Study On Horizontal Centrifugal Casting Process Of Magnesium Alloy And Its Properties Of The Sheets Prepared By The Rolling Process

As one of the lightest structural metallic materials,magnesium alloys were widely used in modern industry,which conform to the trend of lightweight and energy conservation.However,there are still many limits in traditional magnesium alloy sheets,such as poor mechanical properties,complex manufacturing process and high cost.In this thesis,the prepared process of AZ91 sheets combined with the horizontal centrifugal casting and hot rolling were investigated,which indicates a new direction for the preparation of AZ91magnesium sheets.The numerical simulation method was applied to investigate the process of AZ91magnesium horizontal centrifugal casting.The influences of the casting process,including rotational speed、pouring rate、preheating temperature of mould and casting method on filling process and temperature field evolution,were analyzed.The research results showed that with the increasing rotating rate of mould,the phenomenon of rain fall was disappeared and the wall thickness of casting pipe was uniform.If the pouring speed is too slow,the molten metal will broken and too fast will cause impact splash.The temperature field was inhomogeneous by using the 25°C preheating temperature of the mould.And the cooling rate was relatively slower when the preheating temperature of the mould was 200°C.The incompletely shape and unevenly thickness caused by fixed pouring channel method.Moving pouring channel method and Layer-by-layer casting method can effectively improve the formability of the casting pipe.And their cooling rate of casting pipe was more quickly than fixed pouring channel method.Layer-by-layer casting process has a more uniform solidification temperature field.The optimized parameters were mould rotating speed1050r/min and pouring rate 2.67kg/s,preheating temperature of the mould at 100°C,Layer-by-layer casting process,respectively.In order to compare the microstructure and mechanical properties of castings that made by three different pouring method of horizontal centrifugal casting,the casting experiments was carried out.By comparing the castings under the three filling processes,it was found that the inner and outer samples of the castings in the layer-by-layer casting process were uniform and the mechanical properties were excellent.The tensile strength and elongation rate of Layer-by-layer casting process reached 189.9MPa and 6.2%,respectively,which was greatly improved compared with the other two processes.The effects of rolling pass reduction and homogenization time on microstructure and mechanical properties of AZ91 magnesium sheets were investigated.Excessive rolling pass reduction can cause sheet faults and cracking.The mechanical properties of the sheet will be improved by reduce the content of theβ-Mg₁₇Al₁₂ in the tissue through appropriately increase the processing time,however longer homogenization time will reduce mechanical properties by the growth of grain.With the increases of rolling passes,the grain size decreases and dynamic recrystallization occurs in the sheet,β-Mg₁₇Al₁₂ is elongated and crushed in the rolling direction.The optimized rolling parameters were 400°C×18h slab homogenization treatment,390°C rolling temperature 15%rolling pass reduction.Using the optimized parameters the tensile strength and elongation of AZ91 magnesium sheets reached368.2MPa and 8.2%respectively.