significantly improved.After the control of pressure and temperature,it is determined that theoptimal forming force of array micro-channel is 4KN,and the optimum forming temperature is 473 K.Under this condition,the filling rate of the remaining samples is 100% except original samples.The surface quality of the micro-channel of the samples which is treated by the HPT is better than that of the original samples,and the surface quality is getting better with the increase of the number of turns of HPT treatment,just as the result of single channel experiment.After HPT treatment of the sample,there are good dimensional accuracy and repeatability,the verticality of micro-channel sidewalls is good,the tops of the micro-channel are flat,cross-sectional shape is regular.In the process of array micro-channel experiment,there is a phenomenon that the filling height of micro-channels which located on the edge of the sample is uneven:the outside parts are higher than that of the inside parts.