Study On The Microstructure, Properties And Deformation Techniques Of Rare Earth Wrought Magnesium Alloys

Research works of this thesis aim at high performance wrought magnesium alloys and mainly focus on the effects of rare earth elements on them. Some typical wrought magnesium alloys, such as AZ31 and AZ61 alloy in Mg-Al-Zn system, ZK60 alloy in Mg-Zn-Zr system are investigated systematically for the relations of their chemical composition, microstructures, deformation behavior, mechanical properties and applications.The chemical reaction in molten magnesium alloy, the grains refine treatment, homogenization treatment of magnesium alloy ingots and the deformation behavior under different plastic deformation conditions are studied. And the effects of heat treatment on the microstructures of alloys and influences of rare earth on the corrosion resistant properties of magnesium alloy are discussed. A magnesium alloy thin plane using for torpedo battery is invented and prepared.The reaction degree of rare earth La, Ce, Nd and Y are studied in molten magnesium alloy based on the calculation of chemical reaction and the analysis of halogen metal properties. Two effective magnesium alloy flux, especially for Mg-RE alloy system to improve the acquirement of rare earth to 90-97%, are prepared.The mechanism and technique of grain refine of minor rare earth in Mg-Al system alloy are investigated. The grain size ofAZ31 alloy change from about 300 u m to 30 V m. The mechanism of grain refine of rare earth on Mg-Al alloy is the increasing of undercooling degree between the solid/liquid interface during solidification and resulting in more nucleus.The mechanical properties and microstructure ofMg-Al-Zn alloy added minor rare earth during rolling and annealing are investigated and the results show that rare earth improve both the strength and elongation ofMg-Al-Zn alloy. The refined recrystallization grain only about 5~20 u m. Different mechanisms exert during hot deformation process in different grain size. In a large size grain (about 40-50 um), the dislocation sliding and twinning are the main deformation mechanism, and in a small size grain (5-20 um), grain boundary sliding is another important mechanism to improve the ductility of magnesium alloy.Plastically deformation behavior and dynamic recrystallization of Mg-6%Zn-0.7%Zr-0.8%Nd and Mg-2.8%Ce-0.7%Zn-0.7%Zr alloys are studied systematically at different deformation temperature and different strain rates. At high temperatures (above 473K), flow behavior is characteristic for hot working accompanied by dynamic recrystallization.Through calculating the deformation activity energy of a Mg-2.8%Ce-0.7%Zn-0.7%Zr alloy, the Mgt2RE compound in Mg-RE alloy can improve the stress exponent, peak stress and deformation activation energy.The dynamic recrystallization grains after extrusion are only 5-10 u m in Mg-6%Zn-0.7%Zr-0.8%Nd alloy and 20-50 u m in Mg-2.8%Ce-0.7%Zn-0.7%Zr and Mg-2.8%Nd-0.7%Zn-0.7%Zr alloy. It makes the extrusion mechanical properties of Mg-Ce-Zr-Zn alloy increase greatly.The mechanism of minor rare earth element improving the corrosion resistance of Mg-Al-Zn, Mg-Zn-Zr alloy is discussed.Based on the understanding of deformation and heat treatment of Magnesium alloy, the hot, warm and cold rolling techniques and a 90 exchanging direction rolling technique are developed to produce a very thin magnesium alloy plane (only 0.3mm thickness) using for torpedo batteries. Such thin plane will be equipped a military torpedo to replace the high cost importing materials.