Study On Microstructure Andproperties Of AZ80 Magnesiumalloy During Friction Stirprocessing

Magnesium alloys are widely used in aerospace,biomedicine,defense and military fields due to their high specific strength,low density,and abundant resources.However,due to its poor formability,its application in engineering is greatly limited.Therefore,improving the formability of magnesium alloys has become the main research direction at present.Traditional processing methods can improve its formability,refine the microstructure and grains,and improve its mechanical properties to a certain extent,but these changes are limited and cannot be applied to engineering on a large scale.Friction stir machining(FSM)is a severe plastic deformation technology,which has been widely used due to its high degree of automation,simple operation,and low energy consumption.Friction stir machining can significantly refine the grain size of materials and improve their comprehensive properties.Therefore,this thesis takes AZ80 magnesium alloy as the research object,conducts friction stir machining on magnesium alloy in air and water,and conducts aging heat treatment on the material after underwater friction stir machining.The effects of process parameters,different water temperatures,and different aging times on the microstructure,mechanical properties,and corrosion resistance of AZ80 magnesium alloy plates are analyzed.The effects of different rotational speeds and feed speeds on the microstructure and properties of magnesium alloy plates were studied by selecting different process parameters and conducting friction stir machining experiments in air.By analyzing the experimental results,it is found that when the rotational speed is 750 r/min and the feed speed is 100 mm/min,a good machined surface is obtained and there are no obvious defects at the cross section;With the increase of rotational speed and the decrease of feed speed,the temperature during magnesium alloy processing increases;With the decrease of rotational speed and the increase of feed speed,the grain size of the material obtained after processing becomes smaller,and at a rotational speed of 300 r/min and a feed speed of 100 mm/min,the finest microstructure with a grain size of 4 μ m is obtained.At the same time,under this process parameter,the maximum hardness and best corrosion resistance of the material are obtained,with a hardness value of 77.9 HV;With the increase of rotation speed and the decrease of feed speed,the tensile strength of the processed material increases.When the rotation speed is 750 r/min and 100mm/min,the maximum tensile strength is obtained,with a strength value of 227 MPa.The tensile strength of the processed material is lower than the strength of the base material.In order to further refine the microstructure and grain size of the material and improve its mechanical properties,underwater friction stir machining was performed at a rotational speed of 1000 r/min and a feed speed of 100 mm/min.The effects of different water temperatures on the microstructure and mechanical properties of magnesium alloy plates were studied.By analyzing the experimental results,it was found that the grain size obtained in water was significantly finer than that in air,and with the decrease of water temperature,the grain size of the processed material became smaller,and the finest microstructure was obtained in ice water,with a grain size of 1.6μ m.At the same time,the material obtained under ice water conditions had the highest hardness and tensile strength,with a hardness value of 106.6HV and a strength value of233 MPa,However,the elongation of the material is significantly lower than in air.In addition,the materials obtained after underwater processing were subjected to aging heat treatment to study the effects of different aging times on the microstructure and mechanical properties of AZ80 magnesium alloy.Through analyzing the experimental results,it is found that the grain size of the obtained material increases with the increase of aging time.When the aging time is 12 h,the maximum hardness is obtained under ice water conditions,with a hardness value of 79 HV,which is lower than the hardness without aging.At the same time,the maximum tensile strength of the material is obtained under this condition,with a strength of 263.7MPa,which is higher than the strength of the base metal and higher than the strength without aging.When the aging time is 8h,The maximum elongation of the material was obtained,with an elongation of 30.62%.